Multi-Energy Metabolic Mechanisms of the Fungus Fusarium oxysporum in Low Oxygen Environments

The fungus Fusarium oxysporum produces energy under hypoxic and anoxic conditions by denitrification (nitrate respiration) and ammonia fermentation respectively. Here we found that glucose repressed both of these metabolisms, whereas it supported another anoxic metabolism, hetero-lactic acid fermentation. Ammonia fermentation occurred only after the glucose present in the medium was metabolized to ethanol via alcohol fermentation. During this transition, clear diauxic growth was observed. Glucose regulated the activity of the enzymes involved in ammonia fermentation, heterolactic acid fermentation, and denitrification. Highest cell growth was supported by hetero-lactic acid fermentation, followed by denitrification and ammonia fermentation. These results indicate that the energy metabolisms of F. oxysporum are dependent not only on environmental 02 tension but also on the carbon source, and that ammonia fermentation is an adaptative mechanism acting physiologically as a secondary fermentative mechanism replacing the primary hetero-lactic acid fermentation.