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Besides metabolic pathways and regulatory networks, transport reactions are also pivotal for understanding amino acid metabolism and production in bacteria. Apart from substrate uptake, this refers to product (amino acid) excretion as well as product re-uptake. Both the mechanistic (kinetic and energetic) as well as structural properties of these transport systems are relevant for understanding their significance and for providing a basis for rational metabolic design. Transport systems have been classified into numerous different carrier families, according to their structural properties and their putative evolutionary relation. The diversity of amino acid uptake and excretion systems in two biotechnologically relevant organisms, namely Escherichia coli K12 and Corynebacterium glutamicum ATCC 13032 is described in this review on the basis of their relation to these different transporter families. Particular functional and molecular properties of specific amino acid excretion systems in these two organisms, in particular those responsible for efflux of lysine (and arginine), threonine, branched chain amino acids, cysteine (and cysteine derivatives) and glutamate are described. A complete list of all secondary and primary transport systems in C. glutamicum putatively related to amino acid transport is provided. [ABSTRACT FROM AUTHOR]