Project description:Clostridium thermocellum forms adherent biofilms on lignocellulosic feedstock in a typical continuous cell-monolayer to efficiently break down and uptake cellulose hydrolysates. The adherent biofilm (i.e., sessile cells) may freely revert to the non-adherent form (i.e., planktonic cells) through generation of offspring cells or microenvironment constraints such as limited surface area. The two interdependent cell populations co-exist and have different contributions to culture activity and growth. We developed a novel bioreactor design to rapidly harvest sessile and planktonic cell populations for omics studies. In RNA-seq analyses, within 3299 protein coding genes, 59% (or 1958 genes) were differentially expressed with a minimum two-fold change between the two cell populations isolated simultaneously at high culture activity. Sessile cells had definitive greater expression of genes involved in catabolism of carbohydrates by glycolysis and pyruvate fermentation, ATP generation by proton gradient, the anabolism of proteins and lipids and cellular functions critical for cell division; planktonic cells had notably higher gene expression for flagellar motility and chemotaxis, cellulosomal cellulases and anchoring scaffoldins, and a range of stress induced homeostasis mechanisms such as oxidative stress protection by antioxidants and flavoprotein co-factors, methionine repair, Fe-S cluster assembly and repair in redox proteins, cell growth control through tRNA thiolation, recovery of damaged DNA by nucleotide excision repair and removal of terminal proteins by proteases. Knowledge of these cellular adaptations will aid the engineering of industrially relevant strains for consolidated bioprocessing of solid lignocellulosic biomass.
