Biosurfactant production by haloalkaliphilic Bacillus strains isolated from Red Sea, Egypt

Abstract

This study aimed to produce biosurfactant by extremophilic marine bacteria. Twenty-one oil-spilled seawater samples were collected from Shalateen, Red Sea, Egypt. Two promising morphologically distinct biosurfactant-producing marine bacteria, SH20 and SH24, were selected. They were grown on minimal salt medium (MSM) and the biosurfactant production was evaluated and detected after 24 h using drop collapsing test, blood hemolysis, emulsification index and surface tension. SH20 and SH24 isolates showed the highest emulsification index 57 and 56%, respectively, and have positive results for hemolysis and drop collapse. The two isolates were identified using 16 S rRNA as Bacillus amyloliquefaciens SH20 and Bacillus thuringiensis SH24. Stability of biosurfactant production by both strains was observed at moderate temperature (30 °C), high alkalinity at pH (11) and high salt concentration (15%). An increase of emulsification index tended to be 60 and 69%, respectively, considering the two strains haloalkiphilic bacteria. To study the stability mechanism for extremophilic biosurfactant producers, the protein profile was determined using SDS-PAGE electrophoresis showing some new detected proteins depends on their culturing conditions. Partially purified biosurfactant from the most active strain B. amyloliquefaciens SH20 was chemically determined by FTIR and GC–MS analysis showed characteristic bands, revealed the presence of non-anionic didemnin surfactant.