Assessment of four different methods for selecting biosurfactant producing extremely halophilic bacteria

Abstract

Biosurfactants are surface active agents with broad range commercial applications in various industries and have considerable advantages over their chemical counterparts. In this study, drop collapse assay, oil spreading assay, emulsification assay and surface tension measurement were compared for their reliability and ease of use to screen biosurfactant producing six extremely halophilic bacteria isolated from saline soil of Chott El Hodna-M’sila (Algeria), which is considered as a thalassohaline environment. Results from screening methods revealed that, CH2 and CH5 strains are potential candidates for biosurfactant production. Among these, there was a very strong negative linear correlation between the emulsification index and surface tension (r_s= - 0.987) and a strong negative linear correlation between the oil spreading technique and surface tension (r_s= - 0.971) and a weaker negative correlation between the drop collapse method and surface tension (r_s= - 0.807), suggesting that strains highly active in any one of these methods were active in other three methods. As every method has its advantages and disadvantages, a combination of different methods is appropriate for a successful screening.

Key words: Biosurfactant, drop collapse, emulsification stability, extremely halophilic bacteria, oil spreading, surface tension.