1
|
Regulation of fadR on the ROS defense mechanism in Shewanalla oneidensis. Biotechnol Lett 2024:10.1007/s10529-024-03487-y. [PMID: 38705963 DOI: 10.1007/s10529-024-03487-y] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/04/2024] [Revised: 03/11/2024] [Accepted: 03/25/2024] [Indexed: 05/07/2024]
Abstract
Protein FadR is known as a fatty acid metabolism global regulator that sustains cell envelope integrity by changing the profile of fatty acid. Here, we present its unique participation in the defense against reactive oxygen species (ROS) in the bacterium. FadR contributes to defending extracellular ROS by maintaining the permeability of the cell membrane. It also facilitates the ROS detoxification process by increasing the expression of ROS neutralizers (KatB, KatG, and AhpCF). FadR also represses the leakage of ROS by alleviating the respiratory action conducted by terminal cytochrome cbb3-type heme-copper oxidases (ccoNOQP). These findings suggest that FadR plays a comprehensive role in modulating the bacterial oxidative stress response, instead of merely strengthening the cellular barrier against the environment. This study sheds light on the complex mechanisms of bacterial ROS defense and offers FadR as a novel target for ROS control research.
Collapse
|
2
|
The electron transport chain of Shewanella oneidensis MR-1 can operate bidirectionally to enable microbial electrosynthesis. Appl Environ Microbiol 2024; 90:e0138723. [PMID: 38117056 PMCID: PMC10807441 DOI: 10.1128/aem.01387-23] [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: 08/11/2023] [Accepted: 11/13/2023] [Indexed: 12/21/2023] Open
Abstract
Extracellular electron transfer is a process by which bacterial cells can exchange electrons with a redox-active material located outside of the cell. In Shewanella oneidensis, this process is natively used to facilitate respiration using extracellular electron acceptors such as Fe(III) or an anode. Previously, it was demonstrated that this process can be used to drive the microbial electrosynthesis (MES) of 2,3-butanediol (2,3-BDO) in S. oneidensis exogenously expressing butanediol dehydrogenase (BDH). Electrons taken into the cell from a cathode are used to generate NADH, which in turn is used to reduce acetoin to 2,3-BDO via BDH. However, generating NADH via electron uptake from a cathode is energetically unfavorable, so NADH dehydrogenases couple the reaction to proton motive force. We therefore need to maintain the proton gradient across the membrane to sustain NADH production. This work explores accomplishing this task by bidirectional electron transfer, where electrons provided by the cathode go to both NADH formation and oxygen (O2) reduction by oxidases. We show that oxidases use trace dissolved oxygen in a microaerobic bioelectrical chemical system (BES), and the translocation of protons across the membrane during O2 reduction supports 2,3-BDO generation. Interestingly, this process is inhibited by high levels of dissolved oxygen in this system. In an aerated BES, O2 molecules react with the strong reductant (cathode) to form reactive oxygen species, resulting in cell death.IMPORTANCEMicrobial electrosynthesis (MES) is increasingly employed for the generation of specialty chemicals, such as biofuels, bioplastics, and cancer therapeutics. For these systems to be viable for industrial scale-up, it is important to understand the energetic requirements of the bacteria to mitigate unnecessary costs. This work demonstrates sustained production of an industrially relevant chemical driven by a cathode. Additionally, it optimizes a previously published system by removing any requirement for phototrophic energy, thereby removing the additional cost of providing a light source. We also demonstrate the severe impact of oxygen intrusion into bioelectrochemical systems, offering insight to future researchers aiming to work in an anaerobic environment. These studies provide insight into both the thermodynamics of electrosynthesis and the importance of the bioelectrochemical systems' design.
Collapse
|
3
|
Strategies of chemolithoautotrophs adapting to high temperature and extremely acidic conditions in a shallow hydrothermal ecosystem. MICROBIOME 2023; 11:270. [PMID: 38049915 PMCID: PMC10696704 DOI: 10.1186/s40168-023-01712-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/24/2023] [Accepted: 10/27/2023] [Indexed: 12/06/2023]
Abstract
BACKGROUND Active hydrothermal vents create extreme conditions characterized by high temperatures, low pH levels, and elevated concentrations of heavy metals and other trace elements. These conditions support unique ecosystems where chemolithoautotrophs serve as primary producers. The steep temperature and pH gradients from the vent mouth to its periphery provide a wide range of microhabitats for these specialized microorganisms. However, their metabolic functions, adaptations in response to these gradients, and coping mechanisms under extreme conditions remain areas of limited knowledge. In this study, we conducted temperature gradient incubations of hydrothermal fluids from moderate (pH = 5.6) and extremely (pH = 2.2) acidic vents. Combining the DNA-stable isotope probing technique and subsequent metagenomics, we identified active chemolithoautotrophs under different temperature and pH conditions and analyzed their specific metabolic mechanisms. RESULTS We found that the carbon fixation activities of Nautiliales in vent fluids were significantly increased from 45 to 65 °C under moderately acidic condition, while their heat tolerance was reduced under extremely acidic conditions. In contrast, Campylobacterales actively fixed carbon under both moderately and extremely acidic conditions under 30 - 45 °C. Compared to Campylobacterales, Nautiliales were found to lack the Sox sulfur oxidation system and instead use NAD(H)-linked glutamate dehydrogenase to boost the reverse tricarboxylic acid (rTCA) cycle. Additionally, they exhibit a high genetic potential for high activity of cytochrome bd ubiquinol oxidase in oxygen respiration and hydrogen oxidation at high temperatures. In terms of high-temperature adaption, the rgy gene plays a critical role in Nautiliales by maintaining DNA stability at high temperature. Genes encoding proteins involved in proton export, including the membrane arm subunits of proton-pumping NADH: ubiquinone oxidoreductase, K+ accumulation, selective transport of charged molecules, permease regulation, and formation of the permeability barrier of bacterial outer membranes, play essential roles in enabling Campylobacterales to adapt to extremely acidic conditions. CONCLUSIONS Our study provides in-depth insights into how high temperature and low pH impact the metabolic processes of energy and main elements in chemolithoautotrophs living in hydrothermal ecosystems, as well as the mechanisms they use to adapt to the extreme hydrothermal conditions. Video Abstract.
Collapse
|
4
|
Evidence that the catalytic mechanism of heme a synthase involves the formation of a carbocation stabilized by a conserved glutamate. Arch Biochem Biophys 2023; 744:109665. [PMID: 37348627 PMCID: PMC10529832 DOI: 10.1016/j.abb.2023.109665] [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: 06/05/2023] [Accepted: 06/07/2023] [Indexed: 06/24/2023]
Abstract
In eukaryotes and many aerobic prokaryotes, the final step of aerobic respiration is catalyzed by an aa3-type cytochrome c oxidase, which requires a modified heme cofactor, heme a. The conversion of heme b, the prototypical cellular heme, to heme o and ultimately to heme a requires two modifications, the latter of which is conversion of a methyl group to an aldehyde, catalyzed by heme a synthase (HAS). The N- and C-terminal halves of HAS share homology, and each half contains a heme-binding site. Previous reports indicate that the C-terminal site is occupied by a heme b cofactor. The N-terminal site may function as the substrate (heme o) binding site, although this has not been confirmed experimentally. Here, we assess the role of conserved residues from the N- and C-terminal heme-binding sites in HAS from prokaryotic (Shewanella oneidensis) and eukaryotic (Saccharomyces cerevisiae) species - SoHAS/CtaA and ScHAS/Cox15, respectively. A glutamate within the N-terminal site is found to be critical for activity in both types of HAS, consistent with the hypothesis that a carbocation forms transiently during catalysis. In contrast, the residue occupying the analogous C-terminal position is dispensable for enzyme activity. In SoHAS, the C-terminal heme ligands are critical for stability, while in ScHAS, substitutions in either heme-binding site have little effect on global structure. In both species, in vivo accumulation of heme o requires the presence of an inactive HAS variant, highlighting a potential regulatory role for HAS in heme o biosynthesis.
Collapse
|
5
|
Abundance and Niche Differentiation of Comammox in the Sludges of Wastewater Treatment Plants That Use the Anaerobic-Anoxic-Aerobic Process. Life (Basel) 2022; 12:life12070954. [PMID: 35888046 PMCID: PMC9322089 DOI: 10.3390/life12070954] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2022] [Revised: 06/20/2022] [Accepted: 06/22/2022] [Indexed: 11/27/2022] Open
Abstract
Complete ammonia oxidizers (comammox), which directly oxidize ammonia to nitrate, were recently identified and found to be ubiquitous in artificial systems. Research on the abundance and niche differentiation of comammox in the sludges of wastewater treatment plants (WWTPs) would be useful for improving the nitrogen removal efficiency of WWTPs. Here, we investigated the relative abundance and diversity of comammox in fifteen sludges of five WWTPs that use the anaerobic−anoxic−aerobic process in Jinan, China, via quantitative polymerase chain reaction and high-throughput sequencing of the 16S rRNA gene and ammonia monooxygenase gene. In the activated sludges in the WWTPs, comammox clade A.1 was widely distributed and mostly comprised Candidatus Nitrospira nitrosa-like comammox (>98% of all comammox). The proportion of this clade was negatively correlated (p < 0.01) with the dissolved oxygen (DO) level (1.7−8 mg/L), and slight pH changes (7.20−7.70) affected the structure of the comammox populations. Nitrospira lineage I frequently coexisted with Nitrosomonas, which generally had a significant positive correlation (p < 0.05) with the DO level. Our study provided an insight into the structure of comammox and other nitrifier populations in WWTPs that use the anaerobic−anoxic−aerobic process, broadening the knowledge about the effects of DO on comammox and other nitrifiers.
Collapse
|
6
|
The electron-bifurcating FeFe-hydrogenase Hnd is involved in ethanol metabolism in Desulfovibrio fructosovorans grown on pyruvate. Mol Microbiol 2022; 117:907-920. [PMID: 35066935 DOI: 10.1111/mmi.14881] [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: 10/17/2021] [Revised: 01/19/2022] [Accepted: 01/19/2022] [Indexed: 11/28/2022]
Abstract
Desulfovibrio fructosovorans, a sulfate-reducing bacterium, possesses six gene clusters encoding six hydrogenases catalyzing the reversible oxidation of H2 into protons and electrons. Among them, Hnd is an electron-bifurcating hydrogenase, coupling the exergonic reduction of NAD+ to the endergonic reduction of a ferredoxin with electrons derived from H2 . It was previously hypothesized that its biological function involves the production of NADPH necessary for biosynthetic purposes. However, it was subsequently demonstrated that Hnd is instead a NAD+ -reducing enzyme, thus its specific function has yet to be established. To understand the physiological role of Hnd in D. fructosovorans, we compared the hnd deletion mutant with the wild-type strain grown on pyruvate. Growth, metabolites production and comsumption, and gene expression were compared under three different growth conditions. Our results indicate that hnd is strongly regulated at the transcriptional level and that its deletion has a drastic effect on the expression of genes for two enzymes, an aldehyde ferredoxin oxidoreductase and an alcohol dehydrogenase. We demonstrated here that Hnd is involved in ethanol metabolism when bacteria grow fermentatively and proposed that Hnd might oxidize part of the H2 produced during fermentation generating both NADH and reduced ferredoxin for ethanol production via its electron bifurcation mechanism.
Collapse
|
7
|
Aerobic Respiration and Its Regulation in the Metal Reducer Shewanella oneidensis. Front Microbiol 2021; 12:723835. [PMID: 34566926 PMCID: PMC8458880 DOI: 10.3389/fmicb.2021.723835] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Accepted: 07/26/2021] [Indexed: 11/23/2022] Open
Abstract
Shewanella oneidensis MR-1 is a facultative anaerobe known for its ability to reduce metal oxides. Anaerobic respiration, especially metal reduction, has been the subject of extensive research. In contrast, S. oneidensis aerobic respiration has received less attention. S. oneidensis expresses cbb3- and aa3-type cytochrome c oxidases and a bd-type quinol oxidase. The aa3-type oxidase, which in other bacteria is the major oxygen reductase under oxygen replete conditions, does not appear to contribute to aerobic respiration and growth in S. oneidensis. Our results indicated that although the aa3-type oxidase does not play a role in aerobic growth on lactate, the preferred carbon source for S. oneidensis, it is involved in growth on pyruvate or acetate. These results highlight the importance of testing multiple carbon and energy sources when attempting to identify enzyme activities and mutant phenotypes. Several regulatory proteins contribute to the regulation of aerobic growth in S. oneidensis including CRP and ArcA. The 3',5'-cAMP phosphodiesterase (CpdA) appears to play a more significant role in aerobic growth than either CRP or ArcA, yet the deficiency does not appear to be the result of reduced oxidase genes expression. Interestingly, the ∆cpdA mutant was more deficient in aerobic respiration with several carbon sources tested compared to ∆crp, which was moderately deficient only in the presence of lactate. To identify the reason for ∆cpdA aerobic growth deficiency, we isolated a suppressor mutant with transposon insertion in SO_3550. Inactivation of this gene, which encodes an anti-sigma factor, restored aerobic growth in the cpdA mutant to wild-type levels. Inactivation of SO_3550 in wild-type cells, however, did not affect aerobic growth. The S. oneidensis genome encodes two additional CRP-like proteins that we designated CrpB and CrpC. Mutants that lack crpB and crpC were deficient in aerobic growth, but this deficiency was not due to the loss of oxidase gene expression.
Collapse
|
8
|
The Shewanella genus: ubiquitous organisms sustaining and preserving aquatic ecosystems. FEMS Microbiol Rev 2020; 44:155-170. [DOI: 10.1093/femsre/fuz031] [Citation(s) in RCA: 43] [Impact Index Per Article: 10.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2019] [Accepted: 01/09/2020] [Indexed: 12/16/2022] Open
Abstract
ABSTRACT
The Gram-negative Shewanella bacterial genus currently includes about 70 species of mostly aquatic γ-proteobacteria, which were isolated around the globe in a multitude of environments such as surface freshwater and the deepest marine trenches. Their survival in such a wide range of ecological niches is due to their impressive physiological and respiratory versatility. Some strains are among the organisms with the highest number of respiratory systems, depending on a complex and rich metabolic network. Implicated in the recycling of organic and inorganic matter, they are important components of organism-rich oxic/anoxic interfaces, but they also belong to the microflora of a broad group of eukaryotes from metazoans to green algae. Examples of long-term biological interactions like mutualism or pathogeny have been described, although molecular determinants of such symbioses are still poorly understood. Some of these bacteria are key organisms for various biotechnological applications, especially the bioremediation of hydrocarbons and metallic pollutants. The natural ability of these prokaryotes to thrive and detoxify deleterious compounds explains their use in wastewater treatment, their use in energy generation by microbial fuel cells and their importance for resilience of aquatic ecosystems.
Collapse
|
9
|
A new mechanistic model for an O 2-protected electron-bifurcating hydrogenase, Hnd from Desulfovibrio fructosovorans. BIOCHIMICA ET BIOPHYSICA ACTA-BIOENERGETICS 2018; 1859:1302-1312. [PMID: 30463674 DOI: 10.1016/j.bbabio.2018.09.364] [Citation(s) in RCA: 27] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Subscribe] [Scholar Register] [Received: 07/18/2018] [Revised: 08/22/2018] [Accepted: 09/16/2018] [Indexed: 10/28/2022]
Abstract
The genome of the sulfate-reducing and anaerobic bacterium Desulfovibrio fructosovorans encodes different hydrogenases. Among them is Hnd, a tetrameric cytoplasmic [FeFe] hydrogenase that has previously been described as an NADP-specific enzyme (Malki et al., 1995). In this study, we purified and characterized a recombinant Strep-tagged form of Hnd and demonstrated that it is an electron-bifurcating enzyme. Flavin-based electron-bifurcation is a mechanism that couples an exergonic redox reaction to an endergonic one allowing energy conservation in anaerobic microorganisms. One of the three ferredoxins of the bacterium, that was named FdxB, was also purified and characterized. It contains a low-potential (Em = -450 mV) [4Fe4S] cluster. We found that Hnd was not able to reduce NADP+, and that it catalyzes the simultaneous reduction of FdxB and NAD+. Moreover, Hnd is the first electron-bifurcating hydrogenase that retains activity when purified aerobically due to formation of an inactive state of its catalytic site protecting against O2 damage (Hinact). Hnd is highly active with the artificial redox partner (methyl viologen) and can perform the electron-bifurcation reaction to oxidize H2 with a specific activity of 10 μmol of NADH/min/mg of enzyme. Surprisingly, the ratio between NADH and reduced FdxB varies over the reaction with a decreasing amount of FdxB reduced per NADH produced, indicating a more complex mechanism than previously described. We proposed a new mechanistic model in which the ferredoxin is recycled at the hydrogenase catalytic subunit.
Collapse
|
10
|
Genomic inference of the metabolism and evolution of the archaeal phylum Aigarchaeota. Nat Commun 2018; 9:2832. [PMID: 30026532 PMCID: PMC6053391 DOI: 10.1038/s41467-018-05284-4] [Citation(s) in RCA: 63] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2017] [Accepted: 06/13/2018] [Indexed: 12/30/2022] Open
Abstract
Microbes of the phylum Aigarchaeota are widely distributed in geothermal environments, but their physiological and ecological roles are poorly understood. Here we analyze six Aigarchaeota metagenomic bins from two circumneutral hot springs in Tengchong, China, to reveal that they are either strict or facultative anaerobes, and most are chemolithotrophs that can perform sulfide oxidation. Applying comparative genomics to the Thaumarchaeota and Aigarchaeota, we find that they both originated from thermal habitats, sharing 1154 genes with their common ancestor. Horizontal gene transfer played a crucial role in shaping genetic diversity of Aigarchaeota and led to functional partitioning and ecological divergence among sympatric microbes, as several key functional innovations were endowed by Bacteria, including dissimilatory sulfite reduction and possibly carbon monoxide oxidation. Our study expands our knowledge of the possible ecological roles of the Aigarchaeota and clarifies their evolutionary relationship to their sister lineage Thaumarchaeota.
Collapse
|
11
|
Comparative genomics sheds light on niche differentiation and the evolutionary history of comammox Nitrospira. ISME JOURNAL 2018. [PMID: 29515170 DOI: 10.1038/s41396-018-0083-3] [Citation(s) in RCA: 145] [Impact Index Per Article: 24.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The description of comammox Nitrospira spp., performing complete ammonia-to-nitrate oxidation, and their co-occurrence with canonical β-proteobacterial ammonia oxidizing bacteria (β-AOB) in the environment, calls into question the metabolic potential of comammox Nitrospira and the evolutionary history of their ammonia oxidation pathway. We report four new comammox Nitrospira genomes, constituting two novel species, and the first comparative genomic analysis on comammox Nitrospira. Unlike canonical Nitrospira, comammox Nitrospira genomes lack genes for assimilatory nitrite reduction, suggesting that they have lost the potential to use external nitrite nitrogen sources. By contrast, compared to canonical Nitrospira, comammox Nitrospira harbor a higher diversity of urea transporters and copper homeostasis genes and lack cyanate hydratase genes. Additionally, the two comammox clades differ in their ammonium uptake systems. Contrary to β-AOB, comammox Nitrospira genomes have single copies of the two central ammonia oxidation pathway operons. Similar to ammonia oxidizing archaea and some oligotrophic AOB strains, they lack genes involved in nitric oxide reduction. Furthermore, comammox Nitrospira genomes encode genes that might allow efficient growth at low oxygen concentrations. Regarding the evolutionary history of comammox Nitrospira, our analyses indicate that several genes belonging to the ammonia oxidation pathway could have been laterally transferred from β-AOB to comammox Nitrospira. We postulate that the absence of comammox genes in other sublineage II Nitrospira genomes is the result of subsequent loss.
Collapse
|
12
|
Pseudomonas pseudoalcaligenes KF707 grown with biphenyl expresses a cytochrome caa 3 oxidase that uses cytochrome c 4 as electron donor. FEBS Lett 2018; 592:901-915. [PMID: 29427514 DOI: 10.1002/1873-3468.13001] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2017] [Revised: 01/30/2018] [Accepted: 02/01/2018] [Indexed: 11/09/2022]
Abstract
Combining peroxidase activity-based heme staining (TMBZ/SDS/PAGE) with mass spectrometry analyses (Nano LC-MS/MS) of protein extracts from wild-type and appropriate mutants, we provide evidence that the polychlorinated biphenyl degrader Pseudomonas pseudoalcaligenes KF707 primarily expresses a caa3 -type cytochrome c oxidase (caa3 -Cox) using cytochrome (cyt) c4 as an electron donor in cells grown with biphenyl versus glucose as the sole carbon source. Homology modeling of KF707 caa3 -Cox using the three-dimensional structure of that from Thermus thermophilus highlights multiple similarities and differences between the proton channels in subunit I of the aa3 - and caa3 -Cox of Paracoccus and Thermus spp., respectively. To our knowledge, this is the first report demonstrating the presence of a caa3 -Cox using cyt c4 as an electron donor in a Pseudomonas species.
Collapse
|
13
|
Biphenyl Modulates the Expression and Function of Respiratory Oxidases in the Polychlorinated-Biphenyls Degrader Pseudomonas pseudoalcaligenes KF707. Front Microbiol 2017; 8:1223. [PMID: 28713350 PMCID: PMC5492768 DOI: 10.3389/fmicb.2017.01223] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/03/2017] [Accepted: 06/16/2017] [Indexed: 11/13/2022] Open
Abstract
Pseudomonas pseudoalcaligenes KF707 is a soil bacterium which is known for its capacity to aerobically degrade harmful organic compounds such as polychlorinated biphenyls (PCBs) using biphenyl as co-metabolite. Here we provide the first genetic and functional analysis of the KF707 respiratory terminal oxidases in cells grown with two different carbon sources: glucose and biphenyl. We identified five terminal oxidases in KF707: two c(c)aa3 type oxidases (Caa3 and Ccaa3), two cbb3 type oxidases (Cbb31 and Cbb32), and one bd type cyanide-insensitive quinol oxidase (CIO). While the activity and expression of both Cbb31 and Cbb32 oxidases was prevalent in glucose grown cells as compared to the other oxidases, the activity and expression of the Caa3 oxidase increased considerably only when biphenyl was used as carbon source in contrast to the Cbb32 oxidase which was repressed. Further, the respiratory activity and expression of CIO was up-regulated in a Cbb31 deletion strain as compared to W.T. whereas the CIO up-regulation was not present in Cbb32 and C(c)aa3 deletion mutants. These results, together, reveal that both function and expression of cbb3 and caa3 type oxidases in KF707 are modulated by biphenyl which is the co-metabolite needed for the activation of the PCBs-degradation pathway.
Collapse
|
14
|
Specific expression and function of the A-type cytochrome c oxidase under starvation conditions in Pseudomonas aeruginosa. PLoS One 2017; 12:e0177957. [PMID: 28542449 PMCID: PMC5436846 DOI: 10.1371/journal.pone.0177957] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2016] [Accepted: 05/05/2017] [Indexed: 11/22/2022] Open
Abstract
Pseudomonas aeruginosa has one A-type (caa3) and multiple C-type (cbb3) cytochrome c oxidases as well as two quinol oxidases for aerobic respiration. The caa3 oxidase is highly efficient in creating a proton gradient across the cell membrane, but it is not expressed under normal growth conditions and its physiological role has not been investigated. In the present study, a mutant strain deficient in the coxBA-PA0107-coxC genes encoding caa3 exhibited normal growth under any test conditions, but it had low relative fitness under carbon starvation conditions, indicating that the expression of caa3 is advantageous under starvation conditions. A mutant that lacked four terminal oxidase gene clusters except for the cox genes was unable to grow aerobically because of low expression level of caa3. However, suppressor mutants that grew aerobically using caa3 as the only terminal oxidase emerged after aerobic subculturing. Analyses of the suppressor mutants revealed that a mutation of roxS encoding a sensor kinase of a two-component regulator RoxSR was necessary for the aerobic growth in synthetic medium. Two additional mutations in the 5′-flanking region of coxB were necessary for the aerobic growth in LB medium. Although the expression level of caa3 was higher in the suppressor mutants, their growth rates were lower than when the other terminal oxidases were utilized, suggesting that caa3 was not suited for utilization as the only terminal oxidase. Overexpression of the cox genes also inhibited the aerobic growth of the wild-type strain. These results indicate that caa3 is tightly regulated to be expressed only under starvation conditions at low level and it functions in cooperation with other terminal oxidases to facilitate survival in nutrient starvation conditions.
Collapse
|
15
|
Loss of OxyR reduces efficacy of oxygen respiration in Shewanella oneidensis. Sci Rep 2017; 7:42609. [PMID: 28195212 PMCID: PMC5307378 DOI: 10.1038/srep42609] [Citation(s) in RCA: 13] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/07/2016] [Accepted: 01/11/2017] [Indexed: 02/02/2023] Open
Abstract
In many bacteria, OxyR is the major regulator controlling cellular response to H2O2. A common phenotype resulting from OxyR loss is reduced growth rate, but the underlying mechanism is unknown. We demonstrated in Shewanella oneidensis, an important research model for applied and environmental microbes, that the defect is primarily due to an electron shortage to major terminal oxidase cytochrome cbb3. The loss of OxyR leads to enhanced production of electron carriers that compete for electrons against cytochrome cbb3, cytochrome bd in particular. We further showed that the oxyR mutation also results in increased production of menaquinone, an additional means to lessen electrons to cytochrome cbb3. Although regulation of OxyR on these biological processes appears to be indirect, these data indicate that the regulator plays a previously underappreciated role in mediating respiration.
Collapse
|
16
|
Evidence for Fast Electron Transfer between the High-Spin Haems in Cytochrome bd-I from Escherichia coli. PLoS One 2016; 11:e0155186. [PMID: 27152644 PMCID: PMC4859518 DOI: 10.1371/journal.pone.0155186] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/14/2016] [Accepted: 04/25/2016] [Indexed: 12/21/2022] Open
Abstract
Cytochrome bd-I is one of the three proton motive force-generating quinol oxidases in the O2-dependent respiratory chain of Escherichia coli. It contains one low-spin haem (b558) and the two high-spin haems (b595 and d) as the redox-active cofactors. In order to examine the flash-induced intraprotein reverse electron transfer (the so-called ''electron backflow''), CO was photolyzed from the ferrous haem d in one-electron reduced (b5583+b5953+d2+-CO) cytochrome bd-I, and the fully reduced (b5582+b5952+d2+-CO) oxidase as a control. In contrast to the fully reduced cytochrome bd-I, the transient spectrum of one-electron reduced oxidase at a delay time of 1.5 μs is clearly different from that at a delay time of 200 ns. The difference between the two spectra can be modeled as the electron transfer from haem d to haem b595 in 3–4% of the cytochrome bd-I population. Thus, the interhaem electron backflow reaction induced by photodissociation of CO from haem d in one-electron reduced cytochrome bd-I comprises two kinetically different phases: the previously unnoticed fast electron transfer from haem d to haem b595 within 0.2–1.5 μs and the slower well-defined electron equilibration with τ ~16 μs. The major new finding of this work is the lack of electron transfer at 200 ns.
Collapse
|
17
|
Expression of terminal oxidases under nutrient-starved conditions in Shewanella oneidensis: detection of the A-type cytochrome c oxidase. Sci Rep 2016; 6:19726. [PMID: 26815910 PMCID: PMC4728554 DOI: 10.1038/srep19726] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/14/2015] [Accepted: 12/17/2015] [Indexed: 11/12/2022] Open
Abstract
Shewanella species are facultative anaerobic bacteria that colonize redox-stratified habitats where O2 and nutrient concentrations fluctuate. The model species Shewanella oneidensis MR-1 possesses genes coding for three terminal oxidases that can perform O2 respiration: a bd-type quinol oxidase and cytochrome c oxidases of the cbb3-type and the A-type. Whereas the bd- and cbb3-type oxidases are routinely detected, evidence for the expression of the A-type enzyme has so far been lacking. Here, we investigated the effect of nutrient starvation on the expression of these terminal oxidases under different O2 tensions. Our results reveal that the bd-type oxidase plays a significant role under nutrient starvation in aerobic conditions. The expression of the cbb3-type oxidase is also modulated by the nutrient composition of the medium and increases especially under iron-deficiency in exponentially growing cells. Most importantly, under conditions of carbon depletion, high O2 and stationary-growth, we report for the first time the expression of the A-type oxidase in S. oneidensis, indicating that this terminal oxidase is not functionally lost. The physiological role of the A-type oxidase in energy conservation and in the adaptation of S. oneidensis to redox-stratified environments is discussed.
Collapse
|
18
|
Regulation of nitrite resistance of the cytochrome cbb3 oxidase by cytochrome c ScyA in Shewanella oneidensis. Microbiologyopen 2014; 4:84-99. [PMID: 25417822 PMCID: PMC4335978 DOI: 10.1002/mbo3.224] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/08/2014] [Revised: 10/24/2014] [Accepted: 11/03/2014] [Indexed: 12/03/2022] Open
Abstract
Cytochrome c proteins, as enzymes to exchange electrons with substrates or as pure electron carriers to shuttle electrons, play vital roles in bacterial respiration and photosynthesis. In Shewanella oneidensis, a research model for the respiratory diversity, at least 42 c-type cytochromes are predicted to be encoded in the genome and are regarded to be the foundation of its highly branched electron transport pathways. However, only a small number of c-type cytochromes have been extensively studied. In this study, we identify soluble cytochrome c ScyA as an important factor influencing the nitrite resistance of a strain devoid of the bd oxidase by utilizing a newly developed transposon mutagenesis vector, which enables overexpression of the gene(s) downstream of the insertion site. We show that when in overabundance ScyA facilitates growth against nitrite inhibition by enhancing nitrite resistance of the cbb3 oxidase. Based on the data presented in this study, we suggest two possible mechanisms underlying the observed effect of ScyA: (1) ScyA increases electron flow to the cbb3 oxidase; (2) ScyA promotes nitrite resistance of the cbb3 oxidase, possibly by direct interaction.
Collapse
|
19
|
Evidence for the requirement of CydX in function but not assembly of the cytochrome bd oxidase in Shewanella oneidensis. Biochim Biophys Acta Gen Subj 2014; 1850:318-28. [PMID: 25316290 DOI: 10.1016/j.bbagen.2014.10.005] [Citation(s) in RCA: 42] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2014] [Revised: 09/25/2014] [Accepted: 10/06/2014] [Indexed: 12/19/2022]
Abstract
BACKGROUND Cytochrome bd oxidase, existing widely in bacteria, produces a proton motive force by the vectorial charge transfer of protons and more importantly, endows bacteria with a number of vitally important physiological functions, such as enhancing tolerance to various stresses. Although extensively studied as a CydA-CydB two-subunit complex for decades, the complex in certain groups of bacteria is recently found to in fact consist of an additional subunit, which is functionally essential. METHODS We investigated the assembly of the CydA-CydB complex using BiFC. We investigated the function of CydX using mutational analysis. RESULTS CydX, a 38-amino-acid inner-membrane protein, is associated with the CydA-CydB complex in Shewanella oneidensis, a facultative anaerobe renowned for its respiratory versatility. It is clear that CydX is neither required for the in vivo assembly of the CydA-CydB complex nor relies on the complex for its translocation and integration into the membrane. The N-terminal segment (1-25 amino acid residues) and short periplasmic overhang of CydX, with respect to functionality, are important whereas the remaining C-terminal segment is rather flexible. CONCLUSION Based on these findings, we postulate that CydX may function by positioning and stabilizing the prosthetic hemes, especially heme d in the CydA-CydB complex although a role of participating in catalytic reaction is not excluded. GENERAL SIGNIFICANCE The work provides novel insights into our understanding of the small subunit of the cytochrome bd oxidase.
Collapse
|
20
|
Chlorate reduction in Shewanella algae ACDC is a recently acquired metabolism characterized by gene loss, suboptimal regulation and oxidative stress. Mol Microbiol 2014; 94:107-25. [PMID: 25099177 DOI: 10.1111/mmi.12746] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 08/01/2014] [Indexed: 12/25/2022]
Abstract
Previous work on respiratory chlorate reduction has biochemically identified the terminal reductase ClrABC and the chlorite detoxifying enzyme Cld. In Shewanella algae ACDC, genes encoding these enzymes reside on composite transposons whose core we refer to as the chlorate reduction composite transposon interior (CRI). To better understand this metabolism in ACDC, we used RNA-seq and proteomics to predict carbon and electron flow during chlorate reduction and posit that formate is an important electron carrier with lactate as the electron donor, but that NADH predominates on acetate. Chlorate-specific transcription of electron transport chain components or the CRI was not observed, but clr and cld transcription was attenuated by oxygen. The major chlorate-specific response related to oxidative stress and was indicative of reactive chlorine species production. A genetic system based on rpsL-streptomycin counter selection was developed to further dissect the metabolism, but ACDC readily lost the CRI via homologous recombination of the composite transposon's flanking insertion sequences. An engineered strain containing a single chromosomal CRI did not grow on chlorate, but overexpression of cld and its neighbouring cytochrome c restored growth. We postulate that the recently acquired CRI underwent copy-number expansion to circumvent insufficient expression of key genes in the pathway.
Collapse
|