Isolation of the phe-operon from G. stearothermophilus comprising the phenol degradative meta-pathway genes and a novel transcriptional regulator.
BACKGROUND
Geobacillus stearothermophilus is able to utilize phenol as a sole carbon source. A DNA fragment encoding a phenol hydroxylase catalyzing the first step in the meta-pathway has been isolated previously. Based on these findings a PCR-based DNA walk was performed initially to isolate a catechol 2,3-dioxygenase for biosensoric applications but was continued to elucidate the organisation of the genes encoding the proteins for the metabolization of phenol.


RESULTS
A 20.2 kb DNA fragment was isolated as a result of the DNA walk. Fifteen open reading frames residing on a low-copy megaplasmid were identified. Eleven genes are co-transcribed in one polycistronic mRNA as shown by reverse transcription-PCR. Ten genes encode proteins, that are directly linked with the meta-cleavage pathway. The deduced amino acid sequences display similarities to a two-component phenol hydroxylase, a catechol 2,3-dioxygenase, a 4-oxalocrotonate tautomerase, a 2-oxopent-4-dienoate hydratase, a 4-oxalocrotonate decarboxylase, a 4-hydroxy-2-oxovalerate aldolase, an acetaldehyde dehydrogenase, a plant-type ferredoxin involved in the reactivation of extradiol dioxygenases and a novel regulatory protein. The only enzymes missing for the complete mineralization of phenol are a 2-hydroxymuconic acid-6-semialdehyde hydrolase and/or 2-hydroxymuconic acid-6-semialdehyde dehydrogenase.


CONCLUSIONS
Research on the bacterial degradation of aromatic compounds on a sub-cellular level has been more intensively studied in gram-negative organisms than in gram-positive bacteria. Especially regulatory mechanisms in gram-positive (thermophilic) prokaryotes remain mostly unknown. We isolated the first complete sequence of an operon from a thermophilic bacterium encoding the meta-pathway genes and analyzed the genetic organization. Moreover, the first transcriptional regulator of the phenol metabolism in gram-positive bacteria was identified. This is a first step to elucidate regulatory mechanisms that are likely to be distinct from modes described for gram-negative bacteria.
Omokoko
Bastian
B
Department of Biotechnology, RWTH Aachen University, Worringer Weg 1, 52074 Aachen, Germany. b.omokoko@biotec.rwth-aachen.de
Jäntges
Uwe K
UK
Zimmermann
Martin
M
Reiss
Monika
M
Hartmeier
Winfried
W
D001406:Bacillaceae / Q000201:enzymology / Q000235:genetics*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D050557:Catechol 2,3-Dioxygenase / Q000235:genetics / Q000378:metabolism*; D002851:Chromatography, High Pressure Liquid; D016386:Chromosome Walking; D002876:Chromosomes, Bacterial / Q000235:genetics; D004269:DNA, Bacterial / Q000235:genetics; D016521:Electrophoresis, Gel, Pulsed-Field; D015723:Gene Library; D005798:Genes, Bacterial; D016366:Open Reading Frames; D009876:Operon; D010636:Phenols / Q000378:metabolism*; D010957:Plasmids; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D016415:Sequence Alignment; D017422:Sequence Analysis, DNA
D001426:Bacterial Proteins; D004269:DNA, Bacterial; D010636:Phenols; D012333:RNA, Messenger; D050557:Catechol 2,3-Dioxygenase