microbial diversity of krishna river delta mangrove ecosystem rhizosphere soils bioprospecting for novel bioemulsifier producers

Abstract

Marine microbial biosurfactants are of great importance due to their structural and functional diversity and industrial applications. Oil contaminated mangrove sediments were collected from Krishna river mangrove ecosystem, Andhra Pradesh, India. A total of 33 strains belonging to different genera were selected and identified in preliminary screening experiments. Among them, Pseudomonas aeruginosa strain KVD-HR42 showed positive results in all the screening experiments as well as good emulsification activity (E24%) and surface tension reduction potential. Therefore, strain KVD-HR42 was selected for further studies. Various nutritional (carbon, nitrogen, amino acids) and environmental factors (temperature, pH, NaCl) were tested for optimization of biosurfactant production. To achieve cost-effective fermentation with high yields, non-edible karanja oil was used as sole carbon source. Biosurfactant production was optimized with statistical approaches. Based on the results of Plackett-Burman design, first-order polynomial model was developed and the following significant variables were determined viz., Karanja oil, sodium nitrate and pH. Response surface methodology experimental design was performed by Box Behnken design to study the concentration of each component. The response plots resulted in the following optimized conditions; Karanja oil (23.85 g/L) sodium nitrate (9.17 g/L) and pH (7.8) which resulted in enhanced (1.2 fold increase) biosurfactant production of 5.90±2.1 g/L at 48 h, and 37oC temperature. Rhamnolipid biosurfactant components were purified and separated in preparative silica gel column chromatography, thin-layer chromatography and high-performance liquid chromatography. The major rhamnolipid components were characterized by nuclear magnetic resonance and electro spray ionization mass spectrometry, as a mixture of di-rhamnolipids and mono-rhamnolipids.