Characterization of the degradation pathway of phloroglucinol (1,3,5-trihydroxybenzene) by a Rhodococcus sp. BPG-8

• Main Author: Armstrong, Stephen Mark
• Format: Thesis
• Language: English
• Published: Memorial University of Newfoundland 1992
• Subjects: Newfoundland
• Online Access: https://research.library.mun.ca/4213/; https://research.library.mun.ca/4213/1/Armstrong_StephenMark.pdf; https://research.library.mun.ca/4213/3/Armstrong_StephenMark.pdf

Rhodococcus sp. BPG-8 was isolated from oil rich soil in Newfoundland and found to utilize numerous aromatic compounds as sources of carbon and energy. Chemical analysis of cell wall composition which included amino acids, sugars, and fatty acids showed complete homology with Rhodococcus erythropolis. Identical profiles for acid production and growth on various substrates occurred. Growth of the isolate on phloroglucinol occurred in the pH range 5-8; with substrate and temperature optima of 8.0 mM and 25°C, respectively. Phloroglucinol induced cells when fed phloroglucinol or resorcinol produced 1,2,3,5-tetrahydroxybenzene and 1,2,4-trihydroxybenzene, respectively. Cell-free extracts of cells grown on phloroglucinol contained a phloroglucinol hydroxylase that also hydroxylated resorcinol. Dioxygenases present in the induced cells carried out the ortho-cleavage of 1,2,3,5- tetrahydroxybenzene while meta-clevage of 1,2,4- trihydroxybenzene appeared to be constitutive. Cell-free extracts also showed inducible activity for the metabolism of acetopyruvate with the accumulation of formate in the supernatant. Tentative degradative pathways for phloroglucinol and fortuitous resorcinol metabolism are discussed. This is the first reported case in which phloroglucinol is metabolized by an oxidative rather than a reductive pathway. The oxidations of 1,2,3,5-tetrahydroxybenzene and 1,2,4- trihydroxybenzene produce superoxide radicals that may have potential deleterious effects on cellular integrity. It has been shown that both superoxide dismutase and catalase retard the auto-oxidation of these molecules by hindering their free radical reaction mechanism with superoxide. A non-inducible NAD(P)H dependent reductase appeared to convert the 2-hydroxy- 1,4-benzoquinone back to 1,2,4-trihydroxybenzene; although similiar effects were not found for 1,2,3,5- tetahydroxybenzene. These novel findings suggest that constitutive non-pathway enzymes may participate in stabilization of intermediates. Partial purification of the ...