Sulfate assimilation in Clostridium thermocellum

Investigation of sulfur metabolism in Clostridium thermocellum DSM 1313 ∆hpt, to determine growth and gene expression when the organism is incubated with either the oxidized (i.e., sulfate) or the reduced and assimilated (i.e., cysteine) forms of sulfur. A sulfite reductase (∆hpt ∆SO3R) knockout mutant to limit sulfur assimilation was created to compare the resulting gene expression patterns by RNAseq transciptomics against the parental strain (∆hpt) when both are grown in the presence of sulfate. Additionally, we bypass the sulfate auxotrophy of the mutant by providing assimilated sulfur in the form of cysteine to determine whether growth is restored to normal and whether methionine can be biosynthesized by yet uncharacterized pathways in this organism. Samples for RNA-seq were taken from mid-exponential phase (OD ~ 0.6) batch cultures grown in MTC on 5 g/l cellobiose. Control strain (∆hpt) and sulfite-reductase-mutant strain (∆hpt∆SO3R) were grown in the presence of either 5.7mM cysteine or 28.2mM sodium sulfate as the only sulfur source