Screening and characterization of arsenite/arsenate oxidizing bacteria from tannery wastes and agriculural soils

Abstract

Ninety-three arsenic resistant bacteria were isolated from 7 tannery waste samples collected from Samutprakan province and 9 agricultural soil samples collected from Nakhonpathom and Petburi Provinces, Thailand by enrichment culture method using medium containing 1.3 mM sodium arsenite. Minimum inhibitory concentration (MIC) of these isolates ranged from 5->40 mM arsenite and 200- >450 mM arsenate. Highly arsenic resistant bacteria (27 isolates) had minimum inhibitory concentrations (MICs) for arsenite and arsenate of >40 mM and >400 mM, respectively. On the basis of morphological, cultural, physiological and biochemical characteristics; ubiquinone system, and 16S rRNA gene sequence analyses, they were identified as following: nine isolates each of Klebsiella (Groups 1 and 8) and Acinetobacter (Groups 2, 3 and 7), four isolates each of Pseudomonas (Groups 4 and 6) and Comamonas (Group 5), and one isolate of Enterobacter (Group 9). Only one isolate in Group 5, Comamonas sp. A3-3, appeared to have potential for bioremediation due to a capability of oxidizing arsenite to arsenate. The arsenite oxidizing activity was confirmed by an arsenic speciation using a XANES spectroscopic method. An efficiency of the arsenite oxidizing activity determined by modified arsenite-iodine titration method was 65.3%. The arsenite oxidizing strain, Comamonas sp. A3-3, which isolated from agricultural soil grew at 40°C, in the presence of 4.5% (w/v) NaCl and at pH 5 to 11. Major cellular fatty acids were C 16:0, C 18:1 ω7c and C 17:0 CYCLO. Ubiquinone with eight isoprene unit (Q-8) was a predominant ubiquinone. DNA G+C content was 69.6 mol%. Phylogenetic analysis using 16S rRNA gene sequences showed that the strain A3-3 was closely related to C. kerstersii LMG 3475T, C. aquatica LMG 2370T and C. koreensis YH12T with 96.9, 96.8 and 96.4% similarities, respectively. The strain A3-3 could be clearly distinguished from C. kerstersii LMG 3475T and related Comamonas species based on its phenotypic characteristics and phylogenetic position. This strain (A3-3T = NBRC 106524T) could be a novel species in the genus Comamonas, for which the name Comamonas terra is proposed.