1. Introduction
Benzoic acid and its salts are widely used in food, pharmaceuticals, and
cosmetics as preservative, as they inhibit growth of several yeasts and
bacteria. Commercially, benzoate is produced by partial oxidation of
toluene with oxygen, catalyzed by cobalt or manganese naphthenates
[1]. This conversion can also be performed by microbes, e.g.,
through the upper pathway encoded on the TOL plasmid pWW0 fromPseudomonas putida mt-2 [2]. Besides environmental issues
that arise from its petrochemical production process, microbially
produced benzoate is considered to be “natural”, which is a major
benefit for applications in food and cosmetics. This, however, requires
the production to start from a bio-based substrate.
Despite its industrial relevance and simple structure, only minor
efforts have been made to develop a microbial host for the bioproduction
of benzoate with only one study demonstrating its de novoproduction [3]. About 460 mg L−1 (3.8 mM) of
benzoate was produced with Streptomyces maritimus in a
fermentation process using a complex medium (5% tryptone, 3%
cornstarch). So far this is the only prokaryotic organism that has been
described to natively synthesize benzoate from l‑phenylalanine
via β-oxidation of trans ‑cinnamoyl-CoA as part of the enterocin
biosynthesis pathway [4].
Pseudomonas taiwanensis is a promising microbial cell factory,
especially regarding the production of aromatics. This has been recently
demonstrated by our group in multiple studies for de novosynthesis of phenol, 4‑hydroxybenzoate, and trans -cinnamate
[5-8]. In this study, a previously generated Pseudomonas
taiwanensis trans -cinnamate overproducer was further engineered
to enable benzoate production from renewable resources in a mineral
medium without supplementation of complex substances or antibiotics. To
our knowledge, this is the first de novo synthesis of benzoate in
a recombinant microbial cell factory. The intrinsic benzoate catabolic
pathway of P. taiwanensis was exploited to produce other
industrially relevant chemicals, namely catechol andcis,cis -muconate, thereby establishing a novel biosynthesis
pathway for these molecules.