ABSTRACT
Surfactants are compounds that lower the surface tension between two phases. Surfactants produced by the biological processes of a number of microorganisms are known as biosurfactants. Their uses cut across a number of industries such as petrochemicals, agrochemicals, metallurgy (mainly bioleaching), foods, cosmetics and pharmaceuticals. This study was aimed at detecting biosurfactant producers among Bacillus sp. isolated from oil polluted soils in Benin City.
Ten soil samples were collected in triplicates from oil spilled soil surfaces of ten different automobile workshops in the Ugbowo and Useluareas of Benin City. Standard bacteriological methods were used for the enumeration of heterotrophic bacterial counts and subsequent isolation of Bacillus sp. from the soil samples using heat shock method. Cultural, morphological, biochemical and molecular techniques were used for the identification of the Bacillus sp. Batch fermentation of Bacillus sp. was carried out on mineral salt medium for 7 days before they were screened for their ability to produce biosurfactants. The biosurfactants were purified and classified using thin layer chromatography. Mean values of the samples were analysed statistically using one-way analysis of variance (one-way ANOVA).
The total heterotrophic bacterial counts ranged from 0.75±0.22×104 cfu/g to 6.92±5.5×104 cfu/g in the sampling locations. The Identified isolates include Bacillus tequilensis, B. subtilis, B. safensis, B. stratosphericus, B. thuringiensis, B. cereus and B. licheniformis.B. tequilensis (20.00 %) was the most frequently isolated organism while the least was B. thuringiensis (8.00 %). Biosurfactant screening showed that all the identified Bacillus sp. isolates were beta haemolytic. All Bacillus isolates except B. stratosphericustested positive to oil displacement and emulsification assay and as such was eliminated as a biosurfactant producer. Isolates had differing emulsification indexes, B. subtilis (51.00 %) had the highest emulsification index while Bacillus thuringiensis (43.00 %) had the least emulsification index. B. tequilensis (0.50) had the least retention factor (RF) value amongst all isolates obtained in the study while B. safensis (0.79) had the highest RF value. All extracted crude biosurfactants were characterized as belonging to the lipopeptide class of biosurfactants. The extracted biosurfactants demonstrated emulsification activity against diesel and kerosene, hence, they can conceivably be employed in the biodegradation of petroleum products. Further study into the enhancement and optimization of biosurfactant production by these organisms is recommended.
