Barnes M.R., Duetz W.A. & Williams P.A. (1997) A
3-(3-hydroxyphenyl)propionic acid catabolic pathway in Rhodococcus globerulus
PWD1: cloning and characterization of the hpp operon.
J. Bacteriol 179:6145-6153.
ABSTRACT
Rhodococcus globerulus PWD1, a soil isolate from a polluted site
in Holland, is able to degrade a broad range of aromatic compounds. A novel
gene cluster has been cloned from the chromosome which appears to encode
a pathway for the degradation of phenolic acids, such as 3-(3-hydroxyphenyl)propionate
(3OHPP). Sequence analysis of a 7 kb region identified five open reading
frames (ORFs). Analysis of mRNA showed that the genes were expressed during
growth on 3OHPP and 3-hydroxyphenylacetate (3OHPA) but not during growth
on m-cresol or succinate. The first ORF
hppA, which appears to be
separately transcribed, shared considerable amino acid identity with a
number of hydroxylases. Transcriptional analysis indicates that the next
four ORFs
hppCBKR, which are tightly clustered, constitute a single
operon. These genes appear to encode a hydroxymuconic semialdehyde hydrolase
HppC, an extradiol dioxygenase HppB, a membrane transport protein HppK
and a member of the IclR family of regulatory proteins HppR. The activities
of HppB and HppC have been confirmed by enzyme assay within
E.coli
hosts. The substrate specificity of HppB expressed from the cloned gene
matches that of the
meta-cleavage dioxygenase expressed from wild
type
Rhodococcus grown on both 3OHPP and 3OHPA, and is considerably
more active against 2,3-dihydroxy acids than against neutral catechols.
The deduced amino acid sequences of the gene products have a recognisable
homology with a broad range of enzymes and proteins involved in biodegradation
and appear most similar to the
mhp operon from
E. coli K-12
which also encodes the degradation of 3-(3-hydroxyphenyl)propionate. We
propose that genes from these and similar pathways may have been one of
the most ubiquitous sources for recruitment of biodegradative genes.
