Identification and Genetic Characterization of Phenol-Degrading Bacteria from Leaf Microbial Communities |
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Authors: | Amarjyoti Sandhu Larry J Halverson Gwyn A Beattie |
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Institution: | (1) Department of Plant Pathology and Interdepartmental Microbiology Program, Iowa State University, Ames, IA 50011, USA;(2) Department of Plant Pathology, Iowa State University, 207 Science I, Ames, IA 50011, USA |
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Abstract: | Microbial communities on aerial plant leaves may contribute to the degradation of organic air pollutants such as phenol. Epiphytic
bacteria capable of phenol degradation were isolated from the leaves of green ash trees grown at a site rich in airborne pollutants.
Bacteria from these communities were subjected, in parallel, to serial enrichments with increasing concentrations of phenol
and to direct plating followed by a colony autoradiography screen in the presence of radiolabeled phenol. Ten isolates capable
of phenol mineralization were identified. Based on 16S rDNA sequence analysis, these isolates included members of the genera
Acinetobacter, Alcaligenes, and Rhodococcus. The sequences of the genes encoding the large subunit of a multicomponent phenol hydroxylase (mPH) in these isolates indicated
that the mPHs of the gram-negative isolates belonged to a single kinetic class, and that is one with a moderate affinity for
phenol; this affinity was consistent with the predicted phenol levels in the phyllosphere. PCR amplification of genes for
catechol 1,2-dioxygenase (C12O) and catechol 2,3-dioxygenase (C23O) in combination with a functional assay for C23O activity
provided evidence that the gram-negative strains had the C12O−, but not the C23O−, phenol catabolic pathway. Similarly, the
Rhodococcus isolates lacked C23O activity, although consensus primers to the C12O and C23O genes of Rhodococcus could not be identified. Collectively, these results demonstrate that these leaf surface communities contained several taxonomically
distinct phenol-degrading bacteria that exhibited diversity in their mPH genes but little diversity in the catabolic pathways
they employ for phenol degradation. |
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