The results presented here indicate that the disassembly is also performed in
a defined order. The loss of flagellar motility at low pH could already be shown for the closely related Rhizobium leguminosarum bv.viciae and A. tumefaciens [50, 58], whereas the more distantly related enterobacteria E. coli and Salmonella enterica serovar Thyphimurium showed an opposite response [59–61]. For cases of induced motility it was argued that at low pH the large ΔpH drives flagellar rotation [62]. Since there are also reports of E coli where it could be demonstrated that motility is lost at low pH [63] the picture is ambiguous. A turndown of the flagellar motility genes of S. meliloti was also observed for other stresses like osmotic Bindarit concentration stress Dactolisib solubility dmso [14, 64], heat shock and nutrient starvation [31]. It is therefore apparent that this response is a general stress response of S. meliloti 1021 and not an answer specific for pH stress. Since cell motility is very energy consumptive, the repression of the selleck inhibitor motility genes is likely to save energy which is needed to face the low pH e.g. by enhancing the EPS I biosynthesis. Figure 5 Map of genes of the flagellar biosynthesis region on the chromosome of S. meliloti 1021 and their expression in response to acidic pH. A part of the flagellar gene region is schematically
displayed with its genes given by open arrows coloured according to the K-means cluster distribution. Gene names are given below. Black arrows indicate known operon structures.
The graph above shows on the Y-axis the time after pH-shift and on the Z-axis for each time point the expression of the corresponding genes by the M-value. For clarity a region of 13 consecutive genes of the flagellar operon (flgA – fliK) has been omitted. The location of the omitted region is indicated by the orthogonal lines. The ending of a flagellar operon within the omitted region is depicted by a dotted black arrow. Conclusion This Ceramide glucosyltransferase study demonstrates the complexity of the cellular response of S. meliloti to adapt to a new environmental conditions. The mechanism of the cell to face the low pH is a mixture of several distinct reactions which follow a particular order in time. By applying K-means clustering analysis the diversity of different responses of individual genes was reduced to 8 main expression profiles. By this method a reasonable distinction between differently behaving up-regulated and down-regulated genes could be performed. Furthermore, within the obtained clusters, groups of genes with functional relationship were often joined together. Additionally, this analysis revealed that within the first 20 minutes after the shift to acidic pH the cell appears to perform the main changes necessary to adapt to the new environmental circumstances on the transcriptional level. The immediate response of S.