Oxidative Metabolism of Phenanthrene and Anthracene by Soil Pseudomonads. The Ring-Fission Mechanism

Abstract

1. Phenanthrene is oxidatively metabolized by soil pseudomonads through trans-3,4-dihydro-3,4-dihydroxyphenanthrene to 3,4-dihydroxyphenanthrene, which then undergoes cleavage. 2. Some properties of the ring-fission product, cis-4-(1-hydroxynaphth-2-yl)-2-oxobut-3-enoic acid, are described. The Fe(2+)-dependent oxygenase therefore disrupts the bond between C-4 and the angular C of the phenanthrene nucleus. 3. An enzyme of the aldolase type converts the fission product into 1-hydroxy-2-naphthaldehyde (2-formyl-1-hydroxynaphthalene). An NAD-specific dehydrogenase is also present in the cell-free extract, which oxidizes the aldehyde to 1-hydroxy-2-naphthoic acid. This is then oxidatively decarboxylated to 1,2-dihydroxynaphthalene, thus allowing continuation of metabolism via the naphthalene pathway. 4. Anthracene is similarly metabolized, through 1,2-dihydro-1,2-dihydroxyanthracene to 1,2-dihydroxyanthracene, in which ring-fission occurs to give cis-4-(2-hydroxynaphth-3-yl)-2-oxobut-3-enoic acid. The position of cleavage is again at the bond between the angular C and C-1 of the anthracene nucleus. 5. Enzymes that convert the fission product through 2-hydroxy-3-naphthaldehyde into 2-hydroxy-3-naphthoic acid were demonstrated. The further metabolism of this acid is discussed. 6. The Fe(2+)-dependent oxygenase responsible for cleavage of all the o-dihydroxyphenol derivatives appears to be catechol 2,3-oxygenase, and is a constitutive enzyme in the Pseudomonas strains used.

Experimental Results and Integrated Modeling of Bacterial Growth on an Insoluble Hydrophobic Substrate (Phenanthrene)

“…The experiment was performed in six replicates for each concentration and time point in order to provide triplicates for separate quantification of biomass and PHE. The mini-cultures were incubated at 30°C, shaken at 135 rpm, and harvested as follows: for N. pentaromativorans, after 0, 4,8,12,24,36,48,96, and 144 h of incubation for initial 10, 25, and 50 mg L −1 PHE concentrations and after 0, 6,12,24,48,96,144,192, and 288 h for initial 100, 200, and 400 mg L −1 PHE concentrations; and for S. yanoikuyae and Sphingomonas sp., after 0, 4,8,12,24,30,36,48, and 96 h for initial 10, 25, and 50 mg L −1 PHE concentrations and after 0, 6,12,24,48,72,96,192, and 288 h for initial 100, 200, and 400 mg L −1 PHE concentrations.…”

“…The substrate metabolized by the microbes is related to bacterial growth via the yield Y (g bacteria g −1 substrate); it is used by microbes both for actual growth (with rate μ in d −1 ) and for maintenance needs r (g substrate g −1 bacteria d −1 ) of microbes decaying with rate b (d −1 ). 33 The experimentally observable growth rate constant is bacterial mass versus time per bacteria, dX (X dt) −1 , and can be obtained from eq 3 as By rearranging, the "true" yield Y (g bacteria g −1 substrate) follows (6) The experimentally derived yield Y exp is the ratio of observed growth dX/dt to change of substrate mass dm M /dt:…”

A novel degradation pathway in the assimilation of phenanthrene by Staphylococcus sp. strain PN/Y via meta-cleavage of 2-hydroxy-1-naphthoic acid: formation of trans-2,3-dioxo-5-(2′-hydroxyphenyl)-pent-4-enoic acid

“…Although salicylaldehyde, salicylic acid and catechol were also produced as intermediates in the metabolism of 1-hydroxy-2-naphthoic acid via 1,2-dihydroxynaphthalene (Evans et al, 1965;Gibson & Subramanian, 1984), the latter compound neither supported oxygen uptake in the resting cells assay nor was metabolized by the cell-free extracts of phenanthrene-or 2-hydroxy-1-naphthoic acidgrown cells of strain PN/Y, indicating absence of such a metabolic pattern of 2-hydroxy-1-naphthoic acid in this study.…”

“…Over the last 60 years, a number of studies on phenanthrene degradation by several Gram-negative and Gram-positive bacterial species have been reported (Evans et al, 1965;Kiyohara et al, 1976Kiyohara et al, , 1982Kiyohara & Nagao, 1978;Barnsley, 1983;Gibson & Subramanian, 1984;Houghton & Shanley, 1994;Adachi et al, 1999;Samanta et al, 1999), where various pathways and metabolic diversity involved in phenanthrene degradation were documented. In general, the metabolic pathway is initiated by the double hydroxylation of the bay-region of phenanthrene by a dioxygenase enzyme to form cis-3,4-phenanthrenedihydrodiol.…”

“…1-Hydroxy-2-naphthoic acid is further degraded by one of the two distinct pathways reported so far. In one of the routes, 1-hydroxy-2-naphthoic acid undergoes oxidative decarboxylation to form 1,2-dihydroxynaphthalene, which is subsequently metabolized by the classical naphthalene degradation pathway via salicylic acid and catechol (Evans et al, 1965;Gibson & Subramanian, 1984). In the other route, 1-hydroxy-2-naphthoic acid undergoes ring cleavage by 1-hydroxy-2-naphthoate dioxygenase in ortho-fashion and is further metabolized via o-phthalic acid and protocatechuic acid (Kiyohara et al, 1976;Houghton & Shanley, 1994;Adachi et al, 1999).…”