The meta Pathway as a Potential Energy-Generating Sequence and its Effects on the Growth Rate during the Utilisation of Aromatics

Abstract

Pseudomonas putida was grown on benzoate in order to determine the maximum growth rate depending on the ortho and/or meta assimilation pathway. Strain KT2440(pWW0), which expressed both the ortho (catechol 1,2-dioxygenase) and meta (catechol 2,3-dioxygenase) pathway under C-limited growth conditions, resulted in a maximum growth rate of μmax of 0.27 h-1 as determined by a transient-state cultivation technique. This rate was similar to the μmax of a strain in which the meta pathway was inactivated by Tn5 transposon mutagenesis. With strain KT2440, in which the meta pathway was eliminated by curing of the plasmid, a maximum growth rate of 0.44 h-1 was reached. By contrast, when using strain PaW94, which was deficient in a functional ortho pathway, the μmax amounted to 0.31 h-1 with transconjugants bearing plasmid pWW0 as a harbour of the meta pathway. Moreover, with transconjugant strains harbouring the TOL≔RP4 hybrid plasmid pWW53-4, the maximum growth rate was as high as 0.58 h-1. Such a high rate was also attained (but not exceeded) by a plasmid-less strain of PaW94 in which the meta pathway was integrated into the chromosome. According to these results, the maximum growth rate was 1.3 times faster when the meta pathway was used compared to the ortho pathway in a chromosomal localisation of both routes. These effects are discussed in terms of an advantage attributed to the manner of energy generation by assimilating phenolic substrates via the meta pathway in comparison with the ortho pathway. The effects on the maximum growth rates may be modulated by the presence or absence of plasmids.