Deep-sea fungi as a source of alkaline and cold-tolerant proteases
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Fungi from coastal environments have been widely studied with respect to the production of secondary metabolites and biotechnologically useful lignocellulolytic enzymes. A few studies on mycology of deep-sea sediments, however, have been carried out. This paper reports a study on alkaline, coldtolerant proteases from deep-sea fungi. A total of 221 deep-sea isolates of fungi from 5000 m in the Central Indian Basin were screened for the enzyme. Many of these grew and produced alkaline protease at 5 and 30ºC and 1 bar pressure. Aspergillus ustus (NIOCC#20) producing the highest amounts of the enzyme was selected for further studies. The growth yield was substantial at 30 and 5ºC at 1 bar and elevated hydrostatic pressures. The fungus produced alkaline, coldtolerant protease when grown at 30ºC and 1 bar pressure. The enzyme was active at combinations of 30º, 5ºC and 50 and 300 bar pressure. However, protease production was negligible when the fungus was grown at 5ºC, under 1 bar or elevated hydrostatic pressures. The enzyme produced at 30ºC and 1 bar pressure was further characterized. The fungus produced a maximum of 1,639 ACU mL-1 of protease by day 7. The enzyme, with molecular mass of 32 kDa and pI values of 6.6 and 6.9 showed several interesting properties. It had a broad pH range of 6 to 10, with an optimum at pH 9. The optimum temperature for protease activity was 45ºC and approximately 10 % of the activity was retained at 2ºC. The enzyme was totally inhibited in the presence of 2 mM PMSF suggesting it to be a serine protease. It was active in the presence of several commercial detergents at 2 g L-1 concentration and in the presence of 0.5 M NaCl, equivalent to 29 parts per thousand salinity. In the presence of stabilizing agents such as glycerol, CaCl2 its thermostability at 60ºC was enhanced. Heavy metal ions copper, Hg, Fe, Ni and Zn did not inhibit the enzyme activity considerably. This study indicates that fungi from deep-sea sediments could be a useful source of proteases.
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