Identification of antimicrobial volatile compounds produced by the marine bacterium <i>Bacillus amyloliquefaciens</i> strain S13 newly isolated from brown alga <i>Zonaria tournefortii</i>

Abstract

The present work focuses on the production and identification of microbial volatile organic compounds (VOCs) associated with antimicrobial properties from Bacillus amyloliquefaciens strain S13 newly isolated from the brown alga Zonaria tournefortii. For this purpose, strain isolated was grown on Luria–Bertani culture medium with 15‰ (w/v) NaCl, with an initial pH 7.2 at 30°C for 48 h under continuous agitation at 180 rpm. The VOCs were sequentially extracted from the supernatant containing extracellular compounds by hydrodistillation using a Clevenger apparatus and analyzed by gas chromatography-mass spectrometry. The main volatile compounds identified are 13-epi-manoyl oxide (29.39%), manool (17.39%), 15,16-dinorlabd-8(20)-en-13-one (13.17%), labda-8(17),13Z-dien-15-ol (9.51%) and 3α-hydroxy-13-epi-manoyl oxide (5.26%) belonging to the labdane-type diterpenes class. Other compounds representing different chemical classes were also identified in the chemical composition. The produced volatile fraction was tested in vitro on antimicrobial activity and their minimum inhibitory concentration (MIC) values against pathogenic microorganisms were estimated. The results indicated that among the tested microorganisms, Saccharomyces cerevisiae (24 ± 0.3 mm; MIC = 64 μg/mL) was the most susceptible to volatile fraction followed by Agrobacterium tumefaciens (20 ± 0.5 mm; MIC = 128 μg/mL) and Bacillus subtilis (18 ± 0.8 mm; MIC = 128 μg/mL).