PahT regulates carbon fluxes in Novosphingobium sp. HR1a and influences its survival in soil and rhizospheres.

Novosphingobium sp. HR1a is a good biodegrader of PAHs and aromatic compounds, and also a good colonizer of rhizospheric environments. It was previously demonstrated that this microbe is able to co-metabolize nutrients existing in root exudates together with the PAHs. We have revealed here that PahT, a regulator of the IclR-family, regulates the central carbon fluxes favouring the degradation of PAHs and mono-aromatic compounds, the ethanol and acetate metabolism and the uptake, phosphorylation and further degradation of mono- and oligo-saccharides through a phosphoenolpyruvate transferase system (PTS). As final products of these fluxes, pyruvate and acetyl-CoA are obtained. The pahT gene is located within a genomic region containing two putative transposons that carry all the genes for PAH catabolism; PahT also regulates these genes. Furthermore, encoded in this genomic region, there are genes that are involved in the recycling of phosphoenolpyruvate, from the obtained pyruvate, which is the motor molecule involved in the saccharide uptake by the PTS system. The co-metabolism of PAHs with different carbon sources, together with the activation of the thiosulfate utilization and an alternative cytochrome oxidase system, also regulated by PahT, represents an advantage for Novosphingobium sp. HR1a to survive in rhizospheric environments.