Microbial catabolic pathways for complex aromatics [article]

Shannu Palamuru, University, The Australian National, University, The Australian National
2016
This thesis concerns the microbial degradation of recalcitrant aromatic compounds, and the enzymes responsible for that degradation. The two foci are guaiacylglycerol-β-guaiacyl ether (GGE), which is a model compound representing a key intermediate in the deconstruction of lignin, and 2,4-dinitroanisole (DNAN), which is a widely used component of explosives. The degradation of these compounds is of interest both because of the insights it provides into the evolution of catabolic pathways and
more » ... lic pathways and because of the potential uses of the microbes and enzymes involved in chemical manufacturing and environmental bioremediation. Chapter 1 reviews the existing literature on the microbial degradation of lignin and nitroaromatic explosives such as DNAN, including consideration of their potential industrial applications. Chapter 2 describes the isolation and characterization of the GGE degrading Erythrobacter sp. SG61-1L strain and compares it with the GGE degradation activity of the previously isolated Sphingomonas sp. SYK-6. SG61-1L was found to degrade GGE significantly more rapidly than SYK-6, although the same pathway appeared to operate in both strains. The first step in GGE degradation by SYK-6 had previously been shown to be catalysed by four stereospecific dehydrogenases and I found seven homologous genes in the SG61-1L genome. These thirteen genes were heterologously expressed in E. coli and the activities of their products were studied with the four stereoisomers of GGE. Two of the SG61-1L enzymes in particular had higher activities for the four GGE isomers than any of the four SYK-6 enzymes. A phylogenetic analysis showed that the GGE dehydrogenase activity of the two strains was mainly confined to a particular subclade of classical short chain dehydrogenases but two enzymes from other clades of these dehydrogenases were also found to have significant GGE activity. Chapter 3 describes the mineralization of DNAN by Nocardioides sp. strain JS1661 and the identification and characterization of a complex demethylase enzym [...]
doi:10.25911/5d66657d9aee3 fatcat:wdrh2q7xk5b6tmxt65dj5itlxm