الملخص الإنجليزي
Marine sources have been known to yield novel compounds with a wide range of bioactivity with various commercial applications. In this study, the abilities of bacteria isolated from eight marine organisms to produce a-amylase were examined. All eight organisms were found to harbor amylase producing bacteria. Two bacteria isolated from the green alga Ulva rigida and the sponge Mycale sp. were further identified and their aamylases were purified and characterized. The bacterial species isolated from the green alga Ulva rigida and sponge Mycale sp. were identified by DNA sequencing as Cellulosimicrobium sp. and Demequina sp., respectively Cellulosimicrobium sp. obtained maximum cell growth and amylase production at 29°C and in the presence of lactose as a carbon source. Optimal cell growth and amylase production by Demequina sp. was observed at 35°C. While lactose enhanced cell growth of Demequina sp., maximum amylase production was found when fructose and glycerol were the available sources of carbon. Both strains grew better in the presence of tryptone, whilst peptone stimulated amylase production. Maximal cell growth and amylase production by both of the strains was found at a medium salinity of 3% NaCl. Characteristics of the amylases extracted from the two strains (Amylase I from Cellulosimicrobium sp. and Amylase II from Demequina sp.) were assayed in the laboratory. Both amylases had the highest activity at 37°C and pH 7. Activity of both the enzymes was reduced in the presence of detergents, such as EDTA, SDS and totally inhibited by the denaturing agent acetone. In the presence of metal ions such as Cu2+ and Zn2+, the two amylases lost some of their activities, whereas Ca2+ and Fe2+ had stimulatory effects on both amylases. Reduction of the amylases activities by EDTA and their enhancement by Ca* indicates the calcium dependence of amylases and suggests that they are metalloenzymes. Results of this study suggest that bacteria associated with marine organisms are novel sources of a-amylases, which can be used for different commercial applications.
