[Isolation and characterization of a sulfate reducing Citrobacter sp. strain SR3]

A sulfate reducing bacterium, designated strain 'SR3', was isolated from sludge of a sulfate-reducing up-flow anaerobic sludge bed (UASB) reactor for treating high concentration sulfate wastewater. It was identified as Citrobacter sp. based upon the phenotypic-characteristics and physiological properties as well as the analysis of the sequence of 16S rDNA. The strain could reduce sulfate under anaerobic and micro-aerobic conditions. The dissimilatory sulphite reductase gene (dsr) was also amplified from this strain's genomic DNA using specific dsr gene primers. In aerobic conditions, the strain couldn't reduce sulfate, but exhibited a highest growth rate. In anaerobic conditions, the optimal growth conditions for this stain were temperature 37 degrees C and initial pH 8.0. Under this conditions,the strain could reduced both SO4(2-) and Cr(VI) at initial Cr(VI) concentrations of 0.4-0.8 mmol synchronously. Its tolerance ability to Cr(VI) concentrations reaches 1.0 mmol. This is the first report about an facultative anaerobe with sulfate reducing function and dissimilatory sulphite reductase gene (dsr).