Project description:Global transcriptome analyses at different stages of growth were applied to monitor growth phase-dependent gene expression in the alpha-proteobacterium Rhodobacter sphaeroides. Low aerated cultures with strong changes in levels of dissolved oxygen during growth, were compared to aerated cultures showing little variation in oxygen levels. Cells were in stationary phase for 12 h or for 57 h before dilution into fresh medium. The majority of genes (78-86%) were not differentially expressed across growth phases. Gene expression in outgrowth phase was strongly influenced by the length of the preceding stationary phase. After 57 h in stationary phase a much larger number of genes was induced after dilution, 39% of which are known to be controlled by the alternative sigma factors RpoHI and/or RpoHII. Growth experiments with mutant strains assign an important function in stationary phase and especially in outgrowth to these sigma factors and genes for both sigma factors showed growth phase-dependent expression. Besides the known consensus sequences for the RpoH sigma factors, some new consensus sequences were identified in subsets of growth phase-dependent genes. Genes for several predicted regulatory proteins exhibited growth phase-specific expression implying a role in growth phase adaptation in alpha-proteobacteria, which needs verification in the future. RNA samples collected from R. sphaeroides 2.4.1 wild type cells in several growth phases were analyzed by two-color microarrays Please note that each sample represents biological triplicates.
