Production of a Novel Thermophilic and Solvent-Tolerant Lipase by Streptomyces sp.: Influence of Organic Solvents

Abstract

A thermophilic Streptomyces sp. producing an extracellular alkaliphilic lipase was selected after screening of 30 bacterial isolates obtained from a water sample of a hot-spring. The Streptomyces sp. designated STL-D8 produced a maximum zone of hydrolysis on the tributyrin (0.5 % v/v) agar plate during primary screening. This bacterial isolate produced 16 U/ml of lipase in the broth containing DMSO (5 % v/v) at 55o C and pH 8 in 48 h. Supplementation of production broth with cottonseed oil (2 %, v/v) enhanced the lipase activity to 17.8 U/ml. Carbon and nitrogen sources were optimized and a mild increase in lipase activity (18.9 U/ ml) was achieved with glucose (0.4 % v/v) added to the production broth. The lipase production by Streptomyces sp. further increased in the presence of yeast extract (0.4 % w/v; 19.6 U/ml) and NaNO3 (0.4 % w/v 24.4 U/ml). Thus a production broth containing cottonseed oil, glucose, yeast extract and NaNO3 was used to optimally produce extracellular lipase by Streptomyces sp. in the presence of selected solvents (dimethyl sulfoxide (DMSO), diethylphathalate (DEP), toluene, xylene, n-pentane, n-hexane, n-heptane, methanol, ethanol, npropanol, isobutanol and n-octanol) added to the broth at 10-40 % (v/v) concentrations. The lipase production was least affected by DMSO, n-pentane and n-hexane (40 % v/v). The lipase production occurred frequently at higher solvent concentration and both the hydrophobic nature (Log P value) as well as the nature of groups in the organic solvent(s) appear to affect the cell growth and lipase production by Streptomyces sp.