Abstract
A thermophilic bacterial strain, Geobacillus sp. ZGt-1, isolated from Zara hot spring in Jordan, was capable of inhibiting the growth of the thermophilic G. stearothermophilus and the mesophilic Bacillus subtilis and Salmonella typhimurium on a solid cultivation medium. Antibacterial activity was not observed when ZGt-1 was cultivated in a liquid medium; however, immobilization of the cells in agar beads that were subjected to sequential batch cultivation in the liquid medium at 60 °C showed increasing antibacterial activity up to 14 cycles. The antibacterial activity was lost on protease treatment of the culture supernatant. Concentration of the protein fraction by ammonium sulphate precipitation followed by denaturing polyacrylamide gel electrophoresis separation and analysis of the gel for antibacterial activity against G. stearothermophilus showed a distinct inhibition zone in 15–20 kDa range, suggesting that the active molecule(s) are resistant to denaturation by SDS. Mass spectrometric analysis of the protein bands around the active region resulted in identification of 22 proteins with molecular weight in the range of interest, three of which were new and are here proposed as potential antimicrobial protein candidates by in silico analysis of their amino acid sequences. Mass spectrometric analysis also indicated the presence of partial sequences of antimicrobial enzymes, amidase and dd-carboxypeptidase.
Highlights
Competition for nutrients and space in a given habitat leads organisms to develop their own strategies for survival and growth, one of which is the secretion of antimicrobial substances resulting in either killing or impairing the growth of competing organisms [1]
A number of studies have reported the production of antibacterial peptides or bacteriocins from extremophiles such as alkaliphilic and thermophilic Bacillus species [3,4,5,6,7] and thermophilic Geobacillus species such as G. thermodentrificans [8] and G. stearothermophilus [9]
Isolation of thermophilic bacterial strains from Zara hot spring sample was performed at 60 ◦C and the isolate Geobacillus sp
Summary
Competition for nutrients and space in a given habitat leads organisms to develop their own strategies for survival and growth, one of which is the secretion of antimicrobial substances resulting in either killing or impairing the growth of competing organisms [1] These antimicrobial substances possess promising clinical and industrial value [2]. Extremophiles, microorganisms living in extreme conditions of pH, temperature, salt concentration, etc., represent one such source [3]. A number of studies have reported the production of antibacterial peptides or bacteriocins from extremophiles such as alkaliphilic and thermophilic Bacillus species [3,4,5,6,7] and thermophilic Geobacillus species such as G. thermodentrificans [8] and G. stearothermophilus [9]
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