Abstract The process of nitrification is highly dependent on the microbial activities and transformation, which is carried out by autotrophic nitrifiers in general, however some heterotrophic nitrifiers also can carry out the process. The diversity of autotrophic and heterotrophic ammonia-oxidizing bacteria in aquaculture ponds in Kaohsiung county was investigated. Ten heterotrophic bacteria were isolated. The nitrification ability and 16S rDNA sequences were determined. Seven of the strains had higher nitrification ability, five of them are belong to the genus of Pseudomonas, and the other two belong to Alcaligenes and Serratia, respectively. Both 16S rDNA and amoA gene sequences results showed that all autotrophic ammonia-oxidizing strains in this study belong to Nitrosomonas genus. From the data of 16S rDNA sequences, the strains isolated from Linyuan Shiang were distinct to the other two sites. Besides, amoA gene represents a very powerful molecular tool for analyzing ammonia-oxidizing bacteria communities due to its specificity and fine-scale resolution of closely related populations.

Includes bibliographical references (p. 63-73).

Denitrification is the process by which bacteria reduce nitrate to dinitrogen gas. Most denitrifying bacteria perform these reactions under anaerobic conditions only. Thiosphaera pantotropha is one of a number of species capable of aerobic denitrification. During aerobic growth T. pantotropha expresses a periplasmic nitrate reductase but under anaerobic growth conditions nitrate is reduced by a membrane-bound nitrate reductase. The periplasmic nitrate reductase is relatively insensitive to azide and does not reduce chlorate. Aerobic denitrification provides a mechanism to dispose of excess reducing equivalents during growth on reduced carbon sources. Numbers of nitrate reducing bacteria, and nitrate and ammonia concentrations were monitored in a Norfolk broad over a 12 month period. Several novel microorganisms capable of aerobic nitrate respiration were isolated from the sediment of this broad. All were shown to express a periplasmic nitrate reductase activity, and the effects of growth rate and carbon substrate on the activity of this enzyme were studied. Of the nine isolates studied, five were shown to be able to reduce nitrate at oxygen concentrations up to 80% of air saturation. The remaining four were shown to be able to reduce nitrate under anaerobic conditions. Analysis of 16S rDNA sequences was used to identify the isolates, seven were assigned to the Genus Aeromonas, and two to the Genus Pseudomonas. Sediment samples were used to establish a microcosm in which changes in the concentration of nitrate, nitrite and ammoniacal nitrogen were monitored.

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