<p>A microorganism was isolated which could grow on unusually high concentrations of the toxic pollutant 4-chlorophenol. Taxonomic studies showed that the microorganism constituted a novel species within the genus <i>Arthrobacter</i> and it was named <i>Arthrobacter chlorophenolicus</i> A6. </p><p><i>A. chlorophenolicus</i> A6 was chromosomally tagged with either the <i>gfp</i> gene, encoding the green fluorescent protein (GFP), or the <i>luc</i> gene, encoding firefly luciferase. When the tagged cells were inoculated into 4-chlorophenol contaminated soil they could completely remove 175 µg/g 4-chlorophenol within 10 days, whereas no loss of 4-chlorophenol was observed in the uninoculated control microcosms. During these experiments the <i>gfp</i> and <i>luc</i> marker genes allowed monitoring of cell number and metabolic status.</p><p>When <i>A. chlorophenolicus</i> A6 was grown on mixtures of phenolic compounds, the strain exhibited a preference for 4-nitrophenol over 4-chlorophenol, which in turn was preferred over phenol. Analysis of growth and degradation data indicated that the same enzyme system was used for removal of 4-chlorophenol and 4-nitrophenol. However, degradation of unbstituted phenol appeared to be mediated by another or an additional enzyme system. The <i>luc</i>-tagged <i>A. chlorophenolicus</i> A6 gave valuable information about growth, substrate depletion and toxicity of the phenolic compounds in substrate mixtures. </p><p>The 4-chlorophenol degradation pathway in <i>A. chlorophenolicus</i> A6 was elucidated. The metabolic intermediate subject to ring cleavage was found to be hydroxyquinol and two different pathway branches led from 4-chlorophenol to hydroxyquinol. A gene cluster involved in 4-chlorophenol degradation was cloned from <i>A. chlorophenolicus A6</i>. The cluster contained two functional hydroxyquinol 1,2-dioxygenase genes and a number of other open reading frames presumed to encode enzymes involved in 4-chlorophenol catabolism. Analysis of the DNA sequence suggested that the gene cluster had partly been assembled by horizontal gene transfer.</p><p>In summary, 4-chlorophenol degradation by <i>A. chlorophenolicus</i> A6 was studied from a number of angles. This organism has several interesting and useful traits such as the ability to degrade high concentrations of 4-chlorophenol and other phenols alone and in mixtures, an unusual and effective 4-chlorophenol degradation pathway and demonstrated ability to remove 4-chlorophenol from contaminated soil.</p>
| Identifer | oai:union.ndltd.org:UPSALLA/oai:DiVA.org:su-159 |
| Date | January 2004 |
| Creators | Nordin, Karolina |
| Publisher | Stockholm University, Department of Biochemistry and Biophysics, Stockholm : Institutionen för biokemi och biofysik |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Doctoral thesis, comprehensive summary, text |
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