Morphologial, physiological and phylogenetic characterization and functional verification of an anaerobic strain SN22-2 with simultaneous capabilities of denitrification and sulfate reduction

Anaerobic bacterium (strain SN22-2) with simultaneous capabilities of denitrification and sulfate reduction was enriched and isolated in a specially designed medium by anaerobic Hungate technology. The characterisation of SN22-2 was conducted from the morphological, physiological and phylogenetic aspects. It was a rod-shaped, gram-negative, 0.2 to 0.7 μm in width and 3.0 to 5.5 μm in length. Most of the fatty acids of SN22-2 were distributed among C12:0–C19-CYC-9 and the main fatty acids consisted of C16:1-CIS-9-FAME, C16:0-FAME, C18:0-FAME and C18:0 DMA. Based on the morphological and physiological characteristics as well as the phylogenetic analysis, SN22-2 was identified as Bacillus coagulans since its 16S rDNA bore 99% resemblance to that of B. coagulans (Accession No. AB240205). The dissimilatory sulfite reductase (Dsr) and the nitrite reductase (nirS) genes were successfully amplified and cloned from strain SN22-2. The removal efficiencies of NO3 and SO4 2were up to 96.48 and 97.98% when the initial concentrations of NO3 and SO4 2were 4368.45 and 586.70 mg/L, respectively. High activities of nitrite reductase and sulfate reductase were detected in the culture medium of SN22-2. The analysis of gene sequences and the enzyme activities as well as the nitrate and sulfate removal efficiency data confirmed that strain SN22-2 had simultaneous denitrifying and sulfate reducing capabilities. The characterization of the present isolate had important ecological implications in treating organic wastewater containing high concentration of sulfate and nitrogen.