Metabolic and regulatory rearrangements underlying glycerol metabolism in Pseudomonas putida KT2440.

While the natural niches of the soil bacterium Pseudomonas putida are unlikely to include significant amounts of free glycerol as a growth substrate, this bacterium is genetically equipped with the functions required for its metabolism. We have resorted to deep sequencing of the transcripts in glycerol-grown P. putida KT2440 cells to gain an insight into the biochemical and regulatory components involved in the shift between customary C sources (e.g. glucose or succinate) to the polyol. Transcriptomic results were contrasted with key enzymatic activities under the same culture conditions. Cognate expression profiles revealed that genes encoding enzymes of the Entner-Doudoroff route and other catabolic pathways, e.g. the gluconate and 2-ketogluconate loops, were significantly downregulated on glycerol. Yet, the compound simultaneously elicited a gluconeogenic response that indicated an efficient channelling of C skeletons back to biomass build-up through the glyoxylate shunt rather than energization of the cells through downwards pathways, i.e. tricarboxylic acid cycle and oxidative phosphorylation. The simultaneous glycolytic and gluconeogenic metabolic regimes on glycerol, paradoxical as they seem, make sense from an ecological point of view by favouring prevalence versus exploration. This metabolic situation was accompanied by a considerably low expression of stress markers as compared with other C sources.