Differences of antibacterial activity spectra and properties of bacteriocins, produced by Geobacillus sp. bacteria isolated from different environments

Ability of bacteriocins to inhibit pathogenic bacteria may depend on the environment inhabited by the producing strain. However, there are just few reports on bacteriocin-producing thermophilic bacteria from unconventional environments. Therefore, in this work we investigated differences in antibacterial activity spectra of microorganisms isolated from two different environments: the oil wells (first collection) and surface soil above the oil pools (second collection). All strains were Gram-positive, rod-shaped, thermophilic and endospore forming bacteria. Using spot-on-lawn method we have demonstrated that strains from the second collection possess higher and broader antibacterial activity spectra than first collection strains. Furthermore, all strains were active against at least 1 of 19 tested pathogenic bacteria. Analysis of antibacterial compounds has shown that all of them were stable in broad temperature and pH ranges, sensitive to proteolytic enzymes, proving their proteonaceus nature. They were all secreted during the exponential growth phase and active against closely related thermophilic bacteria, which suggest that these substances are most likely bacteriocins. Most of the bacteriocins had molecular masses under 20 kDa. Plasmid isolation and elimination experiments suggest that bacteriocins are most likely chromosome-encoded. Our results confirm the differences between antibacterial spectra of bacteriocins produced by bacterial strains isolated from different environmental niches