Abstract

In order to study the microbiology of chromium tolerance and reduction at a fly ash dumping site in South Africa, 15 core samples were investigated. It was shown that the 30 year old dumping site exhibited high concentrations of Cr (VI) ranging from 1.6 to 9.6 mg/g. From this contaminated fly ash dumping site, 67 chromium resistant bacteria (CRB) growing in liquid medium in presence of a high chromium concentration (500 µg/ml) were isolated. Full sequencing and phylogenetic analyses of the 16S rRNA gene allowed unambiguous identification of five Staphylococcispecies distributed non-homogeneously through the depth profile of the site. There was a discrepancy in the way the five species tolerated chromium at 250 and 500 µg/ml in anaerobic conditions in the presence or absence of nitrate (KNO₃). Their potential to reduce chromium under these conditions was also demonstrated.

Key words: Fly Ash, chromium contamination, chromium resistant bacteria, Cr (VI) reduction.

Abbreviation

CRB, Chromium resistant bacteria; NAD, nicotinamide adenine dinucleotide; ROS, reactive oxygen species; FA, fly ash; PCR, polymerase chain reaction; SDS, sodium dodecyl sulfate; ARDRA, amplification rDNA Restriction Analysis; ABTS, 2,2’-azino-bis(3-ethylbenzo-thiazoline-6-sulfonic acid) diammonium salts.