Effect of carbon and nitrogen metabolism on nitrate reductase activity of Rhodobacter capsulatus E1F1

Abstract

The phototrophic bacterium Rhodobacter capsulatus E1F1 possesses an assimilatory, inducible nitrate reductase that is regulated by carbon and nitrogen metabolism. Nitrate reductase activity was detected in cells cultured with amino acids and nitrate as simultaneous nitrogen source but it required an additional carbon source such as D,L-malate. A significant rise in nitrate reductase activity was observed in media with increasing nitrate concentrations up to 10 mM KNO3, although higher nitrate concentrations had an inhibitory effect. Growth yield, generation time, and nitrate reductase activity were also dependent on the concentration of D,L-malate in cells growing with 10 mM nitrate. In carbon-starved cells, nitrate reductase activity dropped even in the presence of nitrate. The intracellular concentration of keto acids such as oxaloacetate or 2-oxoglutarate fluctuated widely depending on the presence of nitrogen and carbon sources in the culture medium. The increase in the intracellular concentration of oxaloacetate or 2-oxoglutarate in R. capsulatus E1F1 correlated well with a rise in nitrate reductase activity. These results suggest that the intracellular carbon–nitrogen balance regulates nitrate uptake in R. capsulatus E1F1, thus affecting the expression of nitrate reductase.Key words: carbon–nitrogen balance, nitrate reductase, Rhodobacter capsulatus.

Regulation ofnapGene Expression and Periplasmic Nitrate Reductase Activity in the Phototrophic BacteriumRhodobacter sphaeroidesDSM158

“…In addition, ammonium has no effect on nap gene expression ( Table 2, Fig. 6), confirming previous observations (10,28).…”

“…On the other hand, the in vitro Nap activity assayed with reduced MV as an artificial electron donor is a measure of the total activity, independent of NapC and the redox state of the quinol pool, even when the Nap system is not being used by the cells due to the absence of an electron supply. In earlier studies, it was observed that MV-Nap activity in R. sphaeroides is higher under heterotrophic aerobic than under phototrophic anaerobic conditions and that the activity is stimulated by nitrate but unaffected by ammonium or the C/N balance (10,28). However, a detailed study on the regulation of Nap activity or nap gene expression under different conditions has not been performed.…”

“…On the other hand, the Nap system from Ralstonia eutropha is maximally expressed under aerobic conditions at the stationary phase of growth and is not induced by nitrate (38), and in Paracoccus pantotrophus, maximal nap expression is found in cells growing aerobically with butyrate, a highly reduced carbon source, even in the absence of nitrate (37). In the phototrophic bacterium R. sphaeroides DSM158, Nap activity is stimulated by nitrate, is not affected by ammonium or by the intracellular C/N balance, and is present under both oxia and anoxia, although activity is higher under aerobic conditions (10,28).In this study we examined the expression of the nap genes from R. sphaeroides DSM158 in response to nitrate, nitrite, and ammonium under both aerobic and anaerobic conditions by …”

Characterization of the expression and activity of the periplasmic nitrate reductase of Paracoccus pantotrophus in chemostat cultures

“…Furthermore, nitrite accumulation did not match nitrate consumption, indicating that, as observed previously (Sears et al, 1997) have been undertaken in Rhodobacter sp. and Escherichia coli (Darwin et al, 1998;Dobao et al, 1994;Gavira et al, 2002;Liu et al, 1999;Reyes et al, 1998;Stewart et al, 2002;Wang et al, 1999). A notable feature of Nap systems is the variation, both within and between organisms, in the physiological functions, as well as the regulation and expression, of nap.…”

Rhodobacter capsulatus gains a competitive advantage from respiratory nitrate reduction during light–dark transitions

“…The Nap system of R. sphaeroides DSM158 is encoded by the napKEFDABC gene cluster, and the regulation of the system has been studied Reyes et al, 1996Reyes et al, , 1998. In vivo Nap activity is not responsive to the intracellular C/N ratio (Dobao et al, 1994), but is regulated by enzyme activation in response to the carbon substrate/electron supply and nitrate concentration (Gavira et al, 2002). Interestingly, in response to nitrate under anaerobic photoheterotrophic conditions with an oxidized carbon substrate, enzyme activation causes increased in vivo Nap activity (Gavira et al, 2002) (see below).…”