Transport of plant-derived sugars and oligosaccharides in Clostridium phytofermentans. Files for RNA expression of Clostridium phytofermentans growing on D-(+)-galactose.. BSL

Elucidating how plant-fermenting bacteria uptake and metabolize sugars is crucial to understand the function of soil and intestinal microbial communities and to develop improved strains for industrial processing of plant biomass. Here we apply functional genomics and targeted gene inactivation to identify the transporters responsible for the uptake of plant polysaccharides and sugars in C. phytofermentans, a model for fermentation of lignocellulosic biomass. We identify candidate ABC transporters associated with growth on a variety of sugars and polysaccharides based on their mRNA expression patterns. We inactivate these transporter genes and isolate C. phytofermentans mutants that metabolize most substrates, but have lost the ability to grow on specific carbon sources including glucose, galactose, cellobiose, and galactan. Single, non-redundant transporters are thus responsible for the uptake of these carbon sources and distinct systems are used for the uptake of oligosaccharides versus the constituent sugars. As a single ABC transporter uptakes both glucose and galactose, we identify the kinases for their intracellular phosphorylation. We discuss how these results further our understanding of sugar transport in clostridia and facilitate engineering of novel strains with altered sugar metabolism.