Abstract
ObjectiveEvaluation of morphology and secondary metabolites production in Aspergillus terreus ATCC 20542 cultures over a wide range of lactose and yeast extract concentrations from 0.2 up to an extremely high level of 200 g l−l.ResultsThe morphological differences of mycelial objects were quantified with the use of morphological parameters calculated by applying the tools of digital image analysis. At 200 g l−l of yeast extract clumps and loose hyphae were recorded instead of pellets commonly observed in submerged cultures of A. terreus. Under these conditions the biosynthesis of (+)-geodin and asterric acid was totally blocked, lovastatin formation was found to be at a relatively low level and biomass production turned out to be greater than in the remaining variants, where the pelleted growth was observed. At 200 g l−l of lactose the production of lovastatin, (+)-geodin and asterric acid was visibly stimulated compared to the media containing 0.2, 2 and 20 g l−l of the sugar substrate, but at the same time no traces of butyrolactone I could be detected in the broth. Lactose at the extremely high concentration of 200 g l−l did not induce the drastic morphological changes observed in the case of 200 g l-1 of yeast extract. It was proved that at the C/N values as low as 4 and as high as 374 A. terreus not only continued to display growth but also exhibited the production of secondary metabolites. The use of cultivation media representing the equivalent C/N ratios led to different metabolic and morphological outcomes depending on the concentration of lactose and yeast extract that contributed to the given C/N value.ConclusionThe extremely high concentration of yeast extract leads to marked morphological changes of A. terreus and the elimination of (+)-geodin and asterric production, while applying the excess of lactose is stimulatory in terms of lovastatin production.
Highlights
The repertoire of fungal secondary metabolites is a rich source of bioactive substances of potential pharmaceutical interest (Adrio and Demain 2003)
The extremely high concentration of yeast extract leads to marked morphological changes of A. terreus and the elimination of (?)-geodin and asterric production, while applying the excess of lactose is stimulatory in terms of lovastatin production
The cultivation of A. terreus American Type Culture Collection (ATCC) 20542 was performed in seven distinct growth media differing with respect to lactose and yeast extract (YE) concentrations and representing various C/N ratios
Summary
The repertoire of fungal secondary metabolites is a rich source of bioactive substances of potential pharmaceutical interest (Adrio and Demain 2003). The efforts aimed at maximizing the yield and productivity of lovastatin are basically centered around the optimization of fungal strains, medium composition, cultivation conditions and, importantly, morphological development (Mulder et al 2015). It was previously demonstrated that the catalog of secondary metabolites biosynthesized by this particular strain under submerged conditions includes lovastatin, and (?)geodin, asterric acid and butyrolactone I (Boruta and Bizukojc 2016). Previous studies revealed that (?)geodin displays antiviral and antimicrobial activities (Rinderknecht et al 1947; Takatsuki et al 1969). The influence of medium composition on the production of multiple secondary metabolites in relation to the morphological parameters has not been studied for A. terreus cultures. The response of the metabolism and morphology of A. terreus to extremely high levels of key medium components, namely
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