Mining Sugar Transporters from Gut Fungi for Improved Fuel & Energy Production

Membrane transporters are cellular gatekeepers that control the uptake of needed substrates and the secretion of valuable fuel products. These transporters are substrate-specific and help determine cell phenotypes. For example, industrial workhorses such as Saccharomyces lack the needed transporters to fully use the sugars from renewable plant biomass and natively secrete toxic fuel compounds. In contrast, anaerobic fungi from the guts of large herbivores thrive on an array of sugars resulting from lignocellulose hydrolysis due to a number of sugar uptake pathways. Here, we mine this diverse phylum for novel sugar transporters using an integrated transcriptomics and phenotyping approach to identify new tools for improved bioprocessing. Three new gut fungal species from distinct genera were sequenced to generate de novo transcriptomes containing hundreds of putative transporters. These transporters were classified into Transporter Classification Database (TCDB) families on the basis of homology and assigned a putative substrate. Substrate predictions were subsequently validated by comparing phenotype against metabolic bottlenecks and the expression profile of predicted transporters to identify transporter candidates responsible for sugar uptake. Transcriptomic sequencing also revealed a number of multidrug transporter candidates which may further increase productivity by increasing fuel tolerance via product secretion.