Date Published: May 20, 2012
Author(s): Katrin Brzonkalik, Dominik Hümmer, Christoph Syldatk, Anke Neumann.
Production of the Alternaria mycotoxins alternariol (AOH), alternariol monomethylether (AME) and tenuazonic acid (TA) by Alternaria alternata DSM 12633 was influenced by pH and carbon to nitrogen (C:N) ratio of the growth medium both in shaking flasks and bioreactor cultivation. The impact of medium pH on mycotoxin production was studied in the range of pH 3.5 – 8. pH values above 5.5 led to a decreased mycotoxin production or inhibited mycotoxin formation completely whereas an acidic pH in the range of 4.0-4.5 was optimal for mycotoxin production. The influence of the C:N ratio was evaluated over the range of 24 to 96. Glucose was used as carbon source and its concentration was altered while nitrogen concentration was kept constant. Growth kinetics and mycotoxin production parameters were studied depending on different C:N ratios. With increasing initial glucose concentration fungal biomass did increase but the maximum specific growth rate was not influenced. The optimal initial C:N ratio for attaining highest mycotoxin concentrations was 72. A higher C:N ratio did not further enhance mycotoxin production.
Mycotoxins are harmful secondary metabolites produced by a wide variety of moulds. Black moulds of the genus Alternaria are able to form several mycotoxins of different chemical classes whereas the polyketide mycotoxins alternariol (AOH) and its methylated derivative alternariol monomethylether (AME) as well as the tetramic acid tenuazonic acid (TA) are best studied ([Coombe et al. 1970]; [Logrieco et al. 2009]; [Patriarca et al. 2007], Figure 1). These compounds have been identified in food products contaminated with Alternaria species: wheat ([Li and Yoshizawa, 2000]) and other grains ([Broggi et al. 2007]), sunflower seeds ([Nawaz et al. 1997]; [Pozzi et al. 2005]), oilseed rape ([Nawaz et al. 1997]), pecans ([Schroeder and Cole 1976]), fruit and fruit juices ([Delgado et al. 1996]; [Lau et al. 2003]), tomato products ([Andersen and Frisvad 2004]; [Motta and Valente Soares 2001]; [Ozcelik et al. 1990]) and olives ([Visconti et al. 1986]).
Although the influences of temperature and water activity on the production of Alternaria toxins were studied extensively, the influence of other abiotic factors was neglected so far. In this study the effects of the two important factors, pH-value and C:N ratio, were elucidated for the first time and it was shown that mycotoxin production was highly affected by these factors.
The authors declare that they have no competing interests.