Energetics of arginine and lysine transport by whole cells and membrane vesicles of strain SR, a monensin-sensitive ruminal bacterium

Abstract

Strain SR, a monensin-sensitive, ammonia-producing ruminal bacterium, grew rapidly on arginine and lysine, but only if sodium was present. Arginine transport could be driven by either an electrical potential or a chemical gradient of sodium. Arginine was converted to ornithine, and it appeared that ornithine efflux created a sodium gradient which in turn drove arginine transport. There was a linear decline in arginine transport as pH was decreased from 7.5 to 5.5, and the cells did not grow at a pH less than 6.0. The Eadie-Hofstee plot was biphasic, and arginine could also be taken by a high-capacity diffusion mechanism. Because arginine was a strong inhibitor of lysine transport and lysine was a weak inhibitor of arginine transport, it appeared that both lysine and arginine were taken up by an arginine-lysine carrier which had a preference for arginine. The rate of lysine fermentation was always proportional to the extracellular lysine concentration, and facilitated diffusion was the dominant mechanism of lysine transport. When SR was grown in continuous culture on arginine or lysine, the theoretical maximal growth yield was similar (13 g of cells per mol of ATP), but the apparent maintenance energy requirement for arginine was greater than lysine (9.4 versus 4.4 mmol of ATP per g of cells per h). On the basis of differences in yield and maintenance energy, it appeared that active arginine transport accounted for approximately 40% of the total ATP.