The quantity and fate of carbon assimilated from ¹⁴CO₂ by Fusarium oxysporum grown under oligotrophic and near oligotrophic conditions

The distribution of ¹⁴C in the medium and metabolites of Fusarium oxysporum (an oligotrophic soil isolate) growing with ¹⁴C-labelled carbon dioxide in the absence of any exogenous carbon source was determined. Of the fixed carbon, approximately half was released into the medium. Of the carbon remaining in the mycelium, 67% was found in the protein fraction. The distribution of labelled carbon in oligotrophically grown Fusarium oxysporum is comparable to that seen in a number of fungi performing anaplerotic carbon dioxide fixation in the presence of an organic carbon source. Of cell carbon, 0·68% was derived from CO₂ under oligotrophic conditions. The specific activity of carbon dioxide assimilation was 259·5 μmol CO₂ g⁻¹ dry weight mycelium. Under near oligotrophic conditions (50 mg l⁻¹ C as sucrose), half of the fixed carbon was again released into the medium, and 0·12% of cell carbon was derived from CO₂.