Effect of ph, temperature and salinity on the production of gamma aminobutyric acid (GABA) from amines by marine bacteria

Abstract Bacteria isolated from sea-water grew on putrescine and spermidine as the sole carbon and nitrogen source, but not on cadaverine. Cell suspensions of one isolate (PU-8) produced gamma aminobutyric acid (GABA) from putrescine in 0.02 M phosphate buffer (pH 7.6) containing 0.33 M NaCl and 15 mM MgCl₂, and three other isolates produced the inducer when gabaculine (a natural inhibitor of GABA metabolism) was added. None of the isolates produced GABA from spermidine either in the absence or presence of gabaculine. Yields of GABA from putrescine were low in the suspension fluid and near stoichiometric quantities could only be obtained by extraction of incubations with methanol. Decreased NaCl (< 0.05 M) or increased pH resulted in an increase of GABA released into the suspension fluid during incubations, although in growth cultures only pH appeared to have a substantial effect. GABA release was not influenced by temperature in the range 17 to 32°C. Replacement of the normal concentration of NaCl (0.33 M) with equivalent LiCl, sodium glucuronate, or sucrose in cell suspensions did not result in increased GABA in the suspension fluid, indicating non-involvement of a sodium or chloride ion-dependent transport system in GABA release. The results show that marine bacteria can produce GABA, an inducer of marine invertebrate larval settlement, and indicate that extenal changes in osmotic pressure and pH which influence GABA release may be important factors to consider in the production of this inducer.