AEM Accepts, published online ahead of print on 6 November 2009

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Appl. Environ. Microbiol. doi:10.1128/AEM.01846-09
Copyright (c) 2009, American Society for Microbiology and/or the Listed Authors/Institutions. All Rights Reserved.

Tetralin-induced and ThnR regulated aldehyde dehydrogenase and -oxidation genes in Sphingomonas macrogolitabida strain TFA

Aroa López-Sánchez, Belén Floriano^*, Eloisa Andújar, Maria José Hernáez, and Eduardo Santero

Centro Andaluz de Biología del Desarrollo, CSIC-Universidad Pablo de Olavide, Seville, Spain

^* To whom correspondence should be addressed. Email: bflopar{at}upo.es.

A new cluster of genes has been found downstream of the previously identified thnA2 gene. The gene products are similar to non-acylating aldehyde dehydrogenases (ThnG) and to proteins representing a complete -oxidation pathway (ThnH to ThnP). ThnG has a non-acylating NAD-dependent pimelic semialdehyde dehydrogenase activity that renders pimelic acid a 7-carbon dicarboxylic acid. For further metabolism via -oxidation, pimelic acid could be acylated by a constitutive acyl-CoA ligase found in TFA or by ThnH, which would transfer coenzyme A from a previously acylated molecule. The first round of -oxidation is expected to render glutaryl-CoA and acetyl-CoA. Glutaryl-CoA dehydrogenase (ThnN) would catalyze the oxidation and decarboxylation of glutaryl-CoA and yield crotonyl-CoA, which enters the central metabolism via acetyl-CoA. Mutagenesis studies have shown that these genes are not essential for growth on tetralin or fatty acids, although a thnG disruption mutant showed threefold less pimelic semialdehyde dehydrogenase activity. Transcriptional analysis indicated that these genes are induced by tetralin, subjected to catabolite repression and regulated by the same regulatory factors previously identified to regulate other thn structural genes. In this work, transcription initiation upstream of thnH and thnM has been detected by primer extension analysis, and putative promoters were identified by sequence analysis. Additionally, binding of the activator ThnR to its putative binding sites at the P_H and P_M promoter regions has been characterized. These results provide a complete characterization of the biodegradation pathway of tetralin to central metabolites and describe the transcriptional organization of the thn operons in S. macrogolitabida strain TFA.