To further explore the relationships and physiology of anaerobic naphthalene-degrading microorganisms, sulfate-reducing bacteria (SRB) were enriched from a Mediterranean sediment with added naphthalene.
Two strains (NaphS3, NaphS6) with oval cells were isolated which showed naphthalene-dependent sulfate reduction.
According to 16S rRNA gene sequences, both strains were Deltaproteobacteria and closely related to each other and to a previously described naphthalene-degrading sulfate-reducing strain (NaphS2) from a North Sea habitat.
Other close relatives were SRB able to degrade alkylbenzenes, and phylotypes enriched anaerobically with benzene.
If in adaptation experiments the three naphthalene-grown strains were exposed to 2-methylnaphthalene, this compound was utilized after a pronounced lag phase, indicating that naphthalene did not induce the capacity for 2-methylnaphthalene degradation.
Comparative denaturing gel electrophoresis of cells grown with naphthalene or 2-methylnaphthalene revealed a striking protein band which was only present upon growth with the latter substrate.
Peptide sequences from this band perfectly matched those of a protein predicted from genomic libraries of the strains.
Sequence similarity (50% identity) of the predicted protein to the large subunit of the toluene-activating enzyme (benzylsuccinate synthase) from other anaerobic bacteria indicated that the detected protein is part of an analogous 2-methylnaphthalene-activating enzyme.
The absence of this protein in naphthalene-grown cells together with the adaptation experiments as well as isotopic metabolite differentiation upon growth with a mixture of d(8)-naphthalene and unlabelled 2-methylnaphthalene suggest that the marine strains do not metabolize naphthalene by initial methylation via 2-methylnaphthalene, a previously suggested mechanism.
The inability to utilize 1-naphthol or 2-naphthol also excludes these compounds as free intermediates.
Results leave open the possibility of naphthalene carboxylation, another previously suggested activation mechanism.
Environ Microbiol (1462-2920)
Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, 28359 Bremen, Germany.
Environ Microbiol. 2009 Jan;11(1):209-19
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