The activity of extracellular enzymes in starved and unstarved cells of a psychrophilic marine vibrio Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/ng451k924

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  • The psychrophilic marine Vibrio sp., ANT-300, was able to utilize a variety of carbon sources that can be considered typical for the marine environment. The organism grew abundantly on glucose and serine. Chitin was hydrolyzed even when it was offered as the only carbon source, while no growth occurred on laminarin which is a common exudate of macroalgae. ANT-300 was not able to hydrolyze either DNA or RNA. Fatty acid ester hydrolysis was shown for Tween 20, 40, 60, 80, and 85. The presence of a fatty acid esterase with biphasic substrate kinetics was demonstrated (K[subscript]m= 22 μM and K[subscript]m= 420 μM). This esterase has a temperature optimum of 35°C, a pH optimum of pH 9, and displayed maximal activity for fatty acid esters of p-nitrophenyl with a chain length of 8 carbon atoms. Both enzyme systems were maintained on starvation, but the K[subscript]m of the low affinity system decreased greatly (K[subscript]m= 79 μM). Calculated on the basis of viable cells and on the basis of direct cell counts there was an increase in activity of the enzyme during the starvation period of 57 days. Although about 30% of the observed activity was due to activity in the supernatant the results did not change when this was factored into the calculations. ANT-300 also has an extracellular alkaline phosphatase with a temperature optimum of 13°C, monophasic substrate kinetics, and an optimal activity for AMP as a substrate in starved and unstarved cells. This phosphatase was maintained on starvation and increased its substrate affinity slightly as indicated by a drop in K[subscript]m from an initial 88 μM to 60 μM. Calculated on a per cell basis for viable and total cell counts the activity increased on starvation but about 30% of this activity was again due to the supernatant. If this was considered in the calculations, an increase in activity could only be assessed for viable cells while there was a decrease for direct counts. It has been demonstrated that ANT-300 maintains one of the extracellular enzyme systems examined over a period of 57 days without an exogenous carbon source and even increases its activity during this time. Biphasic kinetics for an extracellular fatty acid esterase have been demonstrated which are maintained on starvation. The results presented in this thesis indicate that starved microorganisms are well prepared to utilize bioavailable dissolved organic carbon (DOC) sources and would therefore influence the composition of DOC even in such nutrient-poor environments as the deep sea.
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