Growth of Escherichia coli BL21 in a glycerol minimal medium was accelerated following supplementation with trace amounts of amino acid (0.35 mM). Of 12 amino acids tested, Arg and Ser gave the highest response, increasing cell growth by 63 and 53 %, respectively, compared to control cells. The ability of amino acids to accelerate cell growth was "switch-like" and was achieved by promoting glycerol utilization, which may be applied to shorten the long lag-phase when glycerol is used as carbon source. Acceleration of cell growth following amino acid supplementation was also observed using lactose minimal medium.