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Characterization of a lipopeptide biosurfactant produced by a crude-oil-emulsifying Bacillus sp. I-15

Ismail, Wael, Al-Rowaihi, Israa S., Al-Humam, Abdulmohsen A., Hamza, Riyad Y., El Nayal, Ashraf M., Bououdina, Mohamed
International Biodeterioration & Biodegradation 2013 v.84 pp. 168-178
Bacillus (bacteria), RNA, bacteria, biosurfactants, carbon, clones, culture media, emulsifiers, glucose, infrared spectroscopy, lipopeptides, operon, petroleum, ribosomal DNA, surface tension, thin layer chromatography
Petroleum-polluted environmental samples were collected to isolate and characterize biosurfactant-producing bacteria. Culturing of the collected samples in LB-broth and enrichments in chemically defined medium (CDM) with various carbon sources yielded 51 strains, some of which produced biosurfactants/bioemulsifiers when challenged with crude oil as a sole carbon source. The I-15 isolate, a Gram-positive, motile bacillus, emulsified crude oil in CDM without reduction in surface tension. Compared to LB-grown cells, the crude oil-grown I-15 cells were surrounded by a transparent zone and produced heavily mucoid colonies on LB-agar plates. When grown with glucose as a sole carbon source, the I-15 strain produced a biosurfactant extracellularly, resulting in a 65% reduction in surface tension of the growth medium. The glucose-grown cells were coccoid to irregular in shape. Biosurfactant production was concomitant with reversible growth decline interrupting the exponential phase. Infrared spectroscopy and thin layer chromatography suggested a lipopeptide structure for the crude biosurfactant. Partial sequences of 10 16S rDNA gene clones from the I-15 strain were highly similar to those of various members of the family Bacillaceae. The I-15 strain is a promising biosurfactant producer and is probably an active indigenous crude oil degrader. Biosurfactant production is accompanied by morphological and physiological alterations. The I-15 strain possesses intragenomic heterogeneity in the rrn (RNA) operons.