STUDIES ON THERMOSTABLE LIPASES OF ALKALOPHILIC BACTERIA ISOLATED FROM AN ALKALINE LAKE

Abstract

Lipases are the triacylglycerol acylhydrolase (E.C.3.1.1.3), and ubiquitous enzyme. Naturally they act on glycerides. Microbial lipases are commercially significant because of low production cost, greater stability and wider availability. Lipases are serine hydrolases which act on lipid water interface. Lipase in the cell may be intracellular, cell bound, extracellular or cytosolic depends on type of cell. They are generally glycoprotein but some are lipoprotein. They catalyses variety of reactions like acidolysis, transesterification, esterification, interesterification, aminolysis, hydrolysis and alcoholysis. Lipase acts in substrate specific and non specific manner, resulting in complete hydrolysis of triglycerides into fatty acids and glycerol. Lipase catalyses various reactions as it have ability to act on wide range of substrates which may be natural or artificial. Lipases are stable in organic solvents, wide pH and temperature and different metal ions. Alkalophilic thermophiles have great potential in detergent and leather industries. The lipases find wide applications in fat and oleochemical industry, textile, detergent, food processing, flavour development and quality improvement, resolution of racemic mixture, as diagnostic tool, in bakery, confectionary and cheese flavouring, cosmetics, tea processing, medical, biosensors, degreasing of leather, effluent treatment, oil biodegradation, paper and pulp, biodiesel production etc. There was a seasonal variation observed in the physico-chemical characteristics of three samples collected. BOD and COD found to be higher, TDS, TSS and TS were found to be much higher whereas, pH, temperature and total alkalinity were found to be unaltered. Total 22 different bacteria were isolated and screened for their ability to secrete extracellular lipase enzyme by strategic screening using tributyrine agar plate and Rhodamine B agar plate assay method. The zone of clearance around the growth of organisms was observed. The zone was due to hydrolysis of tributyrine oil due to action of extracellular lipase secreted by an organism. The true lipase producers only showed orange colored fluorescence when exposed to UV light. The bacterial isolates were subjected to check their ability to grow on different medias. Only 9 isolates showed growth on all media. Nine representative isolates were subjected to surface and submerged growth condition to check their ability to secrete lipase more extracellularly. Cultures labeled as SSL-3 (0.130 µM/ml), SSL-4 (0.168 µM/ml) and SSL-12 (0.131µM/ml) gave highest lipase production under stationary fermentation condition newline