On the Enigma of Glutathione-Dependent Styrene Degradation in Gordonia rubripertincta CWB2

Abstract

Among bacteria, only a single styrene-specific degradation pathway has been reported so far. It comprises the activity of styrene monooxygenase, styrene oxide isomerase, and phenylacetaldehyde dehydrogenase, yielding phenylacetic acid as the central metabolite. The alternative route comprises ring-hydroxylating enzymes and yields vinyl catechol as central metabolite, which undergoes meta-cleavage. This was reported to be unspecific and also allows the degradation of benzene derivatives. However, some bacteria had been described to degrade styrene but do not employ one of those routes or only parts of them. Here, we describe a novel "hybrid" degradation pathway for styrene located on a plasmid of foreign origin. As putatively also unspecific, it allows metabolizing chemically analogous compounds (e.g., halogenated and/or alkylated styrene derivatives). Gordonia rubripertincta CWB2 was isolated with styrene as the sole source of carbon and energy. It employs an assembled route of the styrene side-chain degradation and isoprene degradation pathways that also funnels into phenylacetic acid as the central metabolite. Metabolites, enzyme activity, genome, transcriptome, and proteome data reinforce this observation and allow us to understand this biotechnologically relevant pathway, which can be used for the production of ibuprofen.IMPORTANCE The degradation of xenobiotics by bacteria is not only important for bioremediation but also because the involved enzymes are potential catalysts in biotechnological applications. This study reveals a novel degradation pathway for the hazardous organic compound styrene in Gordonia rubripertincta CWB2. This study provides an impressive illustration of horizontal gene transfer, which enables novel metabolic capabilities. This study presents glutathione-dependent styrene metabolization in an (actino-)bacterium. Further, the genomic background of the ability of strain CWB2 to produce ibuprofen is demonstrated.

Keywords: genomic island; glutathione S-transferase; glutathione in actinobacteria; horizontal gene transfer; hybrid gene cluster; microbial ibuprofen production; proteomics; styrene monooxygenase; transcriptomics; xenobiotic compounds.

FIG 1

Comparison of the styrene degradation cluster of Gordonia rubripertincta CWB2 with homologous clusters, as found in the strains Rhodococcus opacus PD630 (NZ_CP003949) (22), Rhodococcus sp. strain AD45 (NZ_CM003191) (58), Nocardioides sp. strain Root240 (NZ_LMIT01000013), Aeromicrobium sp. strain Root495 (NZ_LMFJ01000002), Rhodococcus sp. ST-10 (AB594506) (13), Rhodococcus opacus 1CP (NZ_CP009112, NZ_CP009111) (48), Pseudomonas sp. strain Y2 (AJ000330) (38, 93), and Sphingopyxis fribergensis Kp5.2 (CP009122) (17). The subclusters of strain CWB2 are indicated (S1 to S4), and gene products are indicated in the legend colored by their (predicted) function. Relevant homologous genes and clusters are emphasized by interspaced conjunctions. Clusters of marked strains are reported to be involved in isoprene (●) or styrene (#) degradation.

FIG 2

Degradation of 4 mM (S)-styrene oxide with crude extract of styrene-grown biomass of Gordonia rubripertincta CWB2 and 5 mM reduced glutathione (yellow circles). Only minor consumption was detected when excluding either reduced glutathione (open circles) or crude extract (×) from the reaction mix.

FIG 3

(a) Proposed novel degradation pathway of styrene in Gordonia rubripertincta CWB2 (see the text for details). (b) Proposed phenylacetic acid degradation pathway of Gordonia rubripertincta CWB2. The genes of the involved enzymes are present on the genome (cluster S4) and upregulated on the transcriptome and the proteins on the proteome level, respectively (see Table 1). Starting from the product of the upper degradation pathway, phenylacetic acid, strain CWB2, is able to metabolize styrene to acetyl-CoA or succinyl-CoA. (Adapted with permission from reference .)