PH-DEPENDENCE AND THERMOSTABILITY OF LIPASES FROM CULTURES FROM THE ARS CULTURE COLLECTION

Previously we used a simple, sensitive agar plate method to screen lipase activity from 1229 selected cultures including 508 bacteria, 479 yeasts, 230 actinomycetes and 12 fungi covering many genera and species. About 25% of the cultures tested were lipase-positive. These lipase-positive strains were further classified as good, moderate or weak enzyme producers. We have expanded our screening method to focus specifically on the pH dependence and thermostability of these lipase activities. The lipases exhibited various pH sensitivities and were divided into three groups: (i) lipases which are active at pH 5.5 but not at pH 7.5-produced by 36 bacteria, 23 yeasts and four actinomycetes; (ii) lipases which are active at pH 7.5 but not at pH 5.5-produced by 17 bacteria, four yeasts, two actinomycetes and one fungus; and (iii) lipases which are active at both pH 5.5 and pH 7.5-produced by 112 bacteria, 90 yeasts, 15 actinomycetes and five fungi. By screening at 60-degrees-C and pH 9.0, we further identified 50 bacteria and 26 yeasts that produce thermostable alkali-tolerant lipases. Product analyses confirmed our screening results. Lipases with specific pH dependency and thermostability have potential to be developed into industrial enzymes.