Transport and Excretion of L-Lysine in Corynebacterium glutamicum

Abstract

L-Lysine transport in Corynebacterium glutamicum was investigated. The bacterium was shown to possess a highly specific, energy-dependent system of active lysine transport. The system transferred lysine into the cells and exchanged intra-and extracellular lysine. Mutations in the transport system did not lead to overproduction of the amino acid. Resting cells of the parent strain, or of its lysine-producer derivatives with a defective transport system, failed to excrete lysine into the medium. An efflux of intracellular lysine could be induced by a hyperosmotic shock, and by different membrane-active substances. It has been suggested that C. ghtamicum cells are equipped with channels (pores) for excreting lysine from the cytoplasm. These channels appeared to open in response to an increase in the intracellular lysine concentration. The channel permeability also depends on the membrane structure.

Lysine uptake and exchange in Corynebacterium glutamicum

“…These results clearly argue for an obligate antiport system and cannot be explained by exchange diffusion, a mechanism generally observed for uniporters in equilibrium (10). Although in the latter case the transport of label in the assay would be similar to an antiport mechanism, which had in fact led to the interpretation of lysine transport as exchange diffusion (15), the effects of ionophores on the initial rate would be completely different.…”

“…Lysine uptake in C. glutamicum was also investigated previously by Luntz al. (15), who suggested a H' symport mechanism for uptake of this amino acid.…”

The Corynebacterium glutamicum aecD gene encodes a C-S lyase with alpha, beta-elimination activity that degrades aminoethylcysteine

“…In C. glutamicum, three mechanisms for AEC resistance have been postulated: (i) alteration of the target enzyme, (ii) drug exclusion from the cell by mutation of the transport system, and (iii) modification of the drug itself. Reports of AEC resistance obtained by the first two mechanisms have been published (23,32,49,65 Degradation of an amino acid is proposed to be a one-step (58) or two-step (50) process. For AEC degradation, a two-step process can be excluded, since neither alanine (initial attack at the PC-S linkage) nor aminoethanepyruvate (primary attack at the a-amino terminus) was detectable in our HPLC analysis.…”

“…The most widespread and industrially important AEC' class is reported to contain an altered aspartokinase enzyme that is insensitive to feedback inhibition, leading to an AEC' phenotype and to excretion of lysine into the medium (23,44,65). A second mutant class exhibits AEC resistance due to a deficiency in the lysine/ AEC uptake system (32,49). AEC' strains of this class do not excrete lysine.…”

YfiK from Escherichia coli Promotes Export of O -Acetylserine and Cysteine

“…For instance, resistance to antibiotics, heavy metal ions, or organic acids may reside in the ability to specifically or nonspecifically expel such compounds. The mechanisms involved range from the change of membrane permeability via coupling to osmotic pressure or the inversion of uptake systems to the existence of specific exporters (4,5,19).…”