Characterization of antimicrobial activity of culturable bacteria isolated from Krubera-Voronja Cave

Abstract

In the present study we aimed to perform the first analysis of antimicrobial activity of bacteria isolated from Krubera-Voronja Cave, with the main focus on their activity against Grampositive bacteria, including Gram-positive pathogens. Using five different media, in total 874 heterotrophic cultures were isolated from water and sediment samples collected in Krubera-Voronja Cave at a depth from 220 m to 1640 m. 14.0% of all isolates demonstrated antibacterial activity against Gram-positive and Gram-negative test microorganisms. Our results show that this percentage was not uniform; it increased with the sampling depth and was the highest in the lower part of the cave. 24 isolates were active exclusively against Gram-positive test strains Micrococcus luteus and Bacillus thuringiensis. Two isolates, namely strains 1350R2-TSA30-6 and 1410WF1-TSA30-2, were chosen for the further work because of the high and comparable activity against both Gram-positive test microorganisms. It was determined that both strains belong to the family Bacillaceae in phylum Firmicutes. The detailed bioactivity analysis of these two Gram-positive strains revealed the different mixtures of volatile compounds with antibacterial activity. The main antibacterial compounds of the strain 1350R2-TSA30-6 are pyrrolopyrazines pyrrolo[1,2-a]pyrazine-1,4-dione, hexahydro- 3-(2-methylpropyl)- and pyrrolo[1,2-a]pyrazine-1,4-dione, hexahydro-3-(phenylmethyl)-. The main antibacterial compound of the strain 1410WF1-TSA30-2 is 1,2-benzenedicarboxylic acid, bis(2-methylpropyl) ester. Mixtures of the volatile antimicrobial compounds of both strains were antagonistic against Gram-positive strains isolated from Krubera-Voronja Cave, and their activity against Gram-positive pathogenic bacteria substantially differed.

Keywords

• antimicrobial
• Bacillus
• cave microorganisms
• Krubera-Voronja Cave
• volatile compound