Screening, stability and antibacterial potential of rhamnolipids from Pseudomonas sp., isolated from hydrocarbon contaminated soil.

ABSTRACT

Surfactant plays an important role in industrial application such as oil recovery, lubricants and emulsifier. But chemical surfactants are toxic to human and other small animals. In recent years, biological based surfactants have gained increasing attention due to their ecofriendly in nature. The present study was focused to isolate biosurfactant producing bacteria, their stability and antibacterial ability from hydrocarbon contaminated and uncontaminated soil collected from different locations in Kanchipuram, Tamil Nadu, India. Biosurfactant producing bacteria were screened by following the haemolytic activity, drop collapsing test, emulsion against kerosene and was further confirmed through surface activity. The stability of the biosurfactant was determined by different physic-chemical conditions like pH, temperature and salinity. A total of 37 strains were selected in three different samples based on cultural characters and finally only 7 strains were confirmed as positive for biosurfactant. Among these strain H11 was considered as potential based on emulsification index (44%), surface activity (34.45 x 10-3 nm-1) and surface tension (23.17 x 10-3 nm-1) and was identified as Pseudomonas sp. The emulsification activity was stable at broad range of pH (4-12), temperature (4-120°C) and salt concentration (0-10%). The biosurfactant was further characterized in HPLC and one major peak was observed at a retention time of 2.033. The antibacterial activity of biosurfactant was high against gram positive pathogenic bacteria than gram negative bacteria. The rhamnolipid produced Pseudomonas sp. may be used as a tool to manage the oil pollution and to control the disease causing bacteria.