Phototrophic Nitrogen Fixation, a Neglected Biogeochemical Process in Mine Tailings?

Biological nitrogen fixation (BNF) has important ecological significance in mine tailing by contributing to the initial accumulation of nitrogen. In addition to chemolithotrophic and heterotrophic BNF, light may also fuel BNF in oligotrophic mine tailings. However, knowledge regarding the occurrence and ecological significance of this biogeochemical process in mine tailings remains ambiguous. The current study observed phototrophic BNF in enrichment cultures established from three primary successional stages (i.e., original tailings, biological crusts, and pioneer plants) of tailings. Notably, phototrophic BNF in tailings may be more active at vegetation stages (i.e., biological crusts and pioneering plants) than in bare tailings. DNA-stable isotope probing identified Roseomonas species as potential aerobic anoxygenic phototrophs responsible for phototrophic BNF. Furthermore, metagenomic binning as well as genome mining revealed that Roseomonas spp. contained essential genes involved in nitrogen fixation, anoxygenic photosynthesis, and carbon fixation, suggesting their genetic potential to mediate phototrophic BNF. A causal inference framework equipped with the structural causal model suggested that the enrichment of putative phototrophic diazotrophic Roseomonas may contribute to an elevated total nitrogen content during primary succession in these mine tailings. Collectively, our findings suggest that phototrophic diazotrophs may play important roles in nutrient accumulation and hold the potential to facilitate ecological succession in tailings.

Microbial Sulfur and Arsenic Oxidation Facilitate the Establishment of Biocrusts during Reclamation of Degraded Mine Tailings.

Degraded tailings generated by the mining of metal ores are major environmental threats to the surrounding ecosystems. Tailing reclamation, however, is often impeded due to adverse environmental conditions, with depleted key nutrients (i.e., nitrogen (N) and phosphorus (P)) and elevated sulfur and metal(loid) concentrations. Formation of biocrusts may significantly accelerate nutrient accumulation and is therefore an essential stage for tailing reclamation. Although suggested to play an important role, the microbial community composition and key metabolisms in biocrusts remain largely unknown and are therefore investigated in the current study. The results suggested that sulfur and arsenic oxidation are potential energy sources utilized by members of predominant biocrust bacterial families, including Beijerinckiaceae, Burkholderiaceae, Hyphomicrobiaceae, and Rhizobiaceae. Accordingly, the S and As oxidation potentials are elevated in biocrusts compared to those in their adjacent tailings. Biocrust growth, as proxied by chlorophyll concentrations, is enhanced in treatments supplemented with S and As. The elevated biocrust growth might benefit from nutrient acquisition services (i.e., nitrogen fixation and phosphorus solubilization) fueled by microbial sulfur and arsenic oxidation. The current study suggests that sulfur- and arsenic-oxidizing microorganisms may play important ecological roles in promoting biocrust formation and facilitating tailing reclamation.

Comparison of microbial taxonomic and functional shift pattern along contamination gradient.

BACKGROUND: The interaction mechanism between microbial communities and environment is a key issue in microbial ecology. Microbial communities usually change significantly under environmental stress, which has been studied both phylogenetically and functionally, however which method is more effective in assessing the relationship between microbial communities shift and environmental changes still remains controversial. RESULTS: By comparing the microbial taxonomic and functional shift pattern along heavy metal contamination gradient, we found that both sedimentary composition and function shifted significantly along contamination gradient. For example, the relative abundance of Geobacter and Fusibacter decreased along contamination gradient (from high to low), while Janthinobacterium and Arthrobacter increased their abundances. Most genes involved in heavy metal resistance (e.g., metc, aoxb and mer) showed higher intensity in sites with higher concentration of heavy metals. Comparing the two shift patterns, there were correlations between them, because functional and phylogenetic ß-diversities were significantly correlated, and many heavy metal resistance genes were derived from Geobacter, explaining their high abundance in heavily contaminated sites. However, there was a stronger link between functional composition and environmental drivers, while stochasticity played an important role in formation and succession of phylogenetic composition demonstrated by null model test. CONCLUSIONS: Overall our research suggested that the responses of functional traits depended more on environmental changes, while stochasticity played an important role in formation and succession of phylogenetic composition for microbial communities. So profiling microbial functional composition seems more appropriate to study the relationship between microbial communities and environment, as well as explore the adaptation and remediation mechanism of microbial communities to heavy metal contamination.

Adsorption behavior of aniline pollutant on polystyrene microplastics.

Microplastic contamination is ubiquitous in aquatic environments. As global plastic production increases, the abundance of microplastic contaminants released into the environment has also continued to soar. The hydrophobic surfaces of plastic particles can adsorb a variety of chemical pollutants, and could therefore facilitate toxin accumulation through the food chain. In this study, the adsorption behavior of aniline, a priority environmental pollutant from industrial production, on the surface of polystyrene microplastics (mPS) was investigated. The results showed that the maximum adsorption capacity of mPS was 0.060 mg/g. Adsorption equilibrium was reached after 24 h, and the pseudo-second-order model was employed to explain the adsorption kinetics of aniline on the mPS particles. The Freundlich models could describe the adsorption isotherms. The potential adsorption mechanisms may include π-π interactions and hydrophobic interactions. pH, ionic strength, and ambient temperature of the solution played important roles in the adsorption process.

Analysis of oral microorganism diversity in healthy individuals before and after chewing areca nuts using PCR-denatured gradient gel electrophoresis.

To analyze oral microbial diversity in the saliva of 8 healthy individuals before and after chewing areca nuts. Saliva samples were collected before chewing areca nuts, after chewing areca nuts for 5 min and after chewing areca nuts for 30 min. DNA was extracted, and microbial diversity was examined using PCR-denaturing gradient gel electrophoresis (PCR-DGGE). When examining DGGE profiles collectively, the bands associated with Streptococcus and Veillonella were the most intense, making them the most prevalent bacteria. Furthermore, the band intensities did not decrease after chewing areca nuts for 5 or 30 min; thus, these bacteria were unaffected. However, when examining some individuals, the band intensities for Streptococcus and Veillonella became more intense after 5 min of chewing and then returned to the pre-chewing level. This difference may be attributed to the mechanical movements of the oral cavity or individual differences. Other bacteria, such as Neisseria, Actinomycetes, and Rothia dentocariosa, were also found to have an increased or decreased prevalence following areca nut-chewing. Since the predominant species that are present following areca nut-chewing include Streptococcus and Veillonella, it would seem likely that these bacteria play an important role in the periodontal diseases associated with areca chewing.

An integrated insight into the response of sedimentary microbial communities to heavy metal contamination.

Response of biological communities to environmental stresses is a critical issue in ecology, but how microbial communities shift across heavy metal gradients remain unclear. To explore the microbial response to heavy metal contamination (e.g., Cr, Mn, Zn), the composition, structure and functional potential of sedimentary microbial community were investigated by sequencing of 16S rRNA gene amplicons and a functional gene microarray. Analysis of 16S rRNA sequences revealed that the composition and structure of sedimentary microbial communities changed significantly across a gradient of heavy metal contamination, and the relative abundances were higher for Firmicutes, Chloroflexi and Crenarchaeota, but lower for Proteobacteria and Actinobacteria in highly contaminated samples. Also, molecular ecological network analysis of sequencing data indicated that their possible interactions might be enhanced in highly contaminated communities. Correspondently, key functional genes involved in metal homeostasis (e.g., chrR, metC, merB), carbon metabolism, and organic remediation showed a higher abundance in highly contaminated samples, indicating that bacterial communities in contaminated areas may modulate their energy consumption and organic remediation ability. This study indicated that the sedimentary indigenous microbial community may shift the composition and structure as well as function priority and interaction network to increase their adaptability and/or resistance to environmental contamination.

Insights into the pH up-shift responsive mechanism of Acidithiobacillus ferrooxidans by microarray transcriptome profiling.

To define the molecular response of Acidithiobacillus ferrooxidans under pH up-shift, temporal gene expression profiles were examined by using whole-genome DNA microarrays for A. ferrooxidans. Approximately 30% of the 3,132 genes represented on the microarray were significantly upregulated over a 160-min period, while about 14% were significantly downregulated. Our results revealed that A. ferrooxidans showed potential self-protection and self-regulation performance in response to pH up-shift stress. Many genes involved in regulation of membrane components were differentially expressed under the pH up-shift stress. Likewise, most of genes involved in phosphate metabolism, sulfur assimilation, and CO(2) fixation were obviously induced. Conversely, the transcription of a polyphosphate kinase gene (AFE1210) associated with phosphate storage was significantly repressed, which probably stemmed from the depletion of polyphosphate. Besides, most of the genes involved in hydrogen uptake were significantly induced, whereas many genes involved in nitrogen fixation were obviously repressed, which suggested that hydrogen uptake and nitrogen fixation could contribute to cytoplasmic pH homeostasis.