The Hydroxyquinol Degradation Pathway in Rhodococcus jostii RHA1 and Agrobacterium Species Is an Alternative Pathway for Degradation of Protocatechuic Acid and Lignin Fragments

• Published in: Applied and environmental microbiology Vol. 86; no. 19; p. 1
• Main Authors: Spence, Edward M, Scott, Heather T, Dumond, Louison, Calvo-Bado, Leonides, di Monaco, Sabrina, Williamson, James J, Persinoti, Gabriela F, Squina, Fabio M, Bugg, Timothy D H
• Format: Journal Article
• Language: English
• Published: United States American Society for Microbiology 01.10.2020
• Subjects: Acids; Agrobacterium; Agrobacterium - metabolism; Bacterial Proteins - genetics; Bacterial Proteins - metabolism; Benzene; Carbon sources; Decarboxylation; Degradation; Gene Deletion; Genes; Genomes; Hydroquinones - metabolism; Hydroxybenzoates - metabolism; Hydroxyquinol 1,2-dioxygenase; Lignin; Lignin - metabolism; Maleylacetate reductase; Metabolic Networks and Pathways; Metabolites; Multigene Family; Oxygenase; Protocatechuate 3,4-dioxygenase; Protocatechuic acid; Reductases; Rhodococcus; Rhodococcus - metabolism; Rhodococcus jostii; Vanillin; lignin degradation; hydroxyquinol pathway; Rhodococcus jostii; Agrobacterium sp
• ISSN: 0099-2240; 1098-5336
• DOI: 10.1128/AEM.01561-20

Deletion of the genes, encoding protocatechuate 3,4-dioxygenase in RHA1, gives a gene deletion strain still able to grow on protocatechuic acid as the sole carbon source, indicating a second degradation pathway for protocatechuic acid. Metabolite analysis of wild-type RHA1 grown on medium containing vanillin or protocatechuic acid indicated the formation of hydroxyquinol (benzene-1,2,4-triol) as a downstream product. Gene cluster ro01857-ro01860 in RHA1 contains genes encoding hydroxyquinol 1,2-dioxygenase and maleylacetate reductase for degradation of hydroxyquinol but also putative mono-oxygenase (ro01860) and putative decarboxylase (ro01859) genes, and a similar gene cluster is found in the genome of lignin-degrading species. Recombinant mono-oxygenase and decarboxylase enzymes in combination were found to convert protocatechuic acid to hydroxyquinol. Hence, an alternative pathway for degradation of protocatechuic acid via oxidative decarboxylation to hydroxyquinol is proposed. There is a well-established paradigm for degradation of protocatechuic acid via the β-ketoadipate pathway in a range of soil bacteria. In this study, we have found the existence of a second pathway for degradation of protocatechuic acid in RHA1, via hydroxyquinol (benzene-1,2,4-triol), which establishes a metabolic link between protocatechuic acid and hydroxyquinol. The presence of this pathway in a lignin-degrading sp. strain suggests the involvement of the hydroxyquinol pathway in the metabolism of degraded lignin fragments.