Catabolism of Alkylphenols in Rhodococcus via a Meta -Cleavage Pathway Associated With Genomic Islands

• Published in: Frontiers in microbiology 2019-08, Vol.10, p.1862-1862
• Main Authors: Levy-Booth, David J, Fetherolf, Morgan M, Stewart, Gordon R, Liu, Jie, Eltis, Lindsay D, Mohn, William W
• Format: Article
• Language: English
• Subjects: alkylphenol; aromatic; catabolism; meta-cleavage; Microbiology; Rhodococcus; transcriptomics
• ISSN: 1664-302X; 1664-302X
• DOI: 10.3389/fmicb.2019.01862

The bacterial catabolism of aromatic compounds has considerable promise to convert lignin depolymerization products to commercial chemicals. Alkylphenols are a key class of depolymerization products whose catabolism is not well-elucidated. We isolated EP4 on 4-ethylphenol and applied genomic and transcriptomic approaches to elucidate alkylphenol catabolism in EP4 and RHA1. RNA-Seq and RT-qPCR revealed a pathway encoded by the genes that degrades 4-ethylphenol the cleavage of 4-ethylcatechol. This process was initiated by a two-component alkylphenol hydroxylase, encoded by the genes, which were upregulated ~3,000-fold. Purified AphAB from EP4 had highest specific activity for 4-ethylphenol and 4-propylphenol (~2,000 U/mg) but did not detectably transform phenol. Nevertheless, a Δ mutant in RHA1 grew on 4-ethylphenol by compensatory upregulation of phenol hydroxylase genes ( ). Deletion of , encoding an extradiol dioxygenase, prevented growth on 4-alkylphenols but not phenol. Disruption of in the β-ketoadipate pathway prevented growth on phenol but not 4-alkylphenols. Thus, 4-alkylphenols are catabolized exclusively cleavage in rhodococci while phenol is subject to cleavage. A putative genomic island encoding genes was identified in EP4 and several other rhodococci. Overall, this study identifies a 4-alkylphenol pathway in rhodococci, demonstrates key enzymes involved, and presents evidence that the pathway is encoded in a genomic island. These advances are of particular importance for wide-ranging industrial applications of rhodococci, including upgrading of lignocellulose biomass.