Description:
<jats:title>ABSTRACT</jats:title>
<jats:p>
Information on anaerobic phenol metabolism by physiological groups of bacteria other than nitrate reducers is scarce. We investigated phenol degradation in the strictly anaerobic iron-reducing deltaproteobacterium
<jats:italic>Geobacter metallireducens</jats:italic>
GS-15 using metabolite, transcriptome, proteome, and enzyme analyses. The results showed that the initial steps of phenol degradation are accomplished by phenylphosphate synthase (encoded by
<jats:italic>pps</jats:italic>
genes) and phenylphosphate carboxylase (encoded by
<jats:italic>ppc</jats:italic>
genes) as known from
<jats:italic>Thauera aromatica</jats:italic>
, but they also revealed some distinct differences. The
<jats:italic>pps</jats:italic>
-
<jats:italic>ppc</jats:italic>
gene cluster identified in the genome is functional, as shown by transcription analysis. In contrast to
<jats:italic>T. aromatica</jats:italic>
, transcription of the
<jats:italic>pps-</jats:italic>
and
<jats:italic>ppc</jats:italic>
-like genes was induced not only during growth on phenol, but also during growth on benzoate. In contrast, proteins were detected only during growth on phenol, suggesting the existence of a posttranscriptional regulation mechanism for these initial steps. Phenylphosphate synthase and phenylphosphate carboxylase activities were detected in cell extracts. The carboxylase does not catalyze an isotope exchange reaction between
<jats:sup>14</jats:sup>
CO
<jats:sub>2</jats:sub>
and 4-hydroxybenzoate, which is characteristic of the
<jats:italic>T. aromatica</jats:italic>
enzyme. Whereas the enzyme of
<jats:italic>T. aromatica</jats:italic>
is encoded by
<jats:italic>ppcABCD</jats:italic>
, the
<jats:italic>pps</jats:italic>
-
<jats:italic>ppc</jats:italic>
gene cluster of
<jats:italic>G. metallireducens</jats:italic>
contains only a
<jats:italic>ppcB</jats:italic>
homologue. Nearby, but oriented in the opposite direction, is a
<jats:italic>ppcD</jats:italic>
homologue that is transcribed during growth on phenol. Genome analysis did not reveal obvious homologues of
<jats:italic>ppcA</jats:italic>
and
<jats:italic>ppcC</jats:italic>
, leaving open the question of whether these genes are dispensable for phenylphosphate carboxylase activity in
<jats:italic>G. metallireducens</jats:italic>
or are quite different from the
<jats:italic>Thauera</jats:italic>
counterparts and located elsewhere in the genome.
</jats:p>