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J Bacteriol, March 1998, p. 1063-1071, Vol. 180, No. 5
Department of Molecular Microbiology,
Received 6 October 1997/Accepted 6 December 1997
The chromosomal region of Pseudomonas sp. strain Y2
involved in the conversion of styrene to phenylacetate (upper catabolic pathway) has been cloned and sequenced. Four catabolic genes, styABCD, and two regulatory genes, stySR, were
identified. This gene cluster when transferred to Escherichia
coli W confers to this phenylacetate-degrading host the ability
to grow on styrene as the sole carbon and energy source. Genes
styABCD are homologous to those encoding the styrene upper
catabolic pathway in Pseudomonas fluorescens ST. Northern
blot analyses have confirmed that genes styABCD constitute
a transcription unit. The transcription start site of the
sty operon was mapped 33 nucleotides upstream of the styA translational start codon. The styS and
styR genes, which form an independent transcriptional unit,
are located upstream of the styABCD operon, and their gene
products show high similarity to members of the superfamily of
two-component signal transduction systems. The styS gene
product is homologous to histidine kinase proteins, whereas the
styR gene product exhibits similarity at its N-terminal
domain with cluster 1 of receiver modules and at its C terminus with
the LuxR/FixJ family 3 of DNA-binding domains. Expression of the
catabolic operon decreased significantly in the absence of the
stySR genes and was restored when the stySR genes were provided in trans in the presence of styrene,
suggesting that the stySR system behaves as a
styrene-inducible positive regulator of the styABCD operon.
Finally, a gene encoding a phenylacetyl-coenzyme A ligase that
catalyzes the first step in the phenylacetate catabolism (styrene lower
catabolic pathway) has been identified upstream of the styS
gene. This activity was found to be induced in Pseudomonas sp. strain Y2 cells grown on styrene but not present in cells grown on
glycerol. These results strongly suggest that the genes responsible for
the complete mineralization of styrene are clustered in the chromosome
of Pseudomonas sp. strain Y2.
0021-9193/98/$04.00+0
Copyright © 1998, American Society for Microbiology. All rights reserved.
Genetic and Functional Analysis of the Styrene
Catabolic Cluster of Pseudomonas sp. Strain Y2
*
Corresponding author. Mailing address: Department of
Molecular Microbiology, Centro de Investigaciones Biológicas,
Velázquez 144, 28006 Madrid, Spain. Phone: 34-1-5611800. Fax:
34-1-5627518. E-mail: cibg160{at}fresno.csic.es.
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