Isolation and Screening of Biosurfactant-Producing Bacteria from Hydrocarbon-Contaminated Soils in Awka, Southeast, Nigeria

Abstract

Background: Biosurfactants are a variety of groups of active compounds produced by various types of microorganisms. Bacterial surfactants are suitable for a range of applications in the oil industry, food, agriculture, pharmaceutical, cosmetics and bioremediation. Therefore, the search for sustainable alternatives to production of chemical biosurfactant is widely being encouraged. Aim: The present study aimed to isolate and screen bacterial species for biosurfactant production. Methodology: Two hundred soil samples collected from hydrocarbon contaminated soils in Awka, Nigeria, were cultured on casein starch agar. The isolates were screened for biosurfactant production stability and antimicrobial activity. Results: Primary screening on the 87 recovered isolates using drop collapse, oil spreading, haemolysis tests showed that 16 isolates (18.39%) were biosurfactant producers. Secondary screening resulted in 9 isolates with good emulsification index (E24) ranging from 42.18% to 74.07%. The culture supernatant of the isolates containing biosurfactants were stable at varying pH (2 – 12), temperature (4 - 121˚C) and salinity (2 – 20%). Most isolates have antimicrobial activity against Escherichia coli and Staphylococcus aureus. Based on oil spreading, emulsification index and antimicrobial activity, four of the isolates, ASP, AS1, DS4, DS8, were selected as most efficient in biosurfactant production. Phylogenetic analysis based on 16S rRNA genes classified ASP as Streptomyces sp, AS1 as Actinomyces sp, DS4 and DS 8 as species of Alcaligenes faecalis. Conclusion: All the species investigated were observed to be active biosurfactant producers. The stability of the biosurfactants, and their antimicrobial nature, make them suitable candidates for use in various industrial sectors.