Cultural characteristics and identification of marine nitrifying bacteria from a closed prawn-culture system in Durban |
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| Abstract: | A closed system, supplied with water from the Indian Ocean and stocked with the prawn Penaeus monodon, was used to identify and study the cultural characteristics of the associated marine nitrifying bacteria. This system provided the ideal environment for the development of nitrifying bacteria, which was monitored by assaying for the oxidation of either ammonia or nitrite. As these organisms grow very slowly, enrichment and fed-batch cultures were prepared to obtain pure cultures. The nitrifying bacteria are chemolithotrophs and can only be identified by observing their arrangement of internal or cytomembranes with the aid of the transmission electron microscope. All five listed genera of marine nitrifying bacteria were observed, namely Nitrosomonas and Nitrosococcus, which oxidize ammonia to nitrite, and Nitrobacter, Nitrococcus and Nitrospina, which oxidize nitrite to nitrate. Nitrosomonas europaea and Nitrobacter winogradskyi represented the dominant organisms in enrichment cultures and were also obtained in pure culture. Examination of the colonial morphology indicated the lack of distinct characteristics that could aid in their identification. A simple, effective method of observing the growth of ammonia-oxidizing bacteria microscopically, based on the breakdown of magnesium ammonium phosphate, is also described. |
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