Regulation of the utilization of 4-hydroxybenzoate and vanillate in batch and continuous cultures of Pseudomonas acidovorans

Abstract

In Pseudomonas acidovorans, the pathways of 4-hydroxybenzoate and vanillate metabolism converge on the early intermediate, protocatechuate, which undergoes meta-cleavage. The methoxyl group of vanillate is almost completely oxidized, as shown by an experiment with (¹⁴C-methoxyl) vanillate. In batch cultures, 4-hydroxybenzoate and vanillate are simultaneously oxidized. Simultaneous oxidation was explained above all by the fact that both substrates mutually repress the ability of the cells to utilize the partner substrate.

If P. acidovorans is growing in a turbidostat on one of the two substrates and is suddenly exposed to an equimolar mixture of both substrates, the respiration rates for the two substrates reciprocate, the $Q_{{\text{O}}_{\text{2}} }^{{\text{max}}}$ for the substrate utilized first passing through a transient minimum, that for the added substrate passing through a transient maximum. Finally, a balance appears to be established, the $Q_{{\text{O}}_{\text{2}} }^{{\text{max}}}$ for 4-hydroxybenzoate being slightly above that for vanillate. Transient phenomena also occur if a chemostat culture with both substrates is suddenly operated as a turbidostat culture or if cells not adapted to either substrate are suddenly exposed to a mixture of both substrates in the turbidostat.

If a chemostat culture of P. acidovorans, growing at the expense of an equimolar mixture of 4-hydroxybenzoate and vanillate, is operated under conditions of increasing oxygen deficiency, the utilization ratio of the two substrates increases in favour of 4-hydroxybenzoate. However, if the culture is operated under conditions of increasing nitrogen deficiency, the utilization ratio increases in favour of vanillate.