Discussion
A bacterium obtains energy from a chemical source by the oxidation of reduced \(\mathrm{NO_{2}^{-}}\), with \(\mathrm{CO_{2}}\) as the principal carbon source. Which one of the following nutritional groups does this bacterium belong to?
Answer: C
The bacterium is a chemoautotroph.
Nutritional groups are named from two choices: the energy source (light, photo-, or chemicals, chemo-) and the carbon source (CO2, auto-, or organic compounds, hetero-). This organism gets energy by oxidising nitrite, a chemical (inorganic) source, and takes its carbon from CO2, so it is a chemoautotroph, specifically a chemolithoautotroph. Nitrite-oxidising bacteria such as Nitrobacter live this way in the nitrogen cycle.
Photoautotrophs and photoheterotrophs use light, which this bacterium does not. A chemoheterotroph would draw its carbon from organic compounds rather than CO2.
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