The ecological coherence of high bacterial taxonomic ranks

Seasonal and interannual variability of the free-living and particle-associated bacteria of a coastal microbiome

Marine microbial communities differ genetically, metabolically, and ecologically according to their lifestyle, and they may respond differently to environmental changes. In this study, we investigated the seasonal dynamics of bacterial assemblies in the free-living (FL) and particle-associated (PA) fractions across a span of 6 years in the Blanes Bay Microbial Observatory in the Northwestern Mediterranean. Both lifestyles showed marked seasonality. The trends in alpha diversity were similar, with lower values in spring-summer than in autumn-winter. Samples from both fractions were grouped seasonally and the percentage of community variability explained by the measured environmental variables was comparable (32% in FL and 31% in PA). Canonical analyses showed that biotic interactions were determinants of bacterioplankton dynamics and that their relevance varies depending on lifestyles. Time-decay curves confirmed a high degree of predictability in both fractions. Yet, 'seasonal' Amplicon Sequence Variants (ASVs) (as defined by Lomb Scargle time series analysis) in the PA communities represented 46% of the total relative abundance while these accounted for 30% in the FL fraction. These results demonstrate that bacteria inhabiting both fractions exhibit marked seasonality, highlighting the importance of accounting for both lifestyles to fully comprehend the dynamics of marine prokaryotic communities.

Unveiling microplastic's role in nitrogen cycling: Metagenomic insights from estuarine sediment microcosms

Marine microplastics (MPs) pollution, with rivers as a major source, leads to MPs accumulation in estuarine sediments, which are also nitrogen cycling hotspots. However, the impact of MPs on nitrogen cycling in estuarine sediments has rarely been documented. In this study, we conducted microcosm experiment to investigate the effects of commonly encountered polyethylene (PE) and polystyrene (PS) MPs, with two MPs concentrations (0.3% and 3% wet sediment weight) based on environmental concentration considerations and dose-response effects, on sediment dissolved oxygen (DO) diffusion capacity and microbial communities using microelectrode system and metagenomic analysis respectively. The results indicated that high concentrations of PE-MPs inhibited DO diffusion during the mid-phase of the experiment, an effect that dissipated in the later stages. Metagenomic analysis revealed that MP treatments reduced the relative abundance of dominant microbial colonies in the sediments. The PCoA results demonstrated that MPs altered the microbial community structure, particularly evident under high concentration PE-MPs treatments. Functional analysis related to the nitrogen cycle suggested that PS-MPs promoted the nitrification, denitrification, and DNRA processes, but inhibited the ANRA process, while PE-MPs had an inhibitory effect on the nitrate reduction process and the ANRA process. Additionally, the high concentration of PE-MPs treatment significantly stimulated the abundance of genus (Bacillus) by 34.1% and genes (lip, pnbA) by 100-187.5% associated with plastic degradation, respectively. Overall, in terms of microbial community structure and the abundance of nitrogen cycling functional genes, PE- and PS- MPs exhibit both similarities and differences in their impact on nitrogen cycling. Our findings highlight the complexity of MP effects on nitrogen cycling in estuarine sediments and high concentrations of PE-MP stimulated plastic-degrading genus and genes.

Anthropogenic activity shapes the assemble and co-occurrence pattern of microbial communities in fishing harbors around the Bohai Economic Circle

This study aimed to elucidate the effects of coastal environmental stress on the composition of sediment bacterial communities and their cooccurrence patterns in fishing harbors around the Bohai Economic Circle, China. Compared with the natural sea area, fishing harbors contained higher levels of organic pollution (organic pollution index = 0.12±0.026) and considerably reduced bacterial richness and evenness. The distributions of sediment microbial communities clustered along the pollutant concentration gradients across fishing harbors. Betaproteobacteria dominated (76%) organically polluted fishing harbors, which were mostly disturbed by anthropogenic activities. However, the harbors also revealed the absence of numerous pathogenic (Coxiella and Legionella) and photosynthetic (Synechococcus and Leptolyngbya) bacteria. Abundant genera, including Thiobacillus and Arenimonas, exhibited a positive correlation with total phosphorus and a negative correlation with total nitrogen in sediments. Meanwhile, Sulfurovum, Psychrobacter, and Woeseia showed the opposite trend. Pollutant accumulation and anthropogenic activities caused the decrease in the sediment microbial diversity and dispersal ability and promoted convergent evolution. Severely polluted harbors with simplified cooccurrence networks revealed the presence of destabilized microbial communities. In addition, the modularity of bacterial networks decreased with organic pollution. Our results provide important insights into the adjustment mechanism of microbial communities to community organization and functions under environmental pollution stress. Overall, this study enhanced our understanding of how microbial communities in coastal sediments adapted and survived amidst anthropogenic activities like oily effluent discharges from large ships, wash water, domestic sewage, garbage, and fisheries wastes. It also examined their resilience to future contamination.

Determinants of microbiome composition: Insights from free-ranging hybrid zebras (Equus quagga × grevyi)

The composition of mammalian gut microbiomes is highly conserved within species, yet the mechanisms by which microbiome composition is transmitted and maintained within lineages of wild animals remain unclear. Mutually compatible hypotheses exist, including that microbiome fidelity results from inherited dietary habits, shared environmental exposure, morphophysiological filtering and/or maternal effects. Interspecific hybrids are a promising system in which to interrogate the determinants of microbiome composition because hybrids can decouple traits and processes that are otherwise co-inherited in their parent species. We used a population of free-living hybrid zebras (Equus quagga × grevyi) in Kenya to evaluate the roles of these four mechanisms in regulating microbiome composition. We analysed faecal DNA for both the trnL-P6 and the 16S rRNA V4 region to characterize the diets and microbiomes of the hybrid zebra and of their parent species, plains zebra (E. quagga) and Grevy's zebra (E. grevyi). We found that both diet and microbiome composition clustered by species, and that hybrid diets and microbiomes were largely nested within those of the maternal species, plains zebra. Hybrid microbiomes were less variable than those of either parent species where they co-occurred. Diet and microbiome composition were strongly correlated, although the strength of this correlation varied between species. These patterns are most consistent with the maternal-effects hypothesis, somewhat consistent with the diet hypothesis, and largely inconsistent with the environmental-sourcing and morphophysiological-filtering hypotheses. Maternal transmittance likely operates in conjunction with inherited feeding habits to conserve microbiome composition within species.

Feammox bacterial biofilm formation in HFMB

Nitrogen pollution has been increasing with the development of industrialization. Consequently, the excessive deposition of reactive nitrogen in the environment has generated the loss of biodiversity and eutrophication of different ecosystems. In 2005, a Feammox process was discovered that anaerobically metabolizes ammonium. Feammox with the use of hollow fiber membrane bioreactors (HFMB), based on the formation of biofilms of bacterial communities, has emerged as a possible efficient and sustainable method for ammonium removal in environments with high iron concentrations. This work sought to study the possibility of implementing, at laboratory scale, an efficient method by evaluating the use of HFMB. Samples from an internal circulation reactor (IC) incubated in culture media for Feammox bacteria. The cultures were enriched in a batch reactor to evaluate growth conditions. Next, HFMB assembly was performed, and Feammox parameters were monitored. Also, conventional PCR and scanning electron microscopy (SEM) analysis were performed to characterize the bacterial communities associated with biofilm formation. The use of sodium acetate presented the best performance for Feammox activity. The HFMB operation showed an ammonium (NH4+) removal of 50%. SEM analysis of the fibers illustrated the formation of biofilm networks formed by bacteria, which were identified as Albidiferax ferrireducens, Geobacter spp, Ferrovum myxofaciens, Shewanella spp., and Anammox. Functional genes Archaea/Bacteria ammonia monooxygenase, nrxA, hzsB, nirS and nosZ were also identified. The implementation of HFMB Feammox could be used as a sustainable tool for the removal of ammonium from wastewater produced because of anthropogenic activities.

Deciphering Microbial Adaptation in the Rhizosphere: Insights into Niche Preference, Functional Profiles, and Cross-Kingdom Co-occurrences

Rhizosphere microbial communities are to be as critical factors for plant growth and vitality, and their adaptive differentiation strategies have received increasing amounts of attention but are poorly understood. In this study, we obtained bacterial and fungal amplicon sequences from the rhizosphere and bulk soils of various ecosystems to investigate the potential mechanisms of microbial adaptation to the rhizosphere environment. Our focus encompasses three aspects: niche preference, functional profiles, and cross-kingdom co-occurrence patterns. Our findings revealed a correlation between niche similarity and nucleotide distance, suggesting that niche adaptation explains nucleotide variation among some closely related amplicon sequence variants (ASVs). Furthermore, biological macromolecule metabolism and communication among abundant bacteria increase in the rhizosphere conditions, suggesting that bacterial function is trait-mediated in terms of fitness in new habitats. Additionally, our analysis of cross-kingdom networks revealed that fungi act as intermediaries that facilitate connections between bacteria, indicating that microbes can modify their cooperative relationships to adapt. Overall, the evidence for rhizosphere microbial community adaptation, via differences in gene and functional and co-occurrence patterns, elucidates the adaptive benefits of genetic and functional flexibility of the rhizosphere microbiota through niche shifts.

Impact of prescribed fire on soil microbial communities in a Southern Appalachian Forest clear-cut

Escalating wildfire frequency and severity, exacerbated by shifting climate patterns, pose significant ecological and economic challenges. Prescribed burns, a common forest management tool, aim to mitigate wildfire risks and protect biodiversity. Nevertheless, understanding the impact of prescribed burns on soil and microbial communities in temperate mixed forests, considering temporal dynamics and slash fuel types, remains crucial. Our study, conducted at the University of Tennessee Forest Resources AgResearch and Education Center in Oak Ridge, TN, employed controlled burns across various treatments, and the findings indicate that low-intensity prescribed burns have none or minimal short-term effects on soil parameters but may alter soil nutrient concentrations, as evidenced by significant changes in porewater acetate, formate, and nitrate concentrations. These burns also induce shifts in microbial community structure and diversity, with Proteobacteria and Acidobacteria increasing significantly post-fire, possibly aiding soil recovery. In contrast, Verrucomicrobia showed a notable decrease over time, and other specific microbial taxa correlated with soil pH, porewater nitrate, ammonium, and phosphate concentrations. Our research contributes to understanding the intricate relationships between prescribed fire, soil dynamics, and microbial responses in temperate mixed forests in the Southern Appalachian Region, which is valuable for informed land management practices in the face of evolving environmental challenges.

Soil pH and carbon quality index regulate the biogeochemical cycle couplings of carbon, nitrogen and phosphorus in the profiles of Isohumosols

Soil biogeochemical cycles are essential for regulating ecosystem functions and services. However, little knowledge has been revealed on microbe-driven biogeochemical processes and their coupling mechanisms in soil profiles. This study investigated the vertical distribution of soil functional composition and their contribution to carbon (C), nitrogen (N) and phosphorus (P) cycling in the humus horizons (A-horizons) and parent material horizons (C-horizons) in Udic and Ustic Isohumosols using shotgun sequencing. Results showed that the diversity and relative abundance of microbial functional genes was influenced by soil horizons and soil types. In A-horizons, the relative abundances of N mineralization and liable C decomposition genes were significantly greater, but the P cycle-related genes, recalcitrant C decomposition and denitrification genes were lower compared to C-horizons. While, Ustic Isohumosols had lower relative abundances of C decomposition genes but higher relative abundances of N mineralization and P cycling-related pathways compared to Udic Isohumosols. The network analysis revealed that C-horizons had more interactions and stronger stability of functional gene networks than in A-horizons. Importantly, our results provide new insights into the potential mechanisms for the coupling processes of soil biogeochemical cycles among C, N and P, which is mediated by specific microbial taxa. Soil pH and carbon quality index (CQI) were two sensitive indicators for regulating the relative abundances and the relationships of functional genes in biogeochemical cycles. This study contributes to a deeper understanding of the ecological functions of soil microorganisms, thus providing a theoretical basis for the exploration and utilization of soil microbial resources and the development of soil ecological control strategies.

SOC bioavailability significantly correlated with the microbial activity mediated by size fractionation and soil morphology in agricultural ecosystems

Despite the fact that physical and chemical processes have been widely proposed to explicate the stabilization mechanisms of soil organic carbon (SOC), thebioavailability of SOC linked to soil physical structure, microbial community structure, and functional genes remains poorly understood. This study aims to investigate the SOC division based on bioavailability differences formed by physical isolation, and to clarify the relationships of SOC bioavailability with soil elements, pore characteristics, and microbial activity. Results revealed that soil element abundances such as SOC, TN, and DOC ranked in the same order as the soil porosity as clay > silt ≥ coarse sand > fine sand in both top and sub soil. In contrast to silt and clay, which had reduced SOC bioavailability, fine sand and coarse sand had dramatically enhanced SOC bioavailability compared to the bulk soil. The bacterial and fungal community structure was significantly influenced by particle size, porosity, and soil elements. Copiotrophic bacteria and functional genes were more prevalent in fine sand than clay, which also contained more oligotrophic bacteria. The SOC bioavailability was positively correlated with abundances of functional genes, C degradation genes, and copiotrophic bacteria, but negatively correlated with abundances of soil elements, porosity, oligotrophic bacteria, and microbial biomass (p < 0.05). This indicated that the soil physical structure divided SOC into pools with varying levels of bioavailability, with sand fractions having more bioavailable organic carbon than finer fractions. Copiotrophic Proteobacteria and oligotrophic Acidobacteria, Firmicutes, and Gemmatimonadetes made up the majority of the bacteria linked to SOC mineralization. Additionally, the fungi Mortierellomycota and Mucoromycota, which are mostly involved in SOC mineralization, may have the potential for oligotrophic metabolism. Our results indicated that particle-size fractionation could influence the SOC bioavailability by restricting SOC accessibility and microbial activity, thus having a significant impact on sustaining soil organic carbon reserves in temperate agricultural ecosystems, and provided a new research direction for organic carbon stability.

Mixing with native broadleaf trees modified soil microbial communities of Cunninghamia lanceolata monocultures in South China

Mixing with different broadleaf trees into the monocultures of Cunninghamia lanceolata is widely adopted as an efficient transformation of the pure C. lanceolata forest. However, it is unclear how native broad-leaved trees influence the belowground ecological environment of the pure C. lanceolata culture plantation in nutrient-poor soil of South China. Herein, we aimed to investigate how a long-time mixing with native broadleaf trees shape soil microbial community of the pure C. lanceolata forest across different soil depth (0-20 cm and 20-40 cm) and to clarify relationships between the modified soil microbial community and those affected soil chemical properties. Using high-throughput sequencing technology, microbial compositions from the mixed C. lanceolata-broadleaf forest and the pure C. lanceolata forest were analyzed. Network analysis was utilized to investigate correlations among microorganisms, and network robustness was assessed by calculating network natural connectivity. Results demonstrated that the content of soil microbial biomass carbon and nitrogen, total phosphorus and pH in mixed forest stand were significantly higher than those in pure forest stand, except for available phosphorus in topsoil (0-20 cm). Simultaneously, the mixed C. lanceolata-broadleaf forest has a more homogeneous bacterial and fungal communities across different soil depth compared with the pure C. lanceolata forest, wherein the mixed forest recruited more diverse bacterial community in subsoil (20-40 cm) and reduced the diversity of fungal community in topsoil. Meanwhile, the mixed forest showed higher bacterial community stability while the pure forest showed higher fungal community stability. Moreover, bacterial communities showed significant correlations with various soil chemical indicators, whereas fungal communities exhibited correlations with only TP and pH. Therefore, the mixed C. lanceolata-broadleaf forest rely on their recruiting bacterial community to enhance and maintain the higher nutrient status of soil while the pure C. lanceolata forest rely on some specific fungi to satisfy their phosphorus requirement for survive strategy.

Taxonomic, Phylogenomic and Bioactivity Profiling of Novel Phycosphere Bacterium from Model Cyanobacterium Synechococcus elongatus PCC 7942

Phycosphere niches host rich microbial consortia that harbor dynamic algae-bacteria interactions with fundamental significance in varied natural ecosystems. Hence, culturing the uncultured microbial majority of the phycosphere microbiota is vital for deep understanding of the intricate mechanisms governing the dynamic interactions, and also to provide novel and rich microbial resources, and to discover new natural bioactive metabolites. Synechococcus elongatus PCC 7942 is a robust model cyanobacterium widely used in environment, synthesis biology, and biotechnology research. To expand the number of novel phycosphere species that were brought into culture and to discover the natural bioactivities, we presented a new yellow-pigmented bacterium named ABI-127-1, which was recovered from the phycosphere of PCC 7942, using an optimized bacterial isolation procedure. Combined polyphasic taxonomic and phylogenomic characterization was performed to confidently identify the new isolate as a potential novel species belonging to the genus Qipengyuania. The observed bioactivity of strain ABI-127-1 with promoting potential towards the growth and CO2 fixation efficiency of the host microalgae was measured. Additionally, the bacterial production of active bioflocculant exopolysaccharides was evaluated after culture optimization. Thus, these findings revealed the potential environmental and biotechnological implications of this new microalgae growth-promoting bacterium isolated from the phycosphere microenvironment.

Microbial responses to long-term warming differ across soil microenvironments

Soil carbon loss is likely to increase due to climate warming, but microbiomes and microenvironments may dampen this effect. In a 30-year warming experiment, physical protection within soil aggregates affected the thermal responses of soil microbiomes and carbon dynamics. In this study, we combined metagenomic analysis with physical characterization of soil aggregates to explore mechanisms by which microbial communities respond to climate warming across different soil microenvironments. Long-term warming decreased the relative abundances of genes involved in degrading labile compounds (e.g. cellulose), but increased those genes involved in degrading recalcitrant compounds (e.g. lignin) across aggregate sizes. These changes were observed in most phyla of bacteria, especially for Acidobacteria, Actinobacteria, Bacteroidetes, Chloroflexi, and Planctomycetes. Microbial community composition was considerably altered by warming, leading to declined diversity for bacteria and fungi but not for archaea. Microbial functional genes, diversity, and community composition differed between macroaggregates and microaggregates, indicating the essential role of physical protection in controlling microbial community dynamics. Our findings suggest that microbes have the capacity to employ various strategies to acclimate or adapt to climate change (e.g. warming, heat stress) by shifting functional gene abundances and community structures in varying microenvironments, as regulated by soil physical protection.

Microeukaryotic plankton evolutionary constraints in a subtropical river explained by environment and bacteria along differing taxonomic resolutions

Microeukaryotic plankton communities are keystone components for keeping aquatic primary productivity. Currently, variations in microeukaryotic plankton diversity have often been explained by local ecological factors but not by evolutionary constraints. We used amplicon sequencing of 100 water samples across five years to investigate the ecological preferences of the microeukaryotic plankton community in a subtropical riverine ecosystem. We found that microeukaryotic plankton diversity was less associated with bacterial abundance (16S rRNA gene copy number) than bacterial diversity. Further, environmental effects exhibited a larger influence on microeukaryotic plankton community composition than bacterial community composition, especially at fine taxonomic levels. The evolutionary constraints of microeukaryotic plankton community increased with decreasing taxonomic resolution (from 97% to 91% similarity levels), but not significant change from 85% to 70% similarity levels. However, compared with the bacterial community, the evolutionary constraints were shown to be more affected by environmental variables. This study illustrated possible controlling environmental and bacterial drivers of microeukaryotic diversity and community assembly in a subtropical river, thereby indirectly reflecting on the quality status of the water environment by providing new clues on the microeukaryotic community assembly.

Endophytic bacterial community structure and diversity of the medicinal plant Mirabilis himalaica from different locations

Endophytic bacteria play important roles in medicinal plant growth, abiotic stress, and metabolism. Mirabilis himalaica (Edgew.) Heimerl is known for its medicinal value as Tibetan traditional plant; however, little is known about the endophytic bacteria associated with this plant in different geographic conditions and vegetal tissues. To compare the endophytic bacterial community associated with this plant in different geographic conditions and vegetal tissues, we collected the leaves, stems, and roots of M. himalaica from five locations, Nongmu college (NM), Gongbujiangda (GB), Zhanang County (ZL), Lang County (LX), and Sangri County (SR), and sequenced the 16S rRNA V5-V7 region with the Illumina sequencing method. A total of 522,450 high-quality sequences and 4970 operational taxonomic units (OTUs) were obtained. The different tissues from different locations harbored unique bacterial assemblages. Proteobacteria and Actinobacteria were the dominant phyla in all the samples, while the dominant genera changed based on the different tissues. The endophytic bacterial structures in the leaf and stem tissues were different compared to root tissues. Redundancy analysis (RDA) showed that the endophytic bacterial community was significantly correlated with pH, available phosphorus (AP), total phosphorus (TP), total nitrogen (TN), and soil organic matter (SOM). These findings suggested that the geographic conditions, climate type, ecosystem type, and tissues determined the endophytic bacterial composition and relative abundances. This conclusion could facilitate an understanding of the relationship and ecological function of the endophytic bacteria associated with M. himalaica and provide valuable information for artificial planting of M. himalaica and identifying and applying functional endophytic bacteria.

Effects of biochar on soil microbial communities: A meta-analysis

Changes in soil microbial communities may impact soil fertility and stability because microbial communities are key to soil functioning by supporting soil ecological quality and agricultural production. The effects of soil amendment with biochar on soil microbial communities are widely documented but studies highlighted a high degree of variability in their responses following biochar application. The multiple conditions under which they were conducted (experimental designs, application rates, soil types, biochar properties) make it difficult to identify general trends. This supports the need to better determine the conditions of biochar production and application that promote soil microbial communities. In this context, we performed the first ever meta-analysis of the biochar effects on soil microbial biomass and diversity (prokaryotes and fungi) based on high-throughput sequencing data. The majority of the 181 selected publications were conducted in China and evaluated the short-term impact (<3 months) of biochar. We demonstrated that a large panel of variables corresponding to biochar properties, soil characteristics, farming practices or experimental conditions, can affect the effects of biochar on soil microbial characteristics. Using a variance partitioning approach, we showed that responses of soil microbial biomass and prokaryotic diversity were highly dependent on biochar properties. They were influenced by pyrolysis temperature, biochar pH, application rate and feedstock type, as wood-derived biochars have particular physico-chemical properties (high C:N ratio, low nutrient content, large pores size) compared to non-wood-derived biochars. Fungal community data was more heterogenous and scarcer than prokaryote data (30 publications). Fungal diversity indices were rather dependent on soil properties: they were higher in medium-textured soils, with low pH but high soil organic carbon. Altogether, this meta-analysis illustrates the need for long-term field studies in European agricultural context for documenting responses of soil microbial communities to biochar application under diverse conditions combining biochar types, soil properties and conditions of use.

Microbial communities in the deep-sea sediments of the South São Paulo Plateau, Southwestern Atlantic Ocean

Microbial communities play a key role in the ocean, acting as primary producers, nutrient recyclers, and energy providers. The São Paulo Plateau is a region located on the southeastern coast of Brazil within economic importance, due to its oil and gas reservoirs. With this focus, this study examined the diversity and composition of microbial communities in marine sediments located at three oceanographic stations in the southern region of São Paulo Plateau using the HOV Shinkai 6500 in 2013. The 16S rRNA gene was sequenced using the universal primers (515F and 926R) by the Illumina Miseq platform. The taxonomic compositions of samples recovered from SP3 station were markedly distinct from those obtained from SP1 and SP2. Although all three stations exhibited a high abundance of Gammaproteobacteria (> 15%), this taxon dominated more than 90% of composition of the A and C sediment layers at SP3. The highest abundance of the archaeal class Nitrososphaeria was presented at SP1, mainly at layer C (~ 21%), being absent at SP3 station. The prediction of chemoheterotrophy and fermentation as important microbial functions was supported by the data. Additionally, other metabolic pathways related to the cycles of nitrogen, carbon and sulfur were also predicted. The core microbiome analysis comprised only two ASVs. Our study contributes to a better understanding of microbial communities in an economically important little-explored region. This is the third microbiological survey in plateau sediments and the first focused on the southern region.

Resource partitioning and amino acid assimilation in a terrestrial geothermal spring

High-temperature geothermal springs host simplified microbial communities; however, the activities of individual microorganisms and their roles in the carbon cycle in nature are not well understood. Here, quantitative stable isotope probing (qSIP) was used to track the assimilation of 13C-acetate and 13C-aspartate into DNA in 74 °C sediments in Gongxiaoshe Hot Spring, Tengchong, China. This revealed a community-wide preference for aspartate and a tight coupling between aspartate incorporation into DNA and the proliferation of aspartate utilizers during labeling. Both 13C incorporation into DNA and changes in the abundance of taxa during incubations indicated strong resource partitioning and a significant phylogenetic signal for aspartate incorporation. Of the active amplicon sequence variants (ASVs) identified by qSIP, most could be matched with genomes from Gongxiaoshe Hot Spring or nearby springs with an average nucleotide similarity of 99.4%. Genomes corresponding to aspartate primary utilizers were smaller, near-universally encoded polar amino acid ABC transporters, and had codon preferences indicative of faster growth rates. The most active ASVs assimilating both substrates were not abundant, suggesting an important role for the rare biosphere in the community response to organic carbon addition. The broad incorporation of aspartate into DNA over acetate by the hot spring community may reflect dynamic cycling of cell lysis products in situ or substrates delivered during monsoon rains and may reflect N limitation.

Ecological mechanisms of biofilm development in the hybrid sludge-biofilm process: Implications for process start-up and optimization

The hybrid sludge-biofilm processes have been widely applied for the construction or upgradation of biological wastewater treatment process. Ecological mechanisms of biofilm development remain unclear in the hybrid ecosystem, because of the intricate interactive effects between sludge and biofilms. Herein, the establishment principles of biofilms with distinct coexisting sludge amounts were uncovered by varying sludge retention times (SRTs) from 5 to 40 days in the hybrid process. With the increasing of SRTs, biofilm biomass decreased with the increase of suspended sludge, resulting in lower biofilm proportion. As estimated by the Gompertz growth model, the increased sludge amounts (i.e., higher SRTs of 20 and 40 days) prolonged the initial colonization stage and decreased the specific development rate of biofilms when compared to lower sludge amounts with the shorter SRTs (i.e., 5 and 10 days). Null model analysis demonstrated that deterministic homogenous selection could facilitate the colonization and accumulation of biofilms with less coexisting sludge (SRT of 10 days). However, stochastic ecological drift and homogenizing dispersal dominated the colonization and accumulation stages of biofilms with more coexisting sludge (SRT of 20 days), respectively. The ecological networks reflected that positively-related taxa presented taxonomic relatedness, whereas high inconsistency of taxonomic relatedness was observed among aggregate forms or development stages as affected by varied SRTs. The high incidence of intra-taxa co-occurrence patterns suggested that taxa with similar ecological niches could be specifically selected in biofilms when being exposed with less coexisting sludge. This study uncovered ecological mechanisms of biofilm development driven by varying the SRTs of suspended sludge, which would help to propose appropriate strategies for the efficient start-up and optimization of the hybrid sludge-biofilm system.

Soil core microbiota drive community resistance to mercury stress and maintain functional stability

Soil microbial communities have resistance to environmental stresses and thus can maintain ecosystem functions such as decomposition, nutrient provisioning, and plant pathogen control. However, predominant factors driving community resistance of soil microbiome to heavy metal pollution stresses and ecosystem functional stability are still unclear, limiting our ability to forecast how soil pollution might affect ecosystem sustainability. Here, we conducted microcosm experiments to estimate the importance of soil microbiome in predicting community resistance to heavy metal mercury (Hg) stress in paired paddy and upland fields. We found that community resistance of soil microbiome was strongly correlated with ecosystem functional stability, so were the individual groups of organisms such as bacteria, saprotrophic fungi, and phototrophic protists. The core phylotypes within soil microbiome had a major contribution to community resistance, which was essential for the maintenance of functional stability. Co-occurrence network further confirmed that community resistances of main ecological clusters were positively correlated with ecosystem functional stability. Together, our results provide new insights into the link between community resistance and functional stability, and highlight the importance of core microbiota in driving community resistance to environmental stresses and maintain functional stability.

Fungal Fight Club: phylogeny and growth rate predict competitive outcomes among ectomycorrhizal fungi

Ectomycorrhizal fungi are among the most prevalent fungal partners of plants and can constitute up to one-third of forest microbial biomass. As mutualistic partners that supply nutrients, water, and pathogen defense, these fungi impact host plant health and biogeochemical cycling. Ectomycorrhizal fungi are also extremely diverse, and the community of fungal partners on a single plant host can consist of dozens of individuals. However, the factors that govern competition and coexistence within these communities are still poorly understood. In this study, we used in vitro competitive assays between five ectomycorrhizal fungal strains to examine how competition and pH affect fungal growth. We also tested the ability of evolutionary history to predict the outcomes of fungal competition. We found that the effects of pH and competition on fungal performance varied extensively, with changes in growth media pH sometimes reversing competitive outcomes. Furthermore, when comparing the use of phylogenetic distance and growth rate in predicting competitive outcomes, we found that both methods worked equally well. Our study further highlights the complexity of ectomycorrhizal fungal competition and the importance of considering phylogenetic distance, ecologically relevant traits, and environmental conditions in predicting the outcomes of these interactions.

Effect of a 12-Week Polyphenol Rutin Intervention on Markers of Pancreatic β-Cell Function and Gut Microbiota in Adults with Overweight without Diabetes

Supplementation with prebiotic polyphenol rutin is a potential dietary therapy for type 2 diabetes prevention in adults with obesity, based on previous glycaemic improvement in transgenic mouse models. Gut microbiota are hypothesised to underpin these effects. We investigated the effect of rutin supplementation on pancreatic β-cell function measured as C-peptide/glucose ratio, and 16S rRNA gene-based gut microbiota profiles, in a cohort of individuals with overweight plus normoglycaemia or prediabetes. Eighty-seven participants were enrolled, aged 18-65 years with BMI of 23-35 kg/m2. This was a 12-week double-blind randomised controlled trial (RCT), with 3 treatments comprising (i) placebo control, (ii) 500 mg/day encapsulated rutin, and (iii) 500 mg/day rutin-supplemented yoghurt. A 2-h oral glucose tolerance test (OGTT) was performed at baseline and at the end of the trial, with faecal samples also collected. Compliance with treatment was high (~90%), but rutin in both capsule and dietary format did not alter pancreatic β-cell response to OGTT over 12 weeks. Gut bacterial community composition also did not significantly change, with Firmicutes dominating irrespective of treatment. Fasting plasma glucose negatively correlated with the abundance of the butyrate producer Roseburia inulinivorans, known for its anti-inflammatory capacity. This is the first RCT to investigate postprandial pancreatic β-cell function in response to rutin supplementation.

Analysis on the properties of hydrolyzed amino acids in typical municipal sludge

In this study, amino acids, proteins, and microbial communities in sludge from different wastewater treatment plants (WWTPs) were analyzed. The results showed that the bacterial communities of different sludge samples were similar at the phylum level, and the dominant bacterial species in sludge samples with the same treatment process were the consistent. The main amino acids in EPS of different layers were different, and the amino acid results of different sludge samples were quite different, but the content of hydrophilic amino acids in all samples was higher than that of hydrophobic amino acids. And the total content of glycine, serine, and threonine related to sludge dewatering was positively correlated with protein content in sludge. In addition, the content of nitrifying bacteria and denitrifying bacteria in sludge was also positively correlated with the content of hydrophilic amino acids. In this study, the correlations between proteins, amino acids, and microbial communities in sludge were analyzed respectively, and the internal relationship was found. And it provided ideas for further study of sludge dewatering characteristics in the future.

Ecological interactions and the underlying mechanism of anammox and denitrification across the anammox enrichment with eutrophic lake sediments

BACKGROUND

Increasing attention has recently been devoted to the anaerobic ammonium oxidation (anammox) in eutrophic lakes due to its potential key functions in nitrogen (N) removal for eutrophication control. However, successful enrichment of anammox bacteria from lake sediments is still challenging, partly due to the ecological interactions between anammox and denitrifying bacteria across such enrichment with lake sediments remain unclear.

RESULTS

This study thus designed to fill such knowledge gaps using bioreactors to enrich anammox bacteria with eutrophic lake sediments for more than 365 days. We continuously monitored the influent and effluent water, measured the anammox and denitrification efficiencies, quantified the anammox and denitrifying bacteria, as well as the related N cycling genes. We found that the maximum removal efficiencies of NH₄⁺ and NO₂^- reached up to 85.92% and 95.34%, respectively. Accordingly, the diversity of anammox and denitrifying bacteria decreased significantly across the enrichment, and the relative dominant anammox (e.g., Candidatus Jettenia) and denitrifying bacteria (e.g., Thauera, Afipia) shifted considerably. The ecological cooperation between anammox and denitrifying bacteria tended to increase the microbial community stability, indicating a potential coupling between anammox and denitrifying bacteria. Moreover, the nirS-type denitrifiers showed stronger coupling with anammox bacteria than that of nirK-type denitrifiers during the enrichment. Functional potentials as depicted by metagenome sequencing confirmed the ecological interactions between anammox and denitrification. Metagenome-assembled genomes-based ecological model indicated that the most dominant denitrifiers could provide various materials such as amino acid, cofactors, and vitamin for anammox bacteria. Cross-feeding in anammox and denitrifying bacteria highlights the importance of microbial interactions for increasing the anammox N removal in eutrophic lakes.

CONCLUSIONS

This study greatly expands our understanding of cooperation mechanisms among anammox and denitrifying bacteria during the anammox enrichment with eutrophic lake sediments, which sheds new insights into N removal for controlling lake eutrophication. Video Abstract.

Implications of Soil Microbial Community Assembly for Ecosystem Restoration: Patterns, Process, and Potential

While it is now widely accepted that microorganisms provide essential functions in restoration ecology, the nature of relationships between microbial community assembly and ecosystem recovery remains unclear. There has been a longstanding challenge to decipher whether microorganisms facilitate or simply follow ecosystem recovery, and evidence for each is mixed at best. We propose that understanding microbial community assembly processes is critical to understanding the role of microorganisms during ecosystem restoration and thus optimizing management strategies. We examine how the connection between environment, community structure, and function is fundamentally underpinned by the processes governing community assembly of these microbial communities. We review important factors to consider in evaluating microbial community structure in the context of ecosystem recovery as revealed in studies of microbial succession: (1) variation in community assembly processes, (2) linkages to ecosystem function, and (3) measurable microbial community attributes. We seek to empower restoration ecology with microbial assembly and successional understandings that can generate actionable insights and vital contexts for ecosystem restoration efforts.

Life history strategies among soil bacteria-dichotomy for few, continuum for many

Study of life history strategies may help predict the performance of microorganisms in nature by organizing the complexity of microbial communities into groups of organisms with similar strategies. Here, we tested the extent that one common application of life history theory, the copiotroph-oligotroph framework, could predict the relative population growth rate of bacterial taxa in soils from four different ecosystems. We measured the change of in situ relative growth rate to added glucose and ammonium using both ¹⁸O-H₂O and ¹³C quantitative stable isotope probing to test whether bacterial taxa sorted into copiotrophic and oligotrophic groups. We saw considerable overlap in nutrient responses across most bacteria regardless of phyla, with many taxa growing slowly and few taxa that grew quickly. To define plausible life history boundaries based on in situ relative growth rates, we applied Gaussian mixture models to organisms' joint ¹⁸O-¹³C signatures and found that across experimental replicates, few taxa could consistently be assigned as copiotrophs, despite their potential for fast growth. When life history classifications were assigned based on average relative growth rate at varying taxonomic levels, finer resolutions (e.g., genus level) were significantly more effective in capturing changes in nutrient response than broad taxonomic resolution (e.g., phylum level). Our results demonstrate the difficulty in generalizing bacterial life history strategies to broad lineages, and even to single organisms across a range of soils and experimental conditions. We conclude that there is a continued need for the direct measurement of microbial communities in soil to advance ecologically realistic frameworks.

Functional comparison of metabolic networks across species

Metabolic phenotypes are pivotal for many areas, but disentangling how evolutionary history and environmental adaptation shape these phenotypes is an open problem. Especially for microbes, which are metabolically diverse and often interact in complex communities, few phenotypes can be determined directly. Instead, potential phenotypes are commonly inferred from genomic information, and rarely were model-predicted phenotypes employed beyond the species level. Here, we propose sensitivity correlations to quantify similarity of predicted metabolic network responses to perturbations, and thereby link genotype and environment to phenotype. We show that these correlations provide a consistent functional complement to genomic information by capturing how network context shapes gene function. This enables, for example, phylogenetic inference across all domains of life at the organism level. For 245 bacterial species, we identify conserved and variable metabolic functions, elucidate the quantitative impact of evolutionary history and ecological niche on these functions, and generate hypotheses on associated metabolic phenotypes. We expect our framework for the joint interpretation of metabolic phenotypes, evolution, and environment to help guide future empirical studies.

Habitats Within the Plant Root Differ in Bacterial Network Topology and Taxonomic Assortativity

The root microbiome is composed of distinct epiphytic (rhizosphere) and endophytic (endosphere) habitats. Differences in abiotic and biotic factors drive differences in microbial community diversity and composition between these habitats, though how they shape the interactions among community members is unknown. Here, we coupled a large-scale characterization of the rhizosphere and endosphere bacterial communities of 30 plant species across two watering treatments with co-occurrence network analysis to understand how root habitats and soil moisture shape root bacterial network properties. We used a novel bootstrapping procedure and null network modeling to overcome some of the limitations associated with microbial co-occurrence network construction and analysis. Endosphere networks had elevated node betweenness centrality versus the rhizosphere, indicating greater overall connectivity among core bacterial members of the root endosphere. Taxonomic assortativity was higher in the endosphere, whereby positive co-occurrence was more likely between bacteria within the same phylum while negative co-occurrence was more likely between bacterial taxa from different phyla. This taxonomic assortativity could be driven by positive and negative interactions among members of the same or different phylum, respectively, or by similar niche preferences associated with phylum rank among root inhabiting bacteria across plant host species. In contrast to the large differences between root habitats, drought had limited effects on network properties but did result in a higher proportion of shared co-occurrences between rhizosphere and endosphere networks. Our study points to fundamentally different ecological processes shaping bacterial co-occurrence across root habitats. [Formula: see text] Copyright © 2023 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Distinct Growth Responses of Tundra Soil Bacteria to Short-Term and Long-Term Warming

Increases in Arctic temperatures have thawed permafrost and accelerated tundra soil microbial activity, releasing greenhouse gases that amplify climate warming. Warming over time has also accelerated shrub encroachment in the tundra, altering plant input abundance and quality, and causing further changes to soil microbial processes. To better understand the effects of increased temperature and the accumulated effects of climate change on soil bacterial activity, we quantified the growth responses of individual bacterial taxa to short-term warming (3 months) and long-term warming (29 years) in moist acidic tussock tundra. Intact soil was assayed in the field for 30 days using ¹⁸O-labeled water, from which taxon-specific rates of ¹⁸O incorporation into DNA were estimated as a proxy for growth. Experimental treatments warmed the soil by approximately 1.5°C. Short-term warming increased average relative growth rates across the assemblage by 36%, and this increase was attributable to emergent growing taxa not detected in other treatments that doubled the diversity of growing bacteria. However, long-term warming increased average relative growth rates by 151%, and this was largely attributable to taxa that co-occurred in the ambient temperature controls. There was also coherence in relative growth rates within broad taxonomic levels with orders tending to have similar growth rates in all treatments. Growth responses tended to be neutral in short-term warming and positive in long-term warming for most taxa and phylogenetic groups co-occurring across treatments regardless of phylogeny. Taken together, growing bacteria responded distinctly to short-term and long-term warming, and taxa growing in each treatment exhibited deep phylogenetic organization. IMPORTANCE Soil carbon stocks in the tundra and underlying permafrost have become increasingly vulnerable to microbial decomposition due to climate change. The microbial responses to Arctic warming must be understood in order to predict the effects of future microbial activity on carbon balance in a warming Arctic. In response to our warming treatments, tundra soil bacteria grew faster, consistent with increased rates of decomposition and carbon flux to the atmosphere. Our findings suggest that bacterial growth rates may continue to increase in the coming decades as faster growth is driven by the accumulated effects of long-term warming. Observed phylogenetic organization of bacterial growth rates may also permit taxonomy-based predictions of bacterial responses to climate change and inclusion into ecosystem models.

Elevated temperature and CO2 strongly affect the growth strategies of soil bacteria

The trait-based strategies of microorganisms appear to be phylogenetically conserved, but acclimation to climate change may complicate the scenario. To study the roles of phylogeny and environment on bacterial responses to sudden moisture increases, we determine bacterial population-specific growth rates by ¹⁸O-DNA quantitative stable isotope probing (¹⁸O-qSIP) in soils subjected to a free-air CO₂ enrichment (FACE) combined with warming. We find that three growth strategies of bacterial taxa - rapid, intermediate and slow responders, defined by the timing of the peak growth rates - are phylogenetically conserved, even at the sub-phylum level. For example, members of class Bacilli and Sphingobacteriia are mainly rapid responders. Climate regimes, however, modify the growth strategies of over 90% of species, partly confounding the initial phylogenetic pattern. The growth of rapid bacterial responders is more influenced by phylogeny, whereas the variance for slow responders is primarily explained by environmental conditions. Overall, these results highlight the role of phylogenetic and environmental constraints in understanding and predicting the growth strategies of soil microorganisms under global change scenarios.

Ecological life strategies of microbes in response to antibiotics as a driving factor in soils

Antibiotics as a selection pressure driving the evolution of soil microbial communities is not well understood. Since microbial functions govern ecosystem services, an ecological framework is required to understand and predict antibiotic-induced functional and structural changes in microbial communities. Therefore, metagenomic studies explaining the impacts of antibiotics on soil microbial communities were mined, and alterations in microbial taxa were analyzed through an ecological lens using Grimes's Competitor-Stress tolerator-Ruderal (CSR) model. We propose considering antibiotics as the primary abiotic factor mentioned in the CSR model and classifying non-susceptible microbial taxa as degraders, resistant, and resilient groups analogous to competitors, stress tolerators, and ruderal strategists, respectively. Firmicutes, Bacteroidetes, Actinobacteria, and Proteobacteria were among the phyla harboring most members with antibiotic-resistant groups. However, some antibiotic-resistant microbes in these phyla could not only tolerate but also subsist solely on antibiotics, while others degraded antibiotics as a part of secondary metabolism. Irrespective of their taxonomic affiliation, microbes with each life strategy displayed similar phenotypic characteristics. Therefore, it is recommended to consider microbial functional traits associated with each life strategy while analyzing the ecological impacts of antibiotics. Also, potential ecological crises posed by antibiotics through changes in microbial community and ecosystem functions were visualized. Applying ecological theory to understand and predict antibiotics-induced changes in microbial communities will also provide better insight into microbial behavior in the background of emerging contaminants and help develop a robust ecological classification system of microbes.

Deciphering the microbial community structures and functions of wastewater treatment at high-altitude area

Introduction: The proper operation of wastewater treatment plants is a key factor in maintaining a stable river and lake environment. Low purification efficiency in winter is a common problem in high-altitude wastewater treatment plants (WWTPs), and analysis of the microbial community involved in the sewage treatment process at high-altitude can provide valuable references for improving this problem. Methods: In this study, the bacterial communities of high- and low-altitude WWTPs were investigated using Illumina high-throughput sequencing (HTS). The interaction between microbial community and environmental variables were explored by co-occurrence correlation network. Results: At genus level, Thauera (5.2%), unclassified_Rhodocyclaceae (3.0%), Dokdonella (2.5%), and Ferribacterium (2.5%) were the dominant genera in high-altitude group. The abundance of nitrogen and phosphorus removal bacteria were higher in high-altitude group (10.2% and 1.3%, respectively) than in low-altitude group (5.4% and 0.6%, respectively). Redundancy analysis (RDA) and co-occurrence network analysis showed that altitude, ultraviolet index (UVI), pH, dissolved oxygen (DO) and total nitrogen (TN) were the dominated environmental factors (p < 0.05) affecting microbial community assembly, and these five variables explained 21.4%, 20.3%, 16.9%, 11.5%, and 8.2% of the bacterial assembly of AS communities. Discussion: The community diversity of high-altitude group was lower than that of low-altitude group, and WWTPs of high-altitude aeras had a unique microbial community structure. Low temperature and strong UVI are pivotal factors contributing to the reduced diversity of activated sludge microbial communities at high-altitudes.

Progress in 'taxonomic sufficiency' in aquatic biological investigations

The 'taxonomic sufficiency' (TS) approach has been applied to algae, protists, invertebrates, and vertebrates, generally by aggregating species-level abundance data to a higher taxonomic level, where genus-level data are often highly correlated with species-level data and are a valid proxy level. The TS approach offers the possibility of a comparison of data from different geographical areas and highlights the effects of contaminants. The TS approach is stable in the face of different researchers and in the comparison of long-term biological survey data. The effectiveness of the TS approach may increase with increasing environmental gradients or spatial area. The TS approach should be avoided when the spatial area is small and small differences in species-level data are considered important, so as not to cancel out the distribution patterns specific to the local environment of the biological taxa.

Genomic analysis of sewage from 101 countries reveals global landscape of antimicrobial resistance

Antimicrobial resistance (AMR) is a major threat to global health. Understanding the emergence, evolution, and transmission of individual antibiotic resistance genes (ARGs) is essential to develop sustainable strategies combatting this threat. Here, we use metagenomic sequencing to analyse ARGs in 757 sewage samples from 243 cities in 101 countries, collected from 2016 to 2019. We find regional patterns in resistomes, and these differ between subsets corresponding to drug classes and are partly driven by taxonomic variation. The genetic environments of 49 common ARGs are highly diverse, with most common ARGs carried by multiple distinct genomic contexts globally and sometimes on plasmids. Analysis of flanking sequence revealed ARG-specific patterns of dispersal limitation and global transmission. Our data furthermore suggest certain geographies are more prone to transmission events and should receive additional attention.

In vitro functional characterization predicts the impact of bacterial root endophytes on plant growth

Utilizing beneficial microbes for crop improvement is one strategy to achieve sustainable agriculture. However, identifying microbial isolates that promote crop growth is challenging, in part because using bacterial taxonomy to predict an isolate's effect on plant growth may not be reliable. The overall aim of this work was to determine whether in vitro functional traits of bacteria were predictive of their in planta impact. We isolated 183 bacterial endophytes from field-grown roots of two tomato species, Solanum lycopersicum and S. pimpinellifolium. Sixty isolates were screened for six in vitro functional traits: auxin production, siderophore production, phosphate solubilization, antagonism to a soilborne pathogen, and the presence of two antimicrobial metabolite synthesis genes. Hierarchical clustering of the isolates based on the in vitro functional traits identified several groups of isolates sharing similar traits. We called these groups 'functional groups'. To understand how in vitro functional traits of bacteria relate to their impact on plants, we inoculated three isolates from each of the functional groups on tomato seedlings. Isolates within the same functional group promoted plant growth at similar levels, regardless of their host origin or taxonomy. Together, our results demonstrate the importance of examining root endophyte functions for improving crop production.

Root exudates and rhizosphere soil bacterial relationships of Nitraria tangutorum are linked to k-strategists bacterial community under salt stress

When plants are subjected to various biotic and abiotic stresses, the root system responds actively by secreting different types and amounts of bioactive compounds, while affects the structure of rhizosphere soil bacterial community. Therefore, understanding plant-soil-microbial interactions, especially the strength of microbial interactions, mediated by root exudates is essential. A short-term experiment was conducted under drought and salt stress to investigate the interaction between root exudates and Nitraria tangutorum rhizosphere bacterial communities. We found that drought and salt stress increased rhizosphere soil pH (9.32 and 20.6%) and electrical conductivity (1.38 and 11 times), respectively, while decreased organic matter (27.48 and 31.38%), total carbon (34.55 and 29.95%), and total phosphorus (20 and 28.57%) content of N. tangutorum rhizosphere soil. Organic acids, growth hormones, and sugars were the main differential metabolites of N. tangutorum under drought and salt stress. Salt stress further changed the N. tangutorum rhizosphere soil bacterial community structure, markedly decreasing the relative abundance of Bacteroidota as r-strategist while increasing that of Alphaproteobacteria as k-strategists. The co-occurrence network analysis showed that drought and salt stress reduced the connectivity and complexity of the rhizosphere bacterial network. Soil physicochemical properties and root exudates in combination with salt stress affect bacterial strategies and interactions. Our study revealed the mechanism of plant-soil-microbial interactions under the influence of root exudates and provided new insights into the responses of bacterial communities to stressful environments.

Guts of the Urban Ecosystem: Microbial Ecology of Sewer Infrastructure

Microbes have inhabited the oceans and soils for millions of years and are uniquely adapted to their habitat. In contrast, sewer infrastructure in modern cities dates back only ~150 years. Sewer pipes transport human waste and provide a view into public health, but the resident organisms that likely modulate these features are relatively unexplored. Here, we show that the bacterial assemblages sequenced from untreated wastewater in 71 U.S. cities were highly coherent at a fine sequence level, suggesting that urban infrastructure separated by great spatial distances can give rise to strikingly similar communities. Within the overall microbial community structure, temperature had a discernible impact on the distribution patterns of closely related amplicon sequence variants, resulting in warm and cold ecotypes. Two bacterial genera were dominant in most cities regardless of their size or geographic location; on average, Arcobacter accounted for 11% and Acinetobacter 10% of the entire community. Metagenomic analysis of six cities revealed these highly abundant resident organisms carry clinically important antibiotic resistant genes blaCTX-M, blaOXA, and blaTEM. In contrast, human fecal bacteria account for only ~13% of the community; therefore, antibiotic resistance gene inputs from human sources to the sewer system could be comparatively small, which will impact measurement capabilities when monitoring human populations using wastewater. With growing awareness of the metabolic potential of microbes within these vast networks of pipes and the ability to examine the health of human populations, it is timely to increase our understanding of the ecology of these systems. IMPORTANCE Sewer infrastructure is a relatively new habitat comprised of thousands of kilometers of pipes beneath cities. These wastewater conveyance systems contain large reservoirs of microbial biomass with a wide range of metabolic potential and are significant reservoirs of antibiotic resistant organisms; however, we lack an adequate understanding of the ecology or activity of these communities beyond wastewater treatment plants. The striking coherence of the sewer microbiome across the United States demonstrates that the sewer environment is highly selective for a particular microbial community composition. Therefore, results from more in-depth studies or proven engineering controls in one system could be extrapolated more broadly. Understanding the complex ecology of sewer infrastructure is critical for not only improving our ability to treat human waste and increasing the sustainability of our cities but also to create scalable and effective sewage microbial observatories, which are inevitable investments of the future to monitor health in human populations.

Microbial genomic trait evolution is dominated by frequent and rare pulsed evolution

On the macroevolutionary time scale, does trait evolution proceed gradually or by rapid bursts (pulses) separated by prolonged periods of stasis or slow evolution? Although studies have shown that pulsed evolution is prevalent in animals, our knowledge about the tempo and mode of evolution across the tree of life is very limited. This long-standing debate calls for a test in bacteria and archaea, the most ancient and diverse forms of life with unique population genetic properties. Using a likelihood-based framework, we show that pulsed evolution is not only present but also prevalent and predominant in microbial genomic trait evolution. We detected two distinct types of pulsed evolution (small frequent and large rare jumps) that are predicted by the punctuated equilibrium and quantum evolution theories. Our findings suggest that major bacterial lineages could have originated in quick bursts and that pulsed evolution is a common theme across the tree of life.

Hierarchical phylogenetic community assembly of soil protists in a temperate agricultural field

Protists are abundant, diverse and perform essential functions in soils. Protistan community structure and its change across time or space are traditionally studied at the species-level but the relative importance of the processes shaping these patterns depends on the taxon phylogenetic resolution. Using 18S rDNA amplicon data of the Cercozoa, a group of dominant soil protists, from an agricultural field in western Germany, we observed a turnover of relatively closely related taxa (from sequence variants to genus-level clades) across soil depth; while across soil habitats (rhizosphere, bulk soil, drilosphere) we observed turnover of relatively distantly related taxa, confirming Paracercomonadidae as a rhizosphere-associated clade. We extended our approach to show that closely related Cercozoa encounter divergent AM fungi across soil depth and that distantly related Cercozoa encounter closely related AM fungi across soil compartments. This study suggests that soil Cercozoa community assembly at the field-scale is driven by niche-based processes shaped by evolutionary legacy of adaptation to conditions primarily related to soil compartment, followed by soil layer, giving a deeper understanding on the selection pressures that shaped their evolution.

Land use and roles of soil bacterial community in the dissipation of atrazine

Atrazine (ATZ) is one of the most widely used herbicides in the world even though it is classified as a carcinogenic endocrine disruptor. This study focused on how land use (grazing versus cultivation in parallel soils, the latter under no-till with a seven-year history of ATZ application) and bacterial community diversity affected ATZ dissipation. Proteobacteria, Bacteroidetes, Firmicutes, Actinobacteria, Acidobacteria, Verrucomicrobia, Planctomycetes, and Gemmatimonadetes were the dominant phyla in both soils. The mineralization of ATZ was much higher in soils under cultivation up to the onset of moderate diversity depletion (dilution =10^-3), corresponding to 44-52% of the amount applied (< 5% in the grazed soil). This was attributed to the higher diversity and complexity of the soils´ bacterial communities which consist of microbial groups that were more adapted as a result of previous exposure to ATZ. In these cases, ATZ dissipation was attributed mainly to mineralization (DT₅₀ = 4-11 d). However, formation of non-extractable ATZ residues was exceptionally important in the other cases (DT₅₀ = 17-44 d). The cultivated soils also presented a higher number of bacterial genera correlated with ATZ dissipation, in which Acidothermus, Aquicela, Arenimonas, Candidatus_Koribacter, Hirschia, MND1, Nitrospira, Occallatibacter, OM27_clade, and Ralstonia are suggested as potential ATZ-degraders. Finally, ATZ dissipation was mostly associated with an abundance of microbial functions related to energy supply and N-metabolism, suggesting co-metabolism is its first biodegradation step.

Shared Microbial Taxa Respond Predictably to Cyclic Time-Varying Oxygen Limitation in Two Disparate Soils

Periodic oxygen (O₂) limitation in humid terrestrial soils likely influences microbial composition, but whether communities share similar responses in disparate environments remains unclear. To test if specific microbial taxa share consistent responses to anoxia in radically different soils, we incubated a rainforest Oxisol and cropland Mollisol under cyclic, time-varying anoxic/oxic cycles in the laboratory. Both soils are known to experience anoxic periods of days to weeks under field conditions; our incubation treatments consisted of anoxic periods of 0, 2, 4, 8, or 12 d followed by 4 d of oxic conditions, repeated for a total of 384 d. Taxa measured by 16S rRNA gene sequences after 48 d and 384 d of experimental treatments varied strongly with increasing anoxic period duration, and responses to anoxia often differed between soils at multiple taxonomic levels. Only 19% of the 30,356 operational taxonomic units (OTUs) occurred in both soils, and most OTUs did not respond consistently to O₂ treatments. However, the OTUs present in both soils were disproportionally abundant, comprising 50% of sequences, and they often had a similar response to anoxic period duration in both soils (p < 0.0001). Overall, 67 OTUs, 36 families, 15 orders, 10 classes, and two phyla had significant and directionally consistent (positive or negative) responses to anoxic period duration in both soils. Prominent OTUs and taxonomic groups increasing with anoxic period duration in both soils included actinomycetes (Micromonosporaceae), numerous Ruminococcaceae, possible metal reducers (Anaeromyxobacter) or oxidizers (Candidatus Koribacter), methanogens (Methanomicrobia), and methanotrophs (Methylocystaceae). OTUs decreasing with anoxic duration in both soils included nitrifiers (Nitrospira) and ubiquitous unidentified Bradyrhizobiaceae and Micromonosporaceae. Even within the same genus, different OTUs occasionally showed strong positive or negative responses to anoxic duration (e.g., Dactylosporangium in the Actinobacteria), highlighting a potential for adaptation or niche partitioning in variable-O₂ environments. Overall, brief anoxic periods impacted the abundance of certain microbial taxa in predictable ways, suggesting that microbial community data may partially reflect and integrate spatiotemporal differences in O₂ availability within and among soils.

Biological Microbial Interactions from Cooccurrence Networks in a High Mountain Lacustrine District

A fundamental question in biology is why some species tend to occur together in the same locations, while others are never observed coexisting. This question becomes particularly relevant for microorganisms thriving in the highly diluted waters of high mountain lakes, where biotic interactions might be required to make the most of an extreme environment. We studied a high-throughput gene data set of alpine lakes (>220 Pyrenean lakes) with cooccurrence network analysis to infer potential biotic interactions, using the combination of a probabilistic method for determining significant cooccurrences and coexclusions between pairs of species and a conceptual framework for classifying the nature of the observed cooccurrences and coexclusions. This computational approach (i) determined and quantified the importance of environmental variables and spatial distribution and (ii) defined potential interacting microbial assemblages. We determined the properties and relationships between these assemblages by examining node properties at the taxonomic level, indicating associations with their potential habitat sources (i.e., aquatic versus terrestrial) and their functional strategies (i.e., parasitic versus mixotrophic). Environmental variables explained fewer pairs in bacteria than in microbial eukaryotes for the alpine data set, with pH alone explaining the highest proportion of bacterial pairs. Nutrient composition was also relevant for explaining association pairs, particularly in microeukaryotes. We identified a reduced subset of pairs with the highest probability of species interactions (“interacting guilds”) that significantly reached higher occupancies and lower mean relative abundances in agreement with the carrying capacity hypothesis. The interacting bacterial guilds could be more related to habitat and microdispersal processes (i.e., aquatic versus soil microbes), whereas for microeukaryotes trophic roles (osmotrophs, mixotrophs, and parasitics) could potentially play a major role. Overall, our approach may add helpful information to guide further efforts for a mechanistic understanding of microbial interactions in situ.

IMPORTANCE A fundamental question in biology is why some species tend to occur together in the same locations, while others are never observed to coexist. This question becomes particularly relevant for microorganisms thriving in the highly diluted waters of high mountain lakes, in which biotic interactions might be required to make the most of an extreme environment. Microbial metacommunities are too often only studied in terms of their environmental niches and geographic barriers since they show inherent difficulties to quantify biological interactions and their role as drivers of ecosystem functioning. Our study highlights that telling apart potential interactions from both environmental and geographic niches may help for the initial characterization of organisms with similar ecologies in a large scope of ecosystems, even when information about actual interactions is partial and limited. The multilayered statistical approach carried out here offers the possibility of going beyond taxonomy to understand microbiological behavior in situ.

Glacier shrinkage will accelerate downstream decomposition of organic matter and alters microbiome structure and function

The shrinking of glaciers is among the most iconic consequences of climate change. Despite this, the downstream consequences for ecosystem processes and related microbiome structure and function remain poorly understood. Here, using a space-for-time substitution approach across 101 glacier-fed streams (GFSs) from six major regions worldwide, we investigated how glacier shrinkage is likely to impact the organic matter (OM) decomposition rates of benthic biofilms. To do this, we measured the activities of five common extracellular enzymes and estimated decomposition rates by using enzyme allocation equations based on stoichiometry. We found decomposition rates to average 0.0129 (% d^-1 ), and that decreases in glacier influence (estimated by percent glacier catchment coverage, turbidity, and a glacier index) accelerates decomposition rates. To explore mechanisms behind these relationships, we further compared decomposition rates with biofilm and stream water characteristics. We found that chlorophyll-a, temperature, and stream water N:P together explained 61% of the variability in decomposition. Algal biomass, which is also increasing with glacier shrinkage, showed a particularly strong relationship with decomposition, likely indicating their importance in contributing labile organic compounds to these carbon-poor habitats. We also found high relative abundances of chytrid fungi in GFS sediments, which putatively parasitize these algae, promoting decomposition through a fungal shunt. Exploring the biofilm microbiome, we then sought to identify bacterial phylogenetic clades significantly associated with decomposition, and found numerous positively (e.g., Saprospiraceae) and negatively (e.g., Nitrospira) related clades. Lastly, using metagenomics, we found evidence of different bacterial classes possessing different proportions of EEA-encoding genes, potentially informing some of the microbial associations with decomposition rates. Our results, therefore, present new mechanistic insights into OM decomposition in GFSs by demonstrating that an algal-based "green food web" is likely to increase in importance in the future and will promote important biogeochemical shifts in these streams as glaciers vanish.

Aridity Threshold Induces Abrupt Change of Soil Abundant and Rare Bacterial Biogeography in Dryland Ecosystems

Aridity, which is increasing worldwide due to climate change, affects the biodiversity and functions of dryland ecosystems. Whether aridification leads to gradual (or abrupt) and systemic (or specific) changes in the biogeography of abundant and rare microbial species is largely unknown. Here, we investigated stress-adaptive changes (aridity-driven, ranging from 0.65 to 0.94) and biogeographic patterns of abundant and rare bacterial communities in different habitats, including agricultural field, forest, wetland, grassland, and desert, in desert oasis transition zones in northern China. We observed abrupt changes at the breakpoint of aridity values (0.92), characterized by diversity (α-diversity and β-diversity), species coexistence, community assembly processes, and phylogenetic niche conservatism. Specifically, when aridity was <0.92, increasing aridity led to more deterministic assembly and species coexistences for the abundant subcommunity, whereas the reverse was observed for the rare subcommunity. The phylogenetic niche conservatism for both subcommunities increased slowly with aridity. When aridity was >0.92, the systemic responses of abundant and rare taxa changed dramatically in a consistent direction, such that both subcommunities rapidly tended to have a more deterministic assembly, species coexistence, and stronger phylogenetic niche conservatism with increasing aridity. In addition, the change rates of abundant taxa were higher than those of rare taxa, indicating the more sensitive responses of abundant taxa along aridity variation. This finding has important implications for understanding the impact of aridity on the structure and function of abundant and rare soil taxa and how diversity maintenance is associated with soil microbiota responding to global change. The abrupt threshold of soil bacteria found can be used for buffering and for building effective adaptation and mitigation measures aimed at maintaining the capacity of drylands for basic ecosystem functioning.

IMPORTANCE Aridity, which is increasing worldwide due to climate change, affects the biodiversity and functions of dryland ecosystems. We provided the first statistical evidence for abrupt changes of species coexistence, ecological processes, and niche conservation of abundant and rare soil bacteria triggered by diversity to abrupt increases in aridity. The abrupt threshold of soil bacterial community response to aridity is spatially heterogeneous at the local scale and should be specified according to local conditions for buffering and for building effective adaptation and mitigation measures aimed at maintaining the capacity of drylands for basic ecosystem functioning.

Antibiotics and antibiotic resistance genes in landfills: A review

Landfill are important reservoirs of antibiotics and antibiotic resistance genes (ARGs). They harbor diverse contaminants, such as heavy metals and persistent organic chemicals, complex microbial consortia, and anaerobic degradation processes, which facilitate the occurrence, development, and transfer of ARGs and antibiotic resistant bacteria (ARB). The main concern is that antibiotics and developed ARGs and ARB may transfer to the local environment via leachate and landfill leakage. In this paper, we provide an overview of established studies on antibiotics and ARGs in landfills, summarize the origins and distribution of antibiotics and ARGs, discuss the linkages among various antibiotics, ARGs, and bacterial communities as well as the influencing factors of ARGs, and evaluate the current treatment processes of antibiotics and ARGs. Finally, future research is proposed to fill the current knowledge gaps, which include mechanisms for the development and transmission of antibiotic resistance, as well as efficient treatment approaches for antibiotic resistance.

Core microbiota drive functional stability of soil microbiome in reforestation ecosystems

Revealing the ecological roles of core microbiota in the maintenance of the functional stability of soil microbiomes is crucial for sustainable ecosystem functioning; however, there is a dearth of whole-soil profile studies on the fundamental topic in microbial ecology, especially in the context of ecological restoration. Here, we explored whether core microbiota influence the temporal changes in the functional stability of soil microbiomes throughout the soil profile (i.e., soil depths of 0-300 cm) during natural succession in restored ex-arable ecosystems, via high-throughput amplicon and metagenomic sequencing. We revealed that core microbiota were essential for the maintenance of the functional stability of soil microbiomes in reforestation ecosystems. Specifically, the core taxa within one cluster of soil network, which had similar ecological preferences, had major contributions to functional stability. Reforestation significantly decreased the functional stability of soil microbiomes, which exhibited significant variations along the vertical soil profile in the reforested soils. Overall, the findings enhance our understanding of the factors driving functional stability in soil microbiomes, and suggests that core microbiota should be considered a key factor and integrated in policy and management activities targeting the enhancement and maintenance of functional stability and ecosystem sustainability in ecological restoration programs.

Biofertilizers: An ecofriendly technology for nutrient recycling and environmental sustainability

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Agriculture plays an important role in a country's economy. In modern intensive agricultural practices, chemical fertilizers and pesticides are applied on large scale to increase crop production in order to meet the nutritional requirements of the ever-increasing world population. However, rapid urbanization with shrinking agricultural lands, dramatic change in climatic conditions and extensive use of agrochemicals in agricultural practices has been found to cause environmental disturbances and public health hazards affecting food security and sustainability in agriculture. Besides this, agriculture soils are continuously losing their quality and physical properties as well as their chemical (imbalance of nutrients) and biological health due to indiscriminate use of agrochemicals. Plant-associated microbes with their plant growth- promoting traits have enormous potential to solve these challenges and play a crucial role in enhancing plant biomass and crop yield under greenhouse and field conditions. The beneficial mechanisms of plant growth improvement include enhanced availability of nutrients (i.e., N, P, K, Zn and S), phytohormone modulation, biocontrol of phytopathogens and amelioration of biotic and abiotic stresses. This plant-microbe interplay is indispensable for sustainable agriculture and these microbes may perform essential role as an ecological engineer to reduce the use of chemical fertilizers. Various steps involved for production of solid-based or liquid biofertilizer formulation include inoculum preparation, addition of cell protectants such as glycerol, lactose, starch, a good carrier material, proper packaging and best delivery methods. In addition, recent developments of formulation include entrapment/microencapsulation, nano-immobilization of microbial bioinoculants and biofilm-based biofertilizers. Thus, inoculation with beneficial microbes has emerged as an innovative eco-friendly technology to feed global population with available resources. This review critically examines the current state-of-art on use of microbial strains as biofertilizers in different crop systems for sustainable agriculture and in maintaining soil fertility and enhancing crop productivity. It is believed that acquisition of advanced knowledge of plant-PGPR interactions, bioengineering of microbial communities to improve the performance of biofertilizers under field conditions, will help in devising strategies for sustainable, environment-friendly and climate smart agricultural technologies to deliver short and long terms solutions for improving crop productivity to feed the world in a more sustainable manner.

Modern intensive agricultural practices face numerous challenges that pose major threats to global food security. In order to address the nutritional requirements of the ever-increasing world population, chemical fertilizers and pesticides are applied on large scale to increase crop production. However, the injudicious use of agrochemicals has resulted in environmental pollution leading to public health hazards. Moreover, agriculture soils are continuously losing their quality and physical properties as well as their chemical (imbalance of nutrients) and biological health. Plant-associated microbes with their plant growth- promoting traits have enormous potential to solve these challenges and play a crucial role in enhancing plant biomass and crop yield. The beneficial mechanisms of plant growth improvement include enhanced nutrient availability, phytohormone modulation, biocontrol of phytopathogens and amelioration of biotic and abiotic stresses. Solid-based or liquid bioinoculant formulation comprises inoculum preparation, addition of cell protectants such as glycerol, lactose, starch, a good carrier material, proper packaging and best delivery methods. Recent developments of formulation include entrapment/microencapsulation, nano-immobilization of microbial bioinoculants and biofilm-based biofertilizers. This review critically examines the current state-of-art on use of microbial strains as biofertilizers and the important roles performed by these beneficial microbes in maintaining soil fertility and enhancing crop productivity.

Inferring microbiota functions from taxonomic genes: a review

Deciphering microbiota functions is crucial to predict ecosystem sustainability in response to global change. High-throughput sequencing at the individual or community level has revolutionized our understanding of microbial ecology, leading to the big data era and improving our ability to link microbial diversity with microbial functions. Recent advances in bioinformatics have been key for developing functional prediction tools based on DNA metabarcoding data and using taxonomic gene information. This cheaper approach in every aspect serves as an alternative to shotgun sequencing. Although these tools are increasingly used by ecologists, an objective evaluation of their modularity, portability, and robustness is lacking. Here, we reviewed 100 scientific papers on functional inference and ecological trait assignment to rank the advantages, specificities, and drawbacks of these tools, using a scientific benchmarking. To date, inference tools have been mainly devoted to bacterial functions, and ecological trait assignment tools, to fungal functions. A major limitation is the lack of reference genomes-compared with the human microbiota-especially for complex ecosystems such as soils. Finally, we explore applied research prospects. These tools are promising and already provide relevant information on ecosystem functioning, but standardized indicators and corresponding repositories are still lacking that would enable them to be used for operational diagnosis.

Seasonal niche differentiation among closely related marine bacteria

Bacteria display dynamic abundance fluctuations over time in marine environments, where they play key biogeochemical roles. Here, we characterized the seasonal dynamics of marine bacteria in a coastal oligotrophic time series station, tested how similar the temporal niche of closely related taxa is, and what are the environmental parameters modulating their seasonal abundance patterns. We further explored how conserved the niche is at higher taxonomic levels. The community presented recurrent patterns of seasonality for 297 out of 6825 amplicon sequence variants (ASVs), which constituted almost half of the total relative abundance (47%). For certain genera, niche similarity decreased as nucleotide divergence in the 16S rRNA gene increased, a pattern compatible with the selection of similar taxa through environmental filtering. Additionally, we observed evidence of seasonal differentiation within various genera as seen by the distinct seasonal patterns of closely related taxa. At broader taxonomic levels, coherent seasonal trends did not exist at the class level, while the order and family ranks depended on the patterns that existed at the genus level. This study identifies the coexistence of closely related taxa for some bacterial groups and seasonal differentiation for others in a coastal marine environment subjected to a strong seasonality.

Enterococcus faecium are associated with the modification of gut microbiota and shrimp post-larvae survival

BACKGROUND

Probiotics are widely used to promote host health. Compared to mammals and terrestrial invertebrates, little is known the role of probiotics in aquatic invertebrates. In this study, eighteen tanks with eight hundred of shrimp post-larvae individuals each were randomly grouped into three groups, one is shrimps administered with E. faecium as probiotic (Tre) and others are shrimps without probiotic-treatment (CK1: blank control, CK2: medium control). We investigated the correlations between a kind of commercial Enterococcus faecium (E. faecium) powder and microbiota composition with function potentials in shrimp post-larvae gut.

RESULTS

We sequenced the 16S rRNA gene (V4) of gut samples to assess diversity and composition of the shrimp gut microbiome and used differential abundance and Tax4Fun2 analyses to identify the differences of taxonomy and predicted function between different treatment groups. The ingested probiotic bacteria (E. faecium) were tracked in gut microbiota of Tre and the shrimps here showed the best growth performance especially in survival ratio (SR). The distribution of SR across samples was similar to that in PCoA plot based on Bray-Curits and two subgroups generated (SL: SR < 70%, SH: SR ≥ 70%). The gut microbiota structure and predicted function were correlated with both treatment and SR, and SR was a far more important factor driving taxonomic and functional differences than treatment. Both Tre and SH showed a low and uneven community species and shorted phylogenetic distance. We detected a shift in composition profile at phylum and genus level and further identified ten OTUs as relevant taxa that both closely associated with treatment and SR. The partial least squares path model further supported the important role of relevant taxa related to shrimp survival ratio.

CONCLUSIONS

Overall, we found gut microbiota correlated to both shrimp survival and ingested probiotic bacteria (E. faecium). These correlations should not be dismissed without merit and will uncover a promising strategy for developing novel probiotics through certain consortium of gut microbiota.