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Kuroda K, Takai M, Sekiguchi T, Ikarashi T, Kurashita H, Nakajima M, Nobu MK, Hatamoto M, Yamaguchi T, Nakaya Y, Satoh H, Yamauchi M, Yamada M, Narihiro T. Development of an internal two-stage upflow anaerobic reactor integrating biostimulation strategies to enhance the degradation of aromatic compounds in wastewater from purified terephthalic acid and dimethyl terephthalate manufacturing processes. WATER RESEARCH 2024; 258:121762. [PMID: 38754297 DOI: 10.1016/j.watres.2024.121762] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/31/2024] [Revised: 05/08/2024] [Accepted: 05/09/2024] [Indexed: 05/18/2024]
Abstract
In this study, we aimed to establish high-rate biological treatment of purified terephthalic acid (PTA) and dimethyl terephthalate (DMT) wastewater that minimizes the inhibitory effects of high concentration benzoate and acetate. To achieve this, we developed a novel bioreactor system and biostimulation strategy. An internal two-stage upflow anaerobic (ITUA) reactor was operated with (i) a packed bed containing green tuff medium underlying (ii) a compartment seeded with anaerobic granular sludge. Ethylene glycol was amended to stimulate syntrophic interactions. Continuous operation of the system for 1,026 days achieve an organic removal rate of 11.0 ± 0.6 kg COD/m3/d. The abundance of aromatic degraders significantly increased during operation. Thus, we successfully developed a high-rate treatment system to treat wastewater from the PTA/DMT manufacturing processes by activating syntrophs in an ITUA reactor.
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Affiliation(s)
- Kyohei Kuroda
- Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 2-17-2-1 Tsukisamu-Higashi, Toyohira-ku, Sapporo, Hokkaido 062-8517 Japan; Division of Environmental Engineering, Faculty of Engineering, Hokkaido University, North-13, West-8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan.
| | - Maho Takai
- Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 2-17-2-1 Tsukisamu-Higashi, Toyohira-ku, Sapporo, Hokkaido 062-8517 Japan; Division of Environmental Engineering, Faculty of Engineering, Hokkaido University, North-13, West-8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan
| | - Takeo Sekiguchi
- Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 2-17-2-1 Tsukisamu-Higashi, Toyohira-ku, Sapporo, Hokkaido 062-8517 Japan; Division of Environmental Engineering, Faculty of Engineering, Hokkaido University, North-13, West-8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan
| | - Tomoya Ikarashi
- Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 2-17-2-1 Tsukisamu-Higashi, Toyohira-ku, Sapporo, Hokkaido 062-8517 Japan; Department of Civil and Environmental Engineering, Nagaoka University of Technology, 1603-1, Kamitomioka, Nagaoka, Niigata 940-2188, Japan
| | - Hazuki Kurashita
- Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 2-17-2-1 Tsukisamu-Higashi, Toyohira-ku, Sapporo, Hokkaido 062-8517 Japan; Department of Science of Technology Innovation, Nagaoka University of Technology, 1603-1, Kamitomioka, Nagaoka, Niigata 940-2188, Japan
| | - Meri Nakajima
- Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 2-17-2-1 Tsukisamu-Higashi, Toyohira-ku, Sapporo, Hokkaido 062-8517 Japan; Division of Environmental Engineering, Faculty of Engineering, Hokkaido University, North-13, West-8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan
| | - Masaru K Nobu
- Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), Central 6, Higashi 1-1-1, Tsukuba, Ibaraki 305-8566, Japan; Institute for Extra-cutting-edge Science and Technology Avant-garde Research (X-star), Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho, Yokosuka, Kanagawa 237-0061, Japan
| | - Masashi Hatamoto
- Department of Civil and Environmental Engineering, Nagaoka University of Technology, 1603-1, Kamitomioka, Nagaoka, Niigata 940-2188, Japan
| | - Takashi Yamaguchi
- Department of Civil and Environmental Engineering, Nagaoka University of Technology, 1603-1, Kamitomioka, Nagaoka, Niigata 940-2188, Japan; Department of Science of Technology Innovation, Nagaoka University of Technology, 1603-1, Kamitomioka, Nagaoka, Niigata 940-2188, Japan
| | - Yuki Nakaya
- Division of Environmental Engineering, Faculty of Engineering, Hokkaido University, North-13, West-8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan
| | - Hisashi Satoh
- Division of Environmental Engineering, Faculty of Engineering, Hokkaido University, North-13, West-8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan
| | - Masahito Yamauchi
- Department of Urban Environmental Design and Engineering, National Institute of Technology, Kagoshima College, 1460-1 Shinkou, Hayato, Kirishima, Kagoshima 899-5193, Japan
| | - Masayoshi Yamada
- Department of Urban Environmental Design and Engineering, National Institute of Technology, Kagoshima College, 1460-1 Shinkou, Hayato, Kirishima, Kagoshima 899-5193, Japan
| | - Takashi Narihiro
- Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology (AIST), 2-17-2-1 Tsukisamu-Higashi, Toyohira-ku, Sapporo, Hokkaido 062-8517 Japan; Division of Environmental Engineering, Faculty of Engineering, Hokkaido University, North-13, West-8, Kita-ku, Sapporo, Hokkaido 060-8628, Japan.
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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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Zhai S, Ji M, Zhao Y, Pavlostathis SG. Biotransformation of 4-Hydroxybenzoic Acid under Nitrate-Reducing Conditions in a MEC Bioanode. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2021; 55:2067-2075. [PMID: 33433204 DOI: 10.1021/acs.est.0c05336] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/12/2023]
Abstract
4-Hydroxybenzoic acid (HBA) is commonly found at high concentrations in waste streams generated by the thermochemical conversion of lignocellulosic biomass to bio-oils and biofuels. The objective of this study was to systematically assess the biotransformation of HBA in the bioanode of a microbial electrolysis cell (MEC) for the production of renewable cathodic H2. A mixed, denitrifying culture, enriched with HBA as the sole electron donor, was used as the anode inoculum. MEC electrochemical performance, H2 yield, HBA biotransformation pathways and products, and the bioanode suspended and biofilm microbial communities were examined. In the absence of nitrate, 60%-100% HBA was converted to phenol, which persisted, resulting in very limited exoelectrogenesis. Under nitrate-reducing conditions, complete HBA degradation was achieved in the MEC bioanode with very low phenol production, resulting in the production of cathodic H2. The predominant bacterial genus in the MEC bioanode (relative abundance 33.4%-41.9%) was the denitrifier Magnetospirillum, which uses the benzoyl-CoA pathway to degrade aromatic compounds. Geobacter accounted for 5.9-7.8% of the MEC bioanode community. Thus, active nitrate reduction in the MEC bioanode led to complete HBA degradation, resulting in a higher extent of exoelectrogenesis and cathodic H2 production. The results of this study provide mechanistic insights into a productive use of HBA and other phenolic compounds typically found in waste streams resulting from the thermochemical conversion of lignocellulosic biomass to biofuels.
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Affiliation(s)
- Siyuan Zhai
- School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0512, United States
- School of Environmental Science and Engineering, Tianjin University, Tianjin 300350, China
- Research Center for Eco-Environmental Sciences, Chinese Academy of Sciences, Beijing 100085, China
| | - Min Ji
- School of Environmental Science and Engineering, Tianjin University, Tianjin 300350, China
- Tianjin Engineering Center of Urban River Eco-Purification Technology, Tianjin 300350, China
| | - Yingxin Zhao
- School of Environmental Science and Engineering, Tianjin University, Tianjin 300350, China
- Tianjin Engineering Center of Urban River Eco-Purification Technology, Tianjin 300350, China
| | - Spyros G Pavlostathis
- School of Civil and Environmental Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332-0512, United States
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Dziuba MV, Zwiener T, Uebe R, Schüler D. Single-step transfer of biosynthetic operons endows a non-magnetotactic Magnetospirillum strain from wetland with magnetosome biosynthesis. Environ Microbiol 2020; 22:1603-1618. [PMID: 32079043 DOI: 10.1111/1462-2920.14950] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2019] [Revised: 02/03/2020] [Accepted: 02/18/2020] [Indexed: 11/28/2022]
Abstract
The magnetotactic lifestyle represents one of the most complex traits found in many bacteria from aquatic environments and depends on magnetic organelles, the magnetosomes. Genetic transfer of magnetosome biosynthesis operons to a non-magnetotactic bacterium has only been reported once so far, but it is unclear whether this may also occur in other recipients. Besides magnetotactic species from freshwater, the genus Magnetospirillum of the Alphaproteobacteria also comprises a number of strains lacking magnetosomes, which are abundant in diverse microbial communities. Their close phylogenetic interrelationships raise the question whether the non-magnetotactic magnetospirilla may have the potential to (re)gain a magnetotactic lifestyle upon acquisition of magnetosome gene clusters. Here, we studied the transfer of magnetosome gene operons into several non-magnetotactic environmental magnetospirilla. Single-step transfer of a compact vector harbouring >30 major magnetosome genes from M. gryphiswaldense induced magnetosome biosynthesis in a Magnetospirillum strain from a constructed wetland. However, the resulting magnetic cellular alignment was insufficient for efficient magnetotaxis under conditions mimicking the weak geomagnetic field. Our work provides insights into possible evolutionary scenarios and potential limitations for the dissemination of magnetotaxis by horizontal gene transfer and expands the range of foreign recipients that can be genetically magnetized.
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Affiliation(s)
- Marina V Dziuba
- Department of Microbiology, University of Bayreuth, Bayreuth, Germany.,Institute of Bioengineering, Research Center of Biotechnology of the Russian Academy of Sciences, Moscow, Russia
| | - Theresa Zwiener
- Department of Microbiology, University of Bayreuth, Bayreuth, Germany
| | - Rene Uebe
- Department of Microbiology, University of Bayreuth, Bayreuth, Germany
| | - Dirk Schüler
- Department of Microbiology, University of Bayreuth, Bayreuth, Germany
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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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Phototrophic Lactate Utilization by Rhodopseudomonas palustris Is Stimulated by Coutilization with Additional Substrates. Appl Environ Microbiol 2019; 85:AEM.00048-19. [PMID: 30902855 DOI: 10.1128/aem.00048-19] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2019] [Accepted: 03/14/2019] [Indexed: 01/09/2023] Open
Abstract
The phototrophic purple nonsulfur bacterium Rhodopseudomonas palustris is known for its metabolic versatility and is of interest for various industrial and environmental applications. Despite decades of research on R. palustris growth under diverse conditions, patterns of R. palustris growth and carbon utilization with mixtures of carbon substrates remain largely unknown. R. palustris readily utilizes most short-chain organic acids but cannot readily use lactate as a sole carbon source. Here we investigated the influence of mixed-substrate utilization on phototrophic lactate consumption by R. palustris We found that lactate was simultaneously utilized with a variety of other organic acids and glycerol in time frames that were insufficient for R. palustris growth on lactate alone. Thus, lactate utilization by R. palustris was expedited by its coutilization with additional substrates. Separately, experiments using carbon pairs that did not contain lactate revealed acetate-mediated inhibition of glycerol utilization in R. palustris This inhibition was specific to the acetate-glycerol pair, as R. palustris simultaneously utilized acetate or glycerol when either was paired with succinate or lactate. Overall, our results demonstrate that (i) R. palustris commonly employs simultaneous mixed-substrate utilization, (ii) mixed-substrate utilization expands the spectrum of readily utilized organic acids in this species, and (iii) R. palustris has the capacity to exert carbon catabolite control in a substrate-specific manner.IMPORTANCE Bacterial carbon source utilization is frequently assessed using cultures provided single carbon sources. However, the utilization of carbon mixtures by bacteria (i.e., mixed-substrate utilization) is of both fundamental and practical importance; it is central to bacterial physiology and ecology, and it influences the utility of bacteria as biotechnology. Here we investigated mixed-substrate utilization by the model organism Rhodopseudomonas palustris Using mixtures of organic acids and glycerol, we show that R. palustris exhibits an expanded range of usable carbon substrates when provided substrates in mixtures. Specifically, coutilization enabled the prompt consumption of lactate, a substrate that is otherwise not readily used by R. palustris Additionally, we found that R. palustris utilizes acetate and glycerol sequentially, revealing that this species has the capacity to use some substrates in a preferential order. These results provide insights into R. palustris physiology that will aid the use of R. palustris for industrial and commercial applications.
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Towards the Response Threshold for p-Hydroxyacetophenone in the Denitrifying Bacterium "Aromatoleum aromaticum" EbN1. Appl Environ Microbiol 2018; 84:AEM.01018-18. [PMID: 29959253 DOI: 10.1128/aem.01018-18] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/28/2018] [Accepted: 06/26/2018] [Indexed: 01/21/2023] Open
Abstract
The denitrifying betaproteobacterium "Aromatoleum aromaticum" EbN1 regulates the capacity to anaerobically degrade p-ethylphenol (via p-hydroxyacetophenone) with high substrate specificity. This process is mediated by the σ54-dependent transcriptional regulator EtpR, which apparently recognizes both aromatic compounds, yielding congruent expression profiles. The responsiveness of this regulatory system was studied with p-hydroxyacetophenone, which is more easily administered to cultures and traced analytically. Cultures of A. aromaticum EbN1 were initially cultivated under nitrate-reducing conditions with a growth-limiting supply of benzoate, upon the complete depletion of which p-hydroxyacetophenone was added at various concentrations (from 500 μM down to 0.1 nM). Depletion profiles of this aromatic substrate and presumptive effector were determined by highly sensitive micro-high-performance liquid chromatography (microHPLC). Irrespective of the added concentration of p-hydroxyacetophenone, depletion commenced after less than 5 min and suggested a response threshold of below 10 nM. This approximation was corroborated by time-resolved transcript profiles (quantitative reverse transcription-PCR) of selected degradation and efflux relevant genes (e.g., pchF, encoding a subunit of predicted p-ethylphenol methylenehydroxylase) and narrowed down to a range of 10 to 1 nM. The most pronounced transcriptional response was observed, as expected, for genes located at the beginning of the two operon-like structures, related to catabolism (i.e., acsA) and potential efflux (i.e., ebA335).IMPORTANCE Aromatic compounds are widespread microbial growth substrates with natural as well as anthropogenic sources, albeit with their in situ concentrations and their bioavailabilities varying over several orders of magnitude. Even though degradation pathways and underlying regulatory systems have long been studied with aerobic and, to a lesser extent, with anaerobic bacteria, comparatively little is known about the effector concentration-dependent responsiveness. A. aromaticum EbN1 is a model organism for the anaerobic degradation of aromatic compounds with the architecture of the catabolic network and its substrate-specific regulation having been intensively studied by means of differential proteogenomics. The present study aims at unraveling the minimal concentration of an aromatic growth substrate (p-hydroxyacetophenone here) required to initiate gene expression for its degradation pathway and to learn in principle about the lower limit of catabolic responsiveness of an anaerobic degradation specialist.
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Rabus R, Boll M, Golding B, Wilkes H. Anaerobic Degradation of p-Alkylated Benzoates and Toluenes. J Mol Microbiol Biotechnol 2016; 26:63-75. [PMID: 26960059 DOI: 10.1159/000441144] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/19/2022] Open
Abstract
The anaerobic degradation of 4-alkylbenzoates and 4-alkyltoluenes is to date a rarely reported microbial capacity. The newly isolated Alphaproteobacterium Magnetospirillum sp. strain pMbN1 represents the first pure culture demonstrated to degrade 4-methylbenzoate completely to CO2 in a process coupled to denitrification. Differential proteogenomic studies in conjunction with targeted metabolite analyses and enzyme activity measurements elucidated a specific 4-methylbenzoyl-coenzyme A (CoA) pathway in this bacterium alongside the classical central benzoyl-CoA pathway. Whilst these two pathways are analogous, in the former the p-methyl group is retained and its 4-methylbenzoyl-CoA reductase (MbrCBAD) is phylogenetically distinct from the archetypical class I benzoyl-CoA reductase (BcrCBAD). Subsequent global regulatory studies on strain pMbN1 grown with binary or ternary substrate mixtures revealed benzoate to repress the anaerobic utilization of 4-methylbenzoate and succinate. The shared nutritional property of betaproteobacterial 'Aromatoleum aromaticum' pCyN1 and Thauera sp. strain pCyN2 is the anaerobic degradation of the plant-derived hydrocarbon p-cymene (4-isopropyltoluene) coupled to denitrification. Notably, the two strains employ two different peripheral pathways for the conversion of p-cymene to 4-isopropylbenzoyl-CoA as the possible first common intermediate. In 'A. aromaticum' pCyN1 a putative p-cymene dehydrogenase (CmdABC) is proposed to hydroxylate the benzylic methyl group, which is subsequently further oxidized to the CoA-thioester. In contrast, Thauera sp. strain pCyN2 employs a reaction sequence analogous to the known anaerobic toluene pathway, involving a distinct branching (4-isopropylbenzyl)succinate synthase (IbsABCDEF).
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Affiliation(s)
- Ralf Rabus
- Institute for Chemistry and Biology of the Marine Environment (ICBM), Carl von Ossietzky University Oldenburg, Oldenburg, Germany
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Hierarchy of Carbon Source Utilization in Soil Bacteria: Hegemonic Preference for Benzoate in Complex Aromatic Compound Mixtures Degraded by Cupriavidus pinatubonensis Strain JMP134. Appl Environ Microbiol 2015; 81:3914-24. [PMID: 25795675 DOI: 10.1128/aem.04207-14] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/24/2014] [Accepted: 03/17/2015] [Indexed: 12/23/2022] Open
Abstract
Cupriavidus pinatubonensis JMP134, like many other environmental bacteria, uses a range of aromatic compounds as carbon sources. Previous reports have shown a preference for benzoate when this bacterium grows on binary mixtures composed of this aromatic compound and 4-hydroxybenzoate or phenol. However, this observation has not been extended to other aromatic mixtures resembling a more archetypal context. We carried out a systematic study on the substrate preference of C. pinatubonensis JMP134 growing on representative aromatic compounds channeled through different catabolic pathways described in aerobic bacteria. Growth tests of nearly the entire set of binary combinations and in mixtures composed of 5 or 6 aromatic components showed that benzoate and phenol were always the preferred and deferred growth substrates, respectively. This pattern was supported by kinetic analyses that showed shorter times to initiate consumption of benzoate in aromatic compound mixtures. Gene expression analysis by real-time reverse transcription-PCR (RT-PCR) showed that, in all mixtures, the repression by benzoate over other catabolic pathways was exerted mainly at the transcriptional level. Additionally, inhibition of benzoate catabolism suggests that its multiple repressive actions are not mediated by a sole mechanism, as suggested by dissimilar requirements of benzoate degradation for effective repression in different aromatic compound mixtures. The hegemonic preference for benzoate over multiple aromatic carbon sources is not explained on the basis of growth rate and/or biomass yield on each single substrate or by obvious chemical or metabolic properties of these aromatic compounds.
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