Methyl substituted naphthalenes raise great environmental and human health concern since they have been shown to be one of the most toxic components in the water soluble fraction of crude and fuel oils. This page describes the microbial degradation of 2-methylnaphthalene under aerobic conditions. An anaerobic 2-methylnaphthalene degradation pathway is presented elsewhere.
A soil isolate, Pseudomonas putida CSV86 is able to grow using 1-and 2-Methylnaphthalene as the sole sources of carbon and energy (Mahajan et al., 1994). In the right-most pathway, the aromatic ring adjacent to the one bearing the methyl moiety is oxidized, resulting in the formation of methylsalicylates and methylcatechols. In the left-most pathway the methyl side chain is hydroxylated and further converted resulting in the formation of naphthoic acid. In addition to this, 2-hydroxymethylnaphthalene formed by the hydroxylation of the methyl group of 2-methylnaphthalene undergoes aromatic ring hydroxylation of the methyl group and the resultant dihydrodiol is further oxidized by a series of enzyme catalyzed reactions to form the end product 4-hydroxymethylcatechol (Mahajan et al., 1994). Other organisms able to degrade 2-Methylnaphthalene include Marinobacter sp. NCE312, Vibrio cyclotrophicus, Neptunomonas naphthovorans, Pseudomonas fluorescens LP6a, and Mycobacterium sp.
Naphthalene dioxygenase, an enzyme in this pathway, is used in a biotechnological process to synthesize the blue jean dye indigo. This versatile enzyme has many other catalytic abilities, which are documented in a table of the Reactions of Naphthalene 1,2-dioxygenase.
The following is a text-format 2-Methylnaphthalene degradation pathway map. Organisms which can initiate the pathway are given, but other organisms may also carry out later steps. Follow the links to find out abut the compounds and reactions.
Graphical Map (20k) | Graphical Map (5k)
2-Methylnaphthalene 2-Methylnaphthalene Pseudomonas putida CSV86 | | | | | | | 2-methylnaphthalene | naphthalene | hydroxylase | 1,2-dioxygenase | | | | | naphthalene | | 1,2-dioxygenase | V V 2-Hydroxymethyl- ------->cis 1,2-Dihydroxy- cis 1,2-Dihydroxy- naphthalene 1,2-dihydro- 1,2-dihydro- | 7-hydroxymethyl- 7-methylnaphthalene | naphthalene | | | | | alcohol | 1,2-dihydroxy- | | dehydrogenase | 1,2-dihydro- V B | | naphthalene | | | dehydrogenase | | | | V V V +---- 2-Naphthaldehyde 1,2-Dihydroxy- 4-Methylsalicylate | | 7-hydroxymethyl- | | | naphthalene | | | | | | | 2-naphthaldehyde | 1,2-dihydroxy- | salicylate V | dehydrogenase | 7-hydroxymethyl- | hydroxylase | | | naphthalene | | A | | dioxygenase | | | | | | V V V V 2-Naphthoate 2-Hydroxy- 4-Methylcatechol | 7-hydroxymethyl- | | chromene-2-carboxylate | | | | | | 2-hydroxy- | | | 7-hydroxymethyl- | +-------------+ | chromene-2-carboxylate | | | isomerase | | | | V V V 4-Formylsalicylic acid 2-Hydroxy- to the 4-hydroxymethyl- p-Xylene Pathway benzalpyruvate | | 2-hydroxy- | 4-hydroxymethyl- | benzalpyruvate | hydratase-aldolase | V 4-Hydroxymethyl- + Pyruvate salicylaldehyde | | 4-hydroxymethyl- | salicylaldehyde | dehydrogenase | | V 4-Hydroxymethylsalicylate | | | salicylate | hydroxylase | | V 4-Hydroxymethylcatechol
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