Clonality, local population structure and gametophyte sex ratios in cryptic species of the Sphagnum magellanicum complex.

BACKGROUND AND AIMS: Sphagnum (peatmoss) comprises a moss (Bryophyta) clade with ~300-500 species. The genus has unparalleled ecological importance because Sphagnum-dominated peatlands store almost a third of the terrestrial carbon pool and peatmosses engineer the formation and microtopography of peatlands. Genomic resources for Sphagnum are being actively expanded, but many aspects of their biology are still poorly known. Among these are the degree to which Sphagnum species reproduce asexually, and the relative frequencies of male and female gametophytes in these haploid-dominant plants. We assess clonality and gametophyte sex ratios and test hypotheses about the local-scale distribution of clones and sexes in four North American species of the S. magellanicum complex. These four species are difficult to distinguish morphologically and are very closely related. We also assess microbial communities associated with Sphagnum host plant clones and sexes at two sites. METHODS: Four hundred and five samples of the four species, representing 57 populations, were subjected to restriction site-associated DNA sequencing (RADseq). Analyses of population structure and clonality based on the molecular data utilized both phylogenetic and phenetic approaches. Multi-locus genotypes (genets) were identified using the RADseq data. Sexes of sampled ramets were determined using a molecular approach that utilized coverage of loci on the sex chromosomes after the method was validated using a sample of plants that expressed sex phenotypically. Sex ratios were estimated for each species, and populations within species. Difference in fitness between genets was estimated as the numbers of ramets each genet comprised. Degrees of clonality [numbers of genets/numbers of ramets (samples)] within species, among sites, and between gametophyte sexes were estimated. Sex ratios were estimated for each species, and populations within species. Sphagnum-associated microbial communities were assessed at two sites in relation to Sphagnum clonality and sex. KEY RESULTS: All four species appear to engage in a mixture of sexual and asexual (clonal) reproduction. A single ramet represents most genets but two to eight ramets were dsumbers ansd text etected for some genets. Only one genet is represented by ramets in multiple populations; all other genets are restricted to a single population. Within populations ramets of individual genets are spatially clustered, suggesting limited dispersal even within peatlands. Sex ratios are male-biased in S. diabolicum but female-biased in the other three species, although significantly so only in S. divinum. Neither species nor males/females differ in levels of clonal propagation. At St Regis Lake (NY) and Franklin Bog (VT), microbial community composition is strongly differentiated between the sites, but differences between species, genets and sexes were not detected. Within S. divinum, however, female gametophytes harboured two to three times the number of microbial taxa as males. CONCLUSIONS: These four Sphagnum species all exhibit similar reproductive patterns that result from a mixture of sexual and asexual reproduction. The spatial patterns of clonally replicated ramets of genets suggest that these species fall between the so-called phalanx patterns, where genets abut one another but do not extensively mix because of limited ramet fragmentation, and the guerrilla patterns, where extensive genet fragmentation and dispersal result in greater mixing of different genets. Although sex ratios in bryophytes are most often female-biased, both male and female biases occur in this complex of closely related species. The association of far greater microbial diversity for female gametophytes in S. divinum, which has a female-biased sex ratio, suggests additional research to determine if levels of microbial diversity are consistently correlated with differing patterns of sex ratio biases.

Porewater constituents inhibit microbially mediated greenhouse gas production (GHG) and regulate the response of soil organic matter decomposition to warming in anoxic peat from a Sphagnum-dominated bog.

Northern peatlands store approximately one-third of terrestrial soil carbon. Climate warming is expected to stimulate the microbially mediated degradation of peat soil organic matter (SOM), leading to increasing greenhouse gas (GHG; carbon dioxide, CO2; methane, CH4) production and emission. Porewater dissolved organic matter (DOM) plays a key role in SOM decomposition; however, the mechanisms controlling SOM decomposition and its response to warming remain unclear. The temperature dependence of GHG production and microbial community dynamics were investigated in anoxic peat from a Sphagnum-dominated peatland. In this study, peat decomposition, which was quantified by GHG production and carbon substrate utilization is limited by terminal electron acceptors (TEA) and DOM, and these controls of microbially mediated SOM degradation are temperature-dependent. Elevated temperature led to a slight decrease in microbial diversity, and stimulated the growth of specific methanotrophic and syntrophic taxa. These results confirm that DOM is a major driver of decomposition in peatland soils contains inhibitory compounds, but the inhibitory effect is alleviated by warming.

Anaerobic selenite-reducing bacteria and their metabolic potentials in Se-rich sediment revealed by the combination of DNA-stable isotope probing, metagenomic binning, and metatranscriptomics.

Microorganisms play a critical role in the biogeochemical cycling of selenium (Se) in aquatic environments, particularly in reducing the toxicity and bioavailability of selenite (Se(IV)). This study aimed to identify putative Se(IV)-reducing bacteria (SeIVRB) and investigate the genetic mechanisms underlying Se(IV) reduction in anoxic Se-rich sediment. Initial microcosm incubation confirmed that Se(IV) reduction was driven by heterotrophic microorganisms. DNA stable-isotope probing (DNA-SIP) analysis identified Pseudomonas, Geobacter, Comamonas, and Anaeromyxobacter as putative SeIVRB. High-quality metagenome-assembled genomes (MAGs) affiliated with these four putative SeIVRB were retrieved. Annotation of functional gene indicated that these MAGs contained putative Se(IV)-reducing genes such as DMSO reductase family, fumarate and sulfite reductases. Metatranscriptomic analysis of active Se(IV)-reducing cultures revealed significantly higher transcriptional levels of genes associated with DMSO reductase (serA/PHGDH), fumarate reductase (sdhCD/frdCD), and sulfite reductase (cysDIH) compared to those in cultures not amended with Se(IV), suggesting that these genes played important roles in Se(IV) reduction. The current study expands our knowledge of the genetic mechanisms involved in less-understood anaerobic Se(IV) bio-reduction. Additinally, the complementary abilities of DNA-SIP, metagenomics, and metatranscriptomics analyses are demonstrated in elucidating the microbial mechanisms of biogeochemical processes in anoxic sediment.

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.

Current Scenario and Future Prospects of Endophytic Microbes: Promising Candidates for Abiotic and Biotic Stress Management for Agricultural and Environmental Sustainability.

Globally, substantial research into endophytic microbes is being conducted to increase agricultural and environmental sustainability. Endophytic microbes such as bacteria, actinomycetes, and fungi inhabit ubiquitously within the tissues of all plant species without causing any harm or disease. Endophytes form symbiotic relationships with diverse plant species and can regulate numerous host functions, including resistance to abiotic and biotic stresses, growth and development, and stimulating immune systems. Moreover, plant endophytes play a dominant role in nutrient cycling, biodegradation, and bioremediation, and are widely used in many industries. Endophytes have a stronger predisposition for enhancing mineral and metal solubility by cells through the secretion of organic acids with low molecular weight and metal-specific ligands (such as siderophores) that alter soil pH and boost binding activity. Finally, endophytes synthesize various bioactive compounds with high competence that are promising candidates for new drugs, antibiotics, and medicines. Bioprospecting of endophytic novel secondary metabolites has given momentum to sustainable agriculture for combating environmental stresses. Biotechnological interventions with the aid of endophytes played a pivotal role in crop improvement to mitigate biotic and abiotic stress conditions like drought, salinity, xenobiotic compounds, and heavy metals. Identification of putative genes from endophytes conferring resistance and tolerance to crop diseases, apart from those involved in the accumulation and degradation of contaminants, could open new avenues in agricultural research and development. Furthermore, a detailed molecular and biochemical understanding of endophyte entry and colonization strategy in the host would better help in manipulating crop productivity under changing climatic conditions. Therefore, the present review highlights current research trends based on the SCOPUS database, potential biotechnological interventions of endophytic microorganisms in combating environmental stresses influencing crop productivity, future opportunities of endophytes in improving plant stress tolerance, and their contribution to sustainable remediation of hazardous environmental contaminants.

Chemolithotrophic Biological Nitrogen Fixation Fueled by Antimonite Oxidation May Be Widespread in Sb-Contaminated Habitats.

Nitrogen (N) deficiency in mining-contaminated habitats usually hinders plant growth and thus hampers tailing revegetation. Biological N fixation (BNF) is an essential biogeochemical process that contributes to the initial accumulation of N in oligotrophic mining-contaminated regions. Previous studies reported that chemolithotrophic rather than heterotrophic diazotrophs frequently dominated in the mining-contaminated regions. Chemolithotrophic diazotrophs may utilize elements abundant in such habitats (e.g., sulfur (S), arsenic (As), and antimony (Sb)) as electron donors to fix N2. BNF fueled by the oxidation of S and As has been detected in previous studies. However, BNF fueled by Sb(III) oxidation (Sb-dependent BNF) has never been reported. The current study observed the presence of Sb-dependent BNF in slurries inoculated from Sb-contaminated habitats across the South China Sb belt, suggesting that Sb-dependent BNF may be widespread in this region. DNA-stable isotope probing identified bacteria associated with Rhodocyclaceae and Rhizobiaceae as putative microorganisms responsible for Sb-dependent BNF. Furthermore, metagenomic-binning demonstrated that Rhodocyclaceae and Rhizobiaceae contained essential genes involved in Sb(III) oxidation, N2 fixation, and carbon fixation, suggesting their genetic potential for Sb-dependent BNF. In addition, meta-analysis indicated that these bacteria are widespread among Sb-contaminated habitats with different niche preferences: Rhodocyclaceae was enriched in river sediments and tailings, while Rhizobiaceae was enriched only in soils. This study may broaden our fundamental understanding of N fixation in Sb-mining regions.

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.

Acetylenotrophic and Diazotrophic Bradyrhizobium sp. Strain I71 from TCE-Contaminated Soils.

Acetylene (C2H2) is a molecule rarely found in nature, with very few known natural sources, but acetylenotrophic microorganisms can use acetylene as their primary carbon and energy source. As of 2018 there were 15 known strains of aerobic and anaerobic acetylenotrophs; however, we hypothesize there may yet be unrecognized diversity of acetylenotrophs in nature. This study expands the known diversity of acetylenotrophs by isolating the aerobic acetylenotroph, Bradyrhizobium sp. strain I71, from trichloroethylene (TCE)-contaminated soils. Strain I71 is a member of the class Alphaproteobacteria and exhibits acetylenotrophic and diazotrophic activities, the only two enzymatic reactions known to transform acetylene. This unique capability in the isolated strain may increase the genus' economic impact beyond agriculture as acetylenotrophy is closely linked to bioremediation of chlorinated contaminants. Computational analyses indicate that the Bradyrhizobium sp. strain I71 genome contains 522 unique genes compared to close relatives. Moreover, applying a novel hidden Markov model of known acetylene hydratase (AH) enzymes identified a putative AH enzyme. Protein annotation with I-TASSER software predicted the AH from the microbe Syntrophotalea acetylenica as the closest structural and functional analog. Furthermore, the putative AH was flanked by horizontal gene transfer (HGT) elements, like that of AH in anaerobic acetylenotrophs, suggesting an unknown source of acetylene or acetylenic substrate in the environment that is selecting for the presence of AH. IMPORTANCE The isolation of Bradyrhizobium strain I71 expands the distribution of acetylene-consuming microbes to include a group of economically important microorganisms. Members of Bradyrhizobium are well studied for their abilities to improve plant health and increase crop yields by providing bioavailable nitrogen. Additionally, acetylene-consuming microbes have been shown to work in tandem with other microbes to degrade soil contaminants. Based on genome, cultivation, and protein prediction analysis, the ability to consume acetylene is likely not widespread within the genus Bradyrhizobium. These findings suggest that the suite of phenotypic capabilities of strain I71 may be unique and make it a good candidate for further study in several research avenues.

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.

The core root microbiome of Spartina alterniflora is predominated by sulfur-oxidizing and sulfate-reducing bacteria in Georgia salt marshes, USA.

BACKGROUND: Salt marshes are dominated by the smooth cordgrass Spartina alterniflora on the US Atlantic and Gulf of Mexico coastlines. Although soil microorganisms are well known to mediate important biogeochemical cycles in salt marshes, little is known about the role of root microbiomes in supporting the health and productivity of marsh plant hosts. Leveraging in situ gradients in aboveground plant biomass as a natural laboratory, we investigated the relationships between S. alterniflora primary productivity, sediment redox potential, and the physiological ecology of bulk sediment, rhizosphere, and root microbial communities at two Georgia barrier islands over two growing seasons. RESULTS: A marked decrease in prokaryotic alpha diversity with high abundance and increased phylogenetic dispersion was found in the S. alterniflora root microbiome. Significantly higher rates of enzymatic organic matter decomposition, as well as the relative abundances of putative sulfur (S)-oxidizing, sulfate-reducing, and nitrifying prokaryotes correlated with plant productivity. Moreover, these functional guilds were overrepresented in the S. alterniflora rhizosphere and root core microbiomes. Core microbiome bacteria from the Candidatus Thiodiazotropha genus, with the metabolic potential to couple S oxidation with C and N fixation, were shown to be highly abundant in the root and rhizosphere of S. alterniflora. CONCLUSIONS: The S. alterniflora root microbiome is dominated by highly active and competitive species taking advantage of available carbon substrates in the oxidized root zone. Two microbially mediated mechanisms are proposed to stimulate S. alterniflora primary productivity: (i) enhanced microbial activity replenishes nutrients and terminal electron acceptors in higher biomass stands, and (ii) coupling of chemolithotrophic S oxidation with carbon (C) and nitrogen (N) fixation by root- and rhizosphere-associated prokaryotes detoxifies sulfide in the root zone while potentially transferring fixed C and N to the host plant. Video Abstract.

Desulfurivibrio spp. mediate sulfur-oxidation coupled to Sb(V) reduction, a novel biogeochemical process.

Antimony (Sb) contamination released from mine tailings represents a global threat to natural ecosystems and human health. The geochemical conditions of Sb tailings, which are oligotrophic and replete in sulfur (S) and Sb, may promote the coupled metabolism of Sb and S. In this study, multiple lines of evidence indicate that a novel biogeochemical process, S oxidation coupled to Sb(V) reduction, is enzymatically mediated by Desulfurivibrio spp. The distribution of Desulfurivibrio covaried with S and Sb concentrations, showing a high relative abundance in Sb mine tailings but not in samples from surrounding sites (i.e., soils, paddies, and river sediments). Further, the metabolic potential to couple S oxidation to Sb(V) reduction, encoded by a non-canonical, oxidative sulfite reductase (dsr) and arsenate reductase (arrA) or antimonate reductase (anrA), respectively, was found to be common in Desulfurivibrio genomes retrieved from metal-contaminated sites in southern China. Elucidation of enzymatically-catalyzed S oxidation coupled to Sb(V) reduction expands the fundamental understanding of Sb biogeochemical cycling, which may be harnessed to improve remediation strategies for Sb mine tailings.

Identification of Antimonate Reducing Bacteria and Their Potential Metabolic Traits by the Combination of Stable Isotope Probing and Metagenomic-Pangenomic Analysis.

Microorganisms play an important role in altering antimony (Sb) speciation, mobility, and bioavailability, but the understanding of the microorganisms responsible for Sb(V) reduction has been limited. In this study, DNA-stable isotope probing (DNA-SIP) and metagenomics analysis were combined to identify potential Sb(V)-reducing bacteria (SbRB) and predict their metabolic pathways for Sb(V) reduction. Soil slurry cultures inoculated with Sb-contaminated paddy soils from two Sb-contaminated sites demonstrated the capability to reduce Sb(V). DNA-SIP identified bacteria belonging to the genera Pseudomonas and Geobacter as putative SbRB in these two Sb-contaminated sites. In addition, bacteria such as Lysinibacillus and Dechloromonas may potentially participate in Sb(V) reduction. Nearly complete draft genomes of putative SbRB (i.e., Pseudomonas and Geobacter) were obtained, and the genes potentially responsible for arsenic (As) and Sb reduction (i.e., respiratory arsenate reductase (arrA) and antimonate reductase (anrA)) were examined. Notably, bins affiliated with Geobacter contained arrA and anrA genes, supporting our hypothesis that they are putative SbRB. Further, pangenomic analysis indicated that various Geobacter-associated genomes obtained from diverse habitats also contained arrA and anrA genes. In contrast, Pseudomonas may use a predicted DMSO reductase closely related to sbrA (Sb(V) reductase gene) clade II to reduce Sb(V), which may need further experiments to verify. This current work represents a demonstration of using DNA-SIP and metagenomic-binning to identify SbRB and their key genes involved in Sb(V) reduction and provides valuable data sets to link bacterial identities with Sb(V) reduction.

Soil metabolome response to whole-ecosystem warming at the Spruce and Peatland Responses under Changing Environments experiment.

In this study, a suite of complementary environmental geochemical analyses, including NMR and gas chromatography-mass spectrometry (GC-MS) analyses of central metabolites, Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) of secondary metabolites, and lipidomics, was used to investigate the influence of organic matter (OM) quality on the heterotrophic microbial mechanisms controlling peatland CO2, CH4, and CO2:CH4 porewater production ratios in response to climate warming. Our investigations leverage the Spruce and Peatland Responses under Changing Environments (SPRUCE) experiment, where air and peat warming were combined in a whole-ecosystem warming treatment. We hypothesized that warming would enhance the production of plant-derived metabolites, resulting in increased labile OM inputs to the surface peat, thereby enhancing microbial activity and greenhouse gas production. Because shallow peat is most susceptible to enhanced warming, increases in labile OM inputs to the surface, in particular, are likely to result in significant changes to CO2 and CH4 dynamics and methanogenic pathways. In support of this hypothesis, significant correlations were observed between metabolites and temperature consistent with increased availability of labile substrates, which may stimulate more rapid turnover of microbial proteins. An increase in the abundance of methanogenic genes in response to the increase in the abundance of labile substrates was accompanied by a shift toward acetoclastic and methylotrophic methanogenesis. Our results suggest that as peatland vegetation trends toward increasing vascular plant cover with warming, we can expect a concomitant shift toward increasingly methanogenic conditions and amplified climate-peatland feedbacks.

Bacteria responsible for antimonite oxidation in antimony-contaminated soil revealed by DNA-SIP coupled to metagenomics.

Antimony (Sb), the analog of arsenic (As), is a toxic metalloid that poses risks to the environment and human health. Antimonite (Sb(III)) oxidation can decrease Sb toxicity, which contributes to the bioremediation of Sb contamination. Bacteria can oxidize Sb(III), but the current knowledge regarding Sb(III)-oxidizing bacteria (SbOB) is limited to pure culture studies, thus underestimating the diversity of SbOB. In this study, Sb(III)-oxidizing microcosms were set up using Sb-contaminated rice paddies as inocula. Sb(III) oxidation driven by microorganisms was observed in the microcosms. The increasing copies and transcription of the arsenate-oxidizing gene, aioA, in the microcosms during biotic Sb(III) oxidation indicated that microorganisms mediated Sb(III) oxidation via the aioA genes. Furthermore, a novel combination of DNA-SIP and shotgun metagenomic was applied to identify the SbOB and predict their metabolic potential. Several putative SbOB were identified, including Paracoccus, Rhizobium, Achromobacter and Hydrogenophaga. Furthermore, the metagenomic analysis indicated that all of these putative SbOB contained aioA genes, confirming their roles in Sb(III) oxidation. These results suggested the concept of proof of combining DNA-SIP and shotgun metagenomics directly. In addition, the identification of the novel putative SbOB expands the current knowledge regarding the diversity of SbOB.

Solar-driven, self-sustainable electrolysis for treating eutrophic river water: Intensified nutrient removal and reshaped microbial communities.

River ecosystems are the most important resource of surface freshwater, but they have frequently been contaminated by excessive nutrient input of nitrogen (N) and phosphorus (P) in particular. An efficient and economic river water treatment technology that possesses the capacity of simultaneous N and P removal is urgently required. In this study, a solar-driven, self-sustainable electrolytic treatment was conducted in situ to intensify N and P removal from eutrophic river water. Solar panel was applied to provide the electrolysis setups with energy (voltage 10 ± 0.5 V), and the current density was controlled to be 0.06 ± 0.02 mA cm-2. Results indicated that the average removal efficiencies of total N (TN) and total P (TP) under electrolysis conditions reached 72.4 ± 11.7 and 13.8 ± 5.3 mg m-2 d-1, which were 3.7- and 4.7-fold higher compared to untreated conditions. Enhanced TN removal mainly reflected the abatement of nitrate N (NO3--N) (80.6 ± 4.1%). The formation of ferric ions through the electro-dissolution of the sacrificial iron anode improved TP removal by coprecipitation with SPS. Combined high-throughput sequencing and statistical analyses revealed that electrolysis significantly reshaped the microbial communities in both the sediment-water interface and suspended sediment (SPS), and hydrogenotrophic denitrifiers (e.g., Hydrogenophaga) were highly enriched under electrolysis conditions. These findings indicated that in situ electrolysis is a feasible and effective technology for intensified nutrient removal from river water.

VV Reduction by Polaromonas spp. in Vanadium Mine Tailings.

Vanadium (V) is an important metal with critical industrial and medical applications. Elevated V contamination, however, can be a threat to the environment and human health. Microorganisms can reduce the more toxic and mobile VV to the less toxic and immobile VIV, which could be a detoxification and energy metabolism strategy adopted by V-reducing bacteria (VRB). The limited understanding of microbial responses to V contamination and the mechanisms for VV reduction, however, hamper our capability to attenuate V contamination. This study focused on determining the microbial responses to elevated V concentration and the mechanisms of VV reduction in V tailings. The bacterial communities were characterized and compared between the V tailings and the less contaminated adjacent mineral soils. Further, VV-reducing enrichments indicated that bacteria associated with Polaromonas, a genus belonging to the family Burkholderiaceae, were potentially responsible for VV reduction. Retrieved metagenome-assembled genomes (MAGs) suggested that the Polaromonas spp. encoded genes (cymA, omcA, and narG) were responsible for VV reduction. Additionally, Polaromonas spp. was metabolically versatile and could use both organic and inorganic electron donors. The metabolic versatility of Polaromonas spp. may be important for its ability to flourish in the V tailings.

Elucidation of the rhizosphere microbiome linked to Spartina alterniflora phenotype in a salt marsh on Skidaway Island, Georgia, USA.

Smooth cordgrass, Spartina alterniflora, dominates salt marshes on the east coast of the United States. While the physicochemical cues affecting S. alterniflora productivity have been studied intensively, the role of plant-microbe interactions in ecosystem functioning remains poorly understood. Thus, in this study, the effects of S. alterniflora phenotype on the composition of archaeal, bacterial, diazotrophic and fungal communities were investigated. Overall, prokaryotic communities were more diverse and bacteria were more abundant in the areas colonized by the tall plant phenotype in comparison to those of short plant phenotype. Diazotrophic methanogens (Methanomicrobia) preferentially colonized the area of the short plant phenotype. Putative iron-oxidizing Zetaproteobacteria and sulfur-oxidizing Campylobacteria were identified as indicator species in the rhizosphere of tall and short plant phenotypes, respectively. Finally, while diazotrophic populations shaped microbial interactions in the areas colonized by the tall plant phenotype, fungal populations filled this role in the areas occupied by the short plant phenotype. The results here demonstrate that S. alterniflora phenotype and proximity to the root zone are selective forces dictating microbial community assembly. Results further reveal that reduction-oxidation chemistry is a major factor driving the selection of belowground microbial populations in salt marsh habitats.

Chemolithoautotropic Diazotrophy Dominates the Nitrogen Fixation Process in Mine Tailings.

Nutrient deficiency, especially bio-available nitrogen deficiency, often impedes the bioremediation efforts of mining generated tailings. Biological nitrogen fixation is a critical process necessary for the initial nitrogen buildup in tailings. Current knowledge regarding the diazotrophs that inhabit tailings is still in its infancy. Therefore, in this study, a comprehensive investigation combining geochemical characterization, sequence analyses, molecular techniques, and activity measurements was conducted to characterize the diazotrophic community residing in tailing environments. Significant differences between tailings and their adjacent soils in prokaryotic and diazotrophic communities were detected. Meanwhile, strong and significant correlations between the absolute abundance of the nitrogen fixation (nifH), carbon fixation (cbbL), sulfur oxidation (soxB), and arsenite oxidation (aioA) genes were observed in the tailings but not in the soils. The reconstructed nif-containing metagenome-assembled genomes (MAGs) suggest that the carbon fixation and sulfur oxidation pathways were important for potential diazotrophs inhabiting the tailings. Activity measurements further confirmed that diazotrophs inhabiting tailings preferentially use inorganic electron donors (e.g., elemental sulfur) compared to organic electron donors (e.g., sucrose), while diazotrophs inhabiting soils preferred organic carbon sources. Collectively, these findings suggest that chemolithoautotrophic diazotrophs may play essential roles in acquiring nutrients and facilitating ecological succession in tailings.

Succession of microbial populations and nitrogen-fixation associated with the biodegradation of sediment-oil-agglomerates buried in a Florida sandy beach.

The Deepwater Horizon (DWH) oil spill contaminated coastlines from Louisiana to Florida, burying oil up to 70 cm depth in sandy beaches, posing a potential threat to environmental and human health. The dry and nutrient-poor beach sand presents a taxing environment for microbial growth, raising the question how the biodegradation of the buried oil would proceed. Here we report the results of an in-situ experiment that (i) characterized the dominant microbial communities contained in sediment oil agglomerates (SOAs) of DWH oil buried in a North Florida sandy beach, (ii) elucidated the long-term succession of the microbial populations that developed in the SOAs, and (iii) revealed the coupling of SOA degradation to nitrogen fixation. Orders of magnitude higher bacterial abundances in SOAs compared to surrounding sands distinguished SOAs as hotspots of microbial growth. Blooms of bacterial taxa with a demonstrated potential for hydrocarbon degradation (Gammaproteobacteria, Alphaproteobacteria, Actinobacteria) developed in the SOAs, initiating a succession of microbial populations that mirrored the evolution of the petroleum hydrocarbons. Growth of nitrogen-fixing prokaryotes or diazotrophs (Rhizobiales and Frankiales), reflected in increased abundances of nitrogenase genes (nifH), catalyzed biodegradation of the nitrogen-poor petroleum hydrocarbons, emphasizing nitrogen fixation as a central mechanism facilitating the recovery of sandy beaches after oil contamination.