Growth of electroautotrophic microorganisms using hydrovoltaic energy through natural water evaporation.

It has been previously shown that devices based on microbial biofilms can generate hydrovoltaic energy from water evaporation. However, the potential of hydrovoltaic energy as an energy source for microbial growth has remained unexplored. Here, we show that the electroautotrophic bacterium Rhodopseudomonas palustris can directly utilize evaporation-induced hydrovoltaic electrons for growth within biofilms through extracellular electron uptake, with a strong reliance on carbon fixation coupled with nitrate reduction. We obtained similar results with two other electroautotrophic bacterial species. Although the energy conversion efficiency for microbial growth based on hydrovoltaic energy is low compared to other processes such as photosynthesis, we hypothesize that hydrovoltaic energy may potentially contribute to microbial survival and growth in energy-limited environments, given the ubiquity of microbial biofilms and water evaporation conditions.

Nonelectroactive clostridium obtains extracellular electron transfer-capability after forming chimera with Geobacter.

Extracellular electron transfer (EET) of microorganisms is a major driver of the microbial growth and metabolism, including reactions involved in the cycling of C, N, and Fe in anaerobic environments such as soils and sediments. Understanding the mechanisms of EET, as well as knowing which organisms are EET-capable (or can become so) is fundamental to electromicrobiology and geomicrobiology. In general, Gram-positive bacteria very seldomly perform EET due to their thick non-conductive cell wall. Here, we report that a Gram-positive Clostridium intestinale (C.i) attained EET-capability for ethanol metabolism only after forming chimera with electroactive Geobacter sulfurreducens (G.s). Mechanism analyses demonstrated that the EET was possible after the cell fusion of the two species was achieved. Under these conditions, the ethanol metabolism pathway of C.i was integrated by the EET pathway of G.s, by which achieved the oxidation of ethanol for the subsequent reduction of extracellular electron acceptors in the coculture. Our study displays a new approach to perform EET for Gram-positive bacteria via recruiting the EET pathway of an electroactive bacterium, which suggests a previously unanticipated prevalence of EET in the microbial world. These findings also provide new perspectives to understand the energetic coupling between bacterial species and the ecology of interspecies mutualisms.

A novel approach for sludge deep-dewatering via flowing-out enhancement but not relying on cell lysis and bound water release.

Effective deep-dewatering is crucial for wastewater sludge management. Currently, the dominant methods focus on promoting cell lysis to release intracellular water, but these techniques often lead to secondary pollution and require stringent conditions, limiting their practical use. This study explores an innovative method using a commercially available complex quaternary ammonium salt surfactant, known as G-agent. This agent remarkably reduces the sludge water content from 98.6 % to 56.8 % with a low dosage (50 mg/g DS) and under neutral pH conditions. This approach surpasses Fenton oxidation in terms of dewatering efficiency and avoids the necessity for cell lysis and bound water release, thereby reducing the risk of secondary pollution in the filtrate, including heavy metals, nitrogen, phosphorus, and other contaminants. The G-agent plays a significant role in destabilizing flocs and enhancing flocculation during the conditioning and initial dewatering stages, effectively reducing the solid-liquid interfacial affinity of the sludge. In the compression filtration stage, the agent's solidification effect is crucial in forming a robust skeleton that improves pore connectivity within the filter cake, leading to increased water permeability, drainage performance and water flow-out efficiency. This facilitates deep dewatering of sludge without cell lysis. The study reveals that the G-agent primarily improves water flow-out efficiency rather than water flowability, indicating that cell lysis and bound water release are not indispensable prerequisites for sludge deep-dewatering. Furthermore, it presents an encouraging prospect for overcoming the limitations associated with conventional sludge deep-dewatering processes.

Azotosporobacter soli gen. nov., sp. nov., a novel nitrogen-fixing bacterium isolated from paddy soil.

A nitrogen-fixing strain designated SG130T was isolated from paddy soil in Fujian Province, China. Strain SG130T was Gram-staining-negative, rod-shaped, and strictly anaerobic. Strain SG130T showed the highest 16S rRNA gene sequence similarities with the type strains Dendrosporobacter quercicolus DSM 1736T (91.7%), Anaeroarcus burkinensis DSM 6283T (91.0%) and Anaerospora hongkongensis HKU 15T (90.9%). Furthermore, the phylogenetic and phylogenomic analysis also suggested strain SG130T clustered with members of the family Sporomusaceae and was distinguished from other genera within this family. Growth of strain SG130T was observed at 25-45 °C (optimum 30 °C), pH 6.0-9.5 (optimum 7.0) and 0-1% (w/v) NaCl (optimum 0.1%). The quinones were Q-8 and Q-9. The polar lipids were phosphatidylserine (PS), phosphatidylethanolamine (PE), glycolipid (GL), phospholipid (PL) and an unidentified lipid (UL). The major fatty acids (> 10%) were iso-C13:0 3OH (26.6%), iso-C17:1 (15.6%) and iso-C15:1 F (11.4%). The genomic DNA G + C content was 50.7%. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between strain SG130T and the most closely related type strain D. quercicolus DSM 1736T (ANI 68.0% and dDDH 20.3%) were both below the cut-off level for species delineation. The average amino acid identity (AAI) between strain SG130T and the most closely related type strain D. quercicolus DSM 1736T was 63.2%, which was below the cut-off value for bacterial genus delineation (65%). Strain SG130T possessed core genes (nifHDK) involved in nitrogen fixation, and nitrogenase activity (106.38 µmol C2H4 g-1 protein h-1) was examined using the acetylene reduction assay. Based on the above results, strain SG130T is confirmed to represent a novel genus of the family Sporomusaceae, for which the name Azotosporobacter soli gen. nov., sp. nov. is proposed. The type strain is SG130T (= GDMCC 1.3312T = JCM 35641T).

Reduced greenhouse gas emission by reactive oxygen species during composting.

Reactive oxygen species (ROS) is produced in the composting, which effectively promote organic matter transformation and humification process, but the effect of ROS on greenhouse gas emissions in this process has not been understood. This study proposed and validated that ROS can effectively reduce greenhouse gas emissions intheprocessofcomposting. Compared with ordinary thermophilic composting (oTC), thermophilic composting (imTC) that was supplemented by iron mineral increased ROS production by 1.38 times, and significantly reduced greenhouse gas emissions by 45.12%. Microbial community analysis showed no significant difference in the abundance of microbes involved in greenhouse gas production between oTC and imTC. Further correlation analysis proved that ROS played a crucial role in influencing greenhouse gas emissions throughout the composting process, especially in the initial phase. These findings provide new strategies for managing livestock and poultry manure to mitigate climate change.

Two novel Fe(III)-reducing bacteria, Geothrix campi sp. nov. and Geothrix mesophila sp. nov., isolated from paddy soils.

In this research, two novel Fe(III)-reducing bacteria, SG10T and SG198T of genus Geothrix, were isolated from the rice field of Fujian Agriculture and Forestry University in Fuzhou, Fujian Province, China. Strains SG10T and SG198T were strictly anaerobic, rod-shaped and Gram-stain-negative. The two novel strains exhibited iron reduction ability, utilizing various single organic acid as the elector donor and Fe(III) as a terminal electron acceptor. Strains SG10T and SG198T showed the highest 16S rRNA sequences similarities to the type strains of Geothrix oryzisoli SG189T (99.0-99.5%) and Geothrix paludis SG195T (99.0-99.7%), respectively. The phylogenetic trees based on the 16S rRNA gene and genome 120 conserved core genes showed that strains SG10T and SG198T belong to the genus Geothrix. Average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between the phylogenetic neighbors and the two isolated strains were 86.1-94.3% and 30.7-59.5%, respectively. The major fatty acids were iso-C15:0, anteiso-C15:0, C16:0 and iso-C13:0 3OH, and MK-8 was the main respiratory quinone. According to above results, the two strains were assigned to the genus Geothrix with the names Geothrix campi sp. nov. and Geothrix mesophila sp. nov. Type strains are SG10T (= GDMCC 1.3406 T = JCM 39331 T) and SG198T (= GDMCC 62910 T = KCTC 25635 T), respectively.

Evolution of triclosan resistance modulates bacterial permissiveness to multidrug resistance plasmids and phages.

The horizontal transfer of plasmids has been recognized as one of the key drivers for the worldwide spread of antimicrobial resistance (AMR) across bacterial pathogens. However, knowledge remain limited about the contribution made by environmental stress on the evolution of bacterial AMR by modulating horizontal acquisition of AMR plasmids and other mobile genetic elements. Here we combined experimental evolution, whole genome sequencing, reverse genetic engineering, and transcriptomics to examine if the evolution of chromosomal AMR to triclosan (TCS) disinfectant has correlated effects on modulating bacterial pathogen (Klebsiella pneumoniae) permissiveness to AMR plasmids and phage susceptibility. Herein, we show that TCS exposure increases the evolvability of K. pneumoniae to evolve TCS-resistant mutants (TRMs) by acquiring mutations and altered expression of several genes previously associated with TCS and antibiotic resistance. Notably, nsrR deletion increases conjugation permissiveness of K. pneumoniae to four AMR plasmids, and enhances susceptibility to various Klebsiella-specific phages through the downregulation of several bacterial defense systems and changes in membrane potential with altered reactive oxygen species response. Our findings suggest that unrestricted use of TCS disinfectant imposes a dual impact on bacterial antibiotic resistance by augmenting both chromosomally and horizontally acquired AMR mechanisms.

Ferrihydrite-mediated methanotrophic nitrogen fixation in paddy soil under hypoxia.

Biological nitrogen fixation (BNF) by methanotrophic bacteria has been shown to play an important role in maintaining fertility. However, this process is still limited to aerobic methane oxidation with sufficient oxygen. It has remained unknown whether and how methanotrophic BNF proceeds in hypoxic environments. Herein, we incubated paddy soils with a ferrihydrite-containing mineral salt medium to enrich methanotrophic bacteria in the presence of methane (20%, v/v) under oxygen constraints (0.27%, v/v). The resulting microcosms showed that ferrihydrite-dependent aerobic methane oxidation significantly contributed (81%) to total BNF, increasing the 15N fixation rate by 13-fold from 0.02 to 0.28 µmol 15N2 (g dry weight soil) -1 d-1. BNF was reduced by 97% when ferrihydrite was omitted, demonstrating the involvement of ferrihydrite in methanotrophic BNF. DNA stable-isotope probing indicated that Methylocystis, Methylophilaceae, and Methylomicrobium were the dominant methanotrophs/methylotrophs that assimilated labeled isotopes (13C or 15N) into biomass. Metagenomic binning combined with electrochemical analysis suggested that Methylocystis and Methylophilaceae had the potential to perform methane-induced BNF and likely utilized riboflavin and c-type cytochromes as electron carriers for ferrihydrite reduction. It was concluded that ferrihydrite mediated methanotrophic BNF by methanotrophs/methylotrophs solely or in conjunction with iron-reducing bacteria. Overall, this study revealed a previously overlooked yet pronounced coupling of iron-dependent aerobic methane oxidation to BNF and improves our understanding of methanotrophic BNF in hypoxic zones.

Body size mediates the functional potential of soil organisms by diversity and community assembly across soil aggregates.

Body size is an important life-history trait that affects organism niche occupancy and ecological interactions. However, it is still unclear to what extent the assembly process of organisms with different body sizes affects soil biogeochemical cycling processes at the aggregate level. Here, we examined the diversity and community assembly of soil microorganisms (bacteria, fungi, and protists) and microfauna (nematodes) with varying body sizes. The microbial functional potential associated with carbon, nitrogen, phosphorus, and sulfur metabolism within three soil aggregate sizes (large macroaggregates, > 2 mm; small macroaggregates, 0.25-2 mm; and microaggregates, < 0.25 mm) were determined by metagenomics. We found that the smallest microbes (bacteria) had higher α-diversity and lower ß-diversity and were mostly structured by stochastic processes, while all larger organisms (fungi, protists, and nematodes) had lower α-diversity and were relatively more influenced by deterministic processes. Structural equation modeling indicated that the microbial functional potential associated with carbon, nitrogen, phosphorus, and sulfur metabolism was mainly influenced by the bacterial and protist diversity in microaggregates. In contrast, the microbial functional potential was primarily mediated by the assembly processes of four organism groups, especially the nematode community in macroaggregates. This study reveals the important roles of soil organisms with different body sizes in the functional potential related to nutrient cycling, and provides new insights into the ecological processes structuring the diversity and community assembly of organisms of different body sizes at the soil aggregate level, with implications for soil nutrient cycling dynamics.

Abiotic Methane Production Driven by Ubiquitous Non-Fenton-Type Reactive Oxygen Species.

Abiotic CH4 production driven by Fenton-type reactive oxygen species (ROS) has been confirmed to be an indispensable component of the atmospheric CH4 budget. While the chemical reactions independent of Fenton chemistry to ROS are ubiquitous in nature, it remains unknown whether the produced ROS can drive abiotic CH4 production. Here, we first demonstrated the abiotic CH4 production at the soil-water interface under illumination. Leveraging this finding, polymeric carbon nitrides (CNx) as a typical analogue of natural geobattery material and dimethyl sulfoxide (DMSO) as a natural methyl donor were used to unravel the underlying mechanisms. We revealed that the ROS, photocatalytically produced by CNx, can oxidize DMSO into CH4 with a high selectivity of 91.5 %. Such an abiotic CH4 production process was further expanded to various non-Fenton-type reaction systems, such as electrocatalysis, pyrocatalysis and sonocatalysis. This work provides insights into the geochemical cycle of abiotic CH4, and offers a new route to CH4 production via integrated energy development.

Three Fe(III)-reducing and nitrogen-fixing bacteria, Anaeromyxobacter terrae sp. nov., Anaeromyxobacter oryzisoli sp. nov. and Anaeromyxobacter soli sp. nov., isolated from paddy soil.

Three microaerophilic bacterial strains, designated SG22T, SG63T and SG29T were isolated from paddy soils in PR China. Cells of these strains were Gram-staining-negative and long rod-shaped. SG22T, SG63T and SG29T showed the highest 16S rRNA gene sequence similarities with the members of the genus Anaeromyxobacter. The results of phylogenetic and phylogenomic analysis also indicated that these strains clustered with members of the genus Anaeromyxobacter. The main respiratory menaquinone of SG22T, SG63T and SG29T was MK-8 and the major fatty acids were iso-C15 : 0, iso-C17 : 0 and C16 : 0. SG22T, SG29T and SG63T not only possessed iron reduction ability but also harboured genes (nifHDK) encoding nitrogenase. The genomic DNA G+C contents of SG22T, SG63T and SG29T ranged from 73.3 to 73.5 %. The average nucleotide identity (ANI) and digital DNA-DNA hybridisation (dDDH) values between SG22T, SG63T and SG29T and the closely related species of the genus Anaeromyxobacter were lower than the cut-off values (dDDH 70 % and ANI 95-96 %) for prokaryotic species delineation. On the basis of these results, strains SG22T, SG63T and SG29T represent three novel species within the genus Anaeromyxobacter, for which the names Anaeromyxobacter terrae sp. nov., Anaeromyxobacter oryzisoli sp. nov. and Anaeromyxobacter soli sp. nov., are proposed. The type strains are SG22T (= GDMCC 1.3185T = JCM 35581T), SG63T (= GDMCC 1.2914T = JCM 35124T) and SG29T (= GDMCC 1.2911T = JCM 35123T).

Community assembly of organisms regulates soil microbial functional potential through dual mechanisms.

Unraveling the influence of community assembly processes on soil ecosystem functioning presents a major challenge in the field of theoretical ecology, as it has received limited attention. Here, we used a series of long-term experiments spanning over 25 years to explore the assembly processes of bacterial, fungal, protist, and nematode communities using high-throughput sequencing. We characterized the soil microbial functional potential by the abundance of microbial genes associated with carbon, nitrogen, phosphorus, and sulfur cycling using GeoChip-based functional gene profiling, and determined how the assembly processes of organism groups regulate soil microbial functional potential through community diversity and network stability. Our results indicated that balanced fertilization (NPK) treatment improved the stochastic assembly of bacterial, fungal, and protist communities compared to phosphorus-deficient fertilization (NK) treatment. However, there was a nonsignificant increase in the normalized stochasticity ratio of the nematode community in response to fertilization across sites. Our findings emphasized that soil environmental factors influenced the assembly processes of the biotic community, which regulated soil microbial functional potential through dual mechanisms. One mechanism indicated that the high phosphorus levels and low soil nutrient stoichiometry may increase the stochasticity of bacterial, fungal, and protist communities and the determinism of the nematode community under NPK treatment, ultimately enhancing soil microbial functional potential by reinforcing the network stability of the biotic community. The other mechanism indicated that the low phosphorus levels and high soil nutrient stoichiometry may increase the stochastic process of the bacterial community and the determinism of the fungal, protist, and nematode communities under NK treatment, thereby enhancing soil microbial functional potential by improving the ß-diversity of the biotic community. Taken together, these results provide valuable insights into the mechanisms underlying the assembly processes of the biotic community that regulate ecosystem functioning.

Foliar N2 O emissions constitute a significant source to atmosphere.

Nitrous oxide (N2 O) is a potent greenhouse gas and causes stratospheric ozone depletion. While the emissions of N2 O from soil are widely recognized, recent research has shown that terrestrial plants may also emit N2 O from their leaves under controlled laboratory conditions. However, it is unclear whether foliar N2 O emissions are universal across varying plant taxa, what the global significance of foliar N2 O emissions is, and how the foliage produces N2 O in situ. Here we investigated the abilities of 25 common plant taxa, including trees, shrubs and herbs, to emit N2 O under in situ conditions. Using 15 N isotopic labeling, we demonstrated that the foliage-emitted N2 O was predominantly derived from nitrate. Moreover, by selectively injecting biocide in conjunction with the isolating and back-inoculating of endophytes, we demonstrated that the foliar N2 O emissions were driven by endophytic bacteria. The seasonal N2 O emission rates ranged from 3.2 to 9.2 ng N2 O-N g-1 dried foliage h-1 . Extrapolating these emission rates to global foliar biomass and plant N uptake, we estimated global foliar N2 O emission to be 1.21 and 1.01 Tg N2 O-N year-1 , respectively. These estimates account for 6%-7% of the current global annual N2 O emission of 17 Tg N2 O-N year-1 , indicating that in situ foliar N2 O emission is a universal process for terrestrial plants and contributes significantly to the global N2 O inventory. This finding highlights the importance of measuring foliar N2 O emissions in future studies to enable the accurate assigning of mechanisms and the development of effective mitigation.

Phage lysate can regulate the humification process of composting.

Phages play a crucial role in orchestrating top-down control within microbial communities, influencing the dynamics of the composting process. Despite this, the impact of phage-induced thermophilic bacterial lysis on humification remains ambiguous. This study investigates the effects of phage lysate, derived explicitly from Geobacillus subterraneus, on simulated composting, employing ultrahigh-resolution mass spectrometry and 16S rRNA sequencing techniques. The results show the significant role of phage lysate in expediting humus formation over 40 days. Notably, the rapid transformation of protein-like precursors released from phage-induced lysis of the host bacterium resulted in a 14.8 % increase in the proportion of lignins/CRAM-like molecules. Furthermore, the phage lysate orchestrated a succession in bacterial communities, leading to the enrichment of core microbes, exemplified by the prevalence of Geobacillus. Through network analysis, it was revealed that these enriched microbes exhibit a capacity to convert protein and lignin into essential building blocks such as amino acids and phenols. Subsequently, these components were polymerized into humus, aligning with the phenol-protein theory. These findings enhance our understanding of the intricate microbial interactions during composting and provide a scientific foundation for developing engineering-ready composting humification regulation technologies.

Interphylum dissemination of NDM-5-positive plasmids in hospital wastewater from Fuzhou, China: a single-centre, culture-independent, plasmid transmission study.

BACKGROUND: The global spread of plasmid-borne carbapenem resistance is an ongoing public health challenge; however, the nature of such horizontal gene transfer events among complex bacterial communities remains poorly understood. We examined the in-situ transfer of the globally dominant New Delhi metallo-ß-lactamase (NDM)-5-positive IncX3 plasmid (denoted pX3_NDM-5) in hospital wastewater to simulate a real-world, One Health antimicrobial resistance context. METHODS: For this transmission study, we tagged pX3_NDM-5 with the green fluorescent protein gene, gfp, using a CRISPR-based method and transferred the plasmid to a donor Escherichia coli strain. Bacteria were extracted from a hospital wastewater treatment plant (Fujian Provincial Maternity and Children's Hospital, Fuzhou, China) as the bacterial recipient community. We mixed this recipient community with the E coli donor strain carrying the gfp-tagged plasmid, both with and without sodium hypochlorite (NaClO) as an environmental stressor, and conducted several culture-based and culture-independent conjugation assays. The conjugation events were observed microscopically and quantified by fluorescence-activated cell sorting. We analysed the taxonomic composition of the sorted transconjugal pool by 16S rRNA gene amplicon sequencing and assessed the stability of the plasmid in the isolated transconjugants and its ability to transfer back to E coli. FINDINGS: We show that the plasmid pX3_NDM-5 has a broad host range and can transfer across various bacterial phyla, including between Gram-negative and Gram-positive bacteria. Although environmental stress with NaClO did not affect the overall plasmid transfer frequency, it reduced the breadth of the transconjugant pool. The taxonomic composition of the transconjugal pool was distinct from that of the recipient communities, and environmental stress modulated the permissiveness of some operational taxonomic units towards the acquisition of pX3_NDM-5. Notably, pX3_NDM-5 transconjugants included the Gram-positive pathogen Enterococcus faecalis, and the plasmid could subsequently be reconjugated back to E coli. These findings suggest that E faecalis could act as a natural shuttle vector for the wide dissemination of pX3_NDM-5 plasmids. INTERPRETATION: Our culture-independent conjugation model simulates natural environmental conditions and challenges the established theory that Gram-negative and Gram-positive bacteria rarely exchange clinically important plasmids. The data show that plasmids disseminate more widely across genera and phyla than previously thought. These findings have substantial implications when considering the spread of antimicrobial resistance across One Health sectors. FUNDING: The Laboratory of Lingnan Modern Agriculture Project, the National Natural Science Foundation of China, the Natural Science Foundation of Fujian Province of China, and the Outstanding Young Research Talents Program of Fujian Agriculture and Forestry University.

Microbial biofilms for self-powered noncontact sensing.

Noncontact sensing technology plays a vital role in the intelligent human-machine interface, as the essential medium for exchanging information between human and electronic devices. To date, several inorganic materials-based noncontact sensing techniques have been used to accurately detect touch, electrical property, and physical motion. However, limited available materials, dependence on additional power supplies, and poor power production performance, have seriously obstructed the practical applications of noncontact sensing technology. Here, we developed simple self-powered noncontact sensors (SNSs) assembled using a typical G. sulfurreducens biofilm as the core component. In noncontact mode, the sensor demonstrated excellent self-powered sensing performance with maximum voltage output of 10 V and a current of 60 nA, a maximum sensing range of 40 cm which is the farthest reported to date. Depending on its excellent sensing characteristic, the SNSs was used to monitor human breathing in this work. Furthermore, an array of united SNSs was able to localize external electric fields and effectively extend the sensing area by increasing the number of devices. Compared to traditional inorganic materials, microbial biofilms have the advantages of wide existence, self-proliferation, low cost, environmental friendliness, and ultra-fast self-healing property (seconds level). The proposed biofilm SNSs in our work provides new insights for noncontact power generation of biomaterials and self-driven sensing.

Two novel alkalitolerant species Pseudalkalibacillus spartinae sp. nov. and Pseudalkalibacillus sedimenti sp. nov.

In this study, two novel alkalitolerant strains (FJAT-53046T and FJAT-53715T) were isolated from sediment samples collected in Zhangzhou, PR China. Phylogeny based on 16S rRNA gene sequences suggested that strains FJAT-53046T and FJAT-53715T were new members of the genus Pseudalkalibacillus. The two novel strains showed the highest 16S rRNA gene sequence similarity to Pseudalkalibacillus hwajinpoensis DSM 16206T, with values of 97.4 and 97.6 %, respectively. The average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) values between the two strains and the reference strain were 77.2 and 79.6 %, 20.9 and 30.2 %, respectively, which were below the prokaryotic species delineation thresholds. The ANI and dDDH values between strains FJAT-53046T and FJAT-53715T were 86.0 and 30.2 %, respectively, suggesting that they belonged to different species in the genus Pseudalkalibacillus. The major respiratory quinone in both strains was MK-7 and the major cellular fatty acids were anteiso-C15 : 0 and anteiso-C17 : 0. Diphosphatidylglycerol, phosphatidylglycerol and phosphatidylethanolamine were the major polar lipids in both novel strains. Combined with results stemming from the determination of physical and biochemical characteristics, chemical properties, and genome analysis, strains FJAT-53046T and FJAT-53715T are proposed to represent two novel species of the genus Pseudalkalibacillus, for which the names Pseudalkalibacillus spartinae sp. nov. and Pseudalkalibacillus sedimenti sp. nov. are proposed. The type strains are FJAT-53046T (=GDMCC 1.3077T=JCM 35611T) and FJAT-53715T (=GDMCC 1.3076T=JCM 35610T), respectively.

Nitrogen fixation and transcriptome of a new diazotrophic Geomonas from paddy soils.

Nitrogen gas (N2) fixation driven by diazotrophs is a crucial process for supplying nitrogen to paddy soil ecosystems. The genus Geomonas has been considered to be an important potential diazotroph in paddy soils, but direct experimental evidence of the nitrogen-fixing ability of Geomonas in pure culture is still lacking. Hence, we aimed to demonstrate this nitrogen-fixing capability and shed light on how this process was regulated in response to ammonium (NH4 +) in Geomonas. In this study, we determined that a key nitrogenase gene (nifH) was present in 50 isolates from paddy soils. Members of Geomonas contained the minimum nitrogen fixation gene cluster (nifBHDKEN) based on genomic analysis, implying Geomonas species had the potential to fix nitrogen. Acetylene reduction assay (ARA), 15N2 isotope labeling, and total nitrogen accumulation assays validated that Geomonas was, indeed, able to fix nitrogen in pure culture. Under nitrogen-fixing conditions, the cell morphology of Geomonas changed from short rod-shaped (with NH4 +) to long rod-shaped and flagella became longer and thicker. The expression of genes correlated to nitrogen fixation in the Geomonas transcriptome was quantified in response to NH4 +. Expression of genes associated with nitrogenase, flavin-based electron bifurcation complexes (such as the FixAB system), NH4 + uptake, and transformation (e.g., glutamine and glutamate synthetases) were significantly upregulated under nitrogen-fixing conditions, suggesting these mechanisms might be involved in N2 fixation in Geomonas. These results were verified by RT-qPCR. Taken together, our results demonstrate that Geomonas species possess the ability to fix N2 and expand our understanding on the ecological significance and potential applications of Geomonas in paddy soil ecosystems. IMPORTANCE The ability of Geomonas species to fix nitrogen gas (N2) is an important metabolic feature for its application as a plant growth-promoting rhizobacterium. This research is of great importance as it provides the first comprehensive direct experimental evidence of nitrogen fixation by the genus Geomonas in pure culture. We isolated a number of Geomonas strains from paddy soils and determined that nifH was present in these strains. This study demonstrated that these Geomonas species harbored genes encoding nitrogenase, as do Geobacter and Anaeromyxobacter in the same class of Deltaproteobacteria. We demonstrated N2-dependent growth of Geomonas and determined regulation of gene expression associated with nitrogen fixation. The research establishes and advances our understanding of nitrogen fixation in Geomonas.

Identifying the role of array electrodes in improving the compost quality of food waste during electric field-assisted aerobic composting.

Low composting temperature and long maturation periods are two major problems during food waste composting. In this study, a novel array-based electric field-assisted aerobic composting (Pin-EAC) process was tested on food waste compost. Pin-EAC increase the composting temperature to 69.3 °C, and improved the germination index by 15%. The Pin-EAC took at least 40% less time to reach the standard compost maturity. The fluorescent spectroscopy results showed that Pin-EAC could increase humic acid and fulvic acid by 33% and 37%, respectively. Pin-EAC could increase the diversity of thermophilic bacteria during composting. The co-occurrence network shown that Pin-EAC are more closely related to oxygen and temperature. This work has initially shown that the use of an electric field could improve food waste composting quality, suggesting that the Pin-EAC process is an effective strategy for high-water and high-oil organic solid waste aerobic composting.