Degradation of phenanthrene by different bacteria: evidence for novel transformation sequences involving the formation of 1-naphthol |
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Authors: | S K Samanta A K Chakraborti R K Jain |
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Institution: | (1) Environmental Biotechnology Laboratory, Institute of Microbial Technology, Sector-39 A, Chandigarh-160036, India e-mail: rkj@lion.imtech.ernet.in Fax: +91-172-690585/690632, IN;(2) National Institute of Pharmaceutical Education and Research, Sector-67, S.A.S. Nagar-160062, India, IN |
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Abstract: | Four polycyclic aromatic hydrocarbon (PAH)- degrading bacteria, namely Arthrobacter sulphureus RKJ4, Acidovorax delafieldii P4-1, Brevibacterium sp. HL4 and Pseudomonas sp. DLC-P11, capable of utilizing phenanthrene as the sole source of carbon and energy, were tested for its degradation using
radiolabelled phenanthrene. 9-14C]Phenanthrene was incubated with microorganisms containing 100 mg/l unlabelled phenanthrene and the evolution of 14CO2 was monitored: within 18 h of incubation, 30.1, 35.6, 26.5 and 2.1% of the recovered radiolabelled carbon was degraded to
14CO2 by RKJ4, P4-1, HL4 and DLC-P11, respectively. When mixtures of other PAHs such as fluorene, fluoranthene and pyrene, in addition
to phenanthrene, were added as additional carbon sources, there was a 36.1 and 20.6% increase in 14CO2 production from 9-14C]phenanthrene in the cases of RKJ4 and HL4, respectively, whereas P4-1 and DLC-P11 did not show any enhancement in 14CO2 production. Although, a combination of many bacteria enhances the degradation of organic compounds, no enhancement in the
degradation of 9-14C]phenanthrene was observed in mixed culture involving all four microorganisms together. However, when different PAHs, as
indicated above, were used in mixed culture, there was a 68.2% increase in 14CO2 production. In another experiment, the overall growth rate of P4-1 on phenanthrene could be enhanced by adding the non-ionic
surfactant Triton X-100, whereas RKJ4, HL4 and DLC-P11 did not show any enhancement in growth. Pathways for phenanthrene degradation
were also analysed by thin-layer chromatography, gas chromatography and gas chromatography-mass spectrometry. Common intermediates
such as o-phthalic acid and protocatechuic acid were detected in the case of RKJ4 and o-phthalic acid was detected in the case of P4-1. A new intermediate, 1-naphthol, was detected in the cases of HL4 and DLC-P11.
HL4 degrades phenanthrene via 1-hydroxy-2-naphthoic acid, 1-naphthol and salicylic acid, whereas DLC-P11 degrades phenanthrene
via the formation of 1-hydroxy-2-naphthoic acid, 1-naphthol and o-phthalic acid. Both transformation sequences are novel and have not been previously reported in the literature. Mega plasmids
were found to be present in RKJ4, HL4 and DLC-P11, but their involvement in phenanthrene degradation could not be established.
Received: 25 May 1999 / Received revision: 16 July 1999 / Accepted: 1 August 1999 |
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