Na⁺-Dependent Transport of Amino Acids and Its Significance for Growth of a Lysine-producing Bacterium

Abstract

A lysine-producing mutant Brevibacterillm flavlIm HUT 8052, a threonine plus methionine (or threonine plus homoserine) auxotroph, grew rapidly as nearly as the wild strain in a medium supplemented with NaCl (60 flg/ml), threonine (100 flg/ml), and methionine (33.3 flg/ml). With NaCl concentrations less than 20 flg/ml, the mutant grew little or very slowly. The peculiar growth behavior of the mutant including the above phenomenon could be reasonably explained by the finding of Na + -dependent amino acids transport and the feedback inhibition of homoserine dehydrogenase by threonine in the bacterium.The threonine transport was stimulated by Na+ and Li+. though the latter being less effective. The transport of threonine was inhibited by serine. The uptake of serine, isoleucine, leucine and valine was also stimulated by Na + 1952 Christensen et a1.1) found that the uptake of glycine and alanine by duck red cells decreased when Na+ in a medium was replaced by K + The stimulatory effect of NaT on the transport of neutral and acidic amino acids has been widely known at present in mammalian cells. In2 )

Secretion of amino acids by bacteria: Physiology and mechanism

“…The different aspects of secretion of this amino acid have recently been elucidated to some extent in C. glutamicum. The situation is further complicated by the fact that an uptake system with significant activity is present in this organism [111][112][113]. Thus, the most complicated situation can be imagined, where in principle all three different possibilities of amino acid effiux (diffusion, uptake inversion and secretion carrier) may be present.…”