Biodegradation of phenanthrene by Pseudomonas sp. strain PP2: novel metabolic pathway, role of biosurfactant and cell surface hydrophobicity in hydrocarbon assimilation.
Pseudomonas sp. strain PP2 isolated in our laboratory efficiently metabolizes phenanthrene at 0.3% concentration as the sole source of carbon and energy. The metabolic pathways for the degradation of phenanthrene, benzoate and p-hydroxybenzoate were elucidated by identifying metabolites, biotransformation studies, oxygen uptake by whole cells on probable metabolic intermediates, and monitoring enzyme activities in cell-free extracts. The results obtained suggest that phenanthrene degradation is initiated by double hydroxylation resulting in the formation of 3,4-dihydroxyphenanthrene. The diol was finally oxidized to 2-hydroxymuconic semialdehyde. Detection of 1-hydroxy-2-naphthoic acid, alpha-naphthol, 1,2-dihydroxy naphthalene, and salicylate in the spent medium by thin layer chromatography; the presence of 1,2-dihydroxynaphthalene dioxygenase, salicylaldehyde dehydrogenase and catechol-2,3-dioxygenase activity in the extract; O(2) uptake by cells on alpha-naphthol, 1,2-dihydroxynaphthalene, salicylaldehyde, salicylate and catechol; and no O(2) uptake on o-phthalate and 3,4-dihydroxybenzoate supports the novel route of metabolism of phenanthrene via 1-hydroxy-2-naphthoic acid --> [alpha-naphthol] --> 1,2-dihydroxy naphthalene --> salicylate --> catechol. The strain degrades benzoate via catechol and cis,cis-muconic acid, and p-hydroxybenzoate via 3,4-dihydroxybenzoate and 3-carboxy- cis,cis-muconic acid. Interestingly, the culture failed to grow on naphthalene. When grown on either hydrocarbon or dextrose, the culture showed good extracellular biosurfactant production. Growth-dependent changes in the cell surface hydrophobicity, and emulsification activity experiments suggest that: (1) production of biosurfactant was constitutive and growth-associated, (2) production was higher when cells were grown on phenanthrene as compared to dextrose and benzoate, (3) hydrocarbon-grown cells were more hydrophobic and showed higher affinity towards both aromatic and aliphatic hydrocarbons compared to dextrose-grown cells, and (4) mid-log-phase cells were significantly (2-fold) more hydrophobic than stationary phase cells. Based on these results, we hypothesize that growth-associated extracellular biosurfactant production and modulation of cell surface hydrophobicity plays an important role in hydrocarbon assimilation/uptake in Pseudomonas sp. strain PP2.
Biotechnology group, BJM School of Biosciences and Bioengineering, Indian Institute of Technology Bombay, 400 076 Powai, Mumbai, India.
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Prabhu
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Phale
D000445:Aldehyde Oxidoreductases / Q000378:metabolism; D001565:Benzoates / Q000378:metabolism; D001673:Biodegradation, Environmental; D002462:Cell Membrane / Q000502:physiology; D002855:Chromatography, Thin Layer; D006838:Hydrocarbons / Q000378:metabolism; D057927:Hydrophobic and Hydrophilic Interactions; D010101:Oxygen Consumption; D010105:Oxygenases / Q000378:metabolism; D010226:Parabens / Q000378:metabolism; D010616:Phenanthrenes / Q000378:metabolism*; D011549:Pseudomonas / Q000145:classification / Q000201:enzymology / Q000235:genetics / Q000378:metabolism*; D012988:Soil Microbiology; D013499:Surface Properties; D013501:Surface-Active Agents / Q000378:metabolism*
D001565:Benzoates; D006838:Hydrocarbons; D010226:Parabens; D010616:Phenanthrenes; D013501:Surface-Active Agents; C031181:phenanthrene; D010105:Oxygenases; D000445:Aldehyde Oxidoreductases; C024246:salicylaldehyde dehydrogenase; C038193:4-hydroxybenzoic acid