Multiple pathways of vanadate reduction and denitrification mediated by denitrifying bacterium Acidovorax sp. strain BoFeN1.

Contamination of aquifers by a combination of vanadate [V(V)] and nitrate (NO3-) is widespread nowadays. Although bioremediation of V(V)- and nitrate-contaminated environments is possible, only a limited number of functional species have been identified to date. The present study demonstrates the effectiveness of V(V) reduction and denitrification by a denitrifying bacterium Acidovorax sp. strain BoFeN1. The V(V) removal efficiency was 76.5 ± 5.41 % during 120 h incubation, with complete removal of NO3- within 48 h. Inhibitor experiments confirmed the involvement of electron transport substances and denitrifying enzymes in the bioreduction of V(V) and NO3-. Cyt c and riboflavin were important for extracellular V(V) reduction, with quinone and EPS more significant for NO3- removal. Intracellular reductive compounds including glutathione and NADH directly reduce V(V) and NO3-. Reverse transcription quantitative PCR confirmed the important roles of nirK and napA genes in regulating V(V) reduction and denitrification. Bioaugmentation by strain BoFeN1 increased V(V) and NO3- removal efficiency by 55.3 % ± 2.78 % and 42.1 % ± 1.04 % for samples from a contaminated aquifer. This study proposes new microbial resources for the bioremediation of V(V) and NO3-contaminated aquifers, and contributes to our understanding of coupled vanadium, nitrogen, and carbon biogeochemical processes.

Asp-tRNAAsn/Glu-tRNAGln amidotransferase A subunit-like amidase mediates the degradation of insecticide flonicamid by Variovorax boronicumulans CGMCC 4969.

The main metabolic product of the pyridinecarboxamide insecticide flonicamid, N-(4-trifluoromethylnicotinyl)glycinamide (TFNG-AM), has been shown to have very high mobility in soil, leading to its accumulation in the environment. Catabolic pathways of flonicamid have been widely reported, but few studies have focused on the metabolism of TFNG-AM. Here, the rapid transformation of TFNG-AM and production of the corresponding acid product N-(4-trifluoromethylnicotinoyl) glycine (TFNG) by the plant growth-promoting bacterium Variovorax boronicumulans CGMCC 4969 were investigated. With TFNG-AM at an initial concentration of 0.86 mmol/L, 90.70 % was transformed by V. boronicumulans CGMCC 4969 resting cells within 20 d, with a degradation half-life of 4.82 d. A novel amidase that potentially mediated this transformation process, called AmiD, was identified by bioinformatic analyses. The gene encoding amiD was cloned and expressed recombinantly in Escherichia coli, and the enzyme AmiD was characterized. Key amino acid residue Val154, which is associated with the catalytic activity and substrate specificity of signature family amidases, was identified for the first time by homology modeling, structural alignment, and site-directed mutagenesis analyses. When compared to wild-type recombinant AmiD, the mutant AmiD V154G demonstrated a 3.08-fold increase in activity toward TFNG-AM. The activity of AmiD V154G was greatly increased toward aromatic L-phenylalanine amides, heterocyclic TFNG-AM and IAM, and aliphatic asparagine, whereas it was dramatically lowered toward benzamide, phenylacetamide, nicotinamide, acetamide, acrylamide, and hexanamid. Quantitative PCR analysis revealed that AmiD may be a substrate-inducible enzyme in V. boronicumulans CGMCC 4969. The mechanism of transcriptional regulation of AmiD by a member of the AraC family of regulators encoded upstream of the amiD gene was preliminarily investigated. This study deepens our understanding of the mechanisms of metabolism of toxic amides in the environment, providing new ideas for microbial bioremediation.

Bacteria associated with Comamonadaceae are key arsenite oxidizer associated with Pteris vittata root.

Pteris vittata (P. vittata), an arsenic (As) hyperaccumulator commonly used in the phytoremediation of As-contaminated soils, contains root-associated bacteria (RAB) including those that colonize the root rhizosphere and endosphere, which can adapt to As contamination and improve plant health. As(III)-oxidizing RAB can convert the more toxic arsenite (As(III)) to less toxic arsenate (As(V)) under As-rich conditions, which may promote plant survial. Previous studies have shown that microbial As(III) oxidation occurs in the rhizospheres and endospheres of P. vittata. However, knowledge of RAB of P. vittata responsible for As(III) oxidation remained limited. In this study, members of the Comamonadaceae family were identified as putative As(III) oxidizers, and the core microbiome associated with P. vittata roots using DNA-stable isotope probing (SIP), amplicon sequencing and metagenomic analysis. Metagenomic binning revealed that metagenome assembled genomes (MAGs) associated with Comamonadaceae contained several functional genes related to carbon fixation, arsenic resistance, plant growth promotion and bacterial colonization. As(III) oxidation and plant growth promotion may be key features of RAB in promoting P. vittata growth. These results extend the current knowledge of the diversity of As(III)-oxidizing RAB and provide new insights into improving the efficiency of arsenic phytoremediation.

Three distinct metabolic phases of polychlorinated biphenyls/biphenyl degrader Acidovorax sp. KKS102 in nutrient broth.

Acidovorax sp. KKS102 is a beta-proteobacterium capable of degrading polychlorinated biphenyls (PCBs). In this study, we examined its growth in liquid nutrient broth supplemented with different carbon sources. KKS102 had at least 3 distinct metabolic phases designated as metabolic phases 1-3, with phase 2 having 2 sub-phases. For example, succinate, fumarate, and glutamate, known to repress the PCB/biphenyl catabolic operon in KKS102, were utilized in phase 1, while acetate, arabinose, and glycerol in phase 2, and glucose and mannose in phase 3. We also showed that the BphQ response regulator mediating catabolite control in KKS102, whose expression level increased moderately through the growth, plays important roles in carbon metabolism in phases 2 and 3. Our study elucidates the hierarchical growth of KKS102 in nutrient-rich media. This insight is crucial for studies exploiting microbial biodegradation capabilities and advancing studies for catabolite regulation mechanisms.

'Omics-guided prediction of the pathway for metabolism of isoprene by Variovorax sp. WS11.

Bacteria that inhabit soils and the leaves of trees partially mitigate the release of the abundant volatile organic compound, isoprene (2-methyl-1,3-butadiene). While the initial steps of isoprene metabolism were identified in Rhodococcus sp. AD45 two decades ago, the isoprene metabolic pathway still remains largely undefined. Limited understanding of the functions of isoG, isoJ and aldH and uncertainty in the route of isoprene-derived carbon into central metabolism have hindered our understanding of isoprene metabolism. These previously uncharacterised iso genes are essential in Variovorax sp. WS11, determined by targeted mutagenesis. Using combined 'omics-based approaches, we propose the complete isoprene metabolic pathway. Isoprene is converted to propionyl-CoA, which is assimilated by the chromosomally encoded methylmalonyl-CoA pathway, requiring biotin and vitamin B12, with the plasmid-encoded methylcitrate pathway potentially providing robustness against limitations in these vitamins. Key components of this pathway were induced by both isoprene and its initial oxidation product, epoxyisoprene, the principal inducer of isoprene metabolism in both Variovorax sp. WS11 and Rhodococcus sp. AD45. Analysis of the genomes of distinct isoprene-degrading bacteria indicated that all of the genetic components of the methylcitrate and methylmalonyl-CoA pathways are not always present in isoprene degraders, although incorporation of isoprene-derived carbon via propionyl-CoA and acetyl-CoA is universally indicated.

Hematite-promoted nitrate-reducing Fe(II) oxidation by Acidovorax sp. strain BoFeN1: Roles of mineral catalysis and cell encrustation.

Although nitrate-reducing Fe(II) oxidizing (NRFO) bacteria can grow sustainably in natural environments, numerous laboratory studies suggested that cell encrustation-induced metabolism limitations and cell death occurred more seriously in the absence of natural minerals. Hence, a study on how natural minerals could affect NRFO is warranted. This study examined the impact of hematite on NRFO by Acidovorax sp. BoFeN1 with different electron donors (acetate and Fe(II), acetate alone, and Fe(II) alone) and with nitrate as an electron acceptor. When acetate and Fe(II) were used as the electron donors, the amount of Fe(II) oxidation and nitrate reduction was enhanced in the presence of hematite, whereas no promotion was observed when only acetate was added as an electron donor. Under the conditions with only Fe(II) added as an electron donor, the level of Fe(II) oxidation was increased from 3.07 ± 0.06 to 3.92 ± 0.02 mM in the presence of hematite and nitrate reduction was enhanced. This suggests that hematite promotes microbial nitrate reduction by accelerating the biological oxidation of Fe(II). The main secondary minerals were goethite and lepidocrocite. After adding hematite, the assemblage of iron minerals on the cell surface decreased, and the cell crusts became thinner, indicating that hematite effectively mitigated cell encrustation. Furthermore, hematite accelerated the chemical oxidation of Fe(II) by nitrite. Hence, hematite can promote the NRFO of Acidovorax sp. BoFeN1 via two possible pathways: (i) hematite acts as nucleation sites to mitigate cell encrustation; (ii) hematite catalyzes the biological and chemical oxidation of Fe(II) through the mineral catalysis effects. This study highlights the importance of existing iron minerals on NRFO and sheds light on the survival strategy of NRFO bacteria in anoxic subsurface environments.

Impaired microbial N-acyl homoserine lactone signalling increases plant resistance to aphids across variable abiotic and biotic environments.

Beneficial bacteria interact with plants using signalling molecules, such as N-acyl homoserine-lactones (AHLs). Although there is evidence that these molecules affect plant responses to pathogens, few studies have examined their effect on plant-insect and microbiome interactions, especially under variable soil conditions. We investigated the effect of the AHL-producing rhizobacterium Acidovorax radicis and its AHL-negative mutant (does not produce AHLs) on modulating barley (Hordeum vulgare) plant interactions with cereal aphids (Sitobion avenae) and earthworms (Dendrobaena veneta) across variable nutrient soils. Acidovorax radicis inoculation increased plant growth and suppressed aphids, with stronger effects by the AHL-negative mutant. However, effects varied between barley cultivars and the presence of earthworms altered interaction outcomes. Bacteria-induced plant defences differed between cultivars, and aphid exposure, with pathogenesis-related and WRKY pathways partly explaining the ecological effects in the more resistant cultivars. Additionally, we observed few but specific indirect effects via the wider root microbiome where the AHL-mutant strain influenced rare OTU abundances. We conclude that bacterial AHL-signalling disruption affects plant-microbial interactions by inducing different plant pathways, leading to increased insect resistance, also mediated by the surrounding biotic and abiotic environment. Understanding the mechanisms by which beneficial bacteria can reduce insect pests is a key research area for developing effective insect pest management strategies in sustainable agriculture.

Concerted action of extracellular and cytoplasmic esterase and urethane-cleaving activities during Impranil biodegradation by Alicycliphilus denitrificans BQ1.

The concerted action of commercial esterases, proteases and amidases has been demonstrated to be relevant in polyurethane (PU) degradation by in vitro experiments. However, the spatial and temporal dynamics of these activities during PU biodegradation by PU-degrading bacteria have not been addressed. Here, we examined the capability of Alicycliphilus denitrificans BQ1 to biodegrade the polyester (PS)-PU Impranil, analyzed the temporal and spatial coordination between the extracellular and cytoplasmic esterase and urethane-cleaving activities, and their independent and combined effects on Impranil biodegradation. A. denitrificans BQ1 grew in Impranil, and its clearing was correlated with the cleavage of ester and urethane groups since early times, with decrements of some Impranil compounds and the appearance of biodegradation products. While extracellular esterase was active at early times with its maximum at 18 h, urethanase appeared at this time and increased up to the end of the analysis (48 h), with the cytoplasmic activities behaving similarly but with lower levels than the extracellular ones. Both enzymatic activities exhibited distinct substrate specificity depending on their cellular localization and cultivation times, suggesting they cleave differentially located groups. As the urethane cleavage occurred since early times, when no urethane-cleaving activity was detected, different proteins should be acting at early and late times. In vitro experiments with independent or combined cellular protein fractions supported the previous deduction and confirmed the concerted action of extracellular and cytoplasmic esterase and urethane-cleaving activities. A two-stage process for Impranil degradation by A. denitrificans BQ1 is proposed.

Host-specific activation of a pathogen effector Aave_4606 from Acidovorax citrulli, the causal agent for bacterial fruit blotch.

RipAY, an effector protein from the plant bacterial pathogen Ralstonia solanacearum, exhibits γ-glutamyl cyclotransferase (GGCT) activity to degrade the host cellular glutathione (GSH) when stimulated by host eukaryotic-type thioredoxins (Trxs). Aave_4606 from Acidovorax citrulli, the causal agent of bacterial fruit blotch of cucurbit plants, shows significant homology to RipAY. Based on its homology, it was predicted that the GGCT activity of Aave_4606 is also stimulated by host Trxs. The GGCT activity of a recombinant Aave_4606 protein was investigated in the presence of various Trxs, such as yeast (ScTrx1), Arabidopsis thaliana (AtTrx-h1, AtTrx-h2, AtTrx-h3, and AtTrx-h5), or watermelon (Cla022460/ClTrx). Unlike RipAY, the GGCT activity of Aave_4606 is stimulated only by AtTrx-h1, AtTrx-h3, AtTrx-h5 and ClTrx from a watermelon, the primary host of A. citrulli, but not by ScTrx1, AtTrx-h2. Interestingly, GGCT activity of Aave_4606 is more efficiently stimulated by AtTrx-h1 and ClTrx than AtTrx-h5. These results suggested that Aave_4606 recognizes host-specific Trxs, which specifically activates the GGCT activity of Aave_4606 to decrease the host cellular GSH. These findings provide new insights into that effector is one of the host-range determinants for pathogenic bacteria via its host-dependent activation.

Biodegradation of 3-Chloronitrobenzene and 3-Bromonitrobenzene by Diaphorobacter sp. Strain JS3051.

Halonitrobenzenes are toxic chemical intermediates used widely for industrial synthesis of dyes and pesticides. Bacteria able to degrade 2- and 4-chloronitrobenzene have been isolated and characterized; in contrast, no natural isolate has been reported to degrade meta-halonitrobenzenes. In this study, Diaphorobacter sp. strain JS3051, previously reported to degrade 2,3-dichloronitrobenzene, grew readily on 3-chloronitrobenzene and 3-bromonitrobenzene, but not on 3-fluoronitrobenzene, as sole sources of carbon, nitrogen, and energy. A Rieske nonheme iron dioxygenase (DcbAaAbAcAd) catalyzed the dihydroxylation of 3-chloronitrobenzene and 3-bromonitrobenzene, resulting in the regiospecific production of ring-cleavage intermediates 4-chlorocatechol and 4-bromocatechol. The lower activity and relaxed regiospecificity of DcbAaAbAcAd toward 3-fluoronitrobenzene is likely due to the higher electronegativity of the fluorine atom, which hinders it from interacting with E204 residue at the active site. DccA, a chlorocatechol 1,2-dioxygenase, converts 4-chlorocatechol and 4-bromocatechol into the corresponding halomuconic acids with high catalytic efficiency, but with much lower Kcat/Km values for fluorocatechol analogues. The results indicate that the Dcb and Dcc enzymes of Diaphorobacter sp. strain JS3051 can catalyze the degradation of 3-chloro- and 3-bromonitrobenzene in addition to 2,3-dichloronitrobenzene. The ability to utilize multiple substrates would provide a strong selective advantage in a habitat contaminated with mixtures of chloronitrobenzenes. IMPORTANCE Halonitroaromatic compounds are persistent environmental contaminants, and some of them have been demonstrated to be degraded by bacteria. Natural isolates that degrade 3-chloronitrobenzene and 3-bromonitrobenzene have not been reported. In this study, we report that Diaphorobacter sp. strain JS3051 can degrade 2,3-dichloronitrobenzene, 3-chloronitrobenzene, and 3-bromonitrobenzene using the same catabolic pathway, whereas it is unable to grow on 3-fluoronitrobenzene. Based on biochemical analyses, it can be concluded that the initial dioxygenase and lower pathway enzymes are inefficient for 3-fluoronitrobenzene and even misroute the intermediates, which is likely responsible for the failure to grow. These results advance our understanding of how the broad substrate specificities of catabolic enzymes allow bacteria to adapt to habitats with mixtures of xenobiotic contaminants.

Evaluating the aerobic xylene-degrading potential of the intrinsic microbial community of a legacy BTEX-contaminated aquifer by enrichment culturing coupled with multi-omics analysis: uncovering the role of Hydrogenophaga strains in xylene degradation.

To develop effective bioremediation strategies, it is always important to explore autochthonous microbial community diversity using substrate-specific enrichment. The primary objective of this present study was to reveal the diversity of aerobic xylene-degrading bacteria at a legacy BTEX-contaminated site where xylene is the predominant contaminant, as well as to identify potential indigenous strains that could effectively degrade xylenes, in order to better understand the underlying facts about xylene degradation using a multi-omics approach. Henceforward, parallel aerobic microcosms were set up using different xylene isomers as the sole carbon source to investigate evolved bacterial communities using both culture-dependent and independent methods. Research outcome showed that the autochthonous community of this legacy BTEX-contaminated site has the capability to remove all of the xylene isomers from the environment aerobically employing different bacterial groups for different xylene isomers. Interestingly, polyphasic analysis of the enrichments disclose that the community composition of the o-xylene-degrading enrichment community was utterly distinct from that of the m- and p-xylene-degrading enrichments. Although in each of the enrichments Pseudomonas and Acidovorax were the dominant genera, in the case of o-xylene-degrading enrichment Rhodococcus was the main player. Among the isolates, two Hydogenophaga strains, belonging to the same genomic species, were obtained from p-xylene-degrading enrichment, substantially able to degrade aromatic hydrocarbons including xylene isomers aerobically. Comparative whole-genome analysis of the strains revealed different genomic adaptations to aromatic hydrocarbon degradation, providing an explanation on their different xylene isomer-degrading abilities.

Biodegradation of octogen and hexogen by Pelomonas aquatica strain WS2-R2A-65 under aerobic condition.

Biodegradation ability of a native bacterial species Pelomonas aquatica strain WS2-R2A-65, isolated from nitramine explosive-contaminated effluent, for octogen (HMX) and hexogen (RDX) under aerobic condition has been explored in this study. Scanning electron microscopy indicated that the isolate WS2-R2A-65 retained its morphology both in the presence and absence of HMX or RDX. During an incubation period of 20 days, the isolate cometabolically degraded 78 and 86% of HMX and RDX with initial concentrations 6 and 60 mg L-1, respectively. The degradation mechanism followed the first-order kinetics for both the nitramines with a 50% degradation time of 9.9 and 7.7 days for HMX and RDX, respectively. Positive electrospray ionisation mass spectroscopy indicates that biodegradation of nitamines follows multiple degradation pathways with one involving ring cleavage via single-electron transfer to nitramines leading to the elimination of single nitrite ion as evident from the formation of methylenedinitramine (MEDINA) and its methyl derivatives. The other pathways involve the reduction of both the nitramines to their nitroso, hydroxylamino and amino derivatives. These metabolites get further ring cleaved to give secondary metabolites viz. N-hydroxymethylmethylenedintramine, N-nitrosoamino and hydrazinyl derivatives leading to simpler less hazardous end products. Thus, the isolate WS2-R2A-65 proves to be an efficient microbial species for bioremediation of nitramines-contaminated effluent.

A Recently Assembled Degradation Pathway for 2,3-Dichloronitrobenzene in Diaphorobacter sp. Strain JS3051.

Diaphorobacter sp. strain JS3051 utilizes 2,3-dichloronitrobenzene (23DCNB), a toxic anthropogenic compound, as the sole carbon, nitrogen, and energy source for growth, but the metabolic pathway and its origins are unknown. Here, we establish that a gene cluster (dcb), encoding a Nag-like dioxygenase, is responsible for the initial oxidation of the 23DCNB molecule. The 2,3-dichloronitrobenzene dioxygenase system (DcbAaAbAcAd) catalyzes conversion of 23DCNB to 3,4-dichlorocatechol (34DCC). Site-directed mutagenesis studies indicated that residue 204 of DcbAc is crucial for the substrate specificity of 23DCNB dioxygenase. The presence of glutamic acid at position 204 of 23DCNB dioxygenase is unique among Nag-like dioxygenases. Genetic, biochemical, and structural evidence indicate that the 23DCNB dioxygenase is more closely related to 2-nitrotoluene dioxygenase from Acidovorax sp. strain JS42 than to the 34DCNB dioxygenase from Diaphorobacter sp. strain JS3050, which was isolated from the same site as strain JS3051. A gene cluster (dcc) encoding the enzymes for 34DCC catabolism, homologous to a clc operon in Pseudomonas knackmussii strain B13, is also on the chromosome at a distance of 2.5 Mb from the dcb genes. Heterologously expressed DccA catalyzed ring cleavage of 34DCC with high affinity and catalytic efficiency. This work not only establishes the molecular mechanism for 23DCNB mineralization, but also enhances the understanding of the recent evolution of the catabolic pathways for nitroarenes. IMPORTANCE Because anthropogenic nitroaromatic compounds have entered the biosphere relatively recently, exploration of the recently evolved catabolic pathways can provide clues for adaptive evolutionary mechanisms in bacteria. The concept that nitroarene dioxygenases shared a common ancestor with naphthalene dioxygenase is well established. But their phylogeny and how they evolved in response to novel nitroaromatic compounds are largely unknown. Elucidation of the molecular basis for 23DCNB degradation revealed that the catabolic pathways of two DCNB isomers in different isolates from the same site were derived from different recent origins. Integrating structural models of catalytic subunits and enzymatic activities data provided new insight about how recently modified enzymes were selected depending on the structure of new substrates. This study enhances understanding and prediction of adaptive evolution of catabolic pathways in bacteria in response to new chemicals.

A Single Bacterium Capable of Oxidation and Reduction of Iron at Circumneutral pH.

Fe(II)-oxidizing microorganisms and Fe(III)-reducing microorganisms, which drive the biogeochemical Fe cycle on the Earth's surface, are phylogenetically and ecologically diverse. However, no single organism capable of aerobic Fe(II) oxidation and anaerobic Fe(III) reduction at circumneutral pH have been reported so far. Here, we report a novel neutrophilic Fe(II)-oxidizing Rhodoferax bacterium, strain MIZ03, isolated from an iron-rich wetland in Japan. Our cultivation experiments demonstrate that MIZ03 represents a much more versatile metabolism for energy acquisition than previously recognized in the genus Rhodoferax. MIZ03 can grow chemolithoautotrophically at circumneutral pH by oxidation of Fe(II), H2, or thiosulfate as the sole electron donor under (micro)aerobic conditions (i.e., using O2 as the sole electron acceptor). In addition, it can reduce Fe(III) or nitrate under anaerobic conditions. Thus, this is the first report demonstrating the presence of a single bacterium capable of both Fe(II) oxidation and Fe(III) reduction at circumneutral pH. The observed physiology was consistent with its 4.9-Mbp complete genome encoding key genes for iron oxidation/reduction (foxEY and mtrABC), for nitrate reduction (narGHI), for thiosulfate oxidation (soxABCDXYZ), and for carbon fixation via the Calvin cycle. Our metagenomic survey suggests that there are more Rhodoferax members capable of Fe(II) oxidation and Fe(III) reduction. Such bifunctional Rhodoferax may have an ecological advantage in suboxic/anoxic environments at circumneutral pH by recycling of Fe as the electron donor and acceptor. IMPORTANCE The biogeochemical cycle of iron (Fe) via reactions of oxidation, reduction, precipitation, and dissolution is involved in the cycle of other ecologically relevant elements, such as C, N, P, S, As, Co, Ni, and Pb. The Fe cycle on the Earth's surface is driven by a variety of Fe(II)-oxidizing microorganisms and Fe(III)-reducing microorganisms. Here, we discovered a novel bacterium, Rhodoferax sp. strain MIZ03, capable of both Fe(II) oxidation and Fe(III) reduction at circumneutral pH, and we report its physiological characteristics and complete genome sequence. The unexpected capability of this bacterium provides novel insights into the Fe cycle in the environment. Moreover, this bacterium will help to better understand the molecular mechanisms of microbial Fe redox cycling as a model organism.

Enrichment and Isolation of Surfactin-degrading Bacteria.

A total of 100 environmental samples were investigated for their ability to degrade 1 g/L surfactin as a substrate. Among them, two enrichment cultures, which exhibited microbial growth as well as surfactin degradation, were selected and further investigated. After several successive cultivations, nanopore sequencing of full-length 16S rRNA genes with MinIONTM was used to analyze the bacterial species in the enrichment cultures. Variovorax spp., Caulobacter spp., Sphingopyxis spp., and Pseudomonas spp. were found to be dominant in these surfactin-degrading mixed cultures. Finally, one strain of Pseudomonas putida was isolated as a surfactin-degrading bacterium. This strain degraded 1 g/L surfactin below a detectable level within 14 days, and C13 surfactin was degraded faster than C15 surfactin.

Stability of pure oxygen aeration-activated sludge system under non-steady food-to-microorganism ratio conditions during petrochemical wastewater treatment.

This study investigates the stability of a pure oxygen aeration-activated sludge system for petrochemical wastewater treatment under high organic concentration and non-steady food-to-microorganism (F/M) ratio conditions. Sludge settling characteristics maintained relatively stable conditions with an F/M ratio variation from 0.15 ± 0.04 to 0.33 ± 0.07 kg COD/kg MLSS⋅d, while the excess F/M ratio (0.44 ± 0.16 kg COD/kg MLSS⋅d) resulted in deterioration of the organic removal and sludge-water separation performances. Loosely bound extracellular polymeric substances (EPS) showed more significant effect on sludge settleability than the tightly bound EPS. The genus Hydrogenophaga was related to organic removal performance, while Zoogloea and Chitinophaga were related to the effluent quality of suspended solids. The excess F/M ratio also caused an increase in Zoogloea and Chitinophaga, whereas the toxicity of petrochemical wastewater resulted in decreased abundance of Hydrogenophaga. These changes caused deterioration of the organic removal and sludge-water separation performances.

A Nag-like dioxygenase initiates 3,4-dichloronitrobenzene degradation via 4,5-dichlorocatechol in Diaphorobacter sp. strain JS3050.

The chemical synthesis intermediate 3,4-dichloronitrobenzene (3,4-DCNB) is an environmental pollutant. Diaphorobacter sp. strain JS3050 utilizes 3,4-DCNB as a sole source of carbon, nitrogen and energy. However, the molecular determinants of its catabolism are poorly understood. Here, the complete genome of strain JS3050 was sequenced and key genes were expressed heterologously to establish the details of its degradation pathway. A chromosome-encoded three-component nitroarene dioxygenase (DcnAaAbAcAd) converted 3,4-DCNB stoichiometrically to 4,5-dichlorocatechol, which was transformed to 3,4-dichloromuconate by a plasmid-borne ring-cleavage chlorocatechol 1,2-dioxygenase (DcnC). On the chromosome, there are also genes encoding enzymes (DcnDEF) responsible for the subsequent transformation of 3,4-dichloromuconate to ß-ketoadipic acid. The fact that the genes responsible for the catabolic pathway are separately located on plasmid and chromosome indicates that recent assembly and ongoing evolution of the genes encoding the pathway is likely. The regiospecificity of 4,5-dichlorocatechol formation from 3,4-DCNB by DcnAaAbAcAd represents a sophisticated evolution of the nitroarene dioxygenase that avoids misrouting of toxic intermediates. The findings enhance the understanding of microbial catabolic diversity during adaptive evolution in response to xenobiotics released into the environment.

Mechanism of carbonate mineralization induced by microbes: Taking Curvibacter lanceolatus strain HJ-1 as an example.

Microbial-induced carbonate precipitation is important in the global carbon cycle, especially in fixing atmospheric CO2. Many simulation experiments have shown that microbes can induce carbonate precipitation, although there is no established understanding of the mechanism. In this study, several mineralization experiments were performed using Curvibacter lanceolatus strain HJ-1, including its secreted extracellular polymeric substances (EPS) and carbonic anhydrase (CA). We found that strain HJ-1, EPS, and CA could promote carbonate precipitation if compared with the respective control experiments (CK). Also, both HJ-1 and EPS1 experiments contained calcite and aragonite, whereas CA experiments formed calcite only. Therefore, HJ-1 and EPS is favorable for carbonate precipitation, especially for aragonite. Besides, the formation of calcite in the EPS2 experiments indicated that EPS contains a trace amount of CA, which might promote CO2 hydration and eventually lead to carbonate precipitation. It was suggested that CA only provide CO32- for the formation of carbonate minerals. In the absence of exogenous HCO3-, the optimized calcification rate followed the order: HJ-1(49.5 %) > CA(6.6 %) > EPS2(4.1 %). In addition, MICP mechanisms was studied, an increase in pH and CO2 hydration by CA play synergetic roles in providing supersaturated alkaline conditions in the system with bacteria. Finally, bacterial cells and EPS promote the formation of calcite and aragonite by acting as nucleation sites.

Identification and characterization of the proteolytic flagellin from the common freshwater bacterium Hylemonella gracilis.

Flagellins are the protein components of bacterial flagella and assemble in up to 20,000 copies to form extracellular flagellar filaments. An unusual family of flagellins was recently discovered that contains a unique metalloprotease domain within its surface-exposed hypervariable region. To date, these proteolytic flagellins (also termed flagellinolysins) have only been characterized in the Gram-positive organism Clostridium haemolyticum, where flagellinolysin was shown to be proteolytically active and capable of cleaving extracellular protein substrates. The biological function of flagellinolysin and its activity in other organisms, however, remain unclear. Here, using molecular biochemistry and proteomics, we have performed an initial characterization of a novel flagellinolysin identified from Hylemonella gracilis, a Gram-negative organism originally isolated from pond water. We demonstrate that H. gracilis flagellinolysin (HgrFlaMP) is an active calcium-dependent zinc metallopeptidase and characterize its cleavage specificity profile using both trypsin and GluC-derived peptide libraries and protein substrates. Based on high-throughput degradomic assays, HgrFlaMP cleaved 784 unique peptides and displayed a cleavage site specificity similar to flagellinolysin from C. haemolyticum. Additionally, by using a set of six protein substrates, we identified 206 protein-embedded cleavage sites, further refining the substrate preference of HgrFlaMP, which is dominated by large hydrophobic amino acids in P1', and small hydrophobic or medium-sized polar residues on the amino-terminal side of the scissile bond. Intriguingly, recombinant HgrFlaMP was also capable of cleaving full-length flagellins from another species, suggesting its potential involvement in interbacterial interactions. Our study reports the first experimentally characterized proteolytic flagellin in a Gram-negative organism, and provides new insights into flagellum-mediated enzymatic activity.

Identification and Functional Analysis of AopN, an Acidovorax Citrulli Effector that Induces Programmed Cell Death in Plants.

Bacterial fruit blotch (BFB), caused by Acidovorax citrulli, seriously affects watermelon and other cucurbit crops, resulting in significant economic losses. However, the pathogenicity mechanism of A. citrulli is not well understood. Plant pathogenic bacteria often suppress the plant immune response by secreting effector proteins. Thus, identifying A. citrulli effector proteins and determining their functions may improve our understanding of the underlying pathogenetic mechanisms. In this study, a novel effector, AopN, which is localized on the cell membrane of Nicotiana benthamiana, was identified. The functional analysis revealed that AopN significantly inhibited the flg22-induced reactive oxygen species burst. AopN induced a programmed cell death (PCD) response. Unlike its homologous protein, the ability of AopN to induce PCD was dependent on two motifs of unknown functions (including DUP4129 and Cpta_toxin), but was not dependent on LXXLL domain. More importantly, the virulence of the aopN mutant of A. citrulli in N. benthamiana significantly decreased, indicating that it was a core effector. Further analysis revealed that AopN interacted with watermelon ClHIPP and ClLTP, which responds to A. citrulli strain Aac5 infection at the transcription level. Collectively, these findings indicate that AopN suppresses plant immunity and activates the effector-triggered immunity pathway.