Biosurfactant – producing bacteria and characteristics of selected biosurfactant from marine samples

Abstract

Oil Spills can occur due to transportation, natural seeps or during routine maintenance of infrastructure. These oil spills devastate the nature and alter the microbial population at the polluted sites. An increase in the concern about environmental protection has recently caused the consideration of biosurfactants as alternatives to synthetic surfactants. Biodegradation by microorganisms is more favorable than chemical treatment for dealing with oil pollution since the microbes modify crude oils in beneficial ways and the end products are environmentally safe to all living things. Due to environmentally friendly character we tried to apply for controlling various environmental pollution. Biosurfactants are a group of surface-active molecules with hydrophilic and hydrophobic moieties. They produced in living surfaces, mostly on microbial cell surfaces or excreted extracellular. Biosurfactants have outstanding advantages, such as high biodegradability, low toxicity, environmental compatibility, high selectivity, and specific activity at extreme temperatures, pH, and salinity, among others. In present study biosurfactants – producing marine bacteria were isolated from oil-spilled seawater collected from Arabian Sea, Mumbai. Total four biosurfactant activity assay tests were used to determine biosurfactant producing activity of marine bacteria. Different screening methods namely, Haemolytic activity assay test, oil displacement test, drop collapsing test and emulsification test were employed. Hemolysis was used as a criterion for the primary isolation of biosurfactant producing-bacteria. Two strains among thirty strains showed highest biosurfactant activity by exhibiting highest emulsification activity (70.5+0.55 and 65.0+0.50) toward n – hexadecane. In addition, selected strains exhibited the highest activity for oil displacement test (3.14+0.02 and 2.55+0.03) and highest emulsification activity against mixtures of different oils (Petroleum + kerosene + diesel in 1:1:1 ratio). Two strains named B4 and B6 were identified by various identification tests. The isolated cultures were designated as B4 (Pseudomonas sp.) and B6 as (Bacillus sp.)The emulsification activity against n – hexadecane of crude extract of strain named B4 and B6 was stable over a different range of NaCl (0-13%). Biosurfactant crude extract from strain B4 and B6 exhibited the increasing emulsifying activity toward n- hexadecane as NaCl increased up to 7%, but emulsification activity was decreased when concentration of NaCl was decreased from 9 % onwards. Above 11% NaCl, no activity was obtained.