Microorganisms are key components for plant biomass breakdown within rumen environments. Gram negative Fibrobacter succinogenes have been identified as being active and dominant cellulolytic members of the rumen. In this study, F. succinogenes type strain S85 was adapted for steady state growth in continuous culture at pH 5.75 and confirmed to grow in the range of pH 5.60-5.65, which is lower than has been reported previously. RNA-seq analysis revealed 268 and 829 genes were differentially expressed at pH 6.1 and 5.65 compared to pH 6.7, respectively. Resequencing analysis identified seven single nucleotide polymorphisms (SNPs) in the sufD, yidE, xylE, rlmM, mscL and dosC genes of acid tolerant strains. Due to the absence of a F. succinogenes genetic system, homologues in Escherichia coli were mutated and complemented and the resulting strains were assayed for acid survival. Complementation with wild-type or acid tolerant F. succinogenes sufD restored the function of E. coli SufDSE, suggesting a possible role for F. succinogenes sufD in acid homeostasis. Recent genetic engineering developments need to be adapted and applied in F. succinogenes to further our understanding of this genus.