Figure 4 Expression of the acs reporter in different chemostat environments at D = 0.15 h -1 . Fluorescence measurements report the expression of

Pacs-gfp in chemostat environments supplied with minimal media supplemented with only D-glucose, only sodium acetate or D-glucose plus sodium acetate. Background fluorescence is the fluorescence of the promoterless strain depicted in black. selleck products The error bars on the plots for mean log expression of Pacs-gfp are standard errors of the mean. The expression of the acs reporter was down-regulated to the greatest extent in chemostats with high concentration of glucose (11.2 mM Glc in the feed). Results from previous studies suggest that under the conditions used here – glucose as the only carbon source, and low dilution rates – the reactions of glyoxylate shunt and gluconeogenesis should be active, which would allow utilization of simple carbon sources such as acetate when glucose is not available [20]. According to population-based studies on bacteria grown on glucose, the shunt operates at the dilution rates from CBL0137 research buy 0.05–0.2 h-1, allowing metabolism of acetyl-CoA to succinate. The reactions of the citric acid cycle are not engaged, and this prevents carbon loss in the form of CO2[33, 41]. When acetate is used as a sole carbon source, the expression

of the phosphoenolpyruvate (PEP) carboxykinase gene pck (a gluconeogenesis enzyme) is up-regulated [40, 42], indicating synthesis of glucose from non-carbohydrate precursors such as acetate [20]. pck is also up-regulated in chemostats containing glucose as a carbon source that are run at low dilution rates [43]. Our experiments at the single-cell level largely support these previous population-based studies. In the following paragraph, we will discuss in more details the gene expression phenotypes that we observed in clonal populations grown in mini-chemostats at low dilution rate of D = 0.15 h-1, Celecoxib and with glucose as the sole carbon source at a feed concentration of 0.56 mM Glc. These are the conditions in which the majority of the

cells expressed both glucose transporters mglB and ptsG, whereas some cells only expressed mglB (Figure  1, Table  3). The fraction of cells that did not express the ribosomal reporter was below 1% (Table  3), and these were the cells that presumably did not grow and divide. The residual concentration of glucose in the mini-chemostats after five check details volume changes (theoretical steady-state concentration [33]) was 1.95 ± 0.13 μM, measured by ion chromatography (our experimental setup did not allow us to accurately measure concentration of acetate). We found that, under these conditions, almost all cells expressed the acs reporter above background level (Figure  4). This may indicate that they either recover cytoplasmic acetate or take up acetate excreted by others.