Profiling of Microbial Communities in the Sediments of Jinsha River Watershed Exposed to Different Levels of Impacts by the Vanadium Industry, Panzhihua, China

Comparative Analyses of Soil Bacterial Colonies of Two Types of Chinese Ginger after a Major Flood Disaster

Ginger, an important cash crop, has been cultivated for thousands of years in China. However, comparative studies on soil bacterial communities of Chinese ginger varieties, especially after flooding, are lacking. Here, we comprehensively compared the bacterial communities of two types of ginger soils from four different locations. Surprisingly, the 100-year flood (20 July 2021, in Henan, China) did not significantly affect the soil bacterial composition compared with previous reports. In contrast, flooding may have brought in nutrients and promoted the propagation of eutrophic bacteria, and Alphaproteobacteria were the most abundant in the Zhangliang region (~25%). However, due to the most severe flooding and inundation, the Zhangliang region, also probably contaminated with polycyclic aromatic hydrocarbons and heavy metals, showed the lowest microbial diversity. Moreover, the geographical location influenced the microbial communities more than did the soil type or ginger variety. These findings help us understand the species and composition of bacteria and infection of ginger after flooding and soaking. Further, the interaction mechanisms underlying these emerging phenomena need to be further investigated. IMPORTANCE There are few comparative studies on the soil bacterial communities of Chinese ginger varieties after flooding. After a 100-year flood (20 July 2021, in Henan, China), we comprehensively compared the bacterial communities of two types of ginger soils from four different locations. Surprisingly, this flood did not significantly affect the soil bacterial composition compared with previous reports. In contrast, it was found that the flooding may have brought in nutrients and promoted the propagation of eutrophic bacteria for the Zhangliang region. However, the flooding had also brought in polycyclic aromatic hydrocarbon and heavy metal contamination. Moreover, we also verified that geographical location influenced the microbial communities more than did the soil type or ginger variety. These findings help us understand the species and composition of bacteria and infection of ginger after flooding and soaking.

Divergent prokaryotic microbial assembly, co-existence patterns and functions in surrounding river sediments of a Cu-polymetallic deposit in Tibet

The exploitation of polymetallic deposits produces large amounts of mine drainage, which poses great challenges to the surrounding aquatic ecosystem. However, the prokaryotic microbial community assembly and co-existence patterns in the polluted area are poorly understood, especially in high-altitude localities. Herein, we investigated the prokaryotic microbial assembly, co-existence patterns and their potential functional responses in surrounding river sediments of a Cu-polymetallic deposit in Tibet. The sediments from mine drainage and surrounding tributaries exhibited distinct geochemical gradients, especially the changes in Cu content. The microbial community structure changed significantly, accompanied by decreased richness and diversity with increased Cu content. Interestingly, the relative abundances of some potential functional bacteria (e.g., Planctomycetota) actually increased as the Cu levels raised. In low contaminated area, ecological drift was the most important assembly process, whereas deterministic processes gained importance with pollution levels. Meanwhile, negative interactions in co-occurrence networks were more frequent with higher modularity and reduced keystone taxa in high contaminated area. Notably, the functions related to ABC transporters and quorum sensing (QS) were more abundant with high Cu content, which helped bacteria work together to cope with the stressful environment. Taken together, the physicochemical gradients dominated by Cu content drove the distribution, assembly and co-existence patterns of microbial communities in surrounding river sediments of a Cu-polymetallic deposit. These findings provide new insights into the maintenance mechanisms of prokaryotic microbial communities in response to heavy metal stress at high altitudes.

Distribution Pattern and Influencing Factors of Heavy Metal Resistance Genes in the Yellow River Sediments of Henan Section

The transformation of heavy metal resistance genes (MRGs) in the environment has attracted increasing attention in recent years. However, few studies have reported the MRG content in the Yellow River, one of the main irrigation water sources in the North China Plain. In this study, we quantified MRG abundance by a metagenomic approach, and assessed the influence on MRGs of both bioavailable and total heavy metal (HM) content. The results indicate that Cu-resistant genes are the most common genes, and the prevalence of arsM needs more attention. Comamonadaceae is the dominant family in the Yellow River, and the presence of organic pollutants may contribute to the prevalence of Vicinamibacteraceae, Nocardioidaceae, and Flavobacteriacea. The results of the Mantel test and Spearman analysis indicate that both the bioavailable fractions and total content of HMs could have little influence on MRGs. Network analysis results indicate that some dominant bacteria could be the potential hosts of some prevalent MRGs, which may exert an adverse impact on human health.

Multiple heavy metal distribution and microbial community characteristics of vanadium-titanium magnetite tailing profiles under different management modes

Vanadium-titanium (V-Ti) magnetite tailings have caused great concern due to their safety hazards and environmental risks. However, the microbial community structure and the key geochemical factors of V-Ti magnetite tailing profiles under different management modes remain unclear. Therefore, we investigated the heavy metal distribution and the microbial community structure of the soils and tailings at varied depths of V-Ti magnetite tailing profiles with and without soil coverage. The results indicated that the topsoil covering measures retarded the acidification of tailings during stockpiling. However, As, Mn, and V in tailings have the ability to migrate to the overlying soil. Based on 16S rRNA gene amplicon sequencing, Proteobacteria was the dominant genus in the topsoil-covered tailings, whereas the most abundant genus in the exposed tailings was Betaproteobacteria. Furthermore, Rhodobacter, Hydrogenophaga, Novosphingobium, and Geobacter enriched in tailings may potentially contribute to V(V) biotransformation and the development of mine bioreremediation technologies. RDA and Spearman correlation analysis showed that pH, EC, Cd, Mn, Pb, and V were the main influencing factors regulating microbial community composition. Overall, this study provides insights for evaluating the soil covering management mode and the engineering applications of microbial technologies to manage V-Ti magnetite tailings.

Unveil the role of dissolved and sedimentary metal(loid)s on bacterial communities and metal resistance genes (MRGs) in an urban river of the Qinghai-Tibet Plateau

Though metal resistance genes (MRGs) are of global concern in aquatic ecosystems, the underlying factors responsible for MRGs dissemination, especially in urban rivers on the vulnerable Qinghai-Tibet Plateau, are rarely known. Here, we collected 64 samples including water and sediments during the wet and dry seasons and effluents from six wastewater treatment plants (WWTPs) during the dry season and measured 50 metal(loid)s, 60 bacterial phyla, and 259 MRGs. We observed the distinct difference of metal(loid)s, bacterial communities, and MRGs between water and sediments and the great seasonal changes in metal(loid)s and bacterial communities instead of MRGs. Thirty-one metal(loid)s were detectable in the water, with relatively low concentrations and no significant effects on the planktonic bacterial communities and MRGs. Interestingly, the WWTPs effluent partially promoted the prevalence of dissolved metal(loid)s, bacterial communities, and MRGs along the river. In the sediments, the average concentrations of 17 metal(loid)s exceeded their corresponding background levels in this region and strongly influenced the bacterial communities and the MRGs. Sedimentary Hg and Cd, mainly sourced from the intensive animal husbandry, were the major pollutants causing ecological risks and largely shaped their corresponding resistomes. Moreover, we found that bacterial communities predominantly determined the variation of MRGs in both water and sediments. Metagenome-assembled genomes further reveals the widespread co-occurrence of MRGs and antibiotic resistance genes (ARGs) in MRG hosts. Our study highlighted the concern of effluents discharged from WWTPs and emphasized the importance of controlling the anthropogenic inputs of sedimentary metal(loid)s in the plateau river ecosystems.

Phytoremediation of cadmium-contaminated sediment using Hydrilla verticillata and Elodea canadensis harbor two same keystone rhizobacteria Pedosphaeraceae and Parasegetibacter

Aquatic macrophytes have been widely employed for in-situ phytoremediation of cadmium (Cd) polluted sediments. But, little is known about the responses of rhizosphere bacteria and their interspecific interactions to phytoremediation. In this study, the α-diversity, community composition, co-occurrence network and keystone species of sediment bacteria in rhizosphere zones of two typical macrophytes, Hydrilla verticillata and Elodea canadensis, were investigated using 16S rRNA gene high-throughput sequencing. The results showed that after fifty days of phytoremediation, a group of specialized sediment bacteria were assembled in the rhizosphere zones closely associated with different host macrophytes. Rhizosphere micro-environments, i.e., the increases of redox potential and organic matter and the decreases of pH, nitrogen and phosphorus, reduced bacterial α-diversity through niche-based species-sorting process, which in turn reduced interspecific mutualistic relationships. But meanwhile, benefiting from the nutrients supplied from macrophyte roots, more bacterial species survived in the highly Cd-contaminated sediments (50 mg kg^-1). In addition, the co-occurrence network revealed that both macrophytes harbored two same keystone bacteria with the high betweenness centrality values, including the family Pedosphaeraceae (genus_unclassified) and genus Parasegetibacter. Their relative abundances were up to 28-fold and 25-fold higher than other keystone species, respectively. Furthermore, these two keystone bacteria were metabolic generalists with vital ecological functions, which posed significant potentials for promoting plant growth and tolerating Cd bio-toxicity. Therefore, the identified keystone rhizobacteria, Pedosphaeraceae and Parasegetibacter, would be potential microbial modulations applied for the future optimization of phytoremediation in Cd-contaminated sediment.