CHROMATE RESISTANCE AND REDUCTION IN Bacillus sp. SFC 500-1 ISOLATED FROM TANNERY SLUDGES.

ONTAÑON O.M; GONZALEZ PS; MEDINA MI; AGOSTINI E.

Rosario

Congreso; IX CONGRESO ARGENTINO DE MICROBIOLOGÍA GENERAL (SAMIGE); 2013

SAMIGE

Hexavalent chromium [Cr (VI)] is a dangerous pollutant which is released into the environment from many industrial processes. Biotransformation of Cr (VI) to relatively non toxic trivalent chromium [Cr (III)] by resistant bacteria has offered an economical as well as eco-friendly option for chromate detoxification and bioremediation. In the present work, the Cr (VI) tolerant strain SFC 500-1 isolated from contaminated tannery sludge was analyzed regarding to its ability for removing and detoxifying the metal by enzymatic reduction to Cr (III). Moreover, the presence of encoding genes for the Cr (VI) efflux pump Chr A, an important defense mechanism against Cr (VI), was evaluated. The isolate was identified as Bacillus sp., according to its morphological and biochemical properties, 16S rRNA gene sequencing and phylogenetic analysis. The strain was able to tolerate Cr (VI) below 200 mg/l; however growth was strongly affected by concentrations up to 50 mg/l. In addition, a fragment of the chrA gene was amplified by PCR, which could indicate the presence of an efflux pump of Cr (VI) as a metal tolerance mechanism. On the other hand, Bacillus sp. SFC 500-1 exhibited Cr (VI) removal capability. Complete reduction of 10 mg/l Cr (VI) was observed in less than 48 h in TY medium. For higher Cr (VI) concentrations (25, 50, 100 mg/l) removal efficiencies were 90%, 50% and 10% respectively, after 3 d of incubation. An enzymatic mechanism involved in such Cr (VI) reduction was demonstrated employing cell-free extracts and filtered culture supernatants. Chromate reductase of the strain SFC 500-1 was found mainly associated with the cell soluble fraction and required NADH as electron donor. The chromate reductase activity would be constitutive. This result is consistent with protein profiles obtained by SDS- PAGE, which remained without changes in cells treated and non-treated with Cr (VI). Taking into account the ability of Bacillus sp. SFC 500-1 to tolerate and remove Cr (VI) from liquid medium via reduction to Cr (III), a less toxic and soluble form, this strain could be considered as a promising candidate for bioremediation of contaminated sites.