Evaluation of haloalkaliphilic sulfur-oxidizing microorganisms with potential application in the effluent treatment of the petroleum industry

Haloalkaliphilic sulfur-oxidizing mixed cultures for the treatment of alkaline saline effluents containing sulfide were characterized and evaluated. The mixed cultures (IMP-PB, IMP-XO and IMP-TL) were obtained from Mexican alkaline soils collected in Puebla (PB), Xochimilco (XO) and Tlahuac (TL), respectively. The Ribosomal Intergenic Spacer Analysis (RISA) revealed bacteria related to Thioalkali-bacterium and Thioalkalivibrio in IMP-XO and IMP-PB mixed cultures. Halomonas strains were detected in IMP-XO and IMP-TL. In addition, an uncultured Bacteroides bacterium was present in IMP-TL. Mixed cultures were evaluated at different pH and NaCl concentrations at 30 degrees C. IMP-PB and IMP-TL expressed thiosulfate-oxidizing activity in the 7.5-10.5 pH range, whereas IMP-XO presented its maximal activity with 19.0 mg O-2 g(protein)(-1) min(-1), at pH 10.6; it was not affected by NaCl concentrations up to 1.7 M. In continuous culture, IMP-XO showed a growth rate of 15 day(-1), productivity of 433.4 mg(protein) l(-1) day(-1) and haloalkaliphilic sulfur-oxidizing activity was also detected up to 170 mM by means of N-methyl-diethanolamine (MDEA). Saline alkaline soil samples are potential sources of haloalkaliphilic sulfur-oxidizing bacteria and the mixed cultures could be applied in the treatment of inorganic sulfur compounds in petroleum industry effluents under alkaline saline conditions.