Abstract
Enzyme activities of ribulose-1,5-bisphosphate carboxylase (RUBPCase) and chemoautotrophic CO2 fixation were measured during batch growth of six marine nitrifying bacteria. The NH4-oxidizer Nitrosococcus oceanus and the NO2-oxidizer Nitrococcus mobilis were also examined during exponential growth at different temperatures, O2 tensions and nitrogen-limited growth rates. Cellular activities of RUBPCase and rates of CO2 fixation varied with age in batch culture, temperature, O2 tension and nitrogen limitation, but there was a significant positive correlation between both parameters. Below 26°C, the ratio of CO2 fixation:RUBPCase did not vary significantly with cellular physiological state. Ratios of chemoautotrophic CO2 fixation:RUBCase activity for the six nitrifiers indicated that the ratio was species dependent. Three NO2-oxidizers had a significantly lower CO2 to enzyme ratio than three NH4-oxidizers.
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