Biomass production and secretion of hydrolytic enzymes are influenced by the structural complexity of the nitrogen source in Fusarium oxysporum and Aspergillus nidulans

The structural complexity of the nitrogen sources strongly affects biomass production and secretion of hydrolytic enzymes in filamentous fungi. Fusari um oxysporum and Aspergillus nidulans were grown in media containing glucos e or starch, and supplemented with a nitrogen source varying from a single ammonium salt (ammonium sulfate) to free amino acids (casamino acids), pept ides (peptone) and protein (gelatin). In glucose, when the initial pH was a djusted to 5.0, for both microorganisms, higher biomass production occurred upon supplementation with a nitrogen source in the peptide form (peptone a nd gelatin). With a close to neutrality pH, biomass accumulation was lower only in the presence of the ammonium salt. When grown in starch, biomass ac cumulation and secretion of hydrolytic enzymes (amylolytic and proteolytic) by Fusarium also depended on the nature of the nitrogen supplement and the pH. When the initial pH was adjusted to 5.0, higher growth and higher amyl olytic activities were detected in the media supplemented with peptone, gel atin and casamino acids. However, at pH 7.0, higher biomass accumulation an d higher amylolytic activities were observed upon supplementation with pept one or gelatin. Ammonium sulfate and casamino acids induced a lower product ion of biomass, and a different level of amylolytic enzyme secretion: high in ammonium sulfate and low in casamino acids. Secretion of proteolytic act ivity was always higher in the media supplemented with peptone and gelatin. Aspergillus, when grown in starch, was not as dependent as Fusarium on the nature of nitrogen source or the pH. The results described in this work in dicate that the metabolism of fungi is regulated not only by pH, but also b y the level of structural complexity of the nitrogen source in correlation to the carbon source.