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Journal Article

Sensitive and selective phenol sensing in denitrifying Aromatoleum aromaticum EbN1T


Wagner,  Tristan
Research Group Microbial Metabolism, Max Planck Institute for Marine Microbiology, Max Planck Society;

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Buschen, R., Lambertus, P., Scheve, S., Horst, S., Song, F., Wöhlbrand, L., et al. (2023). Sensitive and selective phenol sensing in denitrifying Aromatoleum aromaticum EbN1T. Microbiology Spectrum. doi:10.1128/spectrum.02100-23.

Cite as: https://hdl.handle.net/21.11116/0000-000D-CB3B-D
Aromatoleum aromaticum EbN1T anaerobically degrades phenol, p-cresol, and p-ethylphenol, each via a distinct peripheral pathway. The compound-specific regulation of each pathway is proposed to occur on the transcriptional level in the case of phenol supposedly mediated by the one-component system PheR. To confirm its predicted function, we generated an unmarked, in-frame deletion mutant (ΔpheR). This mutant did not express the ppsA1 gene, which encodes the A1 subunit of phenol-activating phenylphosphate synthase. The expression of ppsA1 was restored by in trans complementation of pheR into the ΔpheR background. The responsiveness to phenol was studied in vivo in benzoate-limited anaerobic cultures by adding, upon benzoate depletion, single defined pulses of phenol (from 100 µM down to 0.1 nM). Time-resolved, targeted transcript profiling by qRT-PCR revealed a response threshold for ppsA1 expression of 30‒50 nM phenol. Notably, ppsA1 expression could not be induced by p-cresol or p-ethylphenol. Conversely, lack of expression was also observed for the additional target genes cmh (p-cresol degradation) and acsA1 (p-ethylphenol degradation) applying phenol or p-ethylphenol as well as phenol or p-cresol as stimuli. Thus, the sensory proteins PheR, PcrS, and EtpR should be highly selective for phenol, p-cresol, and p-ethylphenol, respectively. The implicated incapability of cross-stimulus binding was corroborated by comparing the predicted 3D structural models of the proteins’ sensory domains. While the ligand-binding pockets share the conserved hydroxy group-anchoring histidine and tryptophane, their distal faces in PcrS and EtpR are, compared to PheR, enlarged to accommodate the bulkier methyl (p-cresol) and ethyl group (p-ethylphenol), respectively.