Arsenic Resistance Mechanisms in Pseudomonas mendocina SMSKVR-3 Strain Isolated from Khetri Copper Mines, Rajasthan,...

An arsenic resistant bacteria SMSKVR-3 has been isolated from the rhizospheric soil of the metal-contaminated site of khetri copper mines situated in the Jhunjhunu district of Rajasthan, India. The strain showed homology with Pseudomonas mendocina strain ATCC 25411. This gram-negative isolate exhibited optimal growth in M9 minimal media with temperature and salt concentration as 30 °C and 0.25% (w/v), respectively, at pH 7.0. The similar growth pattern and SEM analysis of this strain exposed to M9 minimal media alone, M9 media supplemented with 300 mM arsenate [As(V)] or M9 media supplemented with 1.34 mM arsenite [As(III)] indicate the existence of the strong arsenic resistance mechanism. The isolate was able to produce siderophores and was able to reduce As(V) to As(III). A decrease in polyP concentration from 354.8 µg/10¹⁰ CFU mL^-1 at 0 h to 0.043 µg/10¹⁰ CFU mL^-1 at 8 h incubation with As(V) was in correlation with the change in intracellular As(V) concentration (116.98 mg L^-1/10¹⁰ cells at 0 h to 88.65 mg L^-1/10¹⁰ at 8 h) with time. This shows the possible role of polyP bodies in the regulation of As(V) concentration inside the cell. The presence of arsC gene in P.mendocina SMSKVR-3 was confirmed by the PCR amplification of arsC gene. The BLAST analysis of the sequenced gene represented 98.59% identity with the P. mendocina S5.2 arsenate reductase. These results indicate that the observed arsenic resistance in SMSKVR-3 is due to a combination of siderophore production, the transformation of As(V) to As(III) by arsenate reductase, multi-drug efflux pump, and polyP bodies mediated metal resistance mechanism.