Relationship between succinate transport and production of extracellular poly(3-hydroxybutyrate) depolymerase in Pseudomonas lemoignei

The relationship between extracellular poly(3-hydroxybutyrate) (PHB) depoly merase synthesis and the unusual properties of a succinate uptake system wa s investigated in Pseudomonas lemoignei. Growth on and uptake of succinate were highly pH dependent, with optima at pH 5.6. Above pH 7, growth on and uptake of succinate were strongly reduced with concomitant derepression of PHB depolymerase synthesis. The specific succinate uptake rates were satura ble by high concentrations of succinate, and maximal transport rates of 110 nmol/mg of cell protein per min were determined between pH 5.6 and 6.8. Th e apparent K-S0.5 values increased with increasing pH from 0.2 mM succinate at pH 5.6 to more than 10 mM succinate at pH 7.6. The uptake of [C-14]succ inate was strongly inhibited by several monocarboxylates. Dicarboxylates al so inhibited the uptake of succinate but only at pH values near the dissoci ation constant of the second carboxylate function (pK(a)2). We conclude tha t the succinate carrier is specific for the monocarboxylate forms of variou s carboxylic acids and is not able to utilize the dicarboxylic forms. The i nability to take up succinate(2-) accounts for the carbon starvation of P. lemoignei observed during growth on succinate at pH values above 7. As a co nsequence the bacteria produce high levels of extracellular PHB depolymeras e activity in an effort to escape carbon starvation by utilization of PHB h ydrolysis products.