HALOTOLERANCE OF THE PHOTOTROPHIC BACTERIUM RHODOBACTER-CAPSULATUS E1F1 IS DEPENDENT ON THE NITROGEN-SOURCE

Phototrophic growth of the moderate halotolerant Rhodobacter capsulatu s strain E1F1 in media containing up to 0.3 M NaCl was dependent on th e nitrogen source used, In these media, increased growth rates and gro ,vth levels were observed in the presence of reduced nitrogen sources such as ammonium and amino acids, When the medium contained an oxidize d nitrogen source (dinitrogen or nitrate), increases in salinity sever ely inhibited phototrophic growth, However, the addition of glycine be taine promoted halotolerance and allowed the cells to grow in 0.2 M Na Cl, Inhibition of diazotrophic growth by salinity was due to a decreas e in nitrogenase activity which was no longer synthesized and reversib ly inactivated, both effects being alleviated by the addition of glyci ne betaine, In R, capsulatus E1F1, inhibition of cell growth in nitrat e by salt was due to a rapid inhibition of nitrate uptake, which led t o a long-term decrease in nitrate reductase activity, probably caused by repression of the enzyme. Addition of glycine betaine immediately r estored nitrate uptake, but the recovery of nitrate reductase activity required several hours, Neither ammonium uptake nor ammonium assimila tion through the glutamine synthetase-glutamate synthase pathway was a ffected by NaCl.