Suppasil Maneerat and Kulnaree Phetrong

pp. 781 - 791

Abstract

Biosurfactant-producing marine bacteria were isolated from oil-spilled seawater collected from harbors and docks in Songkhla Province, Thailand. Haemolytic activity, emulsification activity toward nhexadecane, emulsion of weathered crude oil, drop collapsing test as well as oil displacement test were used to
determine biosurfactant producing activity of marine bacteria. Among two-hundred different strains, 40 strains exhibited clear zone on blood agar plates. Only eight strains had haemolytic activity and were able to emulsify weathered crude oil in marine broth during cultivation. Eight strains named SM1-SM8 were identified by 16S rRNA as Myroides sp. (SM1); Vibrio paraheamolyticus (SM2); Bacillus subtilis (SM3);Micrococcus luteus (SM4); Acinetobacter anitratus (SM6); Vibrio paraheamolyticus (SM7) and Bacillus pumilus (SM8). However, SM5 could not be identified. Strain SM1 showed the highest emulsification activity against weathered crude oil, by which the oil was emulsified within 24 h of cultivation. In addition, strain SM1 exhibited the highest activity for oil displacement test and emulsification test toward n-hexadecane. The emulsification activity against n-hexadecane of crude extract of strain SM1 was stable over a broad range of temperature (30-121°C), pH (5-12) and salt concentration (0-9% NaCl), whereas CaCl₂ showed an adverse effect on emulsifying activity.