The effect of incubation time, temperature and pH variations on the surface tension of biosurfactant produced by Bacillus spp.

Abstract

The efficiency of biosurfactant are measured by the required concentration of surfactant to produce significant reduction in the surface tension of liquid i.e. water. Factors such as incubation period, temperature and pH can affect the growth of biosurfactant producing bacteria, their ability to produce biosurfactant and reduce surface tension. Hence, the aim of this study is to investigate the effect of incubation time, temperature and pH variations on the surface tension of biosurfactant produced by Bacillus subtilis and Bacillus tequilensis. It was found as the growth of both B.subtilis and B.tequilensis and biosurfactant formation increase with the incubation period, there is a reduction in surface tension. The surface tension was reduced to 30 mN/m by B.subtilis culture after 18 hours. Meanwhile, the surface tension by B.tequilensis culture successfully reduced after 48 hours of incubation period. Cell free culture of B.subtilis and B.tequilensis also exhibited a good level of temperature stability where high temperatures (45°C and 55°C) did not cause any significant effect in the surface tension. As for the effect of pH, B.subtilis and B.tequilensis tend to reduce the surface tension more, which was between 30 to 40 mN/m at higher pH (6, 8, 10, 12). The findings revealed the applicability of the produced biosurfactant from Bacillus spp. depends on their incubation time and stability at different temperature and pH.