Characterization of cell-associated bioemulsifier from Myroides sp. SM1, a marine bacterium

Abstract

Emulsification activity of bioemulsifier derived from Myroides sp. SM1, a marine bacterium, isolated from oil-spilled seawater in Songkhla Lake, Thailand, was investigated. Cell suspension and culture supernatantwere able to emulsify weathered crude oil effectively, especially with increasing incubation time as evidenced by the smaller droplet size of weathered crude oil. Weathered crude oil in marine broth inoculatedwith Myroides sp. SM1 was completely emulsified within 6 h with the coincidental attachment of cells around the oil droplet. When mixing the cells with various hydrocarbons, cells migrated to hydrocarbon phasedifferently. Myroides sp. SM1 adhered to weathered crude oil to the highest extent, indicating that those cells used had the high affinity to weathered crude oil. However, weathered crude oil and other hydrocarbons were not used by Myroides sp. SM1 as sole carbon source in a minimal salt medium. Myroides sp. SM1 cultivatedin marine broth reached stationary phase at 24 h; however, no differences in cell density were observed from 30 h to 48 h of cultivation time. Emulsifying activity toward weathered crude oil was found in cellsuspension cultivated for 12 h and no differences in activities were noticeable in those cultivated for 12-48 h. Chloroform-methanol mixture at the ratio of 1:1 (v/v) was the most effective solvent to extract cell-associated bioemulsifier from Myroides sp. SM1. The crude bioemulsifier was capable of emulsifying weathered crudeoil in a broad pH range (5-12) and in the presence of NaCl up to 1.54 M and MgCl2 up to 0.1 M. The bioemulsifier was stable when heated at a temperature ranging from 30 to 121oC.

Keywords

• cell-associated bioemulsifier
• Myroides sp. SM1
• marine bacteria
• weathered crude oil
• oil-spilled seawater