The Crc/CrcZ-CrcY global regulatory system helps integrating gluconeogenic and glycolytic metabolism in Pseudomonas putida. Pseudomonas putida KT2440

In metabolically versatile bacteria, carbon catabolite repression (CCR) facilitates the preferential assimilation of the most efficient carbon sources, improving growth rate and fitness. In Pseudomonas putida, the Crc protein and the CrcZ and CrcY small RNAs (sRNAs), which are believed to antagonise Crc, are key players in CCR. Contrary to what occurs in other bacterial species, succinate or glucose elicit a weak CCR in this bacterium. We combined metabolic, transcriptomics and constraints-based metabolic flux analyses to clarify whether P. putida prefers succinate or glucose, and the role of the Crc/CrcZ-CrcY regulatory system in their metabolization. Succinate was consumed faster than glucose and allowed a higher growth rate. However, both compounds were co-metabolised when provided simultaneously. The levels of CrcZ and CrcY were lower when both substrates were present than when only one of them was provided, suggesting a role for Crc in coordinating metabolism. Metabolic reconstructions suggested that, when both substrates are present, Crc works to organize a metabolism in which carbon compounds flow in two opposite directions: from glucose to pyruvate, and from succinate to pyruvate. Therefore, Crc serves not only to favour the assimilation of preferred compounds, but also to balance the carbon fluxes, optimising metabolism and growth. Overall design: mRNA profiles of Pseudomonas putida KT2440, KTCRC and KT2440-ZY during glucose and succinate co-feeding generated by deep sequencing, in duplicate, using Illumina technology