Structure of surfactants and glutamate efflux by Corynebacterium glutamicum

Corynebacterium glutamicum is used for the industrial production of glutamate (Glu). Efflux of Glu is induced by addition of surfactants to the medium. These surfactants are known to modify the bacterial envelope structure. The significance of the water-soluble part of the surfactant molecules in this efflux phenomenon has not been extensively studied. This paper describes the effect of this water-soluble part of the surfactants on growth and Glu production by C. glutamicum ATCC 13032, The surfactants studied were a C18-saturated fatty acid esterified with polyoxyethylene glycol (POEFE), polyoxypropylene glycol (POPFE) and polyoxyethylene-polyoxypropylene glycol (POAFE). POPFE, was the less water-soluble and showed few effects on the growth of the cells and the excretion of Glu. POEFE which was the less hydrophobic was the most toxic but allowed the highest production of Glu. POAFE which had an intermediary hydrophobicity showed intermediary effects on growth and Glu production. The early stages of exponential growth phase was the best time for the addition of the surfactants in the culture to obtain the highest efflux of Glu. This efflux was related to a decrease in the bacteria respiratory properties but although the free polymers, POE, POA and POP affected bacterial respiration they did not influence the efflux of Glu as this phenomenon was only observed with the whole surfactant molecule. (C) 2000 Elsevier Science Ltd. All rights reserved.