cells were grown for at least one day in low pH media. The time resolved expression profile of the S. meliloti 1021 exo genes and flagellar genes following a shift to acidic pH Overall the number of differentially expressed genes belonging to the group of EPS I Nirogacestat price biosynthesis genes and to the group of genes involved in flagellar biosynthesis and motility is striking. Most exo genes were joined together in cluster B whereas most flagellar genes were grouped together in cluster F. Furthermore, it is noticeable
that the expression of the two groups of genes displayed oppositional characteristics. The EPS I biosynthesis ISRIB in vivo genes responded with a fast then constant induction for the duration of the time course, whereas the flagellar genes were increasingly down-regulated. For A. tumefaciens a similar response in succession to pH stress could be identified [50]. In case of A. tumefaciens the transcriptome profiling was performed after 7 hours of growth in low pH. Also in our experiment the expressional characteristics of the exo and flagellar genes indicated that
their response to acidic pH conditions lasts longer than the monitored period of one hour. The regulator coding gene chvI was with most of the exo genes distributed to cluster B. Like in A. tumefaciens the gene chvI was up-regulated together with several genes Selleck Oligomycin A responsible for the succinoglycan biosynthesis [50], although it is believed that chvI is a negative regulator of the exo genes [51]. A closer view on the individual expression levels of the genes of the EPS I biosynthesis gene cluster on pSymB during the time course (Fig. 4) reveals the high induction levels for
the majority of the exo genes. The maximum induction in the observation see more period was always reached at 63 minutes after pH shift. Besides the eight exo genes found in cluster B, three exo genes grouped in cluster A and C. The exo genes in cluster A (exoV and exoH) were among the strongest up-regulated genes in this experiment. The products of these genes are responsible for the final steps of the EPS I biosynthesis. They are involved in the succinylation and pyruvilation of EPS I. It could already be shown for S. meliloti that a mutant strain of exoH is sensitive to low pH [52], indicating a particular impact of exoH on the pH tolerance and of the EPS I biosynthesis genes on the pH tolerance in general. The higher expression value of exoH compared to other exo genes might also be caused by its position as the first gene in a large operon (exoHKLAMONP) [53]. The central genes of this operon (exoA and exoM) did not show a significant change in their expression level during the time course in contrast to the bordering genes. This might be caused by mRNA instability and degradation effects.