Characterization of Cr(VI)-reducing indigenous bacteria from a long-term tannery waste-contaminated soil

This paper investigated the Cr (VI) detoxification potential of 4 novel bacterial strains isolated from a long-term tannery waste-contaminated soil. Molecular techniques were used to identify the bacterial strains using 16 S rDNA gene sequencing. The Cr (VI) detoxification capacity of the bacteria was determined by 1,5-diphenylcarbazide (DPC) methods. The identified bacterial strains were Bacillus subterraneus MMKT-10, Klebsiella quasivariicola MMKT-15, Acinetobacter seohaensis MMKT-19, and Staphylococcus saprophyticus MMKT-25. All the strains showed maximum tolerance concentration (MTC) of Cr (VI) up to 4000 mg/L. However, in terms of Cr(VI) reduction rate, K. quasivariicola can be considered the most efficient, reducing the two preliminary Cr(VI) concentrations (10 and 20 mg/L) at 15 and 18 h, respectively, while the rest of the strains needed 30 h to reduce the same concentrations from the culture medium. The favorable temperature for Cr(VI) detoxification ranged from 30-40 degrees C. However, 100 % Cr (VI) reduction was achieved by all the strains at 35 0C. Interestingly, all the bacterial strains reduced a significant amount of Cr (VI) at 50 0C, indicative of their thermotolerant nature. The ideal pH for Cr (VI) reduction was 7 for B. subterraneus MMKT-10 and K. quasivariicola MMKT-15, whereas it was 8 for Acinetobacter seohaensis MMKT-19 and Staphylococcus saprophyticus MMKT-25. The indigenous bacterial strains isolated in this study could be one of the promising candidates for the detoxification of Cr (VI) contaminated sites.