Prospecting the biodiversity of the fungal family Ustilaginaceae for the production of value-added chemicals

Abstract

BackgroundUstilaginaceae (belonging to the smut fungi) are commonly known for their plant pathogenicity. Although these microbes lead to yield reduction of cereal production, they can also have an economically positive side. Ustilaginaceae naturally produce a versatile range of value-added chemicals with potential applications in the food, pharmaceutical, and chemical industry.ResultsIn this study 68 Ustilaginaceae of 13 species were screened for the production of organic acids, polyols, and glycolipids from glucose to characterize their biodiversity and identify potential novel strains for biocatalysis of these valuable chemicals. Ustilago cynodontis, Ustilago maydis, Ustilago avenae, and Sporisorium exsertum were identified as promising production organisms for itaconate, malate, succinate, and erythritol, respectively. The influence of buffer concentration (pH) on acid production was investigated. Selected strains with best itaconate and malate production were characterized in more detail in bioreactor experiments obtaining total acid concentrations of up to 47 ± 1 g L−1.ConclusionThe identification and detailed characterization of these producers of valuable chemicals highlights the potential of these unicellular smut fungi for industrial applications and is a further step towards the biotechnological utilization of Ustilaginaceae.Electronic supplementary materialThe online version of this article (doi:10.1186/s40694-014-0002-y) contains supplementary material, which is available to authorized users.

Activating Intrinsic Carbohydrate-Active Enzymes of the Smut Fungus Ustilago maydis for the Degradation of Plant Cell Wall Components

“…Total RNA was extracted from the respective strains grown in screening medium (21) supplemented with 20 g liter Ϫ1 glucose for 12 h using the Tri Reagent (Roth, Karlsruhe, Germany), according to the manufacturer's instructions. Ten micrograms of total RNA was treated with 2 U of DNase I (New England BioLabs, Frankfurt am Main, Germany) for 10 min at 37°C to remove residual genomic DNA and subsequently purified by phenol-chloroform extraction and sodium acetate precipitation.…”

“…As a plant pathogen, U. maydis possesses a limited but complete set of hydrolases that in theory enable the utilization of complex substrates, like cellulose, xylan, or pectin, for growth (21,38,43,44). However, transcription studies revealed that gene expression for most of these CAZymes is restricted to the phase of infection, when the fungus invades the plant and proliferates, while they are often dormant during the industrially relevant yeast-like growth (45).…”

“…Organic acids, for example, are considered bio-based substitutes for traditional petroleum-derived products (17,18). Among these, itaconic acid is a promising and versatile building block, i.e., for the production of polymers, adhesives, and coatings, and in the future possibly also for the generation of biofuels (19)(20)(21). Commercial itaconic acid production is currently achieved biotechnologically with engineered strains of Aspergillus terreus.…”

“…Members of the Ustilaginaceae smut fungi are promising natural producers of organic acids (21,26,27). Within this group of biotrophic plant pathogens, Ustilago maydis is of increasing interest, not least due to its long history of intensive investigation as a paradigm of plant-pathogen interaction (28).…”

“…Certain U. maydis strains, such as the wild-type isolate MB215, can produce high concentrations of itaconate as well as other compounds, such as malate, succinate, hydroxyparaconate, and erythritol (21,31), some of which are considered top value-added platform chemicals (17). Remarkably, itaconic acid synthesis in U. maydis wild-type isolates already yields about twice as much as A. terreus strains did in early development, underpinning the potential of this organism and the resulting need for further research into this direction (24).…”