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The present study enlightens the role of the antagonistic potential of nonpathogenic strain B21 against sulfate-reducing bacteria (SRB) consortium. The inhibitor effects of strain B21 were compared with those of the chemical biocide tetrakishydroxymethylphosphonium sulfate (THPS), generally used in the petroleum industry. The biological inhibitor exhibited much better and effective performance. Growth of SRB in coculture with bacteria strain B21 antagonist exhibited decline in SRB growth, reduction in production of sulfides, with consumption of sulfate. The observed effect seems more important in comparison with the effect caused by the tested biocide (THPS). Strain B21, a dominant facultative aerobic species, has salt growth requirement always above 5% (w/v) salts with optimal concentration of 10-15%. Phylogenetic analysis based on partial 16S rRNA gene sequences showed that strain B21 is a member of the genus Bacillus, being most closely related to Bacillus qingdaonensis DQ115802 (94.0% sequence similarity), Bacillus aidingensis DQ504377 (94.0%), and Bacillus salarius AY667494 (92.2%). Comparative analysis of partial 16S rRNA gene sequence data plus physiological, biochemical, and phenotypic features of the novel isolate and related species of Bacillus indicated that strain B21 may represent a novel species within the genus Bacillus, named Bacillus sp. (EMBL, FR671419). The results of this study indicate the application potential of Bacillus strain B21 as a biocontrol agent to fight corrosion in the oil industry.

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