Taxonomy and physiology of Pseudoxanthomonas arseniciresistens sp. nov., an arsenate and nitrate-reducing novel gammaproteobacterium from arsenic contaminated groundwater, India
Abstract:Reductive transformation of toxic arsenic (As) species by As reducing bacteria (AsRB) is a key process in As-biogeochemical-cycling within the subsurface aquifer environment. In this study, we have characterized a Gram-stain-negative, non-spore-forming, rod-shaped As reducing bacterium designated KAs 5-3T, isolated from highly As-contaminated groundwater of India. Strain KAs 5-3T displayed high 16S rRNA gene sequence similarity to the members of the genus Pseudoxanthomonas, with P. mexicana AMX 26BT (99.25% si… Show more
“…Linear regression and correlation analysis of growth vs coupled reduction profile with stoichiometric imbalance indicated the cellular As uptake during reduction by IIIJ3-1 and its cellular compartmentalization. The observed phenomena corroborated earlier reports on cellular and extracellular adsorption of As during growth by some As-transforming bacterial members from diverse habitat [ 35 , 65 – 67 ]. Fig.…”
Section: Discussionsupporting
confidence: 91%
“…WB-3 [32], Rhizobium arsenicireducens KAs 5-22 T [16], Pseudoxanthomonas arseniciresistens KAs 5-3 T [34]; Achromobacter sp. KAs 3-5 [35] and Firmicutes viz. B. arsenicus [36], B. indicus [37] have been isolated from BDP (West Bengal) and characterized thoroughly.…”
Background: Microbe-mediated redox transformation of arsenic (As) leading to its mobilization has become a serious environmental concern in various subsurface ecosystems especially within the alluvial aquifers. However, detailed taxonomic and eco-physiological attributes of indigenous bacteria from As impacted aquifer of Brahmaputra river basin has remained under-studied. Results: A newly isolated As-resistant and-transforming facultative anaerobic bacterium IIIJ3-1 from Ascontaminated groundwater of Jorhat, Assam was characterized. Near complete 16S rRNA gene sequence affiliated the strain IIIJ3-1 to the genus Bacillus and phylogenetically placed within members of B. cereus sensu lato group with B. cereus ATCC 14579(T) as its closest relative with a low DNA-DNA relatedness (49.9%). Presence of iC17:0, iC15:0 fatty acids and menaquinone 7 corroborated its affiliation with B. cereus group, but differential hydroxy-fatty acids, C18:2 and menaquinones 5 & 6 marked its distinctiveness. High As resistance [Maximum Tolerable Concentration = 10 mM As 3+ , 350 mM As 5+ ], aerobic As 3+ (5 mM) oxidation, and near complete dissimilatory reduction of As 5+ (1 mM) within 15 h of growth designated its physiological novelty. Besides O 2 , cells were found to reduce As 5+ , Fe 3+ , SO 4 2− , NO 3 − , and Se 6+ as alternate terminal electron acceptors (TEAs), sustaining its anaerobic growth. Lactate was the preferred carbon source for anaerobic growth of the bacterium with As 5+ as TEA. Genes encoding As 5+ respiratory reductase (arr A), As 3+ oxidase (aioB), and As 3+ efflux systems (ars B, acr3) were detected. All these As homeostasis genes showed their close phylogenetic lineages to Bacillus spp. Reduction in cell size following As exposure exhibited the strain's morphological response to toxic As, while the formation of As-rich electron opaque dots as evident from SEM-EDX possibly indicated a sequestration based As resistance strategy of strain IIIJ3-1.
“…Linear regression and correlation analysis of growth vs coupled reduction profile with stoichiometric imbalance indicated the cellular As uptake during reduction by IIIJ3-1 and its cellular compartmentalization. The observed phenomena corroborated earlier reports on cellular and extracellular adsorption of As during growth by some As-transforming bacterial members from diverse habitat [ 35 , 65 – 67 ]. Fig.…”
Section: Discussionsupporting
confidence: 91%
“…WB-3 [32], Rhizobium arsenicireducens KAs 5-22 T [16], Pseudoxanthomonas arseniciresistens KAs 5-3 T [34]; Achromobacter sp. KAs 3-5 [35] and Firmicutes viz. B. arsenicus [36], B. indicus [37] have been isolated from BDP (West Bengal) and characterized thoroughly.…”
Background: Microbe-mediated redox transformation of arsenic (As) leading to its mobilization has become a serious environmental concern in various subsurface ecosystems especially within the alluvial aquifers. However, detailed taxonomic and eco-physiological attributes of indigenous bacteria from As impacted aquifer of Brahmaputra river basin has remained under-studied. Results: A newly isolated As-resistant and-transforming facultative anaerobic bacterium IIIJ3-1 from Ascontaminated groundwater of Jorhat, Assam was characterized. Near complete 16S rRNA gene sequence affiliated the strain IIIJ3-1 to the genus Bacillus and phylogenetically placed within members of B. cereus sensu lato group with B. cereus ATCC 14579(T) as its closest relative with a low DNA-DNA relatedness (49.9%). Presence of iC17:0, iC15:0 fatty acids and menaquinone 7 corroborated its affiliation with B. cereus group, but differential hydroxy-fatty acids, C18:2 and menaquinones 5 & 6 marked its distinctiveness. High As resistance [Maximum Tolerable Concentration = 10 mM As 3+ , 350 mM As 5+ ], aerobic As 3+ (5 mM) oxidation, and near complete dissimilatory reduction of As 5+ (1 mM) within 15 h of growth designated its physiological novelty. Besides O 2 , cells were found to reduce As 5+ , Fe 3+ , SO 4 2− , NO 3 − , and Se 6+ as alternate terminal electron acceptors (TEAs), sustaining its anaerobic growth. Lactate was the preferred carbon source for anaerobic growth of the bacterium with As 5+ as TEA. Genes encoding As 5+ respiratory reductase (arr A), As 3+ oxidase (aioB), and As 3+ efflux systems (ars B, acr3) were detected. All these As homeostasis genes showed their close phylogenetic lineages to Bacillus spp. Reduction in cell size following As exposure exhibited the strain's morphological response to toxic As, while the formation of As-rich electron opaque dots as evident from SEM-EDX possibly indicated a sequestration based As resistance strategy of strain IIIJ3-1.
“…The genomic DNA of isolates (P2, DF22) was extracted using DNA minikit protocol following SDS-Lysozyme lysis and subsequent purification using phenol:chloroform:isoamyl alcohol and ethanol (Mohapatra et al, 2018). The 16S rRNA gene was amplified by PCR with bacterial universal primers (27F: 5 -AGAGTTTGATCCTGGCTCAG-3 and 1492R: 5 -TACCTTGTTACGACTT-3 ).…”
Section: Isolation and Identification Of Ldpe Degrading Bacterial Strmentioning
Exploring the catabolic repertoire of natural bacteria for biodegradation of plastics is one of the priority areas of biotechnology research. Low Density Polyethylene (LDPE) is recalcitrant and poses serious threats to our environment. The present study explored the LDPE biodegradation potential of aerobic bacteria enriched from municipal waste dumpsite and bentonite based drilling fluids from a deep subsurface drilling operation. Considerable bacterial growth coupled with significant weight loss of the LDPE beads (∼8%), change in pH to acidic condition and biofilm cell growth around the beads (CFU count 105–106/cm2) were noted for two samples (P and DF2). The enriched microbial consortia thus obtained displayed high (65–90%) cell surface hydrophobicity, confirming their potential toward LDPE adhesion as well as biofilm formation. Two LDPE degrading bacterial strains affiliated to Stenotrophomonas sp. and Achromobacter sp. were isolated as pure culture from P and DF2 enrichments. 16S rRNA gene sequences of these isolates indicated their taxonomic novelty. Further biodegradation studies provided strong evidence toward the LDPE metabolizing ability of these two organisms. Atomic Fore Microscopy (AFM) and Scanning Electron Microscopy (SEM) revealed considerable damage (in terms of formation of cracks, grooves, etc.) on the micrometric surface of the LDPE film. Analysis of the average roughness (Ra), root mean square roughness (Rq), average height (Rz), maximum peak height (Rp), and maximum valley depth (Rv) (nano-roughness parameters) through AFM indicated 2–3 fold increase in nano-roughness of the LDPE film. FTIR analysis suggested incorporation of alkoxy (1000–1090 cm–1), acyl (1220 cm–1), nitro (1500–1600 cm–1), carbonyl (1720 cm–1) groups into the carbon backbone, formation of N-O stretching (1360 cm–1) and chain scission (905 cm–1) in the microbially treated LDPEs. Increase in carbonyl index (15–20 fold), double bond index (1.5–2 fold) and terminal double bond index (30–40 fold) confirmed that biodegraded LDPEs had undergone oxidation, vinylene formation and chain scission. The data suggested that oxidation and dehydrogenation could be the key steps allowing formation of low molecular weight products suitable for their further mineralization by the test bacteria. The study highlighted LDPE degrading ability of natural bacteria and provided the opportunity for their development in plastic remediation process.
“…Among the consortium, the highest abundant bacterium was related to genus Pseudoxanthomonas , of which the closest member was P. suwonensis with the ANI of 76.7%. Although an isolate from this genus has been reported able to reduce As(V), it was phylogenetically distant from P. suwonensis (Mohapatra et al, 2018), implying the different metabolisms between species in the same genus. Additionally, arsB whose gene product could expel As(III) and thus confer As-resistance (Fu et al, 2009), was not found in the assembled genome of putative Pseudoxanthomonas sp., indicating this species had no capacibility for As(V) reduction in our experiment.…”
Heavy metal pollution has become an increasingly serious problem worldwide. Co-contamination with toxic mercury (Hg) and arsenic (As) presents a particularly difficult bioremediation trouble. By oxidizing the greenhouse gas methane, methanotrophs have been demonstrated to have high denitrification activity in eutrophic waters, indicating their possible potential for use in bioremediation of Hg(II) and As(V) in polluted water. Using metagenomics, a novel Methylocystis species (HL18), which was one of the most prevalent bacteria (9.9% of the relative abundance) in a CH4-based bio-reactor, is described here. The metagenomic-assembled genome (MAG) HL18 had gene products whose average amino acid identity against other known Methylocystis species varied from 69 to 85%, higher than the genus threshold but lower than the species boundary. Genomic analysis indicated that HL18 possessed all the genes necessary for the reduction of Hg(II) and As(V). Phylogenetic investigation of mercuric reductase (MerA) found that the HL18 protein was most closely affiliated with proteins from two Hg(II)-reducing bacteria, Bradyrhizobium sp. strain CCH5-F6 and Paracoccus halophilus. The genomic organization and phylogeny of the genes in the As(V)-reducing operon (arsRCCB) had significant identity with those from a As(V)-reducing bacterium belonging to the Rhodopseudomonas genus, indicating their reduction capability of As(V). Further analysis found that at least eight genera of methanotrophs possess both Hg(II) and As(V) reductases, illustrating the generally overlooked metabolic potential of methanotrophs. These results suggest that methanotrophs have greater bioremediation potential in heavy metal contaminated water than has been appreciated and could play an important role in the mitigation of heavy metal toxicity of contaminated wastewater.
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