Biosurfactant production by Pseudomonas aeruginosa isolated from aquaculture farm soil and its optimisation

Abstract

In the present study, aquaculture farm soil was screened for biosurfactant producing bacteria. A total of 43 morphologically distinct colonies were isolated from the farm soil and their biosurfactant production was evaluated employing different screening methods. Fourteen biosurfactant producing bacterial isolates were selected based on the formation of dark blue halos on cetyl trimethyl ammonium bromide (CTAB) agar, emulsifcation index, oil spreading assay and BATH (Bacterial adhesion to hydrocarbons) assay. Based on the results, the bacterial isolate BHI 9 with highest production of biosurfactant was selected for further studies. The bacterial isolate BHI 9 was found to be Gram negative, slender long rod and oxidase as well as catalyase positive. The isolate was identified as Pseudomonas aeruginosa based on 16S rDNA sequence analysis. Optimisation studies were carried out at different temperatures (25, 30, 35 and 40 degree celsius) using four different carbon sources (1 percentage) i.e., glucose, sucrose, maltose and starch and four nitrogen sources (1percentage) viz., peptone, ammonium nitrate, beef extract and yeast extract, at different pH (6, 7, 8, 9 and 10) and NaCl levels (0.5, 1.0, 1.5 and 2.0 percentage). Emulsification index and bacterial biomass (OD600) were recorded at 24, 48, 72 and 96 h intervals. Optimum conditions for biosurfactant production by this bacterium was obtained when glucose and yeast extract were used as carbón and nitrogen sources respectively, maintaining a temperature of 35 degree celsius pH 8 and NaCl 1.5 percentage, measured in terms of emulsification index and bacterial biomass. This is the first report on biosurfactant producing bacteria isolated from aquaculture farm soil that can find its application in various fields.