Control of nitrogen and carbon metabolism in cyanobacteria

In the unicellular cyanobacteria that do not fix molecular nitrogen, intera ctions between N assimilation and C metabolism occur through the signal tra nsducer P-II and the global nitrogen regulator NtcA. Under high CO2 concent ration, P-II liganded to ATP and bound to 2-oxoglutarate becomes phosphoryl ated and negatively controls the high affinity transport for bicarbonate. I n contrast, under low CO2, P-II being only liganded to ATP becomes dephosph orylated and negatively controls the nitrate/nitrite active transport syste m. The redox state of the cells together with NtcA also modulate the phosph orylation state of P-II. Moreover, the regulation of the expression of the gene encoding P-II is at least in part NthA-dependent. This network of tran scriptional and post-transcriptional regulations allows cells to rapidly ac climate by adjusting their carbon and nitrogen metabolism in response to ch anges in environmental conditions.