Both pH and salinity shape the microbial communities of the lakes in Badain Jaran Desert, NW China

Intestinal microbial community well explain larval growth than feed types

Black soldier fly larvae (BSFL) are considered a sustainable ingredient in livestock feed. However, addressing issues related to feed substrate and intestinal microbiota is essential to ensure optimal larval development. The aim of this study was to assess and elucidate the contribution of substrate nutrients and intestinal microbes to protein and fat synthesis in BSFL. The results showed that larvae that were fed high-quality feed (chicken feed) had high fat biomass, while larvae that were fed medium-quality feed (wheat bran) had high protein biomass. These results indicate that the original nutritional content of the feed cannot fully explain larval growth and nutrient utilization. However, the phenomenon could be explained by the functional metabolism of intestinal microbes. Chicken feed enhanced the fatty acid metabolism of middle intestine microorganisms in larvae within 0-7 days. This process facilitated larval fat synthesis. In contrast, wheat bran stimulated the amino acid metabolism in posterior intestine microorganisms in larvae within 4-7 days, leading to better protein synthesis. The findings of this study highlight the importance of the microbial functional potential in the intestine in regulating protein and lipid synthesis in BSFL, which is also influenced by the type of feed. In conclusion, our study suggests that both feed type and intestinal microbes play a crucial role in efficiently converting organic waste into high-quality insect protein and fat. Additionally, a mixed culture of chicken feed and wheat bran was found to be effective in promoting larval biomass while reducing feed costs. KEY POINTS: • Intestinal microbes explain BSFL growth better than feed substrates. • Chicken feed promotes fatty acid synthesis in the middle intestine • Wheat bran promotes amino acid synthesis in the posterior intestine.

Trophic level plays an enhanced role in shaping microbiota structure and assembly in lakes with decreased salinity on the Qinghai-Tibet and Inner Mongolia Plateaus

Plateau lakes characterized by salinization and eutrophication are essential aquatic ecosystems. A myriad of microorganisms serve as crucial biological resources in plateau lakes and drive the elemental cycles of these ecosystems. Currently, there is a paucity of knowledge regarding the impacts of salinization and eutrophication dynamics on the microbiota in plateau lakes. Here, high-throughput sequencing of the 16S ribosomal RNA genes (V4 region) was used to characterize microbial community structure and assembly in plateau lakes with different salinities and trophic levels. Water samples were collected at 191 sites across 24 lakes on the Qinghai-Tibet and Inner Mongolia Plateaus in northern China. The results showed that high salinity considerably reduced microbial alpha-diversity and niche breadth while increasing within-group similarity among various lake types. High salinity additionally decreased the complexity of microbial networks and enhanced network robustness. The assembly of microbial communities was primarily governed by deterministic processes in high-salinity and eutrophic low-salinity lakes. At decreased salinity, trophic level played a leading role in shaping microbial community structure, and the ecological processes shifted from deterministic processes driven by high salinity to eutrophication-driven deterministic processes. The biomarkers also varied from taxa adapted to high-salinity environments (e.g., Nanoarchaeaeota, Rhodothermia) to those suited for living in freshwater and low-salinity habitats (e.g., Alphaproteobacteria, Actinobacteria). In the case of eutrophication, Actinobacteria, Chloroflexi, and Cyanobacteria became the dominant taxa. Our findings indicate that decreased salinity enables trophic level to play an enhanced role in shaping microbial community structure and assembly in plateau lakes. This study enriches our knowledge about the ecological impacts of salinization and eutrophication in plateau lakes.

Cefotaxime Exposure-Caused Oxidative Stress, Intestinal Damage and Gut Microbial Disruption in Artemia sinica

Cefotaxime (CTX) is an easily detectable antibiotic pollutant in the water environment, but little is known about its toxic effects on aquatic invertebrates, especially on the intestine. Here, we determined the oxidative stress conditions of A. sinica under CTX exposure with five concentrations (0, 0.001, 0.01, 0.1 and 1 mg/L) for 14 days. After that, we focused on changes in intestinal tissue morphology and gut microbiota in A. sinica caused by CTX exposure at 0.01 mg/L. We found malondialdehyde (MDA) was elevated in CTX treatment groups, suggesting the obvious antibiotic-induced oxidative stress. We also found CTX exposure at 0.01 mg/L decreased the villus height and muscularis thickness in gut tissue. The 16S rRNA gene analysis indicated that CTX exposure reshaped the gut microbiota diversity and community composition. Proteobacteria, Actinobacteriota and Bacteroidota were the most widely represented phyla in A. sinica gut. The exposure to CTX led to the absence of Verrucomicrobia in dominant phyla and an increase in Bacteroidota abundance. At the genus level, eleven genera with an abundance greater than 0.1% exhibited statistically significant differences among groups. Furthermore, changes in gut microbiota composition were accompanied by modifications in gut microbiota functions, with an up-regulation in amino acid and drug metabolism functions and a down-regulation in xenobiotic biodegradation and lipid metabolism-related functions under CTX exposure. Overall, our study enhances our understanding of the intestinal damage and microbiota disorder caused by the cefotaxime pollutant in aquatic invertebrates, which would provide guidance for healthy aquaculture.

Interactions between water quality and microbes in epiphytic biofilm and superficial sediment of lake in trophic agriculture area

Epiphytic and superficial sediment biofilm-dwelling microbial communities play a pivotal role in water quality regulation and biogeochemical cycling in shallow lakes. However, the interactions are far from clear between water physicochemical parameters and microbial community on aquatic plants and in surface sediments of lake in trophic agriculture area. This study employed Illumina sequencing, Partial Least Squares Path Modeling (PLS-PM), and physico-chemical analytical methods to explore the interactions between water quality and microbes (bacteria and eukaryotes) in three substrates of trophic shallow Lake Cyohoha North, Rwanda. The Lake Cyohoha was significantly polluted with total phosphorus (TP), total nitrogen (TN), nitrate nitrogen (NO3-N), and ammonia nitrogen (NH3-N) in the wet season compared to the dry season. PLS-PM revealed a strong positive correlation (+0.9301) between land use types and physico-chemical variables in the rainy season. In three substrates of the trophic lake, Proteobacteria, Cyanobacteria, Firmicutes, and Actinobacteria were dominant phyla in the bacterial communities, and Rotifers, Platyhelminthes, Gastrotricha, and Ascomycota dominated in microeukaryotic communities. As revealed by null and neutral models, stochastic processes predominantly governed the assembly of bacterial and microeukaryotic communities in biofilms and surface sediments. Network analysis revealed that the microbial interconnections in Ceratophyllum demersum were more stable and complex compared to those in Eichhornia crassipes and sediments. Co-occurrence network analysis (|r| > 0.7, p < 0.05) revealed that there were complex interactions among physicochemical parameters and microbes in epiphytic and sediment biofilms, and many keystone microbes on three substrates played important role in nutrients removal, food web and microbial community stable. These findings emphasize that eutrophic water influence the structure, composition, and interactions of microbes in epiphytic and surface sediment biofilms, and provided new insights into the interconnections between water quality and microbial community in presentative substrates in tropical lacustrine ecosystems in agriculturally polluted areas. The study provides useful information for water quality protection and aquatic plants restoration for policy making and catchment management.

Alterations in the composition and metabolite profiles of the saline-alkali soil microbial community through biochar application

Saline-alkali soil poses significant chanllenges to sustainable development of agriculture. Although biochar is commonly used as a soil organic amendment, its microbial remediation mechanism on saline-alkali soil requires further confirmation. To address this, we conducted a pot experiment using cotton seedlings to explore the potential remediation mechanism of rice straw biochar (BC) at three different levels on saline-alkaline soil. The results showed that adding of 2% biochar greatly improved the quality of saline-alkaline soil by reducing pH levels, electrical conductivity (EC), and water-soluble ions. Moreover, biochar increased the soil organic matter (SOM), nutrient availability and extracellular enzyme activity. Interestingly, it also reduced soil salinity and salt content in various cotton plant tissues. Additionally, biochar had a notable impact on the composition of the microbial community, causing changes in soil metabolic pathways. Notably, the addition of biochar promoted the growth and metabolism of dominant salt-tolerant bacteria, such as Proteobacteria, Bacteroidota, Acidobacteriota, and Actinobacteriota. By enhancing the positive correlation between microorganisms and metabolites, biochar alleviated the inhibitory effect of salt ions on microorganisms. In conclusion, the incorporation of biochar significantly improves the soil microenvironment, reduces soil salinity, and shows promise in ameliorating saline-alkaline soil conditions.

Surge of native rare taxa in tailings soil induced by peat bacterial invasion

The pivotal role of the native bacterial community in maintaining soil health, particularly in degraded tailings environments, is often overlooked. This study utilized peat, rich in microorganisms, to investigate its impact on soil function and native bacteria response in copper tailings-soil. Through 16S rRNA gene sequencing, changes in nutrient cycling, organic matter decomposition, and microbial activity were assessed post one-year peat remediation. Results from FEAST and cluster analysis revealed that peat-derived species disproportionately influenced tailings microbial community remediation, supported by the microbial invasion theory. Tailings responded positively to these species, with optimal function achieved at 5 % peat dosage. Peat biomarkers (Actinobacteriota, Bacteroida, Chloroflexi, and Firmicutes) played key roles in heavy metal removal and nutrition fixation. The Random Forest model and co-occurrence network highlighted contributions from native rare species (Dependentiae and Latescibacterota) activated by peat addition. These insights underscore the resilience of rare taxa and provide a foundation for soil health restoration in tailings areas. By emphasizing the importance of peat as a potential exogenous solution for activating indigenous microbial functions, these findings offer valuable insights for developing effective and sustainable remediation strategies in mining-affected regions.

Impact of artificial mixing and oxygenation on bacteria in a water transfer reservoir: Community succession and the role in water quality improvement

Artificial mixing and oxygenation induced by water-lifting aerations (WLAs) have the potential to improve water quality in reservoirs. However, there is a limited understanding of the bacterial community composition, assembly, and mechanisms behind water quality improvement under the influence of WLAs, especially in a water transfer reservoir. Here, the dynamics and relationship between water quality, bacterial diversity, and composition during the pre-operation, in-operation, and post-operation stages of WLAs were analyzed using high-throughput sequencing technology to explore the effects of artificially regulated bacteria on water quality improvement. WLAs operation led to the elimination of water stratification, significant bottom oxygenation, and reduction in nutrient concentrations. In addition, the operation of WLAs significantly changed the bacterial community composition, with an increase in richness, negligible difference in diversity, and a significant increase in the abundance of species with pollutant degradation functions, resulting in a shift from stochastic to deterministic processes of the bacterial community assembly. As a result, enhancement of the dominant bacteria responsible for organic matter degradation and denitrification and suppression of the emergence of algae-related bacteria were observed during the WLAs operation, and the ecosystem stability improved. Multiple analyses indicated a direct correlation between artificial mixing and oxygenation; changes in the bacterial community; and the reduction of nitrogen, phosphorus, and permanganate index in the water column. This study provides novel insights into in situ water quality enhancement and a valuable reference for understanding bacterial change patterns under artificially intervened conditions in water transfer reservoirs.

Different Responses of Bacteria and Archaea to Environmental Variables in Brines of the Mahai Potash Mine, Qinghai-Tibet Plateau

Salt mines feature both autochthonous and allochthonous microbial communities introduced by industrialization. It is important to generate the information on the diversity of the microbial communities present in the salt mines and how they are shaped by the environment representing ecological diversification. Brine from Mahai potash mine (Qianghai, China), an extreme hypersaline environment, is used to produce potash salts for hundreds of millions of people. However, halophiles preserved in this niche during deposition are still unknown. In this study, using high-throughput 16S rRNA gene amplicon sequencing and estimation of physicochemical variables, we examined brine samples collected from locations with the gradient of industrial activity intensity and discrete hydrochemical compositions in the Mahai potash mine. Our findings revealed a highly diverse bacterial community, mainly composed of Pseudomonadota in the hypersaline brines from the industrial area, whereas in the natural brine collected from the upstream Mahai salt lake, most of the 16S rRNA gene reads were assigned to Bacteroidota. Halobacteria and halophilic methanogens dominated archaeal populations. Furthermore, we discovered that in the Mahai potash mining area, bacterial communities tended to respond to anthropogenic influences. In contrast, archaeal diversity and compositions were primarily shaped by the chemical properties of the hypersaline brines. Conspicuously, distinct methanogenic communities were discovered in sets of samples with varying ionic compositions, indicating their strong sensitivity to the brine hydrochemical alterations. Our findings provide the first taxonomic snapshot of microbial communities from the Mahai potash mine and reveal the different responses of bacteria and archaea to environmental variations in this high-altitude aquatic ecosystem.

Archaeal lipids

The major archaeal membrane glycerolipids are distinguished from those of bacteria and eukaryotes by the contrasting stereochemistry of their glycerol backbones, and by the use of ether-linked isoprenoid-based alkyl chains rather than ester-linked fatty acyl chains for their hydrophobic moieties. These fascinating compounds play important roles in the extremophile lifestyles of many species, but are also present in the growing numbers of recently discovered mesophilic archaea. The past decade has witnessed significant advances in our understanding of archaea in general and their lipids in particular. Much of the new information has come from the ability to screen large microbial populations via environmental metagenomics, which has revolutionised our understanding of the extent of archaeal biodiversity that is coupled with a strict conservation of their membrane lipid compositions. Significant additional progress has come from new culturing and analytical techniques that are gradually enabling archaeal physiology and biochemistry to be studied in real time. These studies are beginning to shed light on the much-discussed and still-controversial process of eukaryogenesis, which probably involved both bacterial and archaeal progenitors. Puzzlingly, although eukaryotes retain many attributes of their putative archaeal ancestors, their lipid compositions only reflect their bacterial progenitors. Finally, elucidation of archaeal lipids and their metabolic pathways have revealed potentially interesting applications that have opened up new frontiers for biotechnological exploitation of these organisms. This review is concerned with the analysis, structure, function, evolution and biotechnology of archaeal lipids and their associated metabolic pathways.

Microbial communities and sediment nitrogen cycle in a coastal eutrophic lake with salinity and nutrients shifted by seawater intrusion

Coastal waters are often influenced by seawater intrusion and terrestrial emissions because of its special location. In this study, the dynamics of microbial community with the role of nitrogen cycle in sediment in a coastal eutrophic lake were studied under a warm season. The water salinity gradually increased from 0.9‰ in June to 4.2‰ in July and 10.5‰ in August because of seawater invasion. Bacterial diversity of surface water was positively related with salinity and nutrients of total nitrogen (TN) as well as total phosphorus (TP), but eukaryotic diversity had no relationship with salinity. In surface water, algae belonging to Cyanobacteria and Chlorophyta were dominant phyla in June with the relative abundances of >60%, but Proteobacteria became the largest bacterial phylum in August. The variation of these predominant microbes had strong relationship with salinity and TN. In sediment, the bacterial and eukaryotic diversity was greater than that of water, and a significantly different microbial community was observed with dominant bacterial phyla Proteobacteria and Chloroflexi, and dominant eukaryotic phyla Bacillariophyta, Arthropoda, and Chlorophyta. Proteobacteria was the only enhanced phylum in the sediment with the highest relative abundance of 54.62% ± 8.34% due to seawater invasion. Denitrifying genera (29.60%-41.81%) were dominant in surface sediment, then followed by microbes related to nitrogen fixation (24.09%-28.87%), assimilatory nitrogen reduction (13.54%-19.17%), dissimilatory nitrite reduction to ammonium (DNRA, 6.49%-10.51%) and ammonification (3.07%-3.71%). Higher salinity caused by seawater invasion enhanced the accumulation of genes involved in dentrificaiton, DNRA and ammonification, but decreased genes related to nitrogen fixation and assimilatory nitrogen reduction. Significant variation of dominant genes of narG, nirS, nrfA, ureC, nifA and nirB mainly caused by the changes in Proteobacteria and Chloroflexi. The discovery of this study would be helpful to understand the variation of microbial community and nitrogen cycle in coastal lake under seawater intrusion.

Metagenomic Analysis Reveals the Response of Microbial Communities and Their Functions in Lake Sediment to Environmental Factors

Jingpo Lake is the largest mountain barrier lake in China and plays a key role in breeding, power generation, and providing a source of drinking water. Microbes are important participants in the formation of lake resources and energy cycles. However, the ecological protection of Jingpo Lake has faced serious challenges in recent years. In this study, we investigate the responses of the microbial community's composition of sediments at five locations to an environmental gradient representing water quality and water-depth changes using a metagenomic sequence. We found that the diversity and composition of the microbiota sediments were altered spatially and correlated with the physicochemical factors of water samples. In the microbial community, relatively lower Chao1, alternating conditional expectations, and Shannon and Simpson indices were found at the shallowest location with higher total phosphorus and chlorophyll a. Furthermore, the Kyoto Encyclopedia of Genes and Genomes analysis revealed that the metabolism function was the most abundant functional classification in Jingpo Lake. The levels of total phosphorus, chlorophyll a and pH were positively correlated with the abundance of Flavobacterium and the bacterial functions of the carbohydrate metabolism and amino acid metabolism. In conclusion, our results reveal the physical and chemical characteristics, as well as the microbial community characteristics, of Jingpo Lake, which provides new insights for studying the relationship between environmental factors and the bacterial community distribution of freshwater ecosystems, in addition to also providing a theoretical basis for the environmental monitoring and protection of the lake.

Effects of water quality and bacterial community composition on dissolved organic matter structure in Daihai lake and the mechanisms

The migration of organic matter in salinized lakes was critical in maintaining ecological balance and material circulation process of inland shallow lakes. To clarify the ecological and microbial mechanism of material transport and transformation, the microbial community structure and the characteristics of dissolved organic matter (DOM) in the sediment of Daihai Lake, a typical saline lake at the Yellow River Basin, were explored with three-dimensional excitation and emission matrix fluorescence (3DEEM), parallel factor analysis (PARAFAC) and 16 S rRNA techniques. The correlation between environmental factors, DOM composition and the bacterial community structure were also studied for identifying the key factors of community formation. DOM in the lake demonstrated both terrigenous and endogenous characteristics. Protein-like materials accounted for 74% of the total fluorescence intensity in the sediment, where 1127 species, 671 genera, 468 families, 157 classes, 317 orders, 59 phyla of microorganisms were detected. Among the top 10 abundant taxa of each level, Firmicutes, Actinobacterota, Acidimicrobiia and Alphaproteobacteria had the greatest influence on the composition and structure of DOM (|R| > 0.7, p < 0.01). Microbial metabolism was a key process of transforming sediment organic matter from terrestrial humic-like to protein-like matter, accounting for 81% of total fluorescence signal in saline lake samples, while salinity, temperature, dissolved oxygen and electrical conductivity also had significant impacts during the process (|R|>0.7, p < 0.05). The research provides fundamental data and enlightenment for the improvement of the saline inland lake environment.

pH mediated assemblage of carbon, nitrogen, and sulfur related microbial communities in petroleum reservoirs

Microorganisms are the core drivers of biogeochemistry processes in petroleum reservoirs and have been widely used to enhance petroleum recovery. However, systematic information about the microbial communities related to the C-N-S cycle in petroleum reservoirs under different pH conditions remains poorly understood. In this study, 16S rRNA gene data from 133 petroleum samples were collected, and 756 C-N-S related genera were detected. The Chao1 richness and Shannon diversity indices for the C-N-S-related microbial communities showed significant differences among different pH conditions and at the lowest levels in acidic conditions with pH values of 4.5-6.5. In addition, pH was the most important factor influencing the C-N-S related microbial communities and contributed to 17.95% of the variation in the methanogenesis community. A total of 55 functional genera were influenced by pH, which accounted for 42.08% of the C-N-S related genera. Among them, the genera Pseudomonas and Arcobacter were the highest and were concentrated in acidic conditions with pH values of 4.5-6.5. In parallel, 56 predicted C-N-S related genes were examined, and pH affected 16 of these genes, including putative chitinase, mcrA, mtrB, cysH, narGHIVYZ, nirK, nirB, nifA, sat, aprAB, and dsrAB. Furthermore, the co-occurrence networks of the C-N-S related microbial communities distinctly varied among the different pH conditions. The acidic environment exhibited the lowest complex network with the lowest keystone taxa number, and Escherichia-Shigella was the only keystone group that existed in all three networks. In summary, this study strengthened our knowledge regarding the C-N-S related microbial communities in petroleum reservoirs under different pH conditions, which is of great significance for understanding the microbial ecology and geochemical cycle of petroleum reservoirs.

Microbial community structure and shift pattern of industry brine after a long-term static storage in closed tank

Brine from Dingyuan Salt Mine (Anhui, China), an athalassohaline hypersaline environment formed in the early tertiary Oligocene, is used to produce table salt for hundreds of millions of people. However, halophiles preserved in this niche during deposition are still unknown. Here, we employed cultivation and high-throughput sequencing strategies to uncover the microbial community and its shift after a long-term storage in the brine collected from Dingyuan Salt Mine. High-throughput sequencing showed (1) in the fresh brine (2021), Cyanobium_stocktickerPCC-6307 spp. (8.46%), Aeromonas spp. (6.91%) and Pseudomonas spp. (4.71%) are the dominant species in bacteria while Natronomonas spp. (18.89%), Halapricum spp. (13.73%), and Halomicrobium spp. (12.35%) in archaea; (2) after a 3-year-storage, Salinibacter spp. (30.01%) and Alcanivorax spp. (14.96%) surpassed Cyanobium_stocktickerPCC-6307 spp. (8.46%) becoming the dominant species in bacteria; Natronomonas spp. are still the dominant species, while Halorientalis spp. (14.80%) outnumbered Halapricum spp. becoming the dominant species in archaea; (3) Alcanivorax spp. and Halorientalis spp. two hydrocarbons degrading microorganisms were enriched in the brine containing hydrocarbons. Cultivation using hypersaline nutrient medium (20% NaCl) combined with high-throughput 16S rRNA gene sequencing showed that (1) the biomass significantly increased while the species diversity sharply declined after a 3-year-storage; (2) Halorubrum spp. scarcely detected from the environment total stocktickerDNA were flourishing after cultivation using AS-168 or NOM medium; (3) twelve possible new species were revealed based on almost full-length 16S rRNA gene sequence similarity search. This study generally uncovered the microbial community and the dominant halophiles in this inland athalassohaline salt mine, and provided a new insight on the shift pattern of dominant halophiles during a long-term storage, which illustrated the shaping of microorganisms in the unique environment, and the adaptation of microbe to the specific environment.

Factors Driving Microbial Community Dynamics and Potential Health Effects of Bacterial Pathogen on Landscape Lakes with Reclaimed Water Replenishment in Beijing, PR China

Assessing the bacteria pathogens in the lakes with reclaimed water as major influents are important for public health. This study investigated microbial communities of five landscape lakes replenished by reclaimed water, then analyzed driven factors and identified health effects of bacterial pathogens. 16S rRNA gene sequence analysis demonstrated that Proteobacteria, Actinobacteria, Cyanobacteria, Firmicutes, and Verrucomicrobia were the most dominant phyla in five landscape lakes. The microbial community diversities were higher in June and July than that in other months. Temperature, total nitrogen and phosphorus were the main drivers of the dominant microbial from the Redundancy analysis (RDA) results. Various potential bacterial pathogens were identified, including Pseudomonas, GKS98_freshwater_group, Sporosarcina, Pseudochrobactrum, Streptomyces and Bacillus, etc, some of which are easily infectious to human. The microbial network analysis showed that some potential pathogens were nodes that had significant health effects. The work provides a basis for understanding the microbial community dynamics and safety issues for health effects in landscape lakes replenished by reclaimed water.

Biogeography, assembly processes and species coexistence patterns of microbial communities in metalloids-laden soils around mining and smelting sites

Microbes are important component in terrestrial ecosystem, which are believed to play vital roles in biogeochemical cycles of metalloids in mining and smelting surroundings. Many studies on microbial diversity and structures have been investigated around mining and smelting sites, whereas the ecological processes and co-occurrence patterns that influence the biogeographic distributions of microbial communities is yet poorly understood. Herein, microbial biogeography, assembly mechanism and co-occurrence pattern around mining and smelting zone were systematically unraveled using 16S rRNA gene sequencing. The 66 microbial phyla co-occurring across all the samples were dominated by Proteobacteria, Chloroflexi, Acidobacteria and Crenarchaeota. Obvious distance-decay (r = 0.3448, p < 0.001) of microbial community was observed across geographic distances. Differences in microbial communities were driven by the joint impacts of soil factors, spatial and metalloids levels. Dispersal limitation dominated the microbial assemblies in whole, SC and GX sites while homogeneous selection governed that in YN site. The changes in pH and Sb level significantly influenced the deterministic and stochastic processes of microbial communities. Network analysis suggested a typical module distribution, which had apparent ecological links among taxa in modules. This study provides first insight of the mechanism to maintain microbial diversity in metalloids-laden biospheres.

Salinity Gradient Controls Microbial Community Structure and Assembly in Coastal Solar Salterns

Salinity acts as a critical environmental filter on microbial communities in natural systems, negatively affecting microbial diversity. However, how salinity affects microbial community assembly remains unclear. This study used Wendeng multi-pond saltern as a model to evaluate the prokaryotic community composition and diversity and quantify the relative importance of ecological processes across salinity gradients. The results showed that low-saline salterns (45–80 g/L) exhibited higher bacterial diversity than high-saline salterns (175–265 g/L). The relative abundance of taxa assigned to Halomicrobiaceae, Rhodobacteraceae, Saprospiraceae, and Thiotrichaceae exhibited a hump-shaped dependence on increasing salinity. Salinity and pH were the primary environmental factors that directly or indirectly determined the composition and diversity of prokaryotic communities. Microbial co-occurrence network dynamics were more complex in the sediment than in the water of salterns. An infer Community Assembly Mechanisms by Phylogenetic-bin-based null model analysis (iCAMP) showed that microbial community assembly in sediment and water differed. Our findings provide more information about microbial community structure and the importance of various ecological processes in controlling microbial community diversity and succession along salinity gradients in water and sediment.

Biomineralization by Extremely Halophilic and Metal-Tolerant Community Members from a Sulfate-Dominated Metal-Rich Environment

The adaptation to adverse environmental conditions can lead to adapted microbial communities that may be screened for mechanisms involved in halophily and, in this case, metal tolerance. At a former uranium mining and milling site in Seelingstädt, Germany, microbial communities from surface waters and sediment soils were screened for isolates surviving high salt and metal concentrations. The high salt contents consisted mainly of chloride and sulfate, both in soil and riverbed sediment samples, accompanied by high metal loads with presence of cesium and strontium. The community structure was dominated by Chloroflexi, Proteobacteria and Acidobacteriota, while only at the highest contaminations did Firmicutes and Desulfobacterota reach appreciable percentages in the DNA-based community analysis. The extreme conditions providing high stress were mirrored by low numbers of cultivable strains. Thirty-four extremely halotolerant bacteria (23 Bacillus sp. and another 4 Bacillales, 5 Actinobacteria, and 1 Gamma-Proteobacterium) surviving 25 to 100 mM SrCl₂, CsCl, and Cs₂SO₄ were further analyzed. Mineral formation of strontium- or cesium-struvite could be observed, reducing bioavailability and thereby constituting the dominant metal and salt resistance strategy in this environment.