For R. tropici it was demonstrated that lpiA is pH responsive and symbiotically relevant [25]. Recently it was shown that lpiA is necessary for the lipid lysyl-phosphatidylglycerol formation in R. tropici in low pH minimal media and confers an increased resistance to the cationic peptide polymyxin B [29]. This points to a modification of the exterior cell selleck screening library wall by a change

of the lipid-structure. In addition smc0612 located downstream of lpiA was also found to be highly expressed, but since its click here expression level was slightly lower it was included in cluster B. The two open reading frames smc00612 and smc00613 are obviously products of a frameshift mutation of the orthologous gene acvB

[28] and are therefore probably not functional. It could be shown that a complementation of S. meliloti 1021 with the lpiA and acvB genes of A. tumefaciens resulted in an enhanced tolerance to acidic pH (C. Sohlenkamp, personal communication). It has been proposed that a modulated or enhanced lipid biosynthesis, as indicated by the high induction of lpiA, can increase the RAD001 cell line biosynthetic need for bicarbonate [30]. A raised demand for bicarbonate can be associated with the strongly up-regulated expression of cah, also found in cluster A. The gene cah is coding for a carbonic anhydrase that catalyses the fixation of bicarbonate. Since this gene was also highly up-regulated in response to phosphate starvation of S. meliloti it seems not to be specific for low pH stress [15]. Another early induction was observed for exoV and exoH coding

for proteins of the exopolysaccharide I biosynthesis (EPS I). The discussion of this and further genes involved in EPS I biosynthesis will be addressed in a later section. The large cluster B contains some exo genes responsible for the biosynthesis of succinoglycan Astemizole and several rpoE2 dependently regulated genes The expression level of the genes comprising cluster B increased to a medium level in the first 10–20 minutes after the pH shift, and remained at this level until the end of the time course experiment (Fig. 2B). Cluster B represents the biggest cluster and includes 74 genes. This cluster mainly consists of genes coding for hypothetical or conserved hypothetical proteins (41 genes) predominantly located on pSymA or on the chromosome. For these genes no further functional prediction can be given. Besides these genes, eight exo genes were found whose products together with the three exo genes grouped in cluster A and C are involved in the synthesis of exopolysaccharide I, also termed succinoglycan. In addition, the gene chvI coding for a regulator is part of this cluster. The genes of the EPS I biosynthesis are discussed in more detail in a following section. The gene katC present in cluster B was annotated as a catalase.