Format

Send to

Choose Destination
J Bacteriol. 2020 Feb 11;202(5). pii: e00595-19. doi: 10.1128/JB.00595-19. Print 2020 Feb 11.

Nanomolar Responsiveness of an Anaerobic Degradation Specialist to Alkylphenol Pollutants.

Author information

1
General and Molecular Microbiology, Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg, Oldenburg, Germany.
2
Human Genetics, Department of Human Medicine, Carl von Ossietzky University of Oldenburg, Oldenburg, Germany.
3
Research Center Neurosensory Science, Carl von Ossietzky University of Oldenburg, Oldenburg, Germany.
4
Sensory Biology of Animals, Institute of Biology and Environmental Sciences (IBU), Carl von Ossietzky University of Oldenburg, Oldenburg, Germany.
5
General and Molecular Microbiology, Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg, Oldenburg, Germany rabus@icbm.de.

Abstract

Anaerobic degradation of p-cresol (4-methylphenol) by the denitrifying betaproteobacterium Aromatoleum aromaticum EbN1 is regulated with high substrate specificity, presumed to be mediated by the predicted σ54-dependent two-component system PcrSR. An unmarked, in-frame ΔpcrSR deletion mutant showed reduced expression of the genes cmh (21-fold) and hbd (8-fold) that encode the two enzymes for initial oxidation of p-cresol to p-hydroxybenzoate compared to their expression in the wild type. The expression of cmh and hbd was restored by in trans complementation with pcrSR in the ΔpcrSR background to even higher levels than in the wild type. This is likely due to ∼200-/∼30-fold more transcripts of pcrSR in the complemented mutant. The in vivo responsiveness of A. aromaticum EbN1 to p-cresol was studied in benzoate-limited anaerobic cultures by the addition of p-cresol at various concentrations (from 100 μM down to 0.1 nM). Time-resolved transcript profiling by quantitative reverse transcription-PCR (qRT-PCR) revealed that the lowest p-cresol concentrations just affording cmh and hbd expression (response threshold) ranged between 1 and 10 nM, which is even more sensitive than the respective odor receptors of insects. A similar response threshold was determined for another alkylphenol, p-ethylphenol, which strain EbN1 anaerobically degrades via a different route and senses by the σ54-dependent one-component system EtpR. Based on these data and theoretical considerations, p-cresol or p-ethylphenol added as a single pulse (10 nM) requires less than a fraction of a second to reach equilibrium between intra- and extracellular space (∼20 molecules per cell), with an estimated Kd (dissociation constant) of <100 nM alkylphenol (p-cresol or p-ethylphenol) for its respective sensory protein (PcrS or EtpR).IMPORTANCE Alkylphenols (like p-cresol and p-ethylphenol) represent bulk chemicals for industrial syntheses. Besides massive local damage events, large-scale micropollution is likewise of environmental and health concern. Next to understanding how such pollutants can be degraded by microorganisms, it is also relevant to determine the microorganisms' lower threshold of responsiveness. Aromatoleum aromaticum EbN1 is a specialist in anaerobic degradation of aromatic compounds, employing a complex and substrate-specifically regulated catabolic network. The present study aims at verifying the predicted role of the PcrSR system in sensing p-cresol and at determining the threshold of responsiveness for alkylphenols. The findings have implications for the enigmatic persistence of dissolved organic matter (escape from biodegradation) and for the lower limits of aromatic compounds required for bacterial growth.

KEYWORDS:

4-ethylphenol; 4-methylphenol; Aromatoleum aromaticum EbN1; alkylphenol; anaerobic degradation; aromatic compound; deletion mutation; regulation; responsiveness; signaling system; transcript profiling

PMID:
31843798
PMCID:
PMC7015708
[Available on 2020-08-11]
DOI:
10.1128/JB.00595-19

Supplemental Content

Full text links

Icon for HighWire
Loading ...
Support Center