Survey of coastal mangrove fungi for xylanase production and optimized culture and assay conditions.

Xylanase activity was detected among 34 of 77 fungal isolates derived from decaying wood, debris and soil samples collected in coastal mangrove environment of Hong Kong. Of those, three isolates CY2809 (Staganospora sp.), CY4786 and CY5040 were chosen for comparison of xylanase production in parallel to HU5048 (Aspergillus awamori), a terrestrial, highly productive isolate. Based on the assessment of mycelial biomass, xylanase activity and content of xylose-equivalent reducing sugars in their liquid cultures, the isolate CY4786 was best for xylanase production in a basal medium containing birchwood xylan (10.0 g/L) as a sole carbon source, yeast extract (2.5 g/L) and sea salts (15.0 g/L) with initial pH 7.8. When assayed at the optimized regime of 50 degrees C and pH 4.6, the activity of xylanase produced by CY4786 in 7d liquid culture at 25 degrees C reached 1.07 x 10(4) unit/mL. The results indicate that the mangrove fungi act as hemicellulose decomposers in the mangrove environment where highly xylanase-productive isolates can be searched for exploitation. A discussion is given on the possible use of the content of xylose-equivalent reducing sugars as an index to simplify conventional xylanase activity assay method for fungal isolate survey.

[Breeding, optimized fermentation and enzymatic properties of a Bacillus licheniformis mutant producing cyclomaltodextrin glucanotransferase].

A bacterial strain 403 selected from various soil was found to produce cyclomaltodextrin glucanotransferase (CGTase) with an activity of 0.95 U/mL after 96 h submerged incubation. A mutant, Bacillus licheniformis CLS403, obtained by means of ultraviolet radiation and diethyl sulfate, enhanced CGTase production by 43% (1.36 U/mL). The optimized conditions for CGTase production of mutant were soluble starch as carbon source, ammonium nitrate as nitrogen source, 35 degrees C and pH 6.5 for incubation. Under these conditions, the production of CGTase by the mutant in submerged peaked at the period of 96 h incubation, two days later than bacterial biomass peak. The resultant CGTase reacted best at 55 degrees C and pH 6.0, and had activities > 90% after 1 h maintenance at 50 degrees C with pH 6.0-7.5. Addition of Ca2+ in the reaction largely enhanced stability of the CGTase activity at 55 degrees C. Based on HPLC analysis, the products of starch hydrolyzed by the CGTase of B. licheniformis CLS403 included much more alpha-cyclodextrin than beta-cyclodextrin but no gamma-cyclodextrin. The total yield of cyclodextrin from starch reached 29.8% with the ratio of the two cyclodextrins 2.47:1.