Communities In River Sediments Research Articles

Impacts of o-cresol spill on composition and function of river sediment and soil microbial communities.

o-Cresol is a toxic substance with strong irritating and corrosive effects on skin and mucous membranes. To date, information on the effects of o-cresol on microbial communities in the natural environment is very limited. In the present study, 16S rRNA sequencing and metagenomic technique were carried out to elucidate the effects of the o-cresol spill on microbial communities in river sediments and nearby soils. o-Cresol spill induced the increase in the relative abundance of phyla Planctomycetes and Gemmatimonadetes, suggesting their resilience to o-cresol-induced stress. Uncultured Gemmatimonadetes genera and the MND1 genus exhibited enrichment, while the Pseudomonas genus dominated across all samples, indicating their potential pivotal roles in adapting to the o-cresol spill. Moreover, o-cresol spill impaired the metabolic functions of microbes but triggered their defense mechanisms. Under o-cresol pressure, microbial functions related to carbon fixation were upregulated and functions associated with sulfur metabolism were downregulated. In addition, the o-cresol spill led to an increase in functional genes related to the conversion of o-cresol to 3-methylcatechol. Several genes involved in the degradation of aromatic compounds were also identified, potentially contributing to the biodegradation of o-cresol. This study provides fresh insights into the repercussions of an abrupt o-cresol spill on microbial communities in natural environments, shedding light on their adaptability, defense mechanisms, and biodegradation potential.

Distribution heterogeneity of sediment bacterial community in the river-lake system impacted by nonferrous metal mines: Diversity, composition and co-occurrence patterns

Metal(loid) pollution caused by mining activities can affect microbial communities. However, knowledge of the diversity, composition, and co-occurrence patterns of bacterial communities in aquatic systems impacted by nonferrous metal mines. Here, the metal(loid) contents and bacterial communities in sediments from the Zijiang River (tributary to mainstream) to Dongting Lake were investigated by geochemical and molecular biology methods. The results indicated that the river sediments had lower pH and higher ecological risk of metal(loid)s than the lake sediment. The diversity and composition of bacterial communities in river sediments significantly (p < 0.05) differed from those in lake sediments, showing distributional heterogeneity. The biomarkers of tributary, mainstream, and lake sediments were mainly members of Deltaproteobacteria, Firmicutes, and Nitrospirae, respectively, reflecting species sorting in different habitats. Multivariate statistical analysis demonstrated that total and bioavailable Sb, As, and Zn were positively correlated with bacterial community richness. pH, TOC, TN, and Zn were crucial factors in shaping the distribution difference of bacterial communities. Environment-bacteria network analysis indicated that pH, SO42−, and total and bioavailable As and Sb greatly influenced the bacterial composition at the genus level. Bacteria-bacteria network analysis manifested that the co-occurrence network in mainstream sediments with a higher risk of metal(loid) pollution exhibited higher modularity and connectivity, which might be the survival mechanism for bacterial communities adapted to metal(loid) pollution. This study can provide a theoretical basis for understanding the ecological status of aquatic systems.

Decoupling the heterogeneity of sediment microbial communities along the urbanization gradients: A Bayesian-based approach

Comprehending the response of microbial communities in rivers along urbanization gradients to hydrologic characteristics and pollution sources is critical for effective watershed management. However, the effects of complex factors on riverine microbial communities remain poorly understood. Thus, we established a bacteria-based index of biotic integrity (Ba-IBI) to evaluate the microbial community heterogeneity of rivers along an urbanization gradient. To examine the response of Ba-IBI to multiple stressors, we employed a Bayesian network based on structural equation modeling (SEM-BN) and revealed the key control factors influencing Ba-IBI at different levels of urbanization. Our findings highlight that waterborne nutrients have the most significant direct impact on Ba-IBI (r = −0.563), with a particular emphasis on ammonia nitrogen, which emerged as the primary driver of microbial community heterogeneity in the Liuyang River basin. In addition, our study confirmed the substantial adverse effects of urbanization on river ecology, as urban land use had the greatest indirect effect on Ba-IBI (r = −0.460). Specifically, the discharge load from wastewater treatment plants (WWTP) was found to significantly negatively affect the Ba-IBI of the entire watershed. In the low urbanized watersheds, rice cultivation (RC) and concentrated animal feeding operations (CAFO) are key control factors, and an increase in their emissions can lead to a sharp decrease in Ba-IBI. In moderately urbanized watersheds, the Ba-IBI tended to decrease as the level of RC emissions increased, while in those with moderate RC emissions, an increase in point source emissions mitigated the negative impact of RC on Ba-IBI. In highly urbanized watersheds, Ba-IBI was not sensitive to changes in stressors. Overall, our study presents a novel approach by integrating Ba-IBI with multi-scenario analysis tools to assess the effects of multiple stressors on microbial communities in river sediments, providing valuable insights for more refined environmental decision-making.

Profiles and spatial distributions of heavy metals, microbial communities, and metal resistance genes in sediments from an urban river.

The occurrence and propagation of resistance genes due to exposure to heavy metals (HMs) in rivers is an emerging environmental issue. Little is known about resistance genes in microbial communities in river sediments with low HM concentrations. The profiles and spatial distributions of HMs, the microbial community, and metal resistance genes (MRGs) were analyzed in sediment samples from the Zhilong River basin in Yangjiang city, near the Pearl River Delta. Concentrations of copper (Cu), cadmium (Cd), lead (Pb), chromium (Cr), and nickel (Ni) were relatively low compared with those in other urban river sediments in China. HM chemical composition and fractions and the structure of the microbial community varied along the main channel, but the composition and abundance of MRGs were relatively homogeneous. Variations in HMs and microbial communities in mid- to upstream areas were related to the presence of tributaries, whose inputs were one of the major factors affecting HM chemical fractions and genera structure in mainstream sediments. There were no significant correlations (p < 0.05) between HM concentrations, bacterial communities, and the MRG profiles; thus, HM concentrations were not the main factor affecting MRGs in sediments. These results contribute to understanding the propagation of MRGs in urban rivers in developing cities.

Distinct mediating patterns between metal filtering and species coexistence of rare and abundant subcommunities in heavily polluted river sediments

It is unknown how anthropogenic pollutants released into freshwater ecosystems affect the assembly processes of microbial communities in river sediment. We used high-throughput sequencing to examine the assembly of rare and abundant subcommunities in a heavily polluted urban river: the Beiyun River in Beijing, China. Although deterministic processes overrode stochastic processes in shaping local rare and abundant subcommunities, there were distinctly different assembly mechanisms of rare and abundant subcommunities. Rare subcommunity assembly was governed more by interspecificinteractions, and environmental selection and dispersal limitation explained only a small fraction of the variation. However, both factors seemed to govern the assembly of abundant subcommunities. Our results implied that microbial co-occurrence associations tended to be higher when rare subcommunities were less driven by community assembly, and that these associations tended to be lower when abundant subcommunities were more driven by community assembly. A balance between the community assembly and species coexistence was exhibited atthesubcommunitylevel. Importantly, we tried to disentangle the assembly process of abundant subcommunities into introduction and colonization processes characterized by the presence/absence and relative abundance datasets. Interestingly, metals explained the highest percentage of spatial variation in the species introduction process. By affecting nutrient availability, metals also shaped the abundant subcommunity in the species colonization process, but this did not surpass nutrient availability. Therefore, disentangling the introduction and colonization processes enhances our understanding of the assembly mechanisms of microbial communities in heavily polluted running water ecosystems at fine geographical scales.

Differential patterns and assembly processes of bacterial communities from distinct microhabitats in a subtropical estuary

Estuarine ecosystems interconnect freshwater and marine environments, and comprise multiple highly dynamic and complex microhabitats. The resident microbiota in estuary is influenced by contrasting microenvironmental heterogeneity. However, the bacterial patterns and assembly processes in different microhabitats of estuarine ecosystem are not well studied. Here, we investigated the bacterial diversity, functions and community assembly mechanisms of mangrove soil, river sediment and overlying water in a subtropical estuary. Results showed that similar profiles of bacterial communities existed in the mangrove soil and river sediment and were dominated by Proteobacteria, Bacteroidetes and Acidobacteria. In terms of different microhabitats, the lowest alpha diversity of bacterial communities was found in overlying water and were dominated by Proteobacteria, Actinobacteria and Bacteroidetes. Meanwhile, the functional potential genes associated with carbon metabolisms were also substantially different in the three microhabitats. The relative abundance of genes connected to aerobic carbon respiration was significantly higher in overlying water than in the other two microhabitats. Bacterial communities in river sediments were enriched for genes associated with aerobic methane oxidation. The strong environmental heterogeneity of the three nearby microhabitats shaped the taxonomic and functional composition of the bacterial communities in estuarine ecosystem. Moreover, the plant rhizosphere effect increased the proportion of the dispersal limitation processes in mangrove soils compared to that in river sediments, while the overlying water was fluid and had less environmental selection processes compared to that in mangrove soil and river sediment. The bacterial communities in river sediment construct a more clustered network, while the overlying water network showed the highest complexity. Our findings reveal the differences of bacterial patterns and community assembly mechanisms in distinct microhabitats of estuarine ecosystems, and provide important insights for a comprehensive understanding of the mechanisms to maintain estuarine wetland conservation under environmental changes.

Promoted microbial denitrification and carbon dioxide fixation via photogenerated electrons stored in novel core/shell memory photocatalysts in darkness.

Excess nitrogen in water and greenhouse gases, especially atmospheric carbon dioxide (CO2) from the rapid development of modern society have become an acute threat to the environment. Herein, novel core/shell structured g-C3N4@WO3 memory photocatalyst was fabricated by coating g-C3N4 on the surface of WO3 nanoparticles and applied in the simultaneous coupling of memory photocatalysts and microbial communities (SCMPMC) for the synergistic removal of microbial nitrate and CO2 fixation in darkness. The results showed that ∼98.6% of nitrate was removed and ∼17.7% of CO2 was fixed in darkness by microorganisms in the presence of g-C3N4@WO3 memory photocatalyst within 48h. Besides, the investigation of the mechanism evidenced that g-C3N4@WO3 memory photocatalyst can promote electron transfer in the SCMPMC system. Moreover, key enzyme activities (i.e., NAR, NIR, CAT, and ETSA) were accelerated, indicating that the activities of enzymes within microorganisms could be remarkably enhanced by the continuous release of stored electrons by the g-C3N4@WO3 memory photocatalyst in the dark. Furthermore, microbial community analysis revealed that the g-C3N4@WO3 memory photocatalyst increased the relative abundance of denitrifiers (i.e., Acidobacterota, Actinobacteria, Chloroflexi, and Proteobacteria) and CO2-assimilating microorganisms (i.e., Pseudomonas), in the treated communities compared with the original community in river sediment, demonstrating the positive effects of g-C3N4@WO3 memory photocatalyst on river sediment microbial communities. The results in this study could shed new light on the establishment of promising synergistic microbial nitrate removal and CO2 fixation methods and mechanisms in darkness.

NosZI microbial community determined the potential of denitrification and nitrous oxide emission in river sediments of Qinghai-Tibetan Plateau

Denitrification in river sediments is the hotspot of nitrogen removal and nosZI gene is essential for reducing nitrous oxide (N2O) emissions. However, few studies tried to link nosZI communities with variations of denitrification rates in sediments along the high-elevation rivers. Here, we investigated the spatial variation of potential denitrification rates of sediments along a section (hereafter YJ) of the middle reaches of the Yarlung Zangbo River in the Qinghai-Tibetan Plateau. We also used the real-time quantitative PCR (qPCR) and high-throughput sequencing techniques to evaluate the abundance and composition of nosZI-containing microbial groups. The influences of physicochemical factors and denitrifier communities on potential denitrification rates were further revealed through structural equation modeling. The obtained results indicated that potential denitrification rates and N2O/(N2O + N2) ratio in the sediments along YJ section were greatly different. Moreover, the alpha diversity and composition of nosZI-containing microbial community in river sediments differed remarkably, mainly driven by the ammonia nitrogen (NH4+-N), organic matter (OM) and pH in sediments. The relative abundances of Zoogloeaceae, Oxalobacteraceae, Rhodospirillaceae and Bradyrhizobiaceae significantly differed among five groups (P < 0.05). Structural equation modeling further suggested that nitrogen nutrients directly influenced the potential denitrification rates, while total phosphorus (TP) showed indirect effects on potential denitrification rates through modulating denitrifier abundances and nosZI community. The abundance and composition of nosZI community were powerful predictors in regulating denitrification rates and N2O/(N2O + N2) ratio. Our findings highlight that the nosZI-containing microbial groups play a non-negligible role in nitrogen removal and N2O mitigation in high-elevation river sediments.

How microorganisms tell the truth of potentially toxic elements pollution in environment

Potentially toxic elements (PTEs) posed a major hazard to microbial community in river sediments, but the way how different kinds of microorganisms responses to elements pollution has not been clearly understood. The target of this research was to discriminate the apposite indicators for diagnosing elements pollution based on the sensitivity of microbial abundance, biodiversity, predicted metabolic functions to PTEs (Cu, Cd, Cr, Ni, Pb, Zn, As and Hg). Considering Huaihe River Basin as the main subject, sediment samples were gathered from 135 sites. Ni, Zn and Cd significantly influenced the microbial communities and predicted functions. In general, the microbial sensitivity to PTEs was bacteria > archaea. Geo-accumulation index and potential ecological risk (PER) index suggested Hg and Cd were the significant contaminates and posed the most serious ecological risk in sediments. Structural Equation Model identified the bioindicators 1/nitrate reduction and rara taxa (Azoarcus) as reflect and speculate Hg and Cd pollution, respectively. PER was predicted by 1/nitrate reduction and rare taxa (Phaeodactylibacter and Illumatobacter). Results elucidated the rather role of rare taxa in indicating PTEs pollution. The findings contributed to provide useful reference for bioremediation of contaminated sediments under PTEs stress.

Metagenomic analysis reveals the response of microbial community in river sediment to accidental antimony contamination

The mining of deposits containing metals like antimony (Sb) causes serious environmental issues that threaten human health and ecological systems. However, information on the effect of Sb on freshwater sediment microorganisms and the mechanism of microbial Sb resistance is still very limited. This was the first attempt to explore microbial communities in river sediments impacted by accidental Sb spill. Metagenomic analysis revealed the high relative abundance of Proteobacteria and Actinobacteria in all the studied river sediments, showing their advantage in resistance to Sb pollution. Under Sb stress, microbial functions related to DNA repair and ion transport were enhanced. Increase in heavy metal resistance genes (HMRGs), particularly Sb transport-related arsB gene, was observed at Sb spill-impacted sites. HMRGs were significantly correlated with ARGs and MGEs, and the abundant MGEs at Sb spill-impacted sites might contribute to the increase in HMRGs and ARGs via horizontal gene transfer. Deinococcus, Sphingopyxis and Paracoccus were identified as potential tolerant genera under Sb pressure and might be related to the transmission of HMRGs and ARGs. This study can add new insights towards the effect of accidental metal spill on sediment microbial community.

Application of Polyaluminium Chloride Coagulant in Urban River Water Treatment Influenced the Microbial Community in River Sediment

Polyaluminium chloride (PAC) has been widely used as a chemical coagulant in water treatment. However, little is known about the impact of PAC performance on the microbial community in sediments. In this study, the archaeal, bacterial, and fungal communities in urban river sediments with and without PAC treatment were investigated. Prokaryotic diversity decreased at the PAC addition site (A2) and increased along with the river flow (from A3 to A4), while eukaryotic diversity was the opposite. The abundance of core microbiota showed a similar trend. For example, the dominant Proteobacteria presented the highest relative abundance in A1 (26.8%) and the lowest in A2 (15.3%), followed by A3 (17.5%) and A4 (23.0%). In contrast, Rozellomycota was more dominant in A2 (56.6%) and A3 (58.1%) than in A1 (6.2%) and A4 (16.3%). Salinity, total dissolved solids, and metal contents were identified as the key physicochemical factors affecting the assembly of core microorganisms. The predicted functions of archaea and fungi were mainly divided into methane cycling and saprotrophic nutrition, respectively, while bacterial function was more diversified. The above findings are helpful to enhance our understanding of microorganism response to PAC and have significance for water treatment within the framework of microecology.

Water diversion induces more changes in bacterial and archaeal communities of river sediments than seasonality

Previous studies have demonstrated that seasonal variation is often the most important factor affecting aquatic bacterial assemblages. Whether anthropogenic activities can dominate community dynamics remains unknown. Based on 16S rRNA high-throughput sequencing technology, this study revealed and compared the relative influence of water diversions and seasonality on bacterial and archaeal communities in river sediments from a region with obvious seasonality. The results indicate that the influence of water diversion on bacteria and archaea in water-receiving river sediments exceeded the influence of seasonal variation. Water diversion affected microbes by increasing EC, salinity, water flow rate, and organic matter carbon and nitrogen contents. Seasonal variations affected microbes by altering water temperature. Diversion responders but no season responders were classified by statistical methods in the microbial community. Diversion responder numbers were related to nitrogen concentrations, complex organic carbon contents and EC values, which were mainly affected by water diversion. With the joint impact of water diversion and seasonality, the correlations of bacterial and archaeal numbers with environmental factors were obviously weakened due to the increases in the ecological niche breadths of microorganisms. Natural seasonal changes in bacterial and archaeal communities were totally altered by changes in salinity, nutrients, and hydrological conditions induced by anthropogenic water diversions. These results highlight that human activity may be a stronger driver than natural seasonality in the alteration of bacterial and archaeal communities.

Different Responses of Bacterial and Archaeal Communities in River Sediments to Water Diversion and Seasonal Changes.

In recent years, different responses of archaea and bacteria to environmental changes have attracted increasing scientific interest. In the mid-latitude region, Fen River receives water transferred from the Yellow River, electrical conductivity (EC), concentrations of Cl− and Na+ in water, total phosphorus (TP), and Olsen phosphorus (OP) in sediments were significantly affected by water transfer. Meanwhile, temperature and oxidation-reduction potential (ORP) of water showed significant seasonal variations. Based on 16S rRNA high-throughput sequencing technology, the composition of bacteria and archaea in sediments was determined in winter and summer, respectively. Results showed that the dominance of bacterial core flora decreased and that of archaeal core flora increased after water diversion. The abundance and diversity of bacterial communities in river sediments were more sensitive to anthropogenic and naturally induced environmental changes than that of archaeal communities. Bacterial communities showed greater resistance than archaeal communities under long-term external disturbances, such as seasonal changes, because of rich species composition and complex community structure. Archaea were more stable than bacteria, especially under short-term drastic environmental disturbances, such as water transfer, due to their insensitivity to environmental changes. These results have important implications for understanding the responses of bacterial and archaeal communities to environmental changes in river ecosystems affected by water diversion.

Impact of long-term industrial contamination on the bacterial communities in urban river sediments

BackgroundThe contamination of the aquatic environment of urban rivers with industrial wastewater has affected the abiotic conditions and biological activities of the trophic levels of the ecosystem, particularly sediments. However, most current research about microorganism in urban aquatic environments has focused on indicator bacteria related to feces and organic pollution. Meanwhile, they ignored the interactions among microorganisms. To deeply understand the impact of industrial contamination on microbial community, we study the bacterial community structure and diversity in river sediments under the influence of different types of industrial pollution by Illumina MiSeq high-throughput sequencing technology and conduct a more detailed analysis of microbial community structure through co-occurrence networks.ResultsThe overall community composition and abundance of individual bacterial groups differed between samples. In addition, redundancy analysis indicated that the structure of the bacterial community in river sediments was influenced by a variety of environmental factors. TN, TP, TOC and metals (Cu, Zn and Cd) were the most important driving factors that determined the bacterial community in urban river sediments (P < 0.01). According to PICRUSt analysis, the bacterial communities in different locations had similar overall functional profiles. It is worth noting that the 15 functional genes related to xenobiotics biodegradation and metabolism were the most abundant in the same location. The non-random assembly patterns of bacterial composition in different types of industrially polluted sediments were determined by a co-occurrence network. Environmental conditions resulting from different industrial pollutants may play an important role in determining their co-occurrence patterns of these bacterial taxa. Among them, the bacterial taxa involved in carbon and nitrogen cycles in module I were relatively abundant, and the bacterial taxa in module II were involved in the repair of metal pollution.ConclusionsOur data indicate that long-term potential interactions between different types of industrial pollution and taxa collectively affect the structure of the bacterial community in urban river sediments.

Interaction type of tetrabromobisphenol A and copper manipulates ammonia-oxidizing archaea and bacteria communities in co-contaminated river sediments

The combined contamination of brominated flame retardants (BFRs) and heavy metals in electronic waste (e-waste) recycling and disposal areas has been a serious concern owing to their environmental persistence and chronic toxicities. Ammonia oxidizers, e.g., ammonia-oxidizing archaea (AOA) and bacteria (AOB) play essential roles in nitrogen cycling and can serve as ideal indicators that reflect the changes in sediment health in response to environmental variables. There is currently very little information available on the combined toxic effects of BFRs and heavy metals on AOA and AOB communities. In this study, two typical e-waste pollutants, tetrabromobisphenol A (TBBPA) and copper (Cu), were selected as target contaminants to investigate the individual and combined effects of both pollutants on AOA and AOB communities in river sediments. Respective treatments of TBBPA (1, 10, and 20 mg/kg wet weight), Cu (100 mg/kg wet weight) and their combined treatments (weight ratios of 1:100, 1:10, and 1:5) were performed in laboratory experiments. High-throughput sequencing was applied to explore the response of ammonia oxidizers to TBBPA and Cu. The interaction types of TBBPA and Cu were calculated by the directional classification system to reveal the individual and combined toxicities of both contaminants to the ammonia oxidizers. On days 15 and 30, the dominant interaction type of TBBPA and Cu was synergistic (62.50%), and the combined contamination exacted selective pressure and inhibition on the AOB and AOA communities. On days 45 and 90, the interaction type shifted to be antagonistic (83.33%), with both the AOB and AOA communities gradually reaching stable population equilibria. The alteration of the interaction type is attributed to the elevated TBBPA/Cu tolerance as the incubation time increased. This study disclosed the interaction types of TBBPA and Cu in contaminated river sediments, and revealed that the combined effect could potentially manipulate AOB and AOA communities.

Long-term effect of water diversion and CSOs on the remediation of heavy metals and microbial community in river sediments.

Untreated combined sewer overflows (CSOs) cause serious water pollution problems. In this study, the effects of CSO-induced heavy metals and the remediation practice of installation of a long-term water diversion (LTWD) on the microbial environment in river sediments were analyzed in an inland river. The Zn, Cd, Cr, and Cu contents in sediments and water were analyzed. DNA extraction and polymerase chain reaction analysis were conducted based on the Illumina MiSeq platform. The results showed that CSOs have a significant adverse impact on the diversity of microbial populations in river sediments. The LTWD is helpful in improving the richness of microorganisms and the proportion of Gram -ves, but it is challenging to reduce the accumulation of heavy metals in the sediment. The correlation analysis shows a strong relationship between some metabolic pathways and Zn and Cd accumulation in river sediments. Some detoxification compound metabolisms are also promoted at these sites. Thus, chronic exposure to environmental heavy metals from CSOs decreases the river microbial community, and further affects the ecological environment of the river. Therefore, without eliminating CSOs or reducing overflow frequency, it is difficult to alleviate the accumulation of heavy metals in river sediments and improve river ecology via water diversion alone.

Response Mechanism of Microbial Communities in River Sediments under Different Hydrodynamic Conditions

This paper studies the response of sedimentary microbial communities to different hydrodynamic conditions through laboratory experiments. The hydrodynamic conditions and flow field distribution in the experimental tank were measured and simulated by acoustic Doppler flowmeter and FLUENT software. The sediment DNA of different culture time and different flow velocity points was extracted and amplified by PCR amplification and high-throughput sequencing. The OTU sequence of the microbial organism.

Interplay between sediment properties and stream flow conditions influences surface sediment organic matter and microbial biomass in a Mediterranean river

River sediment physical properties are linked to flow and are important for the attachment of microorganisms. The objective of this study was to assess the relationship between physical characteristics of surface sediments in a Mediterranean river and their organic matter content and microbial biomass. To do this, we analyzed particle-size distribution, organic matter content, chlorophyll-a, and bacterial density in sediments collected along a 54 km reach under three flow conditions (i.e., drought, low-flow, and base-flow). Multiple regression analysis revealed that during the drought condition, sediment heterogeneity and porosity regulated bacterial density and organic matter content and that bacterial density tended to be lower as the proportion of mud increased. However, under the low-flow and base-flow conditions, bacterial density was related to percent mud, which may provide more surface area for colonization than cobbles. Algal biomass was affected by sediment particle-size distribution only under the base-flow condition, when chlorophyll-a content was enhanced by sediment heterogeneity and a higher relative abundance of sand, suggesting that when biomass declines due to increased shear stress, sediment particle-size distribution becomes more determinant for algal colonization. Our results highlight the importance of considering the interplay of sediment particle-size distribution and flow regime when studying microbial communities in river sediments.

Response of microbial communities to elevated thallium contamination in river sediments

The study of microbial communities in river sediments contaminated by thallium (Tl) is necessary to achieve the information for in-situ microbially mediated bioremediation. However, little is known about the microbial community in Tl-contaminated river sediments. In the present study, we characterized the microbial community and their responses to Tl pollution in river sediments from the Tl-mineralized Lanmuchang area, Southwest Guizhou, China. Illumina sequencing of 16S rRNA amplicons revealed that over 40 phyla belong to the domain bacteria. In all samples, Proteobacteria, Cyanobacteria, and Actinobacteria were the most dominant phyla. Based on the UPGMA (Unweighted Pair Group Method with Arithmetic Mean) tree and PCoA (Principal Coordinates Analysis) analysis, microbial composition of each segment was distinct, indicating in-situ geochemical parameters (including Tl, sulfate, TOC, Eh, and pH) had influenced on the microbial communities. Moreover, canonical correspondence analysis (CCA) was employed to further elucidate the impact of geochemical parameters on the distribution of microbial communities in local river sediments. The results indicated that a number of microbial communities including Cyanobacteria, Spirochaete, Hydrogenophaga, and Acinetobacter were positively correlated with total Tl, suggesting potential roles of these microbes to Tl tolerance or to biogeochemical cycling of Tl. Our results suggested a reliable location for the microbial community’s diversity in the presence of high concentrations of Tl and might have a potential association for in-situ bioremediation strategies of Tl-contaminated river. Overall, in situ microbial community could provide a useful tool for monitoring and assessing geo-environmental stressors in Tl-polluted river sediments.

The effect of biogenic and chemically manufactured silver nanoparticles on the benthic bacterial communities in river sediments

This study was conducted to determine and compare the effect of chemically-synthesised and biogenic silver nanoparticles on the benthic bacterial community structure in mesocosms containing sediment from three rivers in geographical sites with different population densities (low, medium, high), and therefore likely to be associated with respective low, moderate and high degrees of anthropogenic input. The nanoparticles were applied at the upper limit expected to accumulate in impacted environments (4 μg kgsed−1).The biomass, concentrations of elements, including selection metals (P, K, Na, K, Ca, Mg, Zn, Cu, Al, Ag) were all significantly higher at the high density than at the low density sites. Bacterial community profiling (terminal restriction fragment length polymorphism and amplicon sequencing) showed that the bacterial community structure in the sediments from the high population density site were resilient to environmental perturbations [adjustment from in-situ to ex-situ (laboratory) conditions], as well as to exposure to silver nanoparticles, with the converse being true for the low population density site. Results obtained from amplicon sequencing were interrogated to the lowest taxonomic level with a relative abundance >5%. Proteobacteria was the most abundant phylum in all the sediments. Notable resistance (increased relative abundance) to one or both forms of silver nanoparticles was seen in the class Thermoleophilia, and the orders Myxococcales, Bacteriodales, Pirellules CCU21 and iii 1–15 (class Acidobacteria 6). Conversely, sensitivity was demonstrated in the family Koribacteraceae and the orders Rhizobiales, Ellin 329 and Gemmatales.It is recommended that pro-active environmental monitoring is performed in aquatic systems receiving point source pollution from wastewater treatment plants in order to assess the accumulation of silver nanoparticles. If necessary, measures should be implemented to mitigate the entry of silver nanoparticles, especially into more vulnerable environments.