The composition, biotic network, and assembly of plastisphere protistan taxonomic and functional communities in plastic-mulching croplands

Stable isotopes and nanoSIMS single-cell imaging reveals soil plastisphere colonizers able to assimilate sulfamethoxazole

The presence and accumulation of both, plastics and antibiotics in soils may lead to the colonization, selection, and propagation of soil bacteria with certain metabolic traits, e.g., antibiotic resistance, in the plastisphere. However, the impact of plastic-antibiotic tandem on the soil ecosystem functioning, particularly on microbial function and metabolism remains currently unexplored. Herein, we investigated the competence of soil bacteria to colonize plastics and degrade 13C-labeled sulfamethoxazole (SMX). Using single-cell imaging, isotope tracers, soil respiration and SMX mineralization bulk measurements we show that microbial colonization of polyethylene (PE) and polystyrene (PS) surfaces takes place within the first 30 days of incubation. Morphologically diverse microorganisms were colonizing both plastic types, with a slight preference for PE substrate. CARD-FISH bacterial cell counts on PE and PS surfaces formed under SMX amendment ranged from 5.36 × 103 to 2.06 × 104, and 2.06 × 103 to 3.43 × 103 hybridized cells mm-2, respectively. Nano-scale Secondary Ion Mass Spectrometry measurements show that 13C enrichment was highest at 130 days with values up to 1.29 atom%, similar to those of the 13CO2 pool (up to 1.26 atom%, or 22.55 ‰). Independent Mann-Whitney U test showed a significant difference between the control plastisphere samples incubated without SMX and those in 13C-SMX incubations (P < 0.001). Our results provide direct evidence demonstrating, at single-cell level, the capacity of bacterial colonizers of plastics to assimilate 13C-SMX from contaminated soils. These findings expand our knowledge on the role of soil-seeded plastisphere microbiota in the ecological functioning of soils impacted by anthropogenic stressors.

New insights of bacterial and eukaryotic phenotypes on the plastics collected from the typical natural habitat of the endangered crocodile lizard

Although accumulating evidence indicates that endangered animals suffer from plastic pollution, this has been largely overlooked. Here, we explored the bacteria and eukaryotes living in the plastics gathered from the natural habitat of the highly endangered crocodile lizard. The results demonstrated that the bacterial and eukaryotic communities on plastics formed a unique ecosystem that exhibited lower diversity than those in the surrounding water and soil. However, microbes displayed a more complex and stable network on plastic than that in water or soil, implying unique mechanisms of stabilization. These mechanisms enhanced their resilience and contributed to the provision of stable ecological services. Eukaryotes formed a simpler and smaller network than bacteria, indicating different survival strategies. The bacteria residing on the plastics played a significant role in carbon transformation and sequestration, which likely impacted carbon cycling in the habitat. Furthermore, microbial exchange between plastics and the crocodile lizard was observed, suggesting that plastisphere serves as a mobile gene bank for the exchange of information, including potentially harmful substances. Overall, microbes on plastic appear to significantly impact the crocodile lizard and its natural habitat via various pathways. These results provided novel insights into risks evaluation of plastic pollution and valuable guidance for government efforts in plastic pollutant control in nature reserves.

The rhizosphere microbiome reduces the uptake of arsenic and tungsten by Blechnum orientale by increasing nutrient cycling in historical tungsten mining area soils

The growth of pioneer plants in metal mining area soil is closely related to their minimal uptake of toxic elements. Pioneer plants can inhibit the uptake of toxic elements by increasing nutrient uptake. However, few studies have focused on the mechanisms by which the rhizosphere microbiome affect nutrient cycling and their impact on the uptake of toxic elements by pioneer plants. In this study, we selected Blechnum orientale to investigate the potential roles of the rhizosphere microbiome in nutrient cycling and plant growth in a historical tungsten (W) mining area. Our results showed that while the arsenic (As) and W contents in the soil were relatively high, the enrichment levels of As and W in the B. orientale were relatively low. Furthermore, we found that the As and W contents in plants were significantly negatively correlated with soil nutrients (S, P and Mo), suggesting that elevated levels of these soil nutrients could inhibit As and W uptake by B. orientale. Importantly, we found that these nutrients were also identified as the most important factors shaping rhizosphere microbial attributes, including microbial diversity, ecological clusters, and keystone OTUs. Moreover, the genera, keystone taxa and microbial functional genes enriched in the rhizosphere soils from mining areas played a key role in nutrient (S, P and Mo) bioavailability, which could further increase the nutrient uptake by B. orientale. Taken together, our results suggest that rhizosphere microorganisms can improve pioneer plant growth by inhibiting toxic element accumulation via the increase in nutrient cycling in former W mining areas.

Bacterial community in the metal(loid)-contaminated marine vertical sediments of Jinzhou Bay: Impacts and adaptations

Metal(loid) discharge has led to severe coastal contamination; however, there remains a significant knowledge gap regarding its impact on sediment profiles and depth-resolved bacterial communities. In this study, geochemical measurements (pH, nutrient elements, total and bioavailable metal(loid) content) consistently revealed decreasing nitrogen, phosphorus, and metal(loid) levels with sediment depth, accompanied by reduced alpha diversity. Principal coordinate analysis indicated distinct community compositions with varying sediment depths, suggesting a geochemical influence on diversity. Ecological niche width expanded with depth, favoring specialists over generalists, but both groups decreased in abundance. Taxonomic shifts emerged, particularly in phyla and families, correlated with sediment depth. Microbe-microbe interactions displayed intricate dynamics, with keystone taxa varying by sediment layer. Zinc and arsenic emerged as key factors impacting community diversity and composition using random forest, network analysis, and Mantel tests. Functional predictions revealed shifts in potential phenotypes related to mobile elements, biofilm formation, pathogenicity, N/P/S cycles, and metal(loid) resistance along sediment profiles. Neutral and null models demonstrated a transition from deterministic to stochastic processes with sediment layers. This study provides insights into the interplay between sediment geochemistry and bacterial communities across sediment depths, illuminating the factors shaping these ecosystems.

Multivariate statistical and bioinformatic analyses for the seasonal variations of actinobacterial community structures in a drinking water reservoir

Actinobacterial community is a conspicuous part of aquatic ecosystems and displays an important role in the case of biogeochemical cycle, but little is known about the seasonal variation of actinobacterial community in reservoir ecological environment. In this study, the high-throughput techniques were used to investigate the structure of the aquatic actinobacterial community and its inducing water quality parameters in different seasons. The results showed that the highest diversity and abundance of actinobacterial community occurred in winter, with Sporichthya (45.42%) being the most abundant genus and Rhodococcus sp. (29.32%) being the most abundant species. Network analysis and correlation analysis suggested that in autumn the dynamics of actinobacterial community were influenced by more factors and Nocardioides sp. SX2R5S2 was the potential keystone species which was negatively correlated with temperature (R = -0.72, P < 0.05). Changes in environmental factors could significantly affect the changes in actinobacterial community, and the dynamics of temperature, dissolved oxygen (DO), and turbidity are potential conspicuous factors influencing seasonal actinobacterial community trends. The partial least squares path modeling further elucidated that the combined effects of DO and temperature not only in the diversity of actinobacterial community but also in other water qualities, while the physiochemical parameters (path coefficient = 1.571, P < 0.05) was strong environmental factors in natural mixture period. These results strengthen our understanding of the dynamics and structures of actinobacterial community in the drinking water reservoirs and provide scientific guidance for further water quality management and protection in water sources.

Depth significantly affects plastisphere microbial evenness, assembly and co-occurrence pattern but not richness and composition

Microplastics have become one of the hot concerns of global marine pollution. In recent years, diversity and abiotic influence factors of plastisphere microbial communities were well documented, but our knowledge of their assembly mechanisms and co-occurrence patterns remains unclear, especially the effects of depth on them. Here, we collected microorganisms on microplastics to investigate how ocean depth affects on microbial diversity, community composition, assembly processes and co-occurrence patterns. Our results indicated that there were similar microbial richness and community compositions but microbial evenness and unique microbes were obviously different in different ocean layers. Our findings also demonstrated that deterministic processes played dominant roles in the assembly of the mesopelagic plastisphere microbial communities, while the bathypelagic microbial community assembly was mainly shaped by stochastic processes. In addition, the co-occurrence networks suggested that the relationships between microorganisms in the mesopelagic layer were more complex and stable than those in the bathypelagic layer. Simultaneously, we also found that Proteobacteria and Actinobacteriota were the most abundant keystones which played important roles in microbial co-occurrence networks at both layers. This study enhanced our understanding of microbial diversity, assembly mechanism, and co-occurrence pattern on plastisphere surfaces, and provided useful insights into microorganisms capable of degrading plastics and microbial remediation.

The soil plastisphere

Understanding the effects of plastic pollution in terrestrial ecosystems is a priority in environmental research. A central aspect of this suite of pollutants is that it entails particles, in addition to chemical compounds, and this makes plastic quite different from the vast majority of chemical environmental pollutants. Particles can be habitats for microbial communities, and plastics can be a source of chemical compounds that are released into the surrounding environment. In the aquatic literature, the term 'plastisphere' has been coined to refer to the microbial community colonizing plastic debris; here, we use a definition that also includes the immediate soil environment of these particles to align the definition with other concepts in soil microbiology. First, we highlight major differences in the plastisphere between aquatic and soil ecosystems, then we review what is currently known about the soil plastisphere, including the members of the microbial community that are enriched, and the possible mechanisms underpinning this selection. Then, we focus on outlining future prospects for research on the soil plastisphere.

Microplastics in the atmosphere: Adsorb on leaves and their effects on the phyllosphere bacterial community

Phyllosphere is the largest interface between the atmosphere and terrestrial ecosystems and serves as a major sink for atmospheric microplastics (MPs). It is also a unique habitat for microbiota with diverse ecological functions. This field study investigated the characteristics of atmospheric MPs adsorbed on leaves with automatic technology, and found their abundance was 3.62 ± 1.29 items cm-2. MPs on leaves were mainly below 80 µm, and dominated by polyamide, polyethene, and rubber. MPs on leaves correlated significantly with the structure and functions of the phyllosphere bacterial community (PBC). Both the MPs abundance and size distribution (MSD) were positively correlated with the α diversity and negatively correlated with the β diversity and network complexity of PBC. PBC functions of environmental and genetic information process were negatively correlated with MPs abundance, and functions related to human diseases and cellular process were positively correlated with MSD significantly. The relative abundance of Sphingomonas was significantly correlated with the MSD, suggesting that Sphingomonas might emerge as the key genus involved in the pathogenicity of PBC mediated by MPs. These results highlighted the ecological health risks of atmospheric MPs as they can be transferred anywhere and potentially increase the pathogenicity of local phyllosphere microflora.

Assembly mechanisms of microbial communities in plastisphere related to species taxonomic types and habitat niches

A lot of plastic floats are presented in the kelp cultivation zone, enabling us to effectively evaluate the differences between surface water (SW) and plastic-attached (PA) microbial communities. In this study, we explored the microbial communities (both bacteria and protists) in SW and PA niches during the kelp cultivation activities. Effects of habitat niches on the diversity and composition of microbial communities were found. Beta partitioning and core taxa analyses showed species turnover and local species pool governed the microbial community assembly, and they contributed more to bacteria and protists, respectively. Based on the results of null model, bacterial communities presented a more deterministic and homogeneous assembly compared to protistan communities. Moreover, microbial communities in PA niche had higher species turnover and homogenizing assembly compared to the SW niche. The results of this study supplemented the theory of microbial community assembly and expanded our understanding of protists in plastisphere.

Redox gradients drive microbial community assembly patterns and molecular ecological networks in the hyporheic zone of effluent-dominated rivers

The impacts of effluent discharge on receiving waterbodies have been a research hotspot. Nonetheless, limited information is available on the microbial community assembly patterns in the hyporheic zones (HZ) responding to the changes in the microenvironments, e.g., solute transport and redox gradient variations. Using two representative effluent-dominated rivers as model systems, the spatio-temporal bacterial community dynamics and assembly patterns in oxic and suboxic zones in the shallow riverbed sediments were disentangled via null model- and neutral model-based approaches. Bacterial dynamics in community composition were observed driven by environmental filtering, i.e., impacts of environmental variables, more than geographic distances, i.e., the depths of sediments. The communities in samples collected in summer were largely shaped by stochasticity, in which homogeneous selection occupied a higher proportion in oxic (∼39%) than in suboxic zone (∼23%). Deterministic processes contributed to a more complex community structure for samples from oxic zones, whereas weakened the interspecies interactions in suboxic zones. The richness and abundances of non-neutral community were confirmed governing the deterministic assembly in oxic zones. Key species ascribed to 'connectors' and 'network hubs' dominated the community assembly variations in samples collected in winter, and in oxic zones, respectively. Significant positive relationships between β-nearest taxon index and dissolved organic nitrogen (DON) and nitrate highlighted their vital roles in community assembly via deterministic selective pressures in oxic zones. The significance thresholds of nitrogen species for community transition in winter (ΔDON: 2.81 mg-N/L, ΔNO3-: 1.09 mg-N/L) were lower than in summer, probably implying that stricter effluent quality standards should be established in colder seasons. Combined, our work poses first insights on the roles of redox zonation in driving microbial community assembly in HZ, which is of significance in guiding ecological remediation processes in effluent-dominated rivers.

Homogenization of bacterial plastisphere community in soil: a continental-scale microcosm study

Microplastics alter niches of soil microbiota by providing trillions of artificial microhabitats, termed the "plastisphere." Because of the ever-increasing accumulation of microplastics in ecosystems, it is urgent to understand the ecology of microbes associated with the plastisphere. Here, we present a continental-scale study of the bacterial plastisphere on polyethylene microplastics compared with adjacent soil communities across 99 sites collected from across China through microcosm experiments. In comparison with the soil bacterial communities, we found that plastispheres had a greater proportion of Actinomycetota and Bacillota, but lower proportions of Pseudomonadota, Acidobacteriota, Gemmatimonadota, and Bacteroidota. The spatial dispersion and the dissimilarity among plastisphere communities were less variable than those among the soil bacterial communities, suggesting highly homogenized bacterial communities on microplastics. The relative importance of homogeneous selection in plastispheres was greater than that in soil samples, possibly because of the more uniform properties of polyethylene microplastics compared with the surrounding soil. Importantly, we found that the degree to which plastisphere and soil bacterial communities differed was negatively correlated with the soil pH and carbon content and positively related to the mean annual temperature of sampling sites. Our work provides a more comprehensive continental-scale perspective on the microbial communities that form in the plastisphere and highlights the potential impacts of microplastics on the maintenance of microbial biodiversity and ecosystem functioning.

Strong bacterial stochasticity and fast fungal turnover in Taihu Lake sediments, China

Understanding the assembly and turnover of microbial communities is crucial for gaining insights into the diversity and functioning of lake ecosystems, a fundamental and central issue in microbial ecology. The ecosystem of Taihu Lake has been significantly jeopardized due to urbanization and industrialization. In this study, we examined the diversity, assembly, and turnover of bacterial and fungal communities in Taihu Lake sediment. The results revealed strong bacterial stochasticity and fast fungal turnover in the sediment. Significant heterogeneity was observed among all sediment samples in terms of environmental factors, especially ORP, TOC, and TN, as well as microbial community composition and alpha diversity. For instance, the fungal richness index exhibited an approximate 3-fold variation. Among the environmental factors, TOC, TN, and pH had a more pronounced influence on the bacterial community composition compared to the fungal community composition. Interestingly, species replacement played a dominant role in microbial beta diversity, with fungi exhibiting a stronger pattern. In contrast, stochastic processes governed the community assembly of both bacteria and fungi, but were more pronounced for bacteria (R2 = 0.7 vs. 0.5). These findings deepen the understanding of microbial assembly and turnover in sediments under environmental stress and provide essential insights for maintaining the multifunctionality of lake ecosystems.

Marine toxin domoic acid alters protistan community structure and assembly process in sediments

Domoic acid (DA)-producing algal blooms have been the issue of worldwide concerns in recent decades, but there has never been any attempt to investigate the effects of DA on microbial ecology in marine environments. Protists are considered to be key regulators of microbial activity, community structure and evolution, we therefore explore the effect of DA on the ecology of protists via metagenome in this work. The results indicate that trace amounts of DA can act as a stressor to alter alpha and beta diversity of protistan community. Among trophic functional groups, consumers and phototrophs are negative responders of DA, implying DA is potentially capable of functional-level effects in the ocean. Moreover, microecological theory reveals that induction of DA increases the role of deterministic processes in microbial community assembly, thus altering the biotic relationships and successional processes in symbiotic patterns. Finally, we demonstrate that the mechanism by which DA shapes protistan ecological network is by acting on phototrophs, which triggers cascading effects in networks and eventually leading to shifts in ecological succession of protists. Overall, our results present the first perspective regarding the effects of DA on marine microbial ecology, which will supplement timely information on the ecological impacts of DA in the ocean.

Laboratory tidal microcosm deciphers responses of sediment archaeal and bacterial communities to microplastic exposure

Microplastics (MPs) are 1-5 mm plastic particles that are serious global contaminants distributed throughout marine ecosystems. However, their impact on intertidal sediment microbial communities is poorly understood. In this study, we conducted a 30-day laboratory tidal microcosm experiment to investigate the effects of MPs on microbial communities. Specifically, we used the biodegradable polymers polylactic acid (PLA) and polybutylene succinate (PBS), as well as the conventional polymers polyethylene terephthalate (PET), polycarbonate (PC), and polyethylene (PE). Treatments with different concentrations (1-5%, w/w) of PLA- and PE-MPs were also included. We analyzed taxonomic variations in archaeal and bacterial communities using 16S rRNA high-throughput sequencing. PLA-MPs at concentrations of 1% (w/w) rapidly altered microbiome composition. Total organic carbon and nitrite nitrogen were the key physicochemical factors and urease was the major enzyme shaping MP-exposed sediment microbial communities. Stochastic processes predominated in microbial assembly and the addition of biodegradable MPs enhanced the contribution of ecological selections. The major keystone taxa of archaea and bacteria were Nitrososphaeria and Alphaproteobacteria, respectively. MPs exposure had less effect on archaeal functions while nitrogen cycling decreased in PLA-MPs treatments. These findings expanded the current understanding of the mechanism and pattern that MPs affect sediment microbial communities.

Arsenic (As) oxidation by core endosphere microbiome mediates As speciation in Pteris vittata roots

Pteris vittata is an arsenic(As)-hyperaccumulator that may be employed in phytoremediation of As-contaminated soils. P. vittata-associated microbiome are adapted to elevated As and may be important for host survival under stresses. Although P. vittata root endophytes could be critical for As biotransformation in planta, their compositions and metabolisms remain elusive. The current study aims to characterize the root endophytic community composition and As-metabolizing potentials in P. vittata. High As(III) oxidase gene abundances and rapid As(III) oxidation activity indicated that As(III) oxidation was the dominant microbial As-biotransformation processes compared to As reduction and methylization in P. vittata roots. Members of Rhizobiales were the core microbiome and the dominant As(III) oxidizers in P. vittata roots. Acquasition of As-metabolising genes, including both As(III) oxidase and As(V) detoxification reductase genes, through horizontal gene transfer was identified in a Saccharimonadaceae genomic assembly, which was another abundant population residing in P. vittata roots. Acquisition of these genes might improve the fitness of Saccharimonadaceae population to elevated As concentrations in P. vittata. Diverse plant growth promoting traits were encoded by the core root microbiome populations Rhizobiales. We propose that microbial As(III) oxidation and plant growth promotion are critical traits for P. vittata survival in hostile As-contaiminated sites.

Water quality determines protist taxonomic and functional group composition in a high-altitude wetland of international importance

Alpine wetland is a natural laboratory for studying the Earth's third polar ecosphere. Protist communities are key components of wetland ecosystems which are extremely vulnerable to environmental change. It is of great importance to study the protist community in relation to environment, which might be the key to understand the ecosystem of the alpine wetlands under global change. In this study, we investigated the composition of protist communities across the Mitika Wetland, a unique alpine wetland hosting tremendous endemic diversity. Using 18S rRNA gene high-throughput sequencing, we evaluated how protist taxonomic and functional group composition is structured by seasonal climate and environmental variation. We found a high relative abundance of Ochrophyta, Ciliophora, and Cryptophyta, each of which showcased a unique spatial pattern in the wet and dry seasons. The proportion of consumers, parasites and phototrophs groups were stable among the functional zones and also between the seasons, with consumers dominating communities in terms of richness, while phototrophic taxa dominated in terms of relative abundance. Protist and each functional group were rather regulated by deterministic than stochastic processes, with water quality having a strong control on communities. Salinity and pH were the most important environmental factors at shaping protistan community. The protist co-occurrence network dominated by the positive edge indicating the communities resisted extreme environmental conditions through close cooperation, and more consumers were determined as the keystones in wet season and more phototrophic taxa in dry season. Our results provided the baseline of the protist taxonomic and functional group composition in the highest wetland, and highlighted environmental selections drive protist distribution, implying the alpine wetland ecosystem are sensitive to climate changes and human activities.

Removal of toilet paper fibers from residential wastewater: a life cycle assessment

Toilet paper has been reported as one of the major insoluble pollutant components in the influent of wastewater treatment plants. Toilet paper fibers contribute to a large production of sewage sludge, resulting in a high treatment cost and high energy consumption. To find energy-efficient, cost-effective, and environment-friendly technologies for fiber removal and resource recovery from wastewater, a life-cycle assessment (LCA) was performed to analyze the wastewater treatment processes, including a sieving process for removing and recovering suspended solids before the biodegradation units. Based on the LCA results, it was estimated that the sieve screening process saved 8.57% of energy consumption. The construction phase of sieving consumed 1.31% energy cost compared with the operation phase. Environmental impact analysis showed that sieving reduced the impacts of climate change, human toxicity, fossil depletion, and particulate matter formation, which reduced the total normalized environmental impacts by 9.46%. The life-cycle analysis of the removal of toilet paper fibers from wastewater revealed the need to use more efficient methods to enhance the recovery of cellulose fibers.

Photo-aging promotes the inhibitory effect of polystyrene microplastics on microbial reductive dechlorination of a polychlorinated biphenyl mixture (Aroclor 1260)

Polychlorinated biphenyls (PCBs) and microplastics (MPs) commonly co-exist in various environments. MPs inevitably start aging once they enter environment. In this study, the effect of photo-aged polystyrene MPs on microbial PCB dechlorination was investigated. After a UV aging treatment, the proportion of oxygen-containing groups in MPs increased. Photo-aging promoted the inhibitory effect of MPs on microbial reductive dechlorination of PCBs, mainly attributed to the inhibition of meta-chlorine removal. The inhibitory effects on hydrogenase and adenosine triphosphatase activity by MPs increased with increasing aging degree, which may be attributed to electron transfer chain inhibition. PERMANOVA showed significant differences in microbial community structure between culturing systems with and without MPs (p < 0.05). Co-occurrence network showed a simpler structure and higher proportion of negative correlation in the presence of MPs, especially for biofilms, resulting in increased potential for competition among bacteria. MP addition altered microbial community diversity, structure, interactions, and assembly processes, which was more deterministic in biofilms than in suspension cultures, especially regarding the bins of Dehalococcoides. This study sheds light on the microbial reductive dechlorination metabolisms and mechanisms where PCBs and MPs co-exist and provides theoretical guidance for in situ application of PCB bioremediation technology.

Distinct distribution patterns and functional potentials of rare and abundant microorganisms between plastisphere and soils

The increasing application of plastic film has caused the "white pollution" of farmlands in greenhouses. To date, most studies on the ecology of the plastisphere have focused on the whole microbial community, with few on the rare and abundant taxa, especially in the terrestrial ecosystems. To understand the plastisphere rare and abundant taxa of bacterial and fungal communities, we collected residues of plastic film from plastic-covered soils in the greenhouse. The plastisphere was significantly different from surrounding soils in terms of alpha- and beta-diversities of abundant and rare taxa. Such discrepancies were greater in rare taxa than in abundant taxa. Besides, the enrichment of soil-borne plant pathogenic fungi in the plastisphere implied that plastic film residues can act as vectors for pathogen transmission. In the plastisphere, the stochastic process governed the assemblies of rare taxa, while deterministic assemblies dominated that of abundant taxa. However, in surrounding soils, the stochastic process played a larger role in abundant taxa as compared to rare taxa. The plastisphere showed a network of less complexity, more competitive connections, and more modules compared to surrounding soils, and rare taxa played greater roles than abundant taxa. There existed obvious discrepancies in the microbial functions between surrounding soils and plastisphere, including carbon, sulfur, nitrogen, and phosphorus cycling, and rare taxa contribute large proportions to the above cycling processes. Altogether, the findings advance our understanding of ecological mechanisms of abundant and rare taxa in the plastisphere in terrestrial ecosystems.

Deciphering the distinct successional patterns and potential roles of abundant and rare microbial taxa of urban riverine plastisphere

Microbial colonization on microplastics has provoked global concern; however, many studies have not considered the successional patterns and potential roles of abundant and rare taxa of the plastisphere during colonization. Hence, we investigate the taxonomic composition, assembly, interaction and function of abundant and rare taxa in the riverine plastisphere by conducting microcosm experiments. Results showed that rare taxa occupied significantly high community diversity and niche breadth than the abundant taxa, which implies that rare taxa are essential components in maintaining the community stability of the plastisphere. However, the abundant taxa played a major role in driving the succession of plastisphere communities during colonization. Both stochastic and deterministic processes signally affected the plastisphere community assemblies; while, the deterministic patterns (heterogeneous selection) were especially pronounced for rare biospheres. Plastisphere microbial networks were shaped by the enhancement of network modularity and reinforcement of positive interactions. Rare taxa played critical roles in shaping stable plastisphere by occupying the key status in microbial networks. The strong interaction of rare and non-rare taxa suggested that multi-species collaboration might be conducive to the formation and stability of the plastisphere. Both abundant and rare taxa were enriched with plentiful functional genes related to carbon, nitrogen, phosphorus and sulfur cycling; however, their potential metabolic functions were significantly discrepant, implying that the abundant and rare microbes may play different roles in ecosystems. Overall, this study strengthens our comprehending of the mechanisms regarding the formation and maintenance of the plastisphere.

Microbiological mechanism for "production while remediating" in Cd-contaminated paddy fields: A field experiment

Security utilization measures (SUMs) for "production while remediating" in moderate and mild Cd-polluted paddy fields had been widely used. To investigate how SUMs drove rhizosphere soil microbial communities and reduced soil Cd bioavailability, a field experiment was conducted using soil biochemical analysis and 16S rRNA high-throughput sequencing. Results showed that SUMs improved rice yield by increasing the number of effective panicles and filled grains, while also inhibiting soil acidification and enhancing disease resistance by improving soil enzyme activities. SUMs also reduced the accumulation of harmful Cd in rice grains and transformed it into FeMn oxidized Cd, organic-bound Cd, and residual Cd in rhizosphere soil. This was partly due to the higher degree of soil DOM aromatization, which helped complex the Cd with DOM. Additionally, the study also found that microbial activity was the primary source of soil DOM, and that SUMs increased the diversity of soil microbes and recruited many beneficial microbes (Arthrobacter, Candidatus_Solibacter, Bryobacter, Bradyrhizobium, and Flavisolibacter) associated with organic matter decomposition, plant growth promotion, and pathogen inhibition. Besides, special taxa (Bradyyrhizobium and Thermodesulfovibrio) involved in sulfate/sulfur ion generation and nitrate/nitrite reduction pathway were observably enriched, which effectively reduced the soil Cd bioavailability through adsorption and co-precipitation. Therefore, SUMs not only changed the soil physicochemical properties (e.g., pH), but also drove rhizosphere microbes to participate in the chemical species transformation of soil Cd, thus reducing Cd accumulation in rice grains.

Plastisphere microbiome: Methodology, diversity, and functionality

Broad topics of the plastisphere in various environments are reviewed, including its methodologies, diversity, functionality, and outlook.

Biodegradable mulch films significantly affected rhizosphere microbial communities and increased peanut yield

Biodegradable mulch films are widely used to replace conventional plastic films in agricultural fields. However, their ecological effects on different microbial communities that naturally inhabit agricultural fields are scarcely explored. Herein, differences in bacterial communities recovered from biofilms, bulk soil, and rhizosphere soil were comparatively assessed for polyethylene film (PE) and biodegradable mulch film (BDM) application in peanut planted fields. The results showed that the plastic film type significantly influenced the bacterial community in different ecological niches of agricultural fields (P < 0.001). Specifically, BDMs significantly increased the diversity and abundance of bacteria in the rhizosphere soil. The bacterial communities in each ecological niche were distinguishable from each other; bacterial communities in the rhizosphere soil showed the most pronounced response among different treatments. Acidobacteria and Pseudomonas were significantly enriched in the rhizosphere soil when BDMs were used. BDMs also increased the rhizosphere soil bacterial network complexity and stability. The enrichment of beneficial bacteria in the rhizosphere soil under BDMs may also have implications for the observed increase in peanut yield. Deepening analyses indicated that Pseudoxanthomonas and Glutamicibacter are biomarkers in biofilms of PE and BDMs respectively. Our study provides new insights into the consequences of the application of different types of plastic films on microbial communities in different ecological niches of agricultural fields.

Insights into growth-affecting effect of nanomaterials: Using metabolomics and transcriptomics to reveal the molecular mechanisms of cucumber leaves upon exposure to polystyrene nanoplastics (PSNPs)

Polystyrene nanoplastics (PSNPs, <100nm), an artificial pollutant that is widespread in the environment, can be assimilated by plants to alter plant gene expression and its metabolic pathway; thus, interfering with physiological homeostasis and growth of plants. Recently, the biosafety and potential environmental risks of PSNPs have attracted enormous attention. However, the knowledge regarding the uptake and phytotoxicity of atmosphere PSNPs subsiding to plant leaves is still limited. Here, we separately applied 50 mg/L and 100 mg/L PSNPs on cucumber leaves to simulate the plant response to the atmosphere PSNPs. We found that the PSNPs can be accumulated on the surface of cucumber leaves and are also able to be uptake by cucumber leaf stomata. The repertoires of metabolomics and transcriptomics from cucumber leaves upon PSNPs treatment demonstrated that the deposition of PSNPs on leaves alters the biosynthesis of various metabolites and the expression of a variety of genes. The leaves exposure to low concentration (50 mg/L) of PSNPs impact the genes involved in carbohydrate metabolism and the biosynthesis of metabolites related to membrane stability maintenance, thereby, probably enhancing plant tolerance to the stress caused by PSNPs. Whereas, exposure to high concentration (100 mg/L) of PSNPs, both nitrogen and carbohydrate metabolism in cucumber leaves are affected, as well as that the photosynthetic capacity was decreased, leading to the threat to plant health. Combined omics technologies, our findings advance our understanding about how the PSNPs released to ecological environment influence the terrestrial plant growth and provide phytotoxic mechanism.

Elevated antimony concentration stimulates rare taxa of potential autotrophic bacteria in the Xikuangshan groundwater

Microbial communities composed of few abundant and many rare species are widely involved in the biogeochemical cycles of elements. Yet little is known about the ecological roles of rare taxa in antimony (Sb) contaminated groundwater. Groundwater samples were collected along an Sb concentration gradient in the Xikuangshan antimony mine area and subjected to high through-put sequencing of 16S rRNA genes to investigate the bacterial communities. Results suggested that both abundant and rare sub-communities were dominated by Betaproteobacteria, Gammaproteobacteria, and Alphaproteobacteria, whereas rare sub-communities showed higher alpha-diversities. Multivariate analysis showed that both the abundant and rare taxa were under the stress of Sb, but the impact on rare taxa was greater. Nitrate explained a large part for the variation of the abundant sub-communities, indicating the critical role of nitrate for their activities under anoxic conditions. In contrast, bicarbonate significantly impacted rare sub-communities, suggesting their potential autotrophic characteristics. To further explore the role of rare taxa in the communities and the mechanism of affecting the community composition, a network was constructed to display the co-occurrence pattern of bacterial communities. The rare taxa contributed most of the network nodes and served as keystone species to maintain the stability of community. Abiotic factors (mainly Sb and pH) and bacterial interspecific interactions (interactions between keystone species and other bacterial groups) jointly affect the community dynamics. Functional prediction was performed to further reveal the ecological function of rare taxa in the Sb-disturbed groundwater environment. The results indicated that the rare taxa harbored much more diverse functions than their abundant counterparts. Notably, elevated Sb concentration promoted some potential autotrophic functions in rare taxa such as the oxidation of S-, N-, and Fe(II)-compounds. These results offer new insights into the roles of rare species in elemental cycles in the Sb-impacted groundwater.

Screening of hazardous groundwater pollutants responsible for microbial ecological consequences by integrated nontargeted analysis and high-throughput sequencing technologies

Organic contaminants, especially hydrophobic organic contaminants (HOCs), pose potential ecological threats even at environmental concentrations. Characterization of HOC profiles and identification of key environmental stressors are vital but still challenging in groundwater quality management. In this study, a strategy for identifying the key environmental stressors among HOCs in groundwater based on integrated chemical monitoring technologies and microbial ecology analysis methods was proposed and applied to typical groundwater samples. Specifically, the characteristics of HOCs were systematically analyzed based on nontargeted and targeted approaches, and microbial community assembly and specific biomarker analysis were combined to determine the major ecological processes and key environmental stressors. The results showed that a total of 234 HOCs were detected in groundwater collected from Tongzhou, Beijing; among them, phthalate esters (PAEs) were screened out as key environmental stressors, considering that they made relatively higher microbial ecology contributions. Furthermore, their influences on the structure and function of the groundwater microbial community were evaluated by adopting high-throughput sequencing and bioinformatics analysis technologies. These findings confirmed PAEs as vital determinants driving microbial assembly, shifting community structure, and regulating community function in groundwater; in addition, the findings validated the feasibility and suitability of the proposed strategy.

Thiobacillus spp. and Anaeromyxobacter spp. mediate arsenite oxidation-dependent biological nitrogen fixation in two contrasting types of arsenic-contaminated soils

As(III) oxidation-dependent biological nitrogen fixing (As-dependent BNF) bacteria use a novel biogeochemical process observed in tailings recently. However, our understanding of microorganisms responsible for As-dependent BNF is limited and whether such a process occurs in As-contaminated soils is still unknown. In this study, two contrasting types of soils (surface soils versus river sediments) heavily contaminated by As were selected to study the occurrence of As-dependent BNF. BNF was observed in sediments and soils amended with As(III), whereas no apparent BNF was found in the cultures without As(III). The increased abundances of the nitrogenase gene (nifH) and As(III) oxidation gene (aioA) suggest that an As-dependent BNF process was catalyzed by microorganisms harboring nifH and aioA. In addition, DNA-SIP demonstrated that Thiobacillus spp. and Anaeromyxobacter spp. were putative As-dependent BNF bacteria in As-contaminated soils and sediments, respectively. Metagenomic analysis further suggested that these taxa contained genes responsible for BNF, As(III) oxidation, and CO₂ fixation, demonstrating their capability for serving as As-dependent BNF. These results indicated the occurrence of As-dependent BNF in various As-contaminated habitats. The contrasting geochemical conditions in different types of soil suggested that these conditions may enrich different As-dependent BNF bacteria (Thiobacillus spp. for soils and Anaeromyxobacter spp. for sediments).

Biotransformation of chloramphenicol by white-rot-fungi Trametes versicolor under cadmium stress

The recalcitrant chloramphenicol (CAP) combined with heavy metals cadmium (Cd) commonly co-existed in the environment, posing threat to environment health. The capacity of Trametes versicolor to remove/biodegrade CAP in air-pulse fluidized-bed reactor was evaluated, even under Cd stress. T. versicolor could remove 44 % CAP of 5 mg/L in 15 days, even 51 % CAP under 1 mg/L Cd stress. Sustained Cd stress inhibited CAP biodegradation and Cd removal in a 5-batches of a 5-days cycle sequential batch reactor. Nine transformation products and two novel pathways were proposed, with initial multi-step transformation reaction into CP2 and allylic alcohol, respectively. Furthermore, the main mechanism of Cd removal by T. versicolor was extracellular surface bioadsorption and intracellular accumulation. This study filled the gap of the mechanism of simultaneous CAP removal/biodegradation and Cd removal by white-rot fungi T. versicolor, which offer a theoretical basis for future application of biological removal of CAP containing wastewater.

Microplastics existence intensified bloom of antibiotic resistance in livestock feces transformed by black soldier fly

Efficient degradation of residual antibiotics in livestock and poultry feces by black soldier flies (BSFs) has been widely reported. Nevertheless, the effects of widely detected microplastics in feces on the dynamic reduction of antibiotics and the transfer of gut bacterial resistome remain unclear. In this study, red fluorescence-labeled microplastics are observed to be abundantly distributed in BSFs gut, which caused epithelial cell damage along with gut peristalsis and friction, thereby releasing reactive oxygen species and activating the antioxidant enzyme system. In addition, they result in not only in inflammatory cytokine release to induce gut inflammation, but fecal hardening because of mucus released from the BSFs, thereby hindering organic mineralization and antibiotic degradation. Besides, the gut pathogenic bacteria easily obtain growth energy and crowded out ecological niches by reducing nitrate produced by inflammatory host cells to nitrite with nitrate reductase. Consequently, linear discriminant analysis effect size and detrended correspondence analysis found that microplastic intake significantly reshape the microbial community structure and cause the significant reduction of several important organic-decomposing bacteria and probiotics (e.g., Pseudomonadales, Coriobacteriales, Lachnospirales, and Ruminococcaceae). In addition, a large number of pathogenic bacteria (e.g., Enterococcaceae, Hungateiclostridiaceae, and Clostridia) are enriched in feces and BSFs gut. Weighted correlation network analysis and bubble diagram analysis indicate that microplastic intake intensified gut colonization of pathogenic bacteria carrying antibiotic-resistant genes/mobile genetic elements, driving the bloom of antibiotic resistance in transformed fecal piles. Therefore, microplastics in feces should be isolated as much as possible before insect transformation.

Arsenic shapes the microbial community structures in tungsten mine waste rocks

Tungsten (W) is a critical material that is widely used in military applications, electronics, lighting technology, power engineering and the automotive and aerospace industries. In recent decades, overexploitation of W has generated large amounts of mine waste rocks, which generate elevated content of toxic elements and cause serious adverse effects on ecosystems and public health. Microorganisms are considered important players in toxic element migrations from waste rocks. However, the understanding of how the microbial community structure varies in W mine waste rocks and its key driving factors is still unknown. In this study, high-throughput sequencing methods were used to determine the microbial community profiles along a W content gradient in W mine waste rocks. We found that the microbial community structures showed clear differences across the different W levels in waste rocks. Notably, arsenic (As), instead of W and nutrients, was identified as the most important predictor influencing microbial diversity. Furthermore, our results also showed that As is the most important environmental factor that regulates the distribution patterns of ecological clusters and keystone ASVs. Importantly, we found that the dominant genera have been regulated by As and were widely involved in As biogeochemical cycling in waste rocks. Taken together, our results have provided useful information about the response of microbial communities to W mine waste rocks.

Response of soil protists to antimony and arsenic contamination

Microorganisms can mediate antimony (Sb) and arsenic (As) transformation and thus change their mobility and toxicity. Having similar geochemical behavior, Sb and As are generally considered to exert similar environmental pressure on microbiome. However, it needs further validation, especially for protists. In this study, the responses of protistan communities to Sb and As were investigated by collecting soils from Xikuangshan Sb mine and Shimen As mine in China. Antimony and As contamination taxonomically and functionally (consumer and phototroph) changed the alpha and beta diversities of protistan communities, but exerted different impacts on the parasitic community. Based on multiple statistical tools, As contamination had a greater impact on protistan communities than Sb. The ecological networks of highly contaminated sites were less complex but highly positively connected compared to less contaminated sites. High As contamination raised the ratio of consumers and decreased the ratio of phototrophs in ecological networks, while the opposite tendency was observed in Sb contaminated soils. High Sb and As contamination enriched different keystone taxa resistant to Sb and As. These results demonstrate that protistan community respond differently to Sb and As.

Indigenous rhizosphere microbial community characteristics of the phytostabilizer Athyrium wardii (Hook.) grown in a Pb/Zn mine tailing

Plant rhizosphere microbiome usually changes dramatically in adaptation to the mine environment to endure high heavy metal concentration, which in turn improves the process of revegetation and phytostabilization of mine tailing and deserves deep investigation. A field study was conducted to investigate the indigenous microbial community of a mining ecotype (ME) of the phytostabilizer Athyrium wardii (Hook.) grown in a Pb/Zn mine tailing and a corresponding non-mining ecotype (NME) grown in an uncontaminated adjacent site. Our study found a slight difference in microbial α-diversity between the ME and NME, and no significant difference between the rhizosphere and bulk soil. Both bacterial and fungal community compositions differed between the ME and NME, for which the differences were mainly driven by pH and metal contaminants. The ME harbored a unique microbial community in the rhizosphere soils different from the bulk soil and NME counterparts. The dominant phyla in the ME rhizosphere were Proteobacteria, Chloroflexi, Actinobacteria, Nitrospirae, and Ascomycota. Several genera from Proteobacteria, Acidobacteria, and Ascomycota were more abundant in the ME rhizosphere than in the NME rhizosphere. Network analysis revealed that keystone taxa were different in the two sites. Some keystone taxa from Gemmatimonadaceae, and Burkholderiaceae and Ascomycota played a critical role in microbial interactions within the mine tailing network. The unique microbial community with high tolerance in the rhizosphere soils of ME may show great benefit for plant growth and metal tolerance of the ME and thereby contributing to the process of revegetation and phytostabilization of mine tailings.

Mycobacteriaceae Mineralizes Micropolyethylene in Riverine Ecosystems

Microplastic (MP) contamination is a serious global environmental problem. Plastic contamination has attracted extensive attention during the past decades. While physiochemical weathering may influence the properties of MPs, biodegradation by microorganisms could ultimately mineralize plastics into CO₂. Compared to the well-studied marine ecosystems, the MP biodegradation process in riverine ecosystems, however, is less understood. The current study focuses on the MP biodegradation in one of the world's most plastic contaminated rivers, Pearl River, using micropolyethylene (mPE) as a model substrate. Mineralization of ¹³C-labeled mPE into ¹³CO₂ provided direct evidence of mPE biodegradation by indigenous microorganisms. Several Actinobacteriota genera were identified as putative mPE degraders. Furthermore, two Mycobacteriaceae isolates related to the putative mPE degraders, Mycobacterium sp. mPE3 and Nocardia sp. mPE12, were retrieved, and their ability to mineralize ¹³C-mPE into ¹³CO₂ was confirmed. Pangenomic analysis reveals that the genes related to the proposed mPE biodegradation pathway are shared by members of Mycobacteriaceae. While both Mycobacterium and Nocardia are known for their pathogenicity, these populations on the plastisphere in this study were likely nonpathogenic as they lacked virulence factors. The current study provided direct evidence for MP mineralization by indigenous biodegraders and predicted their biodegradation pathway, which may be harnessed to improve bioremediation of MPs in urban rivers.

Immobile Iron-Rich Particles Promote Arsenic Retention and Regulate Arsenic Biotransformation in Treatment Wetlands

Remediation of arsenic (As)-contaminated wastewater by treatment wetlands (TWs) remains a technological challenge due to the low As adsorption capacity of wetland substrates and the release of adsorbed As to pore water. This study investigated the feasibility of using immobile iron-rich particles (IIRP) to promote As retention and to regulate As biotransformation in TWs. Iron-rich particles prepared were immobilized in the interspace of a gravel substrate. TWs with IIRP amendment (IIRP-TWs) achieved a stable As removal efficiency of 63 ± 4% over 300 days, while no As removal or release was observed in TWs without IIRP after 180 days of continuous operation. IIRP amendment provided additional adsorption sites and increased the stability of adsorbed As due to the strong binding affinity between As and Fe oxides. Microbially mediated As(III) oxidation was intensified by iron-rich particles in the anaerobic bottom layer of IIRP-TWs. Myxococcus and Fimbriimonadaceae were identified as As(III) oxidizers. Further, metagenomic binning suggested that these two bacterial taxa may have the capability for anaerobic As(III) oxidation. Overall, this study demonstrated that abiotic and biotic effects of IIRP contribute to As retention in TWs and provided insights into the role of IIRP for the remediation of As contamination.

Characterization of diazotrophic root endophytes in Chinese silvergrass (Miscanthus sinensis)

BACKGROUND

Phytoremediation is a potentially cost-effective way to remediate highly contaminated mine tailing sites. However, nutrient limitations, especially the deficiency of nitrogen (N), can hinder the growth of plants and impair the phytoremediation of mine tailings. Nevertheless, pioneer plants can successfully colonize mine tailings and exhibit potential for tailing phytoremediation. Diazotrophs, especially diazotrophic endophytes, can promote the growth of their host plants. This was tested in a mine-tailing habitat by a combination of field sampling, DNA-stable isotope probing (SIP) analysis, and pot experiments.

RESULTS

Bacteria belonging to the genera Herbaspirillum, Rhizobium, Devosia, Pseudomonas, Microbacterium, and Delftia are crucial endophytes for Chinese silvergrass (Miscanthus sinensis) grown in the tailing, the model pioneer plant selected in this study. Further, DNA-SIP using 15N2 identified Pseudomonas, Rhizobium, and Exiguobacterium as putative diazotrophic endophytes of M. sinensis. Metagenomic-binning suggested that these bacteria contained essential genes for nitrogen fixation and plant growth promotion. Finally, two diazotrophic endophytes Rhizobium sp. G-14 and Pseudomonas sp. Y-5 were isolated from M. sinensis. Inoculation of another pioneer plant in mine tailings, Bidens pilosa, with diazotrophic endophytes resulted in successful plant colonization, significantly increased nitrogen fixation activity, and promotion of plant growth.

CONCLUSIONS

This study indicated that diazotrophic endophytes have the potential to promote the growth of pioneer plant B. pilosa in mine tailings. Video Abstract.

Characterization of arsenic-metabolizing bacteria in an alkaline soil

Arsenite (As(III)) is more toxic, mobilizable and bioavailable than arsenate (As(V)). Hence, the transformations between As(III) and As(V) are crucial for the toxicity and mobility of arsenic (As). However, As transformation and microbial communities involved in alkaline soils are largely unknown. Here we investigate two major pathways of As transformation, i.e., As(III) oxidation and As(V) reduction, and identify the bacteria involved in the alkaline soil by combining stable isotope probing with shotgun metagenomic sequencing. As(III) oxidation and significant increase of the aioA genes copies were observed in the treatments amended with As(III) and NO₃^-, suggesting that As(III) oxidation can couple with nitrate reduction and was mainly catalyzed by the microorganisms containing aioA genes. As(V) reduction was detected in the treatments amended with As(V) and acetate where the abundance of arrA gene significantly increased, indicating that microorganisms with arrA genes were the key As(V) reducers. Acidovorax, Hydrogenophaga, and Ramlibacter were the putative nitrate-dependent As(III) oxidizers, and Deinococcus and Serratia were the putative respiratory As(V) reducers. These findings will improve our understanding of As metabolism and are meaningful for mapping out bioremediation strategies of As contamination in alkaline environment.

Vanadate reducing bacteria and archaea may use different mechanisms to reduce vanadate in vanadium contaminated riverine ecosystems as revealed by the combination of DNA-SIP and metagenomic-binning

Vanadium (V) is a transitional metal that poses health risks to exposed humans. Microorganisms play an important role in remediating V contamination by reducing more toxic and mobile vanadate (V(V)) to less toxic and mobile V(IV). In this study, DNA-stable isotope probing (SIP) coupled with metagenomic-binning was used to identify microorganisms responsible for V(V) reduction and determine potential metabolic mechanisms in cultures inoculated with a V-contaminated river sediment. Anaeromyxobacter and Geobacter spp. were identified as putative V(V)-reducing bacteria, while Methanosarcina spp. were identified as putative V(V)-reducing archaea. The bacteria may use the two nitrate reductases NarG and NapA for respiratory V(V) reduction, as has been demonstrated previously for other species. It is proposed that Methanosarcina spp. may reduce V(V) via anaerobic methane oxidation pathways (AOM-V) rather than via respiratory V(V) reduction performed by their bacterial counterparts, as indicated by the presence of genes associated with anaerobic methane oxidation coupled with metal reduction in the metagenome assembled genome (MAG) of Methanosarcina. Briefly, methane may be oxidized through the "reverse methanogenesis" pathway to produce electrons, which may be further captured by V(V) to promote V(V) reduction. More specially, V(V) reduction by members of Methanosarcina may be driven by electron transport (CoMS-SCoB heterodisulfide reductase (HdrDE), F₄₂₀H₂ dehydrogenases (Fpo), and multi-heme c-type cytochrome (MHC)). The identification of putative V(V)-reducing bacteria and archaea and the prediction of their different pathways for V(V) reduction expand current knowledge regarding the potential fate of V(V) in contaminated sites.

HiLi-chip: A high-throughput library construction chip for comprehensive profiling of environmental microbial communities

Investigating the contribution and associations of environmental microbes to ecological health and human well-being is in great demand with the goal of One Health proposed. To achieve the goal, there is an urgent need for accurate approaches to obtaining a large amount of high-resolution molecular information from various microbes. In this study, we developed a high-throughput library construction chip (HiLi-Chip) for profiling environmental microbial communities and evaluated its performance. The HiLi-Chip showed high conformity with the conventional Pacbio method in terms of α-diversity, community composition of abundant bacteria (>83%), as well as rare taxa (>84%) and human pathogens detection (>67%), indicating its advantages of accuracy, high-throughput, cost-efficiency, and broad practicability. It is suggested that the optimal strategy of the HiLi-Chip was a 2.4 μL PCR mixture per sample (∼2.4 ng DNA) with a 216-sample × 24-replicate format. We have successfully applied the HiLi-Chip to the Jiulongjiang River and identified 51 potential human bacterial pathogens with a total relative abundance of 0.22%. Additionally, under limited nutrients and similar upstream environments, bacteria tended to impose competitive pressures, resulting in a more connected network at the downstream river confluence (RC). Whereas narrow niche breadth of bacteria and upstream environmental heterogeneity probably promoted niche complementary and environment selection leading to fewer links at RC in the midsection of the river. Core bacteria might represent the entire bacterial community and enhance network stability through synergistic interactions with other core bacteria. Collectively, our results demonstrate that the HiLi-Chip is a robust tool for rapid comprehensive profiling of microbial communities in environmental samples and has significant implications for a profound understanding of environmental microbial interactions.

Primary Succession Changes the Composition and Functioning of the Protist Community on Mine Tailings, Especially Phototrophic Protists

Primary succession in mine tailings is a prerequisite for tailing vegetation. Microorganisms, including bacteria, fungi, and protists, play an important role in this process in the driving force for improving the nutritional status. Compared to bacteria and fungi, protist populations have rarely been investigated regarding their role in mine tailings, especially for those inhabiting tailings associated with primary succession. Protists are the primary consumers of fungi and bacteria, and their predatory actions promote the release of nutrients immobilized in the microbial biomass, as well as the uptake and turnover of nutrients, affecting the functions of the wider ecosystems. In this study, three different types of mine tailings associated with three successional stages (original tailings, biological crusts, and Miscanthus sinensis grasslands) were selected to characterize the protistan community diversity, structure, and function during primary succession. Some members classified as consumers dominated the network of microbial communities in the tailings, especially in the original bare land tailings. The keystone phototrophs of Chlorophyceae and Trebouxiophyceae showed the highest relative abundance in the biological crusts and grassland rhizosphere, respectively. In addition, the co-occurrences between protist and bacterial taxa demonstrated that the proportion of protistan phototrophs gradually increased during primary succession. Further, the metagenomic analysis of protistan metabolic potential showed that abundances of many functional genes associated with photosynthesis increased during the primary succession of tailings. Overall, these results suggest that the primary succession of mine tailings drives the changes observed in the protistan community, and in turn, the protistan phototrophs facilitate the primary succession of tailings. This research offers an initial insight into the changes in biodiversity, structure, and function of the protistan community during ecological succession on tailings.