Effect of thermophilic microbial agents on nitrogen transformation, nitrogen functional genes, and bacterial communities during bean dregs composting

This study explored how a thermophilic microbial agent altered nitrogen transformation, nitrogen functional genes, and bacterial communities during bean dregs composting with (T) and without (CK) a thermophilic microbial agent for 15 days. The results showed that the maximum temperature in T reached 73 °C and remained above 70 °C for 8 days, while that in CK was only 65 °C. The pH in T had essentially stabilized on day 7, while that in CK was still increasing. On day 15, the seed germination index (GI) of T (95%) reached maturity (defined by GI ≥ 85%), while the GI of CK was only 36%. The concentrations of total nitrogen, water-soluble nitrogen, ammonia nitrogen, and nitrate nitrogen in T (2.5%, 18.9 g/kg, 8.75 g/kg, and 1.69 g/kg) were all lower than those in CK (3.6%, 28.9 g/kg, 12.75 g/kg, and 6.82 g/kg). During composting, Bacillus played a major role in nitrogen reduction, nitrogen mineralization, denitrification, and the conversion between nitrite and nitrate. Weissella played a major role in nitrogen assimilation. Komagataeibacter and Bacillus played a major role in nitrogen fixation in CK and T, respectively. Nitrification was not observed during composting. The nosZ gene, which converts nitrous oxide to nitrogen, was found only in T. Network analysis suggested that the average number of neighbours in T was 3.30% higher than that in CK and the characteristic path length in T was 14.15% higher than that in CK. Therefore, the thermophilic microbial agents could cause nitrogen loss but promote the maturity of bean dregs, which have great potential application.

Insights into the microbiome assembly during different growth stages and storage of strawberry plants

BACKGROUND

Microbiome assembly was identified as an important factor for plant growth and health, but this process is largely unknown, especially for the fruit microbiome. Therefore, we analyzed strawberry plants of two cultivars by focusing on microbiome tracking during the different growth stages and storage using amplicon sequencing, qPCR, and microscopic approaches.

RESULTS

Strawberry plants carried a highly diverse microbiome, therein the bacterial families Sphingomonadaceae (25%), Pseudomonadaceae (17%), and Burkholderiaceae (11%); and the fungal family Mycosphaerella (45%) were most abundant. All compartments were colonized by high number of bacteria and fungi (10⁷-10¹⁰ marker gene copies per g fresh weight), and were characterized by high microbial diversity (6049 and 1501 ASVs); both were higher for the belowground samples than in the phyllosphere. Compartment type was the main driver of microbial diversity, structure, and abundance (bacterial: 45%; fungal: 61%) when compared to the cultivar (1.6%; 2.2%). Microbiome assembly was strongly divided for belowground habitats and the phyllosphere; only a low proportion of the microbiome was transferred from soil via the rhizosphere to the phyllosphere. During fruit development, we observed the highest rates of microbial transfer from leaves and flowers to ripe fruits, where most of the bacteria occured inside the pulp. In postharvest fruits, microbial diversity decreased while the overall abundance increased. Developing postharvest decay caused by Botrytis cinerea decreased the diversity as well, and induced a reduction of potentially beneficial taxa.

CONCLUSION

Our findings provide insights into microbiome assembly in strawberry plants and highlight the importance of microbe transfer during fruit development and storage with potential implications for food health and safety.

Aeration increases soil bacterial diversity and nutrient transformation under mulching-induced hypoxic conditions

Soil oxygen (O₂) deficiency induced by organic mulching is easy to overlook. Aeration has been shown to potentially alleviate soil hypoxia stress. However, the responses of soil bacterial communities to such mulching-induced hypoxic conditions and aeration remain elusive. Therefore, a three-year field experiment, consisting of mulching (T1), mulching with aeration (TA1, poor aeration; TA2, strong aeration), and no-mulching (CK) treatments, was conducted in bamboo (Phyllostachys praecox) plantations. According to our results, the strong aeration treatment (TA2) alleviated soil acidification, increased soil nutrient availability, and significantly increased soil O₂ content by 18.44% (P < 0.05) when compared with T1. In addition, TA2 significantly increased soil β-glucosidase, invertase, urease, and acid phosphatase activities compared with CK and T1 (P < 0.05). The alpha diversity indices with TA2 treatment were the highest, indicating that aeration increased the species richness and diversity of bacteria. The changes in bacterial community composition associated with TA2 treatment (i.e., an increase in Firmicutes, Verrucomicrobia, and Faecalibacterium abundance and a decrease in Chloroflexi and Bradyrhizobium abundance) were mainly related to nutrient and O₂ content. Mantel Test results suggested that soil O₂ content and temperature were the key factors shaping bacterial community composition. Structural equation modeling revealed that soil O₂ content had a positive and direct influence on bacterial community diversity. Functional annotation of prokaryotic taxa predicted that TA2 significantly increased the relative abundance of bacterial communities associated with nitrification, nitrogen fixation, and ureolysis. Our results demonstrated that optimal soil aeration conditions (17.60% of O₂ content) could enhance the diversity and function of soil bacterial communities. Overall, the findings of this study could serve as a benchmark for alleviating soil hypoxia caused by organic mulches, which is important for increasing the functionality of nutrient cycling bacterial communities in the soil.

Indigenous microbial populations of abandoned mining sites and their role in natural attenuation

Environmental contamination by toxic effluents discharged by anthropogenic activities including the mining industries has increased extensively in the recent past. Microbial communities and their biofilms inhabiting these extreme habitats have developed different adaptive strategies in metabolizing and transforming the persistent pollutants. They also play a crucial role in natural attenuation of these abandoned mining sites and act as a major driver of many biogeochemical processes, which helps in ecological rehabilitation and is a viable approach for restoration of wide stretches of land. In this review, the types of mine wastes including the overburden and mine drainage and the types of microbial communities thriving in such environments were probed in detail. The types of biofilms formed along with their possible role in metal bioremediation were also reviewed. This review also provides an overview of the shift in microbial communities in natural reclamation process and also provides an insight into the restoration of the enzyme activities of the soils which may help in further revegetation of abundant mining areas in a sustainable manner. Moreover, the role of indigenous microbiota in bioremediation of heavy metals and their plant growth-promoting activity weres discussed to assess their role in phytoremedial processes.

Deciphering the characterization, ecological function and assembly processes of bacterial communities in ship ballast water and sediments

Various microorganisms are transported worldwide via the water and sediments inside ship ballast tanks. Nevertheless, the ecological functions and assembly processes of bacterial communities in ballast water and sediments remain poorly understood. Here, we investigated the bacterial composition, community assembly processes, and putative functions through analyses of 70 ballast water and sediment samples obtained from various ships. The results showed that the ballast sediments contained a higher diversity of bacterial communities, whereas the ballast water was characterized by the dominance of Proteobacteria. Both the composition and potential function structures of bacterial communities were clearly different between the ballast water and sediment samples. The ballast water exhibited an abundance of microorganisms that involved in sulfur oxidation, whereas the bacterial species associated with nitrogen metabolism were abundant in the sediments. Co-occurrence network analysis revealed that the communities in ballast sediment samples possessed more complex network structures with higher modularity and positive associations among bacterial populations. Stochastic processes, especially the dispersal limitation process played the most important influence in the assembly of the communities in ballast water. Meanwhile, the bacterial communities in the ballast sediments were primarily governed by the homogeneous selection of determinacy. The results from this study will help us understand the ecological processes related to the bacterial communities in the ballast tanks and provide a foundation for the management of ballast water and sediments.

Intraspecific and interspecific quorum sensing of bacterial community affects the fate of antibiotic resistance genes during chicken manure composting under penicillin G stress

In this study, the effects of penicillin G (PENG) on the fate of bacterial communities and β-lactamase antibiotic resistance genes (ARGs) during chicken manure composting were assessed, to illustrate the roles of PENG in ARGs behavior. The results showed that the total absolute abundances of 9 ARGs and 4 mobile genetic elements (MGEs) was significantly increased by PENG (P < 0.05). Dozens of potential hosts for ARGs were predominantly affiliated with Firmicutes, Proteobacteria, and Actinobacteria. Meanwhile, the higher concentration of PENG significantly increased the abundance of luxI and luxS in quorum sensing (QS) (P < 0.05), which enhanced the frequency of inter/intraspecific gene "communication." Redundancy analysis and structural equation modeling further revealed that QS had a strong regulatory role in horizontal gene transfer of ARGs mediated via MGEs. These results provide new insight into the mechanism of ARGs propagation in aerobic composting modified by PENG.

Seasonal and short-term variations of bacteria and pathogenic bacteria on road deposited sediments

The bacteria (including pathogenic bacteria) attached to road deposited sediments (RDS) may interrelate with the microbe in the atmosphere, soil and water through resuspension and wash-off, and is of great significance to human and ecological health. However, the characteristics of bacterial communities with different time scale on RDS were unknown to dates. Climate change prolonged the dry days between rain events in many areas, making the varied trend of bacterial communities might be more significant in short term. This study revealed the characteristics of bacterial communities on RDS in urban and suburban areas through seasonal and daily scale. The correlations between other factors (land use, particle size, and chemical components) and the bacterial communities were also analyzed. It was found that the season showed a higher association with the bacterial community diversity than land use and particle size in urban areas. The bacterial community diversity increased substantially throughout the short-term study period (41 days) and the variation of dominant bacteria could be fitted by quadratic function in suburbs. In addition, urbanization notably increased the bacterial community diversity, while the potential pathogenic bacteria were more abundant in the suburban areas, coarse RDS (>75 μm), and in spring. The chemical components on RDS showed special correlations with the relative abundance of dominant bacteria. The research findings would fill the knowledge gap on RDS bacterial communities and be helpful for the future research on the assembly process of bacterial communities.

Evolution of prokaryotic colonisation of greenhouse plastics discarded into the environment

Current knowledge on the capacity of plastics as vectors of microorganisms and their ability to transfer microorganisms between different habitats (i.e. air, soil and river) is limited. The objective of this study was to characterise the evolution of the bacterial community adhered to environmental plastics [low-density polyethylene (LDPE)] across different environments from their point of use to their receiving environment destination in the sea. The study took place in a typical Mediterranean intermittent river basin in Larnaka, Cyprus, characterised by a large greenhouse area whose plastic debris may end up in the sea due to mismanagement. Five locations were selected to represent the environmental fate of greenhouse plastics from their use, through their abandonment in soil and subsequent transport to the river and the sea, taking samples of plastics and the surrounding environments (soil and water). The bacterial community associated with each sample was studied by 16S rRNA metabarcoding; also, the main physicochemical parameters in each environmental compartment were analysed to understand these changes. The identification and chemical changes in greenhouse plastics were tracked using Attenuated Total Reflection Fourier Transform Infra-red spectroscopy (ATR-FTIR). Scanning Electron Microscope (SEM) analysis demonstrated an evolution of the biofilm at each sampling location. β-diversity studies showed that the bacterial community adhered to plastics was significantly different from that of the surrounding environment only in samples taken from aqueous environments (freshwater and sea) (p-value p-value > 0.05). The environmental parameters (pH, salinity, total nitrogen and total phosphorus) explained the differences observed at each location to a limited extent. Furthermore, bacterial community differences among samples were lower in plastics collected from the soil than in plastics taken from rivers and seawater. Six genera (Flavobacterium, Altererythrobacter, Acinetobacter, Pleurocapsa, Georgfuchsia and Rhodococcus) were detected in the plastic, irrespective of the sampling location, confirming that greenhouse plastics can act as possible vectors of microorganisms between different environments: from their point of use, through a river system to the final coastal receiving environment. In conclusion, this study confirms the ability of greenhouse plastics to transport bacteria, including pathogens, between different environments. Future studies should evaluate these risks by performing complete sequencing metagenomics to decipher the functions of the plastisphere.

Spatial distribution and community structure of microbiota associated with cowpea aphid (Aphis craccivora Koch)

Aphid populations were collected on cowpea, dolichos, redgram and black gram from Belagavi and Udupi locations. The samples were shotgun sequenced using the Illumina NovaSeq 6000 system to understand the spatial distribution and community structure of microbiota (especially bacteria) associated with aphids. In the present study, we identified obligatory nutritional symbiont Buchnera aphidicola and facultative symbionts Rickettsia sp. and Bacteroidetes endosymbiont of Geopemphigus sp. in all the aphid samples studied, although in varied abundance. On the other hand, Serratia symbiotica, Arsenophonus sp. and Acinetobacter sp. were only found in aphids on specific host plants, suggesting that host plants might influence the bacterial community structure. Furthermore, our study revealed that microbiota other than bacteria were highly insignificant in the aphid populations. Additionally, functional annotation of aphid metagenomes identified several pathways and enzymes involved in various physiological and ecological functions. Amino acid and vitamin biosynthesis-related pathways were predominant than carbohydrate metabolism, owing to their feeding habit and nutritional requirement. Chaperones related to stress tolerance such as GroEL and DnaK were identified. Enzymes involved in toxic chemical metabolisms such as glutathione transferase, phosphodiesterases and ABC transferases were observed. These enzymes may confer resistance to pesticides in the aphid populations. Overall, our results support the importance of host plants in structuring bacterial communities in aphids and show the functional roles of symbionts in aphid survival and development. Thus, these findings can be the basis for further detailed investigations and devising better strategies to manage the pests in field conditions.

SUPPLEMENTARY INFORMATION

The online version contains supplementary material available at 10.1007/s13205-022-03142-1.

Physicochemical characteristics and flavor profiles of fermented fish sauce (budu) during fermentation in commercial manufacturing plant

This study was done by dynamically monitoring the changes in bacterial composition, physicochemical characteristics, and volatile substances during fermentation of fermented fish sauce (budu). The degree of hydrolysis, TCA-soluble peptides, and nitrogen contents increased as the fermentation time progressed. A continuous decrease in peroxide value and thiobarbituric acid reactive substances was noted over 60 days of fermentation. A total of 44 volatile compounds were detected, and increases in volatile compounds, such as 2-methylbutanal, 3-methylbutanal, benzaldehyde, and 2-ethyl furan, with low odor thresholds values, might contribute to budu's flavor of the final product. Additionally, the relationship between evolving microbiota and the formation of flavor compounds was analyzed, and halophilic lactic acid bacteria was identified to be the most important bacterial contributing to flavor and aroma development. This finding will provide important information for improving the quality of budu in terms of flavor characteristics.

Variations in antibiotic resistance genes and removal mechanisms induced by C/N ratio of substrate during composting

For a comprehensive insight into the potential mechanism of the removal of antibiotic resistance genes (ARGs) removal induced by initial substrates during composting, we tracked the dynamics of physicochemical properties, bacterial community composition, fungal community composition, the relative abundance of ARGs and mobile genetic genes (MGEs) during reed straw and cow manure composting with different carbon to nitrogen ratio. The results showed that the successive bacterial communities were mainly characterized by the dynamic balance between Firmicutes and Actinobacteria, while the fungal communities were composed of Ascomycota. During composting, the interactions between bacteria and fungi were mainly negative. After composting, the removal efficiency of ARGs in compost treatment with C/N ≈ 26 (LL) was higher than that in compost treatment with C/N ≈ 35 (HL), while MGEs were completely degraded in HL and enriched by 2.3% in LL. The large reduction in the relative abundance of ARGs was possibly due to a decrease in the potential host bacterial genera, such as Advenella, Tepidimicrobium, Proteiniphilum, Acinetobacter, Pseudomonas, Flavobacteria and Arcbacter. Partial least-squares path modeling (PLS-PM) revealed that the succession of bacterial communities played a more important role than MGEs in ARGs removal, while indirect factors of the fungal communities altered the profile of ARGs by affecting the bacterial communities. Both direct and indirect factors were affected by composting treatments. This study provides insights into the role of fungal communities in affecting ARGs and highlights the role of different composting treatments with different carbon to nitrogen ration on the underlying mechanism of ARGs removal.

Geographic and position-based variations in phyllospheric bacterial communities present on flue-cured tobacco

Although tobacco leaves (TLs) contain abundant bacteria, how the geography and leaf position of TLs affect these bacteria is unclear. Here, TLs at different positions from Henan (HN, strong flavor style) and Yunnan (YN, fresh flavor style) provinces were collected, and the bacteria were characterized by Illumina sequencing at harvest and 1 year of storage. Bacterial communities were very different between TLs originating from different geographical areas and positions, and beta diversity analysis showed that leaf position was the most important factor for phyllospheric bacterial communities, followed by geographical area and storage time. At the genus level, Subdoligranulum, Thermus, and Acinetobacter were obviously more abundant in HN than in YN, while Blautia and Ruminococcus were significantly more abundant in YN. These differences in bacterial communities decreased after 1 year of storage, indicating that the microbiota tends to become similar during tobacco processing. Storage time also affected the phyllospheric bacteria of TLs, as the bacterial communities shifted significantly on both HN and YN TLs after 1 year of storage. Significant differences in the predicted genes were also observed between the different geographic locations and leaf positions. Potential human pathogens, including Acinetobacter, Methylobacterium, and Escherichia-Shigella, were greatly different between TLs originating from different areas and positions. These data suggested that geographic variations and positions were associated with phyllospheric bacterial communities on TLs, which may be related to not only the flavor style and quality of TLs but also the potential health risks to humans. KEY POINTS: • Tobacco leaf position and tobacco growth location affected bacterial communities. • Microbial communities of TLs shifted significantly after one year of storage. • Potential human pathogens differed at different leaf positions and growth locations.

Bacterial community dynamics following antibiotic exposure in a trematode parasite

Parasites harbour rich microbial communities that may play a role in host-parasite interactions, from influencing the parasite's infectivity to modulating its virulence. Experimental manipulation of a parasite's microbes would be essential, however, in order to establish their causal role. Here, we tested whether indirect exposure of a trematode parasite within its snail intermediate host to a variety of antibiotics could alter its bacterial community. Based on sequencing the prokaryotic 16S ssrRNA gene, we characterised and compared the bacterial community of the trematode Philophthalmus attenuatus before, shortly after, and weeks after exposure to different antibiotics (penicillin, colistin, gentamicin) with distinct activity spectra. Our findings revealed that indirectly treating the parasites by exposing their snail host to antibiotics resulted in changes to their bacterial communities, measured as their diversity, taxonomic composition, and/or the relative abundance of certain taxa. However, alterations to the parasite's bacterial community were not always as predicted from the activity spectrum of the antibiotic used. Furthermore, the bacterial communities of the parasites followed significantly divergent trajectories in the days post-exposure to antibiotics, but later converged toward a new state, i.e. a new bacterial community structure different from that pre-exposure. Our results confirm that a trematode's microbial community can be experimentally altered by antibiotic exposure while within its snail host, with the dynamic nature of the bacterial assemblage driving it to a new state over time after the perturbation. This research opens new possibilities for future experimental investigations of the functional roles of microbes in host-parasite interactions.

Bacterial community demonstrates stronger network connectivity than fungal community in desert-grassland salt marsh

The diversity of soil bacterial and fungal communities is closely related to the soil characteristics and vegetation types in salt marsh ecosystems, but the biogeographic patterns and driving factors in desert-grassland salt marsh (DGSM) are still unclear. In this study, we divided sample plots according to the dominant species in Jiantan Lake wetland of a typical DGSM in Northwestern China. The effects of different environmental factors and halophytes on the structure of soil bacterial and fungal communities were investigated using soil physicochemical characterization and high-throughput sequencing analysis. The diversity of bacterial communities in bulk soil and three dominant halophytes (Kalidium cuspidatum, Nitraria tangutorum and Sophora alopecuroides) were the main factors affecting soil physicochemical properties and halophyte vegetation coverage. Proteobacteria, Bacteroides and Gemmatimonadetes had the highest abundance in bulk soil and the lowest in Sophora alopecuroides sample soil; the opposite was true for Acidobacteria and Chloroflexi. The abundance of Ascomycota in bulk soil and Sophora alopecuroides sample soil was higher than Kalidium cuspidatum and Nitraria tangutorum sample soils, whereas the Mortierellomycota was the highest in Nitraria tangutorum sample soil. Co-occurrence network analysis showed that halophyte cover increased the connectivity and complexity of the bacterial-fungal interaction network, and the halophytic shrub sample soil had a more stable network relationship than the halophytic herb soil. The key taxa of each plot were identified through network relationships. It was found that the keystone taxa of Proteobacteria, Firmicutes, Ascomycota and Chytridiomycota played important roles in maintaining community functions, and most of them were not significantly influenced by soil physicochemical properties. The results of this study provide new insights for a deeper understanding of the halophytes that drive the multifunctionality and stability of soil ecosystems in DGSM.

Comparing sediment preservation methods for genomic biomonitoring of coastal marine ecosystems

To avoid loss of genetic information in environmental DNA (eDNA) field samples, the preservation of nucleic acids during field sampling is a critical step. In the development of standard operating procedures (SOPs) for eDNA-based compliance monitoring, the effect of different routinely used sediment preservations on biological community structures serving as bioindicators has gone untested. We compared eDNA metabarcoding results of marine bacterial communities from sample aliquots that were treated with a nucleic acid preservation solution (treated samples) and aliquots that were frozen without further treatment (non-treated samples). Sediment samples were obtained from coastal locations subjected to different stressors (aquaculture, urbanization, industry). DNA extraction efficiency, bacterial community profiles, and measures of alpha- and beta-diversity were highly congruent between treated and non-treated samples. As both preservation methods provide the same relevant information to environmental managers and regulators, we recommend the inclusion of both methods into SOPs for biomonitoring in marine coastal environments.

Effects of bioturbation by tubificid worms on biogeochemical processes, bacterial community structure and diversity in heterotrophic wetland sediments

Bioturbation activity of tubificid worms has been recognized as a key process influencing organic matter processing and nutrient cycling in benthic aquatic ecosystems. This activity is expected to modify benthic microbial communities by affecting the physical and chemical environment in sediments. Nevertheless, quantifications of bacterial community changes associated with bioturbation in freshwater ecosystems are still lacking. The present study aimed at evaluating the impact of tubificid worms on bacterial community structure using NGS approach (16S metabarcoding) and long (6 months) laboratory experiments on four heterotrophic wetland sediments. Worm bioturbation activity significantly stimulated biogeochemical processes at the water-sediment interface but only had a marginally significant effect on bacterial community structures. Yet, bacterial diversity was consistently reduced in presence of worms. Such decrease could be associated with the stimulation of organic matter mineralization by worms, leading to a reduction of the diversity of trophic niches available for bacterial species. The slight changes in bacterial community structures induced by bioturbation did not appear to control biogeochemical processes. Thus, the stimulation of biogeochemical processes by worm bioturbation was more associated with a stimulation of the initial bacterial community than with a drastic change in bacterial communities induced by worms.

Interactions between heavy metals and bacteria in mangroves

Environmental heavy metal pollution has become a serious problem in recent years. Therefore, our study investigated seven heavy metal-contaminated mangroves (Beihai, Fangchenggang, Hainan, Hongkong, Shenzhen, Yunxiao, and Zhanjiang) in southern China, and found that they were particularly polluted with Zn and Pb. These heavy metals were mainly distributed in the surface sediments of the mangroves. Among these seven mangroves, the Shenzhen mangrove was the most polluted site, whereas the Beihai mangrove was the least polluted. Moreover, the bacterial communities in the mangroves were significantly associated with heavy metal contamination. For instance, Fusibacter was significantly correlated with Pb, Zn, Cu, Co, Ni, Cd, and Ag (P < 0.05, R = -0.47). Syntrophorhabdus was also significantly correlated with heavy metals (P < 0.05, R = 0.63). Furthermore, Geo-Chip analyses were conducted to demonstrate the involvement of many functional genes in heavy metal transport, particularly Ni transport. Our results also demonstrated that the heavy metals could be transported by various bacteria. For example, Pseudomonas and Burkholderia were involved in various heavy metal transportation mechanisms, particularly for Ni and Zn, suggesting that these bacteria could be used for heavy metal remediation. Therefore, our study provides insights into the interactions between bacterial communities and heavy metals, which could enable the development of novel mangrove protection strategies.

The Himalayan Onion (Allium wallichii Kunth) Harbors Unique Spatially Organized Bacterial Communities

Plant-associated microorganisms are known to contribute with various beneficial functions to the health and productivity of their hosts, yet the microbiome of most plants remains unexplored. This especially applies to wild relatives of cultivated plants, which might harbor beneficial microorganisms that were lost during intensive breeding. We studied bacterial communities of the Himalayan onion (Allium wallichii Kunth), a wild relative of onion native to mountains in East Asia. The bacterial community structure was assessed in different plant microhabitats (rhizosphere, endosphere, anthosphere) by sequencing of 16S rRNA gene fragment amplicons. Targeted bioinformatic analyses were implemented in order to identify unique features in each habitat and to map the overall community in the first representative of the Amaryllidaceae plant family. The highest bacterial diversity was found for bulk soil (Shannon index, H' 9.3) at the high-altitude sampling location. It was followed by the plant rhizosphere (H' 8.9) while communities colonizing flowers (H' 6.1) and the endosphere (H' 6.5 and 5.6) where less diverse. Interestingly, we observed a non-significant rhizosphere effect. Another specificity of the microbiome was its high evenness in taxonomic distribution, which was so far not observed in plant microbiomes. Pseudomonas was identified among additional 10 bacterial genera as a plant-specific signature. The first insights into the microbiome of a plant in the widespread Allium genus will facilitate upcoming comparisons with its domesticated relatives while additionally providing a detailed microbiome mapping of the plant's microhabitats to facilitate bioresource mining.

Links between microbial compositions and metabolites during aerobic composting under amoxicillin stress was evaluated by 16S rRNA sequencing and gas chromatography-mass spectrometry: Benefit for the plant growth

The purpose of this study was to identify the relationship between core bacteria and metabolites during aerobic composting and analyze the effects of metabolites on plant growth. The results revealed that amoxicillin might affect the generation and transformation of metabolites by reconstructs the bacterial communities. The peak area ratios (PAR) of esters and fatty acids (FAs) were increased, while sterols decreased during composting. Furthermore, the correlation analysis showed that the production of FAs, esters and sterols is strongly correlated with Oceanobacillus, Corynebacterium, Psychrobacter, Xanthomonadaceae, Pusillimonas and Gracilibacillus. Moreover, 36 key metabolites were screened out, the PAR of the propanoic acid ethyl ester and oleic acid that benefit plant growth were increased in amoxicillin groups. However, the PAR of environmental pollutants, such as n-hexadecanoic acid and 3β, 5β-Cholestan-3-ol is the opposite. Therefore, composting can eliminate the environmental risks caused by antibiotic residues in feces and promote plant growth.

Comparison of anaerobic co-digestion of pig manure and sludge at different mixing ratios at thermophilic and mesophilic temperatures

The objective of this study is to assess the effects of the mixing ratio on the methane production and digestate dewaterability of co-digestion of pig manure (P) and sludge (S). Batch experiments were carried out at five different P/S mixing ratios at mesophilic and thermophilic temperatures. Compared to sludge anaerobic digestion, co-digestion of pig manure with sludge increased methane yield 83.0%-136.5% at mesophilic temperature and 31.3%-68.0% at thermophilic temperature. The normalized capillary suction time (NCST) and total solids (TS) of sediment (centrifugal dewatering) increased when pig manure proportion of substrate increased. The NCST at thermophilic temperatures (4.87-17.58 s g^-1-TSS) was higher than that at mesophilic temperatures (1.89-10.95 s g^-1-TSS). However, the TS of sediment was close at thermophilic and mesophilic temperatures. The results indicated that anaerobic co-digestion of pig manure and sludge at a proper mixing ratio (P/S = 2:1) provides a good choice for energy recovery and land utilization.

Distinct profile of bacterial community and antibiotic resistance genes on microplastics in Ganjiang River at the watershed level

Microplastics are of great public concern due to their wide distribution and the potential risk to humans and animals. In this study, the microplastic pollution associated with bacterial communities, human pathogenic bacteria, and antibiotic resistance genes (ARGs) were investigated compared to water, sediment, and natural wood particles. Microplastics were widely distributed in surface water of the Ganjiang River at a watershed level with an average value of 407 particles m^-3. The fragment was the main microplastic shape found in the basin. Microplastics had significantly higher observed species and Chao1 index of bacterial communities than those in water, but comparable to wood particles. However, there was no difference in the microplastics pollution and alpha diversity indices of bacterial between different reaches along the Ganjiang River. Flavobacterium, Rhodoferax, Pseudomonas, and Janthinobacterium on the microplastics were all found to be enriched compared with water and sediment. Principal component analysis of the composition and function profile of bacterial communities showed that microplastics provide a new microbial niche in the Ganjiang River, which was distinct from water, sediment, and natural wood. Pseudomonas genus dominated the composition of human pathogenic bacteria on the microplastics, which was significantly different from water and sediment. No difference was observed in the relative abundance of total ARGs among the four media. However, microplastic and wood particles showed similar composition patterns of ARGs compared with water and sediment.

Integrating experiments with system-level biogeochemical modeling to understand nitrogen cycling of reservoir sediments at elevated hydrostatic pressure

Impoundment of rivers to construct reservoirs for hydropower and irrigation greatly increase the hydrostatic pressure acting on river sediments with potential repercussions for ecosystem-level microbial activity and metabolism. Understanding the functioning and responses of key biogeochemical cycles such as that of nitrogen cycling to shifting hydrostatic pressure is needed to estimate and predict the systemic nutrient dynamics in deep-water reservoirs. We studied the functioning of bacterial communities involved in nitrogen transformation in bioreactors maintained under contrasting hydrostatic pressures (0.5 MPa-3.0 MPa) and complemented the experimental approach with a functional gene-informed biogeochemical model. The model predictions were broadly consistent with observations from the experiment, suggesting that the rates of N₂O production decreased while the sediment concentration of nitrite increased significantly with increasing pressure, at least when exceeding 1.0 MPa. Changes in nitrite reduction (nirS) and aerobic ammonia oxidation (amoA) genes abundances were in accordance with the observed changes in N₂O production and nitrite levels. Moreover, the model predicted that the higher pressures (P > 1.5 MPa) would intensify the inhibition of N₂ production via denitrification and result in an accumulation of ammonia in the sediment along with a decrease in dissolved oxygen. The results imply that increased hydrostatic pressure caused by dam constructions may have a strong effect on microbial nitrogen conversion, and that this may result in lower nitrogen removal.

Long-term effects of liquid swine manure land surface application in an apple orchard field on soil bacterial community and heavy metal contents in apple (Malus pumila Mill.)

This study investigated the impact of liquid swine manure (LSM) land surface application in an apple orchard on soil health and copper (Cu) and zinc (Zn) in soil and apple. Three apple plots were selected, among which two for LSM application for 5 (AY5) and 11 (AY11) years with different application rates, a long-term inorganic fertilizer application plot as the control treatment (AY0). The soil and apple samples were collected for analysis of soil physicochemical properties, bacterial diversity and abundance, and the contents of Cu and Zn in soil and apple. Results showed that the LSM application significantly increased the concentration of soil nutrients with the highest in AY5, which has a high application rate of LSM. After 5 or 11 years applied, the content of total nitrogen (TN) in AY5 and AY11 increased by 125.2% and 96.7%, total phosphorus (TP) increased by 167.6% and 148.6%, and soil organic matter (SOM) increased by 180.7% and 120.6%, respectively. The AY5 treatment significantly lowered OTUs and decreased Shannon index trend with a negative correlation between soil organic matter and Shannon index. The six predominant bacterial phyla in different treatments were similar, but the LSM application significantly increased the abundance of Chloroflexi and Firmicutes. However, the abundance of Actinobacteria and Acidobacteria significantly decreased in AY5 as compared to control treatment, followed by a significant positive correlation between the abundance of Acidobacteria and soil pH. Besides, LSM application significantly increased the contents of soil Cu, Zn, and apple Zn. Overall, the results illustrated that appropriate application rate of LSM can effectively improve apple orchard soil quality and bacterial community structure, but it will increase the risk of heavy metal accumulation in soil and apples.

Community-level dormancy potential regulates bacterial beta-diversity succession during the co-composting of manure and crop residues

This study aimed to disclose the bacterial diversity succession during the co-composting of manure and crop residues and to provide new insight into the role of community-level dormancy potential in diversity succession. Illumina sequencing and PICRUSt-estimated metagenomes were used for this purpose. The bacterial richness and phylogenetic diversity decreased in the early and middle stages of composting and were maintained to a stable status in the late stage. Both composting phases and raw materials impacted the aforementioned alpha diversity significantly, while the composting phases had a greater (80%-94%) impact than the raw materials (1%-18%). Bacterial beta-diversity succession exhibited selectivity as the composting proceeded, and the dominant taxa changed into salt- and heat-resistant genera such as Bacillus, Glycomyces, and Halocella. Meanwhile, Georgenia, Actinomadura, and Ruminofilibacter were identified as the dominant predictor taxa of bacterial community succession in composting. Roughly, the abundance of genes underlying dormancy strategies, including sporulation factors (spo0A gene), toxin-antitoxin systems (dinJ/yafP, mazF/E, hipA/O, and relA/E genes), and resuscitation-promoting factors (rpfC gene), increased as composting proceeded and reached the highest in the thermophilic or maturation phases. Co-occurring relationships between bacterial communities and genes underlying dormancy strategies in different composting phases comprised multiple associations dominated by positive edges (50%-97%). The stability in genes underlying dormancy strategies and aggregate dormancy potential had a positive linear correlation with that in bacterial beta diversity (R² = 0.26-0.42; P < 0.05), but not related significantly to that in richness and phylogenetic diversity. This study highlighted the importance of understanding how community-level dormancy strategies mediated microbial succession in composting to better predict compost maturity and product quality.

Bacterial diversity and predicted enzymatic function in a multipurpose surface water system - from wastewater effluent discharges to drinking water production

BACKGROUND

Rivers and lakes are used for multiple purposes such as for drinking water (DW) production, recreation, and as recipients of wastewater from various sources. The deterioration of surface water quality with wastewater is well-known, but less is known about the bacterial community dynamics in the affected surface waters. Understanding the bacterial community characteristics -from the source of contamination, through the watershed to the DW production process-may help safeguard human health and the environment.

RESULTS

The spatial and seasonal dynamics of bacterial communities, their predicted functions, and potential health-related bacterial (PHRB) reads within the Kokemäenjoki River watershed in southwest Finland were analyzed with the 16S rRNA-gene amplicon sequencing method. Water samples were collected from various sampling points of the watershed, from its major pollution sources (sewage influent and effluent, industrial effluent, mine runoff) and different stages of the DW treatment process (pre-treatment, groundwater observation well, DW production well) by using the river water as raw water with an artificial groundwater recharge (AGR). The beta-diversity analysis revealed that bacterial communities were highly varied among sample groups (R = 0.92, p <  0.001, ANOSIM). The species richness and evenness indices were highest in surface water (Chao1; 920 ± 10) among sample groups and gradually decreased during the DW treatment process (DW production well; Chao1: 320 ± 20). Although the phylum Proteobacteria was omnipresent, its relative abundance was higher in sewage and industrial effluents (66-80%) than in surface water (55%). Phyla Firmicutes and Fusobacteria were only detected in sewage samples. Actinobacteria was more abundant in the surface water (≥13%) than in other groups (≤3%). Acidobacteria was more abundant in the DW treatment process (≥13%) than in others (≤2%). In total, the share of PHRB reads was higher in sewage and surface water than in the DW treatment samples. The seasonal effect in bacterial communities was observed only on surface water samples, with the lowest diversity during summer.

CONCLUSIONS

The low bacterial diversity and absence of PHRB read in the DW samples indicate AGR can produce biologically stable and microbiologically safe drinking water. Furthermore, the significantly different bacterial communities at the pollution sources compared to surface water and DW samples highlight the importance of effective wastewater treatment for protecting the environment and human health.