Characterization of the enzymatic chromate reductase activity of Streptomyces sp. MC1

POLTI, MARTA ALEJANDRA; AMOROSO, MARÍA JULIA; ABATE; CARLOS MAURICIO

Rosario

Congreso; V Congreso Argentino de Microbiología General; 2008

Sociedad Argentina de Microbiología General

In natural water and subsurface soils, chromium occurs in two major oxidation states: III and VI. Cr(VI) is approximately 1,000-fold more cytotoxic and mutagenic than Cr(III). As the application of Cr is extensive in several industries, chromium-associated pollution is an increasing problem. With advances in biotechnology, bioremediation has become one of the most rapidly developing fields in environmental restoration, utilizing microorganisms to reduce the concentration and toxicity of heavy metals. In recent years, more and more attentions are put on the remediation of Cr(VI) contamination with chromate resistant microorganisms. Actinomycetes are the dominant bacteria population in soils; also their metabolic diversity and particular growth characteristics indicate them as potential agents for bioremediation. Considering that Cr(VI) is more toxic than Cr(III), the treatment strategy could include the reduction of Cr(VI) to Cr(III).There are microorganisms that are able to grow with Cr(VI) and reduce it to Cr(III). This biological reduction may provide a less costly and more environmentally friendly approach to remediation. Previously, we isolated a Cr(VI) resistant actinomycete, Streptomyces sp. MC1. This strain showed ability to reduce enzymatically Cr(VI) in minimal medium. There is not reports on characterization of  chromate reductase enzyme in Streptomyces strains. The aim of this work was to characterize the chromate reductase enzyme of Streptomyces sp. MC1, a chromate reducing strain. Streptomyces sp. MC1 was grew in minimal medium without and with Cr(VI) 1 mM. After four days of growth, cells were harvested, crushed and resuspended in water. Enzyme activity was determinate in supernatant of culture(S), cell wall (CW), cytoplasmatic fraction (CF) and whole cell (WC), using sodium phosphate or citrate buffer to obtain pH between 5 at 8, NADH or NADPH as electron source, and Cr(VI) as substrate. Reactions were incubated from 19 to 41 ºC. The highest activity was observed in CF. Cr(VI) reduction was better in presence of NADH than NAD(P)H; also the optimum activity was found at pH 7 and 30 ºC. This activity was constitutive, however it was enhanced 200% when Streptomyces sp. MC1 was cultivated in presence of Cr(VI). This is the first time that chromate reductase enzyme was characterized in a Streptomyces strain. These results are the first step for studying the possibility to use Streptomyces sp. MC1 in Cr(VI) bioremediation process.