Analysis of a microbial community oxidizing inorganic sulfide and mercaptans

Successful treatment of refinery spent-sulfidic caustic (which results from the addition of sodium hydroxide solutions to petroleum refinery waste str eams) was achieved in a bioreactor containing an enrichment culture immobil ized in organic polymer beads with embedded powdered activated carbon (Bio- Sep). The aerobic enrichment culture had previously been selected using a g as mixture of hydrogen sulfide and methyl mercaptan (MeSH) as the sole carb on and energy sources. The starting cultures for the enrichment consisted o f several different Thiobacilli spp. (T. thioparus, T. denitrificans, T. th iooxidans, and T. neopolitanus), as well as activated sludge from a refiner y aerobic wastewater treatment system and sludge from an industrial anaerob ic digester. Microscopic examination (light and SEM) of the beads and of mi crobial growth on the walls of the bioreactor revealed a great diversity of microorganisms. Further characterization was undertaken starting with cult urable aerobic heterotrophic microorganisms (sequencing of PCR-amplified DN A coding for 16S rRNA, Gram staining) and by PCR amplification of DNA codin g for 16S rRNA extracted directly from the cell mass, followed by the separ ation of the PCR products by DGGE (denaturing gradient gel electrophoresis) . Eight prominent bands from the DGGE gel were sequenced and found to be cl osest to sequences of uncultured Cytophagales (3 bands), Gram-positive cocc i (Micrococcineae), alpha proteobacteria. (3 bands), and an unidentified be ta proteobacterium. Culturable microbes included several genera of fungi as well as various Gram-positive and Gram-negative heterotrophic bacteria not seen in techniques using direct DNA extraction.