Abstract
BackgroundFilamentous fungi are well known for their ability to degrade lignocellulosic biomass and have a natural ability to convert certain products of biomass degradation, for example glucose, into various organic acids. Organic acids are suggested to give a competitive advantage to filamentous fungi over other organisms by decreasing the ambient pH. They also have an impact on the ecosystem by enhancing weathering and metal detoxification. Commercially, organic acids can be used as chemical intermediates or as synthons for the production of biodegradable polymers which could replace petroleum-based or synthetic chemicals. One of the advantages of filamentous fungi as biotechnological production platforms for synthetic biology is their ability to degrade vegetal biomass, which is a promising feedstock for the biotechnological production of organic acids. The Fungal Culture Collection of the International Centre of Microbial Resources (CIRM-CF), curated by our laboratory, contains more than 1600 strains of filamentous fungi, mainly Basidiomycetes and Ascomycetes. The natural biodiversity found in this collection is wide, with strains collected from around the world in different climatic conditions. This collection is mainly studied to unravel the arsenal of secreted lignocellulolytic enzymes available to the fungi in order to enhance biomass degradation. While the fungal biodiversity is a tremendous reservoir for “green” molecules production, its potentiality for organic acids production is not completely known.ResultsIn this study, we screened 40 strains of Ascomycota and 26 strains of Basidiomycota, representing the distribution of fungal diversity of the CIRM-CF collection, in order to evaluate their potential for organic acid and ethanol production, in a glucose liquid medium. We observed that most of the filamentous fungi are able to grow and acidify the medium. We were also able to discriminate two groups of filamentous fungi considering their organic acid production at day 6 of incubation. This first group represented fungi co-producing a wide variety of organic acids and ethanol at concentrations up to 4 g.L−1 and was composed of all the Aspergilli and only 3 other Ascomycota. The second group was composed of the remaining Ascomycota and all the Basidiomycota which produced mainly ethanol. Among the Basidiomycota, two strains produced oxalic acid and one strain produced gluconic and formic acid. Six strains of Aspergillus producing high concentrations of oxalic, citric and gluconic acids, and ethanol were selected for metabolism analysis.ConclusionThese results illustrate the versatility in metabolites production among the fungal kingdom. Moreover, we found that some of the studied strains have good predispositions to produce valuable molecules. These strains could be of great interest in the study of metabolism and may represent new models for synthetic biology or consolidated bioprocessing of biomass.Electronic supplementary materialThe online version of this article (doi:10.1186/s40694-014-0001-z) contains supplementary material, which is available to authorized users.
Highlights
Filamentous fungi are well known for their ability to degrade lignocellulosic biomass and have a natural ability to convert certain products of biomass degradation, for example glucose, into various organic acids
For saprophytic and wood-decaying fungi, this pH acidification, caused by oxalic acid production, leads to an acid-catalyzed hydrolysis of holocellulose [5,6,7]. Concerning their direct interaction with the environment, organic acids participate in metal detoxification by metal complexion and oxalic acid plays a major role in biomass degradation [4]
The second group was composed of the remaining Ascomycota and Basidiomycota producing mainly ethanol
Summary
Filamentous fungi are well known for their ability to degrade lignocellulosic biomass and have a natural ability to convert certain products of biomass degradation, for example glucose, into various organic acids. Fungal natural production of organic acids is thought to have many key roles in nature depending on the type of fungi producing them These roles are either due to the pH decrease consecutive to their secretion or to direct interaction of the organic acid with the environment [3,4]. For saprophytic and wood-decaying fungi, this pH acidification, caused by oxalic acid production, leads to an acid-catalyzed hydrolysis of holocellulose [5,6,7] Concerning their direct interaction with the environment, organic acids participate in metal detoxification by metal complexion and oxalic acid plays a major role in biomass degradation [4]. To better understand their role in the ecosystem, these studies have focused on plant/fungi symbiosis [9,13], or growth on complex substrates [12,14,15,16], and are often focused on wood-decay or mycorrhizal fungal species
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