Isolation and characterization of arsenite-oxidizing bacteria from arsenic-contaminated soils in Thailand

Two hundred and eighty-eight arsenic-resistant bacteria were isolated by an enrichment culture method from a total of 69 arsenic-contaminated soil-samples collected from Dantchaeng district in Suphanburi province (47 samples), and from Ron Phiboon district in Nakhon Sri Thammarat province (22 samples), in Central and Southern Thailand, respectively. Twenty-four of the 288 isolated arsenic-resistant bacteria were found to be arsenite-oxidizing bacteria. On the basis of their morphological, cultural, physiological, biochemical and chemotaxonomic characteristics, and supported by phylogenetic analysis based upon their 16S rRNA gene sequences, they were divided into five groups, within the genera Acinetobacter, Flavobacterium, Pseudomonas, Sinorhizobium and Sphingomonas, respectively. Within genera, phylogenetic analysis using the 16S rRNA gene sequences suggested that they were comprised of at least ten species, five isolates being closely related to known bacteria (Acinetobacter calcoaceticus NCCB 22016^T, Pseudomonas plecoglossicida FPC951^T, Ps. knackmussii B13^T, Sinorhizobium morelense Lc04^T, and Sphingomonas subterranea IFO16086^T). The other five proposed species are likely to be new species closely related to Flavobacterium johnsoniae, Sinorhizobium morelense, Acinetobacter calcoaceticus and Pseudomonas plecoglossicida, but this awaits further characterization for confirmation of the taxonomic status. No overlap in isolated species or strains was observed between the two sites. The strain distribution and characterization are described.     

Flavobacterium arsenitoxidans sp. nov., an arsenite-oxidizing bacterium from Thai soil

An arsenite-oxidizing bacterium, strain S2-3H^T, was isolated from arsenic-contaminated soil sample collected from Dantchaeng district, Suphanburi province, Thailand and was characterized based on polyphasic taxonomic study. The strain was observed to be a Gram-stain negative, aerobic, yellow pigmented, non-spore forming and rod-shaped bacterium. Major menaquinone was MK-6. Iso-C_15:0, iso-C_15:0 3OH, C_16:1 ω7c/C_16:1 ω6c, C_16:0, iso-C_17:0 3OH, and C_16:0 3OH were the predominant cellular fatty acids. The polar lipid profile consisted of phosphatidylethanolamine, unidentified phospholipids and unidentified aminophospholipids. The DNA G+C content was 37.0 mol%. Phylogenetic analysis using 16S rRNA sequence showed that strain S2-3H^T is affiliated to the genus Flavobacterium, and is closely related to F. defluvii KCTC 12612^T (97.0 %) and F. johnsoniae NBRC 14942^T (97.0 %). The strain S2-3H^T could be clearly distinguished from the related Flavobacterium species by its physiological and biochemical characteristics as well as its phylogenetic position and DNA–DNA relatedness. Therefore, the strain represents a novel species of the genus Flavobacterium, for which the name Flavobacterium arsenitoxidans sp. nov. (type strain S2-3H^T = KCTC 22507^T = NBRC 109607^T = PCU 331^T = TISTR 2238^T) is proposed.