Production, characterization and bioactivities of biosurfactants from newly isolated strictly halophilic bacteria

Abstract

Eight distinct halophilic bacteria isolated from extreme saline soil samples of Khewra Salt Mines, Pakistan, were investigated for biosurfactant production. Isolates were identified by physiological, phenotypic and genetic characterization. Using 16S rDNA sequence analysis, the strains MB590, MB591, MB593, MB594, MB595 and MB596 were identified as Halomonas elongata, MB588 as Halobacillus karajiensis, and MB589 as Alkalibacillus almallahensis. Preliminary screening of biosurfactant production in halophilic bacteria was done by multiple screening assays. All biosurfactants showed significant emulsification properties and remarkably low surface tension values (up to 16.5 dynes/cm). Structural characterization of partially purified biosurfactants using Gas chromatography–mass spectrometry (GC–MS) and Fourier-transform infrared spectroscopy (FTIR) techniques indicated different fatty acids, glycolipid derivatives and a novel antimicrobial peptide furanomycin. These biosurfactants exhibited strong bioactivities against bacterial/fungal pathogens i.e. Klebsiella pneumoniae (86.5 %), Staphylococcus aureus (97.75 %), Bacillus subtilis (97 %), Enterococcus faecalis (97.6 %), E. coli (54.5 %), Aspergillus niger (87.75 %), Aspergillus fumigatus (93.1 %), Aspergillus flavus (80.4 %), and Fusarium solani (89.05 %). Additionally, biosurfactants also showed 85 % free radical scavenging activity indicating their antioxidant potential. The present study revealed the potential of halophilic bacterial biosurfactants as effective antimicrobial agents against various pathogens, and their possible applications in the biomedical field.