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Rezumat articol ediţie STUDIA UNIVERSITATIS BABEŞ-BOLYAI
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Rezumat: Mannans are the major constituents of the hemicellulose fraction in softwoods, being widesread in plant tissues. Mannanase is an important enzyme involved in degradation of mannan, production of bioactive oligosaccharides, and biobleaching of kraft pulp (Moreira & Filho, 2008). Acidic and neutral-pH mannanases are more commonly found, however, few studies of halophilic mannanases are yet known. We aimed at the isolation of halophilic strains capable of producing salt stable mannan-degrading enzymes using commercial salt made in Japan as inoculum. The commercial salt samples were spread on the agar plates and incubated at 37 °C for 3 weeks. In total, six strains were isolated that produced clear zone around colonies on agar plates, containing 0.2% Locust Been Gum (LBG), when flooded with 0.1% Congo-red solution. The result of 16S rRNA gene sequence analysis indicated that the strain ManD738 was similar to Haloarcula quadrata strain JCM 11048T (99.5%); the strains ManD500, ManD722 and ManD381 were similar to Haloarcula japonica strain JCM 7785T (99.2%), and the strains ManD261 and ManD777 were similar to Halobacterium noricense strain JCM 15102T (99.2%). Mannanase activity was determined by measuring the increase of reducing sugar released from mannan using the modified dinitrosalicylic acid (DNS) method. The extracellular mannanase produced from strain ManD738 in supernatant showed optimum NaCl concentration at 3.5 M, optimum temperature at 70 °C, and pH optimum at 7.0. The mannanase produced by strain ManD738 was stable at the temperature of 50-75°C and showed 50% relative activity at 0.5 M NaCl and 4.5 M NaCl, respectively.
Keywords: haloarchaea, halophilic mannanase. |
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