Abstract
Geobacillus sp. JF8 is a thermophilic biphenyl and naphthalene degrader. To identify the naphthalene degradation genes, cis-naphthalene dihydrodiol dehydrogenase was purified from naphthalene-grown cells, and its N-terminal amino acid sequence was determined. Using a DNA probe encoding the N-terminal region of the dehydrogenase, a 10-kb DNA fragment was isolated. Upstream of nahB, a gene for dehydrogenase, there were two open reading frames which were designated as nahAc and nahAd, respectively. The products of nahAc and nahAd were predicted to be alpha and beta subunit of ring-hydroxylating dioxygenases, respectively. Phylogenetic analysis of amino acid sequences of NahB indicated that it did not belong to the cis-dihydrodiol dehydrogenase group that includes those of classical naphthalene degradation pathways. Downstream of nahB, four open reading frames were found, and their products were predicted as meta-cleavage product hydrolase, monooxygenase, dehydrogenase, and gentisate 1,2-dioxygenase, respectively. A reverse transcriptase-PCR analysis showed that transcription of nahAcAd was induced by naphthalene. These findings indicate that we successfully identified genes involved in the upper pathway of naphthalene degradation from a thermophilic bacterium.
Highlights
Naphthalene degradation pathways and their enzymes have been extensively studied in mesophilic bacteria including Pseudomonas species
In the the genes relatedrelated to naphthalene degradation were isolated andisolated characterized
An enzyme, which characterized from a thermophilic PCB and naphthalene degrader, Geobacillus sp. strain JF8
Summary
Naphthalene degradation pathways and their enzymes have been extensively studied in mesophilic bacteria including Pseudomonas species. Their degradation genes are organized in three operons: one of them encodes the enzymes involved in conversion of naphthalene to salicylate Microorganisms 2020, 8, 44; doi:10.3390/microorganisms8010044 www.mdpi.com/journal/microorganisms dioxygen to naphthalene by naphthalene 1,2-dioxygenase (NahA enzyme), and it is converted to cis1,2-dihydroxy-1,2-dihydronaphthalene (DDNP) (Figure 1). DDNP is dehydrated and converted to 1,2-dihydroxynaphthalene (DHNP) by 1,2-dihydroxy-1,2-dihydronaphthalene dehydrogenase (NahB enzyme) (Figure 1). Another dioxygen is added to DHNP by 1,2dihydroxynaphthalene dioxygenase (NahC enzyme) and the DHNP is cleaved at the meta position Microorganisms. The salicylate could be degraded via catechol or gentisate [1,8,9]
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