ISOLATION OF BIO-SURFACTANT PRODUCING ACTINOMYCETES FROM TERRESTRIAL AND MARINE SOILS

Bio-surfactants, produced by microorganisms are important biotechnology products, owing to their modes of action, low toxicity, relative ease of preparation, and widespread applicability as an industrial, medicinal and in food industries. The present study was done to isolate the bio-surfactant producing Actinomycetes from three different types of soil samples contaminated with petroleum spillages from Naval Dockyard (NDYS), deep marine sediment from sea-bed (DMS), and with poultry litter (PLS), collected from around Visakhapatnam. Thirty isolates of soil Actinomycetes were initially screened in Humic-acid vitamin-salts agar-plates, to identify their bio-surfactant activity by Oil-displacement method. Only seven of these thirty isolates, namely, PLS-1, PLS-2, PLS-4, PLS-9, NDYS-3, NDYS-4, and DMS-1, showed promising bio-surfactant activity, compared to sodium-laryl-sulfate as standard. These seven isolates were further subjected to preliminary screening methods (modified drop collapse method, Para film-M method, and lipase activity method), to identify bio-surfactant production. Three of these seven isolates, namely, PLS-1 from poultry littered soil, NDYS-4 from petroleum contaminated soil from the naval dockyard, and DMS-1 from deep marine sediment, showed maximum bio-surfactant production. Of these three, only two isolates showed a positive result for phenol H₂SO₄ and blue agar plate methods. This indicated that the isolated bio-surfactant was Rhamnolipid in nature. This result was further confirmed by orcinol assay, taking L-rhamnose as standard. Bio-surfactant production from these two isolates was further evaluated by surface-tension measurement (Drop-count) method and emulsification index. It was concluded that this Rhamnolipid has permeabilizing effects on Gram-positive and Gram-negative human bacterial strains, reinforcing their potentiality in antibacterial activity.