Abstract
Biosurfactants synthesized by microorganisms are chemically diverse and have gained interest industrially due to their surface and interfacial tensions-reducing activities. In this study Bacillus species from contaminated soils were screened and characterized for biosurfactant production. The study was carried out at the Microbiology Laboratory, Federal University of Agriculture Makurdi, Nigeria. The Bacillus species were isolated from kerosene shops, palm oil shops, nearby restaurants, mechanic workshops and abattoir effluents- contaminated soil samples collected from Makurdi metropolis. The Bacillus spp. were screened for biosurfactants production potentials using various screening methods (oil spreading, beta haemolysis, drop collapse and emulsification index). Specific primers were used to amplify the srfAA (surfactin gene) gene in the Bacillus isolates and the nucleotide sequences were determined at Inqaba Biotec, South Africa. The screening results were statistically analysed using analysis of variance (ANOVA) at 95 % confidence level. Isolate RT7(4)B exhibited the ability to produce biosurfactant, as well as the highest emulsification index (E24) of 73.25 % while isolate PO7(3)C gave the highest oil displacement of 6.77 mm. The supernatant obtained from isolate RT7(4)B showed reduction in surface tension of up to 30.26 mN/m. The isolates gave positive results for biosurfactant production when subjected to drop collapse and Beta haemolytic tests. The Polymerase chain reaction (PCR) results revealed amplifications of srfAA gene from 7 isolates. Based on these findings, the isolates used in this study can be utilized for biosurfactant production, and can also be useful for bioremediation and industrial biotechnology applications.
 Keywords: Biosurfactants; emulsification index; Bacillus; surface tension; Drop collapse
Highlights
IntroductionThe Bacillus spp. were screened for biosurfactants production potentials using various screening methods (oil spreading, beta haemolysis, drop collapse and emulsification index)
The Bacillus species were isolated from kerosene shops, palm oil shops, nearby restaurants, mechanic workshops and abattoir effluentscontaminated soil samples collected from Makurdi metropolis
Among the isolates obtained from the different contaminated soil samples, the potential biosurfactantproducing isolates were confirmed as Bacillus licheniformis, Bacillus subtilis, Bacillus cereus, Bacillus thuringiensis and Lysinibacillus fusiformis by morphological and biochemical characteristics (Table 1)
Summary
The Bacillus spp. were screened for biosurfactants production potentials using various screening methods (oil spreading, beta haemolysis, drop collapse and emulsification index). Results revealed amplifications of srfAA gene from 7 isolates. Based on these findings, the isolates used in this study can be utilized for biosurfactant production, and can be useful for bioremediation and industrial biotechnology applications. Bacillus species have been used in many industrial processes ; several studies have implicated them in producing lipopeptide type of biosurfactant (Saisa-ard et al, 2013; Anitha et al, 2015; Okore et al, 2017). The srfAA found in the srfA operon plays a major function in the biosynthesis of biosurfactants (Roongsawang et al, 2002)
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