Relationship between Fatty‐Acid and Phenol Synthesis in Aspergillus fumigatus

Investigations have been conducted into the relationship between fatty acid and phenol synthesis in submerged cultures of Aspergillus fumigatus. Both groups of metabolites are derived from acetate but phenol synthesis only occurs at a late stage in the incubation period and is dependent on a change in the internal environment of the mycelium. Secretion of acetate‐derived phenols commenced many hours after exhaustion of ammonium ions from the culture medium, or transfer of mycelium to glucose solution. Lipid synthesis, however, was maintained at this stage and continued into the phenol‐secreting phase when sufficient glucose was present to provide the necessary substrates. The additional lipid formed was identified as triglyceride. The composition of fatty acids in the total lipids was very similar to that found in other Aspergillus sp. and related Ascomycetes and consisted principally of C 18:2 with c 16:0 , c 16:1 , C 18:0 and C 18:1 . Addition of 4‐fluorophenylalanine, but not cycloheximide, caused a rapid reduction in fatty acid synthetase activity and lipid synthesis, and abolished formation of orsellinic acid and trihydroxytoluene, the normal secreted products. Certain enzymes examined, including the dehydrogenases of the pentose phosphate pathway, maintained their specific activity during the “stationary” phase whereas fatty acid synthetase was present at greatly reduced activity. The activity of ATP citrate lyase was severely reduced to an undetectable level after approximately 40 h incubation; acetyl‐CoA would therefore not be made available for fatty acid, phenol or ergosterol synthesis after this time. Initiation of phenol synthesis cannot be ascribed simply to diversion of substrates from fatty acid synthesis or to reduction in fatty acid synthetase activity.