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Pak. J. Bot., 42(6): 4285-4298, 2010.

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TEHREEMA IFTIKHAR*^{2, 1}, MUBASHIR NIAZ^@ AND IKRAM UL HAQ¹

Abstract: This is a comparative study for the optimization of cultural conditions for both wild and mutant strains of R. microsporous var. oligosporus. Out of all the 7 different culture media evaluated, M5 gave highest units of extracellular lipases 3.16 ± 0.02^a U mL^-1 (W) and 10.99±0.02^a U mL^-1 (M). The effect of incubation temperature (15-45^oC), initial pH (4.0 -10.0), inoculum size (0.5-3.5 mL) and volume of the medium (25-150 mL) on the production of extracellular lipase by both wild and mutant strains was investigated in shake flask. The rate of fermentation was also studied and found that maximum extracellular lipase was obtained after an incubation of 48 h by both wild and mutant strains. In the presence of soybean meal (0.4%) the maximum lipolytic activity was approximately 1.27 (W) & 1.42 (M) times higher than that in the absence of additive. Different additional carbon sources were added to basal medium with the aim of improving extracellular lipases production. Tween 80 showed considerable increase in lipases production by both wild (5.52 ± 0.005^a U mL^-1) and mutant (19.13 ± 0.005^a U mL^-1) strains as compared to others. Maximum extracellular activity of lipase 5.85 ± 0.01^a U mL^-1 (W) & 28.32 ± 0.01^a U mL^-1 (M) was obtained when 0.8% of casein was added in the fermentation medium as an organic nitrogen source. Maximum extracellular production of lipases 8.31 ± 0.01^a U mL^-1 (W) and 34.34 ± 0.01^a U mL^-1 (M) was observed when 0.8% (NH₄)₂C₂O₄ was added in the substrate as an additional inorganic nitrogen source.

*Corresponding author: pakaim2001@yahoo.com/tehreema@gmail.com; 92-42-36854508 (Res), 92-41-9201488 (Off)