Submerged culture of Penicillium sclerotiorum for production of rotiorin alkaloids by using biosynthetic and chemical catalytic cascade reactions

Unveiling the fungal color palette: pigment analysis of Fusarium solani species complex and Curvularia verruculosa clinical isolates

Fungal species in the Nectriaceae, such as Fusarium spp. (Hypocreales: Nectriaceae), are etiologic agents of hyalohyphomycosis capable of producing violaceous or yellowish pigments under certain conditions, while Curvularia spp. (Pleosporales: Pleosporaceae) are agents of phaeohyphomycosis and typically produce melanin in their cell walls. In nectriaceous and pleosporaceous fungi, these pigments are mainly constituted by polyketides (e.g., azaphilones, naphthoquinones, and hydroxyanthraquinones). Considering the importance of pigments synthesized by these genera, this work focused on the selective extraction of pigments produced by eight Fusarium solani species complex and one Curvularia verruculosa isolate recovered from dermatomycosis specimens, their separation, purification, and posterior chemical analysis. The pigments were characterized through spectral and acid-base analysis, and their maximum production time was determined. Moreover, spectral identification of isolates was carried out to approach the taxonomic specificity of pigment production. Herein we describe the isolation and characterization of three acidic pigments, yellowish and pinkish azaphilones (i.e., coaherin A and sclerotiorin), and a purplish xanthone, reported for the first time in the Nectriaceae and Pleosporaceae, which appear to be synthesized in a species-independent manner, in the case of fusaria.

Terminal carboxylation of branched carbon chain contributing to acidic stability of azaphilone pigments from a new isolate of Talaromyces amestolkiae

Red Monascus pigments, a series of natural azaphilone alkaloids, have been utilized in China as a traditional food colorant for over 1000 years. However, instability under an acidic condition is its drawback. A new strain of Talaromyces amestolkiae was isolated in the present work, which produced the azaphilone talaromycorubrin and the corresponding azaphilone alkaloid (N-MSG-talaromycorubramine) exhibiting good stability even at pH below 3. The azaphilone alkaloid with acidic stability, an alternative of Chinese traditional red Monascus pigments, is potential for application as natural food colorant in acidic foods. The acidic stability of azaphilone alkaloid also benefits for direct fermentation of N-MSG-talaromycorubramine under a low pH condition. More importantly, correlation relationship between the terminal carboxylation of branched carbon chain of azaphilone and the stability of azaphilone alkaloids under an acidic condition is set up for the first time, which makes designing other acidic stable azaphilone alkaloids via genetic engineering become possible.

Nitrogen Enriched Solid-State Cultivation for the Overproduction of Azaphilone Red Pigments by Penicillium sclerotiorum SNB-CN111

Azaphilones are microbial specialized metabolites employed as yellow, orange, red or purple pigments. In particular, yellow azaphilones react spontaneously with functionalized nitrogen groups, leading to red azaphilones. In this study, a new two-step solid-state cultivation process to produce specific red azaphilones pigments was implemented, and their chemical diversity was explored based on liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) and a molecular network. This two-step procedure first implies a cellophane membrane allowing accumulating yellow and orange azaphilones from a Penicillium sclerotiorum SNB-CN111 strain, and second involves the incorporation of the desired functionalized nitrogen by shifting the culture medium. The potential of this solid-state cultivation method was finally demonstrated by overproducing an azaphilone with a propargylamine side chain, representing 16% of the metabolic crude extract mass.

Azaphilone alkaloids: prospective source of natural food pigments

Azaphilone, biosynthesized by polyketide synthase, is a class of fungal metabolites. In this review, after brief introduction of the natural azaphilone diversity, we in detail discussed azaphilic addition reaction involving conversion of natural azaphilone into the corresponding azaphilone alkaloid. Then, setting red Monascus pigments (a traditional food colorant in China) as example, we presented a new strategy, i.e., interfacing azaphilic addition reaction with living microbial metabolism in a one-pot process, to produce azaphilone alkaloid with a specified amine residue (red Monascus pigments) during submerged culture. Benefit from the red Monascus pigments with a specified amine residue, the influence of primary amine on characteristics of the food colorant was highlighted. Finally, the progress for screening of alternative azaphilone alkaloids (production from interfacing azaphilic addition reaction with submerged culture of Talaromyces sp. or Penicillium sp.) as natural food colorant was reviewed. KEY POINTS: • Azaphilic addition reaction of natural azaphilone is biocompatible • Red Monascus pigment is a classic example of azaphilone alkaloids • Azaphilone alkaloids are alterative natural food colorant.