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Buschen R, Lambertus P, Scheve S, Horst S, Song F, Wöhlbrand L, Neidhardt J, Winklhofer M, Wagner T, Rabus R. Sensitive and selective phenol sensing in denitrifying Aromatoleum aromaticum EbN1 T. Microbiol Spectr 2023; 11:e0210023. [PMID: 37823660 PMCID: PMC10715001 DOI: 10.1128/spectrum.02100-23] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2023] [Accepted: 09/05/2023] [Indexed: 10/13/2023] Open
Abstract
IMPORTANCE Aromatic compounds are globally abundant organic molecules with a multitude of natural and anthropogenic sources, underpinning the relevance of their biodegradation. A. aromaticum EbN1T is a well-studied environmental betaproteobacterium specialized on the anaerobic degradation of aromatic compounds. The here studied responsiveness toward phenol in conjunction with the apparent high ligand selectivity (non-promiscuity) of its PheR sensor and those of the related p-cresol (PcrS) and p-ethylphenol (EtpR) sensors are in accord with the substrate-specificity and biochemical distinctiveness of the associated degradation pathways. Furthermore, the present findings advance our general understanding of the substrate-specific regulation of the strain's remarkable degradation network and of the concentration thresholds below which phenolic compounds become essentially undetectable and as a consequence should escape substantial biodegradation. Furthermore, the findings may inspire biomimetic sensor designs for detecting and quantifying phenolic contaminants in wastewater or environments.
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Affiliation(s)
- Ramona Buschen
- General and Molecular Microbiology, Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
| | - Pia Lambertus
- General and Molecular Microbiology, Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
| | - Sabine Scheve
- General and Molecular Microbiology, Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
| | - Simon Horst
- General and Molecular Microbiology, Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
| | - Fei Song
- Human Genetics, Department of Human Medicine, Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
| | - Lars Wöhlbrand
- General and Molecular Microbiology, Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
| | - John Neidhardt
- Human Genetics, Department of Human Medicine, Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
| | - Michael Winklhofer
- Research Center Neurosensory Science, Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
- Sensory Biology of Animals, Institute of Biology and Environmental Sciences (IBU), Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
| | - Tristan Wagner
- Max Planck Research Group Microbial Metabolism, Max Planck Institute for Marine Microbiology, Bremen, Germany
| | - Ralf Rabus
- General and Molecular Microbiology, Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
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Systems Biology of Aromatic Compound Catabolism in Facultative Anaerobic Aromatoleum aromaticum EbN1 T. mSystems 2022; 7:e0068522. [PMID: 36445109 PMCID: PMC9765128 DOI: 10.1128/msystems.00685-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/03/2022] Open
Abstract
Members of the genus Aromatoleum thrive in diverse habitats and use a broad range of recalcitrant organic molecules coupled to denitrification or O2 respiration. To gain a holistic understanding of the model organism A. aromaticum EbN1T, we studied its catabolic network dynamics in response to 3-(4-hydroxyphenyl)propanoate, phenylalanine, 3-hydroxybenzoate, benzoate, and acetate utilized under nitrate-reducing versus oxic conditions. Integrated multi-omics (transcriptome, proteome, and metabolome) covered most of the catabolic network (199 genes) and allowed for the refining of knowledge of the degradation modules studied. Their substrate-dependent regulation showed differing degrees of specificity, ranging from high with 3-(4-hydroxyphenyl)propanoate to mostly relaxed with benzoate. For benzoate, the transcript and protein formation were essentially constitutive, contrasted by that of anoxia-specific versus oxia-specific metabolite profiles. The matrix factorization of transcriptomic data revealed that the anaerobic modules accounted for most of the variance across the degradation network. The respiration network appeared to be constitutive, both on the transcript and protein levels, except for nitrate reductase (with narGHI expression occurring only under nitrate-reducing conditions). The anoxia/nitrate-dependent transcription of denitrification genes is apparently controlled by three FNR-type regulators as well as by NarXL (all constitutively formed). The resequencing and functional reannotation of the genome fostered a genome-scale metabolic model, which is comprised of 655 enzyme-catalyzed reactions and 731 distinct metabolites. The model predictions for growth rates and biomass yields agreed well with experimental stoichiometric data, except for 3-(4-hydroxyphenyl)propanoate, with which 4-hydroxybenzoate was exported. Taken together, the combination of multi-omics, growth physiology, and a metabolic model advanced our knowledge of an environmentally relevant microorganism that differs significantly from other bacterial model strains. IMPORTANCE Aromatic compounds are abundant constituents not only of natural organic matter but also of bulk industrial chemicals and fuel components of environmental concern. Considering the widespread occurrence of redox gradients in the biosphere, facultative anaerobic degradation specialists can be assumed to play a prominent role in the natural mineralization of organic matter and in bioremediation at contaminated sites. Surprisingly, differential multi-omics profiling of the A. aromaticum EbN1T studied here revealed relaxed regulatory stringency across its four main physiological modi operandi (i.e., O2-independent and O2-dependent degradation reactions versus denitrification and O2 respiration). Combining multi-omics analyses with a genome-scale metabolic model aligned with measured growth performances establishes A. aromaticum EbN1T as a systems-biology model organism and provides unprecedented insights into how this bacterium functions on a holistic level. Moreover, this experimental platform invites future studies on eco-systems and synthetic biology of the environmentally relevant betaproteobacterial Aromatoleum/Azoarcus/Thauera cluster.
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Weiten A, Kalvelage K, Neumann-Schaal M, Buschen R, Scheve S, Winklhofer M, Rabus R. Nanomolar responsiveness of marine Phaeobacter inhibens DSM 17395 toward carbohydrates and amino acids. Microb Physiol 2022; 32:108-121. [PMID: 35468615 DOI: 10.1159/000524702] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2022] [Accepted: 03/29/2022] [Indexed: 11/19/2022]
Abstract
Phaeobacter inhibens DSM 17395 is a heterotrophic member of the ubiquitous, marine Roseobacter group and specialized in the aerobic utilization of carbohydrates and amino acids via pathways widespread among roseobacters. The in vivo responsiveness of P. inhibens DSM 17395 was studied with non-adapted cells (succinate-grown), which were exposed to a single pulse (100-0.01 µM) each of N-acetylglucosamine, mannitol, xylose, leucine, phenylalanine or tryptophan (effectors). Responsiveness was then determined by time-resolved transcript analyses (qRT-PCR) of 'degradation' and 'uptake' genes selected based on previously reported substrate-specific proteome profiles. The transcriptional response thresholds were: 50-100 nM for nagK (N-acetylglucosamine kinase), paaA (ring 1,2-phenylacetyl-CoA epoxidase), and kynA (tryptophan 2,3-dioxygenase), 10-50 nM for xylA (xylose isomerase), and around 10 nM for mtlK (mannitol 2-dehydrogenase). A threshold for leucine could not be determined due to the elevated intrinsic presence of leucine in the exometabolome of succinate-grown cells (no effector addition). Notably, the response thresholds for presumptive carbohydrate-binding proteins of ABC-transporters were in the same range or even lower: 10-100 nM for c27930 (N-acetylglucosamine) and even below 10 nM for c13210 (mannitol) and xylF (xylose). These results shed new light on the sensory/regulatory sensitivity of a well-studied roseobacter for recognizing potential substrates at low ambient concentrations and on the concentration threshold below which these might escape biodegradation ('emergent recalcitrance' concept of DOM persistence).
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Affiliation(s)
- Arne Weiten
- General and Molecular Microbiology, Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
| | - Kristin Kalvelage
- General and Molecular Microbiology, Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
| | - Meina Neumann-Schaal
- Research Group Metabolomics, Leibniz Institute DSMZ-German Collection of Microorganisms and Cell Cultures GmbH, Braunschweig, Germany
- Research Group Bacterial Metabolism, Braunschweig Integrated Centre of Systems Biology (BRICS), Technische Universität Carolo-Wilhelmina zu Braunschweig, Braunschweig, Germany
| | - Ramona Buschen
- General and Molecular Microbiology, Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
| | - Sabine Scheve
- General and Molecular Microbiology, Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
| | - Michael Winklhofer
- Sensory Biology of Animals, Institute of Biology and Environmental Sciences (IBU), Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
- Research Center Neurosensory Science, Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
| | - Ralf Rabus
- General and Molecular Microbiology, Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University of Oldenburg, Oldenburg, Germany
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Responsiveness of Aromatoleum aromaticum EbN1 T to Lignin-Derived Phenylpropanoids. Appl Environ Microbiol 2021; 87:AEM.03140-20. [PMID: 33741621 DOI: 10.1128/aem.03140-20] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/23/2020] [Accepted: 03/09/2021] [Indexed: 11/20/2022] Open
Abstract
The betaproteobacterial degradation specialist Aromatoleum aromaticum EbN1T utilizes several plant-derived 3-phenylpropanoids coupled to denitrification. In vivo responsiveness of A. aromaticum EbN1T was studied by exposing nonadapted cells to distinct pulses (spanning 100 µM to 0.1 nM) of 3-phenylpropanoate, cinnamate, 3-(4-hydroxyphenyl)propanoate, or p-coumarate. Time-resolved, targeted transcript analyses via quantitative reverse transcription-PCR of four selected 3-phenylpropanoid genes revealed a response threshold of 30 to 50 nM for p-coumarate and 1 to 10 nM for the other three tested 3-phenylpropanoids. At these concentrations, transmembrane effector equilibration is attained by passive diffusion rather than active uptake via the ABC transporter, presumably serving the studied 3-phenylpropanoids as well as benzoate. Highly substrate-specific enzyme formation (EbA5316 to EbA5321 [EbA5316-21]) for the shared peripheral degradation pathway putatively involves the predicted TetR-type transcriptional repressor PprR. Accordingly, relative transcript abundances of ebA5316-21 are lower in succinate- and benzoate-grown wild-type cells than in an unmarked in-frame ΔpprR mutant. In trans-complementation of pprR into the ΔpprR background restored wild-type-like transcript levels. When adapted to p-coumarate, the three genotypes had relative transcript abundances similar to those of ebA5316-21 despite a significantly longer lag phase of the pprR-complemented mutant (∼100-fold higher pprR transcript level than the wild type). Notably, transcript levels of ebA5316-21 were ∼10- to 100-fold higher in p-coumarate- than succinate- or benzoate-adapted cells across all three genotypes. This indicates the additional involvement of an unknown transcriptional regulator. Furthermore, physiological, transcriptional, and (aromatic) acyl-coenzyme A ester intermediate analyses of the wild type and ΔpprR mutant grown with binary substrate mixtures suggest a mode of catabolite repression of superior order to PprR.IMPORTANCE Lignin is a ubiquitous heterobiopolymer built from a suite of 3-phenylpropanoid subunits. It accounts for more than 30% of the global plant dry material, and lignin-related compounds are increasingly released into the environment from anthropogenic sources, i.e., by wastewater effluents from the paper and pulp industry. Hence, following biological or industrial decomplexation of lignin, vast amounts of structurally diverse 3-phenylpropanoids enter terrestrial and aquatic habitats, where they serve as substrates for microbial degradation. This raises the question of what signaling systems environmental bacteria employ to detect these nutritionally attractive compounds and to adjust their catabolism accordingly. Moreover, determining in vivo response thresholds of an anaerobic degradation specialist such as A. aromaticum EbN1T for these aromatic compounds provides insights into the environmental fate of the latter, i.e., when they could escape biodegradation due to too low ambient concentrations.
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Nanomolar Responsiveness of an Anaerobic Degradation Specialist to Alkylphenol Pollutants. J Bacteriol 2020; 202:JB.00595-19. [PMID: 31843798 DOI: 10.1128/jb.00595-19] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/20/2019] [Accepted: 12/09/2019] [Indexed: 12/14/2022] Open
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.
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