Identification of new enzymes potentially involved in anaerobic naphthalene degradation by the sulfate-reducing enrichme
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ORIGINAL PAPER
Identification of new enzymes potentially involved in anaerobic naphthalene degradation by the sulfate-reducing enrichment culture N47 Franz D. Bergmann • Drazˇenka Selesi Rainer U. Meckenstock
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Received: 11 July 2010 / Revised: 4 November 2010 / Accepted: 10 December 2010 / Published online: 8 January 2011 Ó Springer-Verlag 2011
Abstract The sulfate-reducing highly enriched culture N47 is capable to anaerobically degrade naphthalene, 2-methylnaphthalene, and 2-naphthoic acid. A proteogenomic investigation was performed to elucidate the initial activation reaction of anaerobic naphthalene degradation. This lead to the identification of an alpha-subunit of a carboxylase protein that was two-fold up-regulated in naphthalene-grown cells compared to 2-methylnaphthalene-grown cells. The putative naphthalene carboxylase subunit showed 48% similarity to the anaerobic benzene carboxylase from an iron-reducing, benzene-degrading culture and 45% to alpha-subunit of phenylphosphate carboxylase of Aromatoleum aromaticum EbN1. A gene for the beta-subunit of putative naphthalene carboxylase was located nearby on the genome and was expressed with naphthalene. Similar to anaerobic benzene carboxylase, there were no genes for gamma- and delta-subunits of a putative carboxylase protein located on the genome which excludes participation in degradation of phenolic compounds. The genes identified for putative naphthalene carboxylase subunits showed only weak similarity to 4-hydroxybenzoate decarboxylase excluding ATP-independent carboxylation. Several ORFs were identified that possibly encode a 2-naphthoate-CoA ligase, which is obligate for activation before the subsequent ring reduction by naphthoyl-CoA reductase. One of these ligases was
Communicated by Joerg Overmann. F. D. Bergmann D. Selesi R. U. Meckenstock (&) Institute of Groundwater Ecology, Helmholtz Zentrum Mu¨nchen—German Research Center for Environmental Health, Ingolsta¨dter Landstrasse 1, 85764 Neuherberg, Germany e-mail: [email protected]
exclusively expressed on naphthalene and 2-naphthoic acid and might be the responsible naphthoate-CoA-ligase. Keywords Anaerobic naphthalene degradation Carboxylation
Introduction Naphthalene is the smallest polycyclic aromatic hydrocarbon and it exhibits a low chemical reactivity due to its aromatic 10p electron system. Since several decades, aerobic naphthalene degradation has been extensively studied and the initial reactions by oxygenase enzymes have been described in detail (Habe and Omori 2003). In contrast, the biochemical mechanism of anaerobic naphthalene degradation with alternative electron acceptors like sulfate or nitrate has not yet been adequately elucidated although several nitrate- and sulfate-reducing pure and highly enriched microbial cultures are available (Zhang and Young 1997; Galushko et al. 1999; Meckenstock et al. 2000; Rockne et al. 2000; Musat et al. 2009). However, in the absence of molecular oxygen, totally different and new biochemical reactions must be use
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