Medium-Chain Fatty Acids Affect Citrinin Production in the Filamentous Fungus Monascus ruber

Abstract

During submerged culture in the presence of glucose and glutamate, the filamentous fungus Monascus ruber produces water-soluble red pigments together with citrinin, a mycotoxin with nephrotoxic and hepatoxic effects on animals. Analysis of the 13 C-pigment molecules from mycelia cultivated with [1-13 C]-, [2-13 C]-, or [1,2-13 C]acetate by 13 C nuclear magnetic resonance indicated that the biosynthesis of the red pigments used both the polyketide pathway, to generate the chromophore structure, and the fatty acid synthesis pathway, to produce a medium-chain fatty acid (octanoic acid) which was then bound to the chromophore by a transesterification reaction. Hence, to enhance pigment production, we tried to short-circuit the de novo synthesis of medium-chain fatty acids by adding them to the culture broth. Of fatty acids with carbon chains ranging from 6 to 18 carbon atoms, only octanoic acid showed a 30 to 50% stimulation of red pigment production, by a mechanism which, in contrast to expectation, did not involve its direct trans-esterification on the chromophore backbone. However, the medium-and long-chain fatty acids tested were readily assimilated by the fungus, and in the case of fatty acids ranging from 8 to 12 carbon atoms, 30 to 40% of their initial amount transiently accumulated in the growth medium in the form of the corresponding methylketone 1 carbon unit shorter. Very interestingly, these fatty acids or their corresponding methylketones caused a strong reduction in, or even a complete inhibition of, citrinin production by M. ruber when they were added to the medium. Several data indicated that this effect could be due to the degradation of the newly synthesized citrinin (or an intermediate in the citrinin pathway) by hydrogen peroxide resulting from peroxisome proliferation induced by medium-chain fatty acids or methylketones.In filamentous fungi, many secondary metabolites with complex chemical structures are synthesized from the polyketide pathway (26,29). These metabolites display a wide range of biological activities, including antibiotic, antifungal, immunosuppressive, and anticancer properties. In this respect, Monascus ruber is an interesting filamentous fungus which can excrete a broad spectrum of colored pigments that are routinely used in Asia as food additives. From previous works (12, 29), a scheme of the hypothetical routes for the biosynthesis of these various pigments in filamentous fungi is depicted in Fig.

Monascus spp.: A source of Natural Microbial Color through Fungal Biofermentation

“…Sodium nitrate supports sporulation, limited growth and gives intermediate pigment yields; the use of ammonium chloride results in repression of conidiation and the sexual cycle and leads to the best pigment yields [21,91]. In this medium, the dramatic pH decrease impairs pigment-amine interactions giving origin to red pigments according to Carels et al [92] and they also reported that nitrogen source determines pH evolution. In addition to ammonium chloride, peptone also yields superior growth and pigment production when compared with sodium nitrate [27,28,92].…”

Optimization of Monascus Pigment Production and its Antibacterial Activity

“…Monascus pigments are used as food colorants and flavouring agents (Hajjaj et al, 2003). Monascus is able to produce strong red pigment including some useful primary metabolites such as ethyl alcohol, acids, esters, and other flavouring compounds and secondary metabolites i.e.…”

Engineering rice based medium for production of lovastatin with Monascus species

“…But the concentration of citrinin, a mycotoxin causing hepatonephrotoxic effects, needs to be controlled during angkak production by genetic mutation of the fungal strain, by adding nutrients like fatty acids to the fermentation medium (Hajjaj et al 2000), or by replacing rice with other solid substrate like dioscorea (Lee et al 2006a) which might change the citrinin concentration in angkak.…”