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% similarity), P. japonensis 12-3T (98.9 0%), P. putridarboris WD-12T (98.02%), and P. indica P15T (97.27%) as closest phylogenetic neighbours. DNA-DNA hybridization study unambiguously indicated that strain KAs 5-3T represented a novel species that was separate from reference strains of P. mexicana AMX 26BT (35.7%), P. japonensis 12-3T (35.5%), P. suwonensis 4M1T (35.5%), P. wuyuanensis XC21-2T (35.0%), P. indica P15T (32.5%), P. daejeonensis TR6-08T (32.0%), and P. putridarboris WD12T (22.1%). The DNA G+C content of strain KAs 5-3T was 64.9 mol %. The predominant fatty acids were C15:0 (37.4%), C16:0 iso (12.6%), C17:1 iso ω9c (10.5%), C15:0 anteiso (9.5%), C11:0 iso 3-OH (8.5%), and C16:1 ω7c/ C16:1 ω6c (7.5%). The major polar lipids were diphosphatidylglycerol, phosphatidyldimethylethanolamine, phosphatidylcholine, and two unknown phospholipids (PL1, PL2). Ubiquinone 8 (Q8) was the predominant respiratory quinone and spermidine was the major polyamine of the strain KAs 5-3T. Cells of strain KAs 5-3T showed the ability to use O2, As5+, NO3-, NO2-, and Fe3+ as terminal electron acceptors as well as to reduce As5+ through the cytosolic process under aerobic incubations. Genes encoding arsenate reductase (arsC) for As-detoxification, nitrate- and nitrite reductase (narG and nirS) for denitrification were detected in the strain KAs 5-3T. Based on taxonomic and physiological data, strain KAs 5-3T is described as a new representative member of the genus Pseudoxanthomonas, for which the name Pseudoxanthomonas arseniciresistens sp. nov. is proposed. The type strain is KAs 5-3T (= LMG 29169T = MTCC 12116T = MCC 3121T).
Highlights
Taxonomic hierarchy of the genus Pseudoxanthomonas denotes its affiliation to the class Gammaproteobacteria, family Xanthomonadaceae of phylum Proteobacteria
Comparison of nearly complete (1,495 nucleotides) 16S rRNA gene sequence indicated taxonomic affiliation of strain KAs 5-3T to the genus Pseudoxanthomonas, with highest sequence similarity to the type strains of P. mexicana AMX 26BT (99.25%), P. japonensis 12-3T (98.9%), Fig 4
The NJ phylogenetic analysis showed that strain KAs 5-3T formed a coherent cluster of monophyletic pattern with the type strains of P. mexicana AMX 26BT and P. japonensis 12-3T and claded to the type members of Pseudoxanthomonas (Fig 1)
Summary
Taxonomic hierarchy of the genus Pseudoxanthomonas denotes its affiliation to the class Gammaproteobacteria, family Xanthomonadaceae of phylum Proteobacteria. The taxon has been subsequently emended by Thierry et al [3] and Lee et al [4] Members of this genus were described as Gram-stain-negative, non-spore forming rods, with iso C15:0 and anteiso C15:0 as major fatty acids, ubiquinone (Q8) as major respiratory quinone and capable of performing strict respiratory metabolism with O2 as preferred terminal electron acceptor [3]. The non-validly described members (but effectively published): P. kaohsiungensis and P. gei are isolated from an oil-polluted site and plant stem respectively [18, 19]. The members of this genus are ecologically important due to their ability to reduce both nitrite and nitrate; degrade a variety of hydrocarbons (including benzene, toluene, ethyl-benzene and o-, m-, p- xylene) [20,21,22]. The role of such organisms in biogeochemical-cycling of As in contaminated groundwater remained highly unexplored
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