DEGRADATION OF GAMMA-AMINOBUTYRIC-ACID (GABA) BY MARINE MICROORGANISMS

By degrading the settlement inducer gamma-aminobutyric acid (GABA), bacteria may affect the larval settlement of sedentary marine invertebrates. Nearly one third of bacterial isolates from surfaces suitable for abalone (Haliotis) settlement were able to grow on GABA as sole carbon source. Compared with similar compounds, GABA was a good source of carbon, nitrogen and energy, and it was utilized concomitantly with glucose. GABA-metabolizing enzymes were constitutive in Pseudomonas fluorescens and inducible in Aeromonas hydrophila. High-affinity (Km: 20-50-mu-M) and low-affinity (K(m): 7-9 mM) uptake systems were produced in response to low and high GABA concentrations, respectively, in the growth medium. Within the ecologically significant temperature range (12-24-degrees-C), specific GABA degradation rates varied 2.5-fold in young cells of P. fluorescens. This organism lost its ability to degrade GABA during the stationary phase. The results suggest that marine bacteria have the potential to affect invertebrate larval settlement by removing GABA from the settlement habitat.