Secretion of amino acids by bacteria: Physiology and mechanism

Abstract

Although representing a common property of microorganisms and beingwidely used for biotechnological purposes, solute secretion has beenrelatively poorly studied in terms of biochemistry. In this review,various examples of metabolite secretion processes by bacteria arediscussed with the emphasis on the mechanisms of amino acid secretion bycoryneform bacteria. Among the metabolic concepts which may be appliedto explain the physiological meaning of metabolite secretion, mainly twoconcepts are dealt with, i.e. the so-called `overflow metabolism' on theone hand and the situation where non-metabolizable intermediates areaccumulated and finally secreted on the other. In the central part ofthis review, the different concepts are discussed which have been putforward to mechanistically explain amino acid secretion under particularmetabolic conditions and in particular strains of bacteria, i.e.secretion mediated (i) by diffusion, (ii) by the participation of aminoacid uptake systems, and (iii) by the use of specific secretion systems.These concepts are then applied to amino acid secretion inCorynebacterium glutamicum, and exemplified by detailed studies on themechanism and regulation of the secretion of lysine, isoleucine andglutamate by C. glutamicum.