Anaerobic gut fungi inhabit the digestive tract of herbivores such as cows and horses, and excel at degrading raw plant biomass into fermentable sugars. Recently, a comprehensive transcriptomic analysis suggested that anaerobic gut fungi possess a large number of transport proteins that are of chief biotechnological interest: transporters for sugars, amino acids, lipids, drugs, and metals. Interestingly, we also identified a plethora of surface-displayed carbohydrate binding modules that are related to prokaryotic sugar uptake proteins, suggesting that the gut fungi may sequester sugars in an unanticipated manner. Here, we set out to produce gut fungal transporters and putative sugar receptors in model microbes for downstream characterization. As a proof-of-principle, we introduced genes encoding gut fungal fluoride transporters into <i>Saccharomyces cerevisiae</i>, and could show that given codon optimization, the yeast produces large quantities of functional and correctly membrane-localized transporters. We are currently expanding our protein set to putative drug- and sugar-transporters from the Major Facilitator superfamily, the Sodium:Solute Symporter family and the Sugars Will Eventually be Exported transporter family. Among target sensor proteins are G-protein coupled receptors with non-canonical carbohydrate binding domains. These results shed much needed light on the physiology of anaerobic gut fungi, and illuminate the role of membrane-embedded proteins for their ability to persist in a competitive environment. Notably, the work expands on the toolbox of receptor and transporter proteins that can be used to enhance the performance and stability of microbial cell factory strains.

Sugar sensors and transporters in biomass-degrading anaerobic fungi

253rd National Meeting (2017)

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