scholarly journals Pyruvate and Lactate Metabolism by Shewanella oneidensis MR-1 under Fermentation, Oxygen Limitation, and Fumarate Respiration Conditions

2011 ◽  
Vol 77 (23) ◽  
pp. 8234-8240 ◽  
Author(s):  
Grigoriy E. Pinchuk ◽  
Oleg V. Geydebrekht ◽  
Eric A. Hill ◽  
Jennifer L. Reed ◽  
Allan E. Konopka ◽  
...  
Keyword(s):  
Electron Acceptor ◽  
Shewanella Oneidensis ◽  
Anaerobic Growth ◽  
Lactate Metabolism ◽  
Content Type ◽  
Substrate Level Phosphorylation ◽  
Formate Oxidation ◽  
Pyruvate Fermentation ◽  
Wide Range ◽  
Substrate Level

ABSTRACTShewanella oneidensisMR-1 is a facultative anaerobe that derives energy by coupling organic matter oxidation to the reduction of a wide range of electron acceptors. Here, we quantitatively assessed the lactate and pyruvate metabolism of MR-1 under three distinct conditions: electron acceptor-limited growth on lactate with O2, lactate with fumarate, and pyruvate fermentation. The latter does not support growth but provides energy for cell survival. Using physiological and genetic approaches combined with flux balance analysis, we showed that the proportion of ATP produced by substrate-level phosphorylation varied from 33% to 72.5% of that needed for growth depending on the electron acceptor nature and availability. While being indispensable for growth, the respiration of fumarate does not contribute significantly to ATP generation and likely serves to remove formate, a product of pyruvate formate-lyase-catalyzed pyruvate disproportionation. Under both tested respiratory conditions,S. oneidensisMR-1 carried out incomplete substrate oxidation, whereby the tricarboxylic acid (TCA) cycle did not contribute significantly. Pyruvate dehydrogenase was not involved in lactate metabolism under conditions of O2limitation but was required for anaerobic growth, likely by supplying reducing equivalents for biosynthesis. The results suggest that pyruvate fermentation byS. oneidensisMR-1 cells represents a combination of substrate-level phosphorylation and respiration, where pyruvate serves as an electron donor and an electron acceptor. Pyruvate reduction to lactate at the expense of formate oxidation is catalyzed by a recently described new type of oxidative NAD(P)H-independentd-lactate dehydrogenase (Dld-II). The results further indicate that pyruvate reduction coupled to formate oxidation may be accompanied by the generation of proton motive force.

scholarly journals Roles of D-Lactate Dehydrogenases in the Anaerobic Growth ofShewanella oneidensisMR-1 on Sugars

2018 ◽  
Vol 85 (3) ◽  
Author(s):  
Takuya Kasai ◽  
Yusuke Suzuki ◽  
Atsushi Kouzuma ◽  
Kazuya Watanabe
Keyword(s):  
Electron Acceptor ◽  
Deletion Mutant ◽  
Shewanella Oneidensis ◽  
Electron Acceptors ◽  
Anaerobic Growth ◽  
Receptor Protein ◽  
Acid Fermentation ◽  
Respiratory Quinone ◽  
Content Type ◽  
Electron Sink

ABSTRACTShewanella oneidensisMR-1 is a facultative anaerobe that respires using a variety of electron acceptors. Although this organism is incapable of fermentative growth in the absence of electron acceptors, its genome encodes LdhA (a putative fermentative NADH-dependentd-lactate dehydrogenase [d-LDH]) and Dld (a respiratory quinone-dependentd-LDH). However, the physiological roles of LdhA in MR-1 are unclear. Here, we examined the activity, transcriptional regulation, and traits of deletion mutants to gain insight into the roles of LdhA in the anaerobic growth of MR-1. Analyses ofd-LDH activity in MR-1 and theldhAdeletion mutant confirmed that LdhA functions as an NADH-dependentd-LDH that catalyzes the reduction of pyruvate tod-lactate.In vivoandin vitroassays revealed thatldhAexpression was positively regulated by the cyclic-AMP receptor protein, a global transcription factor that regulates anaerobic respiratory pathways in MR-1, suggesting that LdhA functions in coordination with anaerobic respiration. Notably, we found that a deletion mutant of all four NADH dehydrogenases (NDHs) in MR-1 (ΔNDH mutant) retained the ability to grow onN-acetylglucosamine under fumarate-respiring conditions, while an additional deletion ofldhAordlddeprived the ΔNDH mutant of this growth ability. These results indicate that LdhA-Dld serves as a bypass of NDH in electron transfer from NADH to quinones. Our findings suggest that the LdhA-Dld system manages intracellular redox balance by utilizingd-lactate as a temporal electron sink under electron acceptor-limited conditions.IMPORTANCENADH-dependent LDHs are conserved among diverse organisms and contribute to NAD+regeneration in lactic acid fermentation. However, this type of LDH is also present in nonfermentative bacteria, including members of the genusShewanella, while their physiological roles in these bacteria remain unknown. Here, we show that LdhA (an NADH-dependentd-LDH) works in concert with Dld (a quinone-dependentd-LDH) to transfer electrons from NADH to quinones during sugar catabolism inS. oneidensisMR-1. Our results indicate thatd-lactate acts as an intracellular electron mediator to transfer electrons from NADH to membrane quinones. In addition,d-lactate serves as a temporal electron sink when respiratory electron acceptors are not available. Our study suggests novel physiological roles ford-LDHs in providing nonfermentative bacteria with catabolic flexibility under electron acceptor-limited conditions.

scholarly journals Substrate-Level Phosphorylation Is the Primary Source of Energy Conservation during Anaerobic Respiration of Shewanella oneidensis Strain MR-1

2010 ◽  
Vol 192 (13) ◽  
pp. 3345-3351 ◽  
Author(s):  
Kristopher A. Hunt ◽  
Jeffrey M. Flynn ◽  
Belén Naranjo ◽  
Indraneel D. Shikhare ◽  
Jeffrey A. Gralnick
Keyword(s):  
Energy Conservation ◽  
Atp Synthase ◽  
Electron Acceptor ◽  
Shewanella Oneidensis ◽  
Proton Motive Force ◽  
Electron Acceptors ◽  
Anaerobic Conditions ◽  
Substrate Level Phosphorylation ◽  
Substrate Level ◽  
Mutant Strains

ABSTRACT It is well established that respiratory organisms use proton motive force to produce ATP via F-type ATP synthase aerobically and that this process may reverse during anaerobiosis to produce proton motive force. Here, we show that Shewanella oneidensis strain MR-1, a nonfermentative, facultative anaerobe known to respire exogenous electron acceptors, generates ATP primarily from substrate-level phosphorylation under anaerobic conditions. Mutant strains lacking ackA (SO2915) and pta (SO2916), genes required for acetate production and a significant portion of substrate-level ATP produced anaerobically, were tested for growth. These mutant strains were unable to grow anaerobically with lactate and fumarate as the electron acceptor, consistent with substrate-level phosphorylation yielding a significant amount of ATP. Mutant strains lacking ackA and pta were also shown to grow slowly using N-acetylglucosamine as the carbon source and fumarate as the electron acceptor, consistent with some ATP generation deriving from the Entner-Doudoroff pathway with this substrate. A deletion strain lacking the sole F-type ATP synthase (SO4746 to SO4754) demonstrated enhanced growth on N-acetylglucosamine and a minor defect with lactate under anaerobic conditions. ATP synthase mutants grown anaerobically on lactate while expressing proteorhodopsin, a light-dependent proton pump, exhibited restored growth when exposed to light, consistent with a proton-pumping role for ATP synthase under anaerobic conditions. Although S. oneidensis requires external electron acceptors to balance redox reactions and is not fermentative, we find that substrate-level phosphorylation is its primary anaerobic energy conservation strategy. Phenotypic characterization of an ackA deletion in Shewanella sp. strain MR-4 and genomic analysis of other sequenced strains suggest that this strategy is a common feature of Shewanella.

Magnetovibrio blakemorei gen. nov., sp. nov., a magnetotactic bacterium ( Alphaproteobacteria : Rhodospirillaceae ) isolated from a salt marsh

2013 ◽  
Vol 63 (Pt_5) ◽  
pp. 1824-1833 ◽  
Author(s):  
Dennis A. Bazylinski ◽  
Timothy J. Williams ◽  
Christopher T. Lefèvre ◽  
Denis Trubitsyn ◽  
Jiasong Fang ◽  
...  
Keyword(s):  
Salt Marsh ◽  
Electron Acceptor ◽  
Anaerobic Growth ◽  
Rrna Gene ◽  
Magnetotactic Bacterium ◽  
Single Chain ◽  
Circular Chromosome ◽  
Terminal Electron Acceptor ◽  
Content Type ◽  
Link Type

A magnetotactic bacterium, designated strain MV-1T, was isolated from sulfide-rich sediments in a salt marsh near Boston, MA, USA. Cells of strain MV-1T were Gram-negative, and vibrioid to helicoid in morphology. Cells were motile by means of a single polar flagellum. The cells appeared to display a transitional state between axial and polar magnetotaxis: cells swam in both directions, but generally had longer excursions in one direction than the other. Cells possessed a single chain of magnetosomes containing truncated hexaoctahedral crystals of magnetite, positioned along the long axis of the cell. Strain MV-1T was a microaerophile that was also capable of anaerobic growth on some nitrogen oxides. Salinities greater than 10 % seawater were required for growth. Strain MV-1T exhibited chemolithoautotrophic growth on thiosulfate and sulfide with oxygen as the terminal electron acceptor (microaerobic growth) and on thiosulfate using nitrous oxide (N2O) as the terminal electron acceptor (anaerobic growth). Chemo-organoautotrophic and methylotrophic growth was supported by formate under microaerobic conditions. Autotrophic growth occurred via the Calvin–Benson–Bassham cycle. Chemo-organoheterotrophic growth was supported by various organic acids and amino acids, under microaerobic and anaerobic conditions. Optimal growth occurred at pH 7.0 and 26–28 °C. The genome of strain MV-1T consisted of a single, circular chromosome, about 3.7 Mb in size, with a G+C content of 52.9–53.5 mol%.Phylogenetic analysis based on 16S rRNA gene sequences indicated that strain MV-1T belongs to the family Rhodospirillaceae within the Alphaproteobacteria , but is not closely related to the genus Magnetospirillum . The name Magnetovibrio blakemorei gen. nov., sp. nov. is proposed for strain MV-1T. The type strain of Magnetovibrio blakemorei is MV-1T ( = ATCC BAA-1436T  = DSM 18854T).

scholarly journals Siderophores Are Not Involved in Fe(III) Solubilization during Anaerobic Fe(III) Respiration by Shewanella oneidensis MR-1

2010 ◽  
Vol 76 (8) ◽  
pp. 2425-2432 ◽  
Author(s):  
Christine M. Fennessey ◽  
Morris E. Jones ◽  
Martial Taillefert ◽  
Thomas J. DiChristina
Keyword(s):  
Electron Acceptor ◽  
Gene Deletion ◽  
Shewanella Oneidensis ◽  
Nitrilotriacetic Acid ◽  
Organic Ligands ◽  
Aerobic Respiration ◽  
Deletion Mutants ◽  
Wild Type ◽  
Voltammetric Techniques ◽  
Wide Range

ABSTRACT Shewanella oneidensis MR-1 respires a wide range of anaerobic electron acceptors, including sparingly soluble Fe(III) oxides. In the present study, S. oneidensis was found to produce Fe(III)-solubilizing organic ligands during anaerobic Fe(III) oxide respiration, a respiratory strategy postulated to destabilize Fe(III) and produce more readily reducible soluble organic Fe(III). In-frame gene deletion mutagenesis, siderophore detection assays, and voltammetric techniques were combined to determine (i) if the Fe(III)-solubilizing organic ligands produced by S. oneidensis during anaerobic Fe(III) oxide respiration were synthesized via siderophore biosynthesis systems and (ii) if the Fe(III)-siderophore reductase was required for respiration of soluble organic Fe(III) as an anaerobic electron acceptor. Genes predicted to encode the siderophore (hydroxamate) biosynthesis system (SO3030 to SO3032), the Fe(III)-hydroxamate receptor (SO3033), and the Fe(III)-hydroxamate reductase (SO3034) were identified in the S. oneidensis genome, and corresponding in-frame gene deletion mutants were constructed. ΔSO3031 was unable to synthesize siderophores or produce soluble organic Fe(III) during aerobic respiration yet retained the ability to solubilize and respire Fe(III) at wild-type rates during anaerobic Fe(III) oxide respiration. ΔSO3034 retained the ability to synthesize siderophores during aerobic respiration and to solubilize and respire Fe(III) at wild-type rates during anaerobic Fe(III) oxide respiration. These findings indicate that the Fe(III)-solubilizing organic ligands produced by S. oneidensis during anaerobic Fe(III) oxide respiration are not synthesized via the hydroxamate biosynthesis system and that the Fe(III)-hydroxamate reductase is not essential for respiration of Fe(III)-citrate or Fe(III)-nitrilotriacetic acid (NTA) as an anaerobic electron acceptor.

scholarly journals Anaerobic α-Amylase Production and Secretion with Fumarate as the Final Electron Acceptor in Saccharomyces cerevisiae

2013 ◽  
Vol 79 (9) ◽  
pp. 2962-2967 ◽  
Author(s):  
Zihe Liu ◽  
Tobias Österlund ◽  
Jin Hou ◽  
Dina Petranovic ◽  
Jens Nielsen
Keyword(s):  
Saccharomyces Cerevisiae ◽  
Protein Folding ◽  
Protein Secretion ◽  
Electron Acceptor ◽  
Anaerobic Growth ◽  
Anaerobic Conditions ◽  
Aerobic Conditions ◽  
Content Type ◽  
Final Electron ◽  
Final Electron Acceptor

ABSTRACTIn this study, we focus on production of heterologous α-amylase in the yeastSaccharomyces cerevisiaeunder anaerobic conditions. We compare the metabolic fluxes and transcriptional regulation under aerobic and anaerobic conditions, with the objective of identifying the final electron acceptor for protein folding under anaerobic conditions. We find that yeast produces more amylase under anaerobic conditions than under aerobic conditions, and we propose a model for electron transfer under anaerobic conditions. According to our model, during protein folding the electrons from the endoplasmic reticulum are transferred to fumarate as the final electron acceptor. This model is supported by findings that the addition of fumarate under anaerobic (but not aerobic) conditions improves cell growth, specifically in the α-amylase-producing strain, in which it is not used as a carbon source. Our results provide a model for the molecular mechanism of anaerobic protein secretion using fumarate as the final electron acceptor, which may allow for further engineering of yeast for improved protein secretion under anaerobic growth conditions.

scholarly journals Growth of Campylobacter jejuni Supported by Respiration of Fumarate, Nitrate, Nitrite, Trimethylamine-N-Oxide, or Dimethyl Sulfoxide Requires Oxygen

2002 ◽  
Vol 184 (15) ◽  
pp. 4187-4196 ◽  
Author(s):  
Michael J. Sellars ◽  
Stephen J. Hall ◽  
David J. Kelly
Keyword(s):  
Energy Conservation ◽  
Dimethyl Sulfoxide ◽  
Campylobacter Jejuni ◽  
Electron Acceptor ◽  
Electron Acceptors ◽  
Anaerobic Growth ◽  
Strictly Anaerobic ◽  
Anaerobic Conditions ◽  
Single Class ◽  
Wide Range

ABSTRACT The human gastrointestinal pathogen Campylobacter jejuni is a microaerophilic bacterium with a respiratory metabolism. The genome sequence of C. jejuni strain 11168 reveals the presence of genes that encode terminal reductases that are predicted to allow the use of a wide range of alternative electron acceptors to oxygen, including fumarate, nitrate, nitrite, and N- or S-oxides. All of these reductase activities were present in cells of strain 11168, and the molybdoenzyme encoded by Cj0264c was shown by mutagenesis to be responsible for both trimethylamine-N-oxide (TMAO) and dimethyl sulfoxide (DMSO) reduction. Nevertheless, growth of C. jejuni under strictly anaerobic conditions (with hydrogen or formate as electron donor) in the presence of any of the electron acceptors tested was insignificant. However, when fumarate, nitrate, nitrite, TMAO, or DMSO was added to microaerobic cultures in which the rate of oxygen transfer was severely restricted, clear increases in both the growth rate and final cell density compared to what was seen with the control were obtained, indicative of electron acceptor-dependent energy conservation. The C. jejuni genome encodes a single class I-type ribonucleotide reductase (RNR) which requires oxygen to generate a tyrosyl radical for catalysis. Electron microscopy of cells that had been incubated under strictly anaerobic conditions with an electron acceptor showed filamentation due to an inhibition of cell division similar to that induced by the RNR inhibitor hydroxyurea. An oxygen requirement for DNA synthesis can thus explain the lack of anaerobic growth of C. jejuni. The results indicate that strict anaerobiosis is a stress condition for C. jejuni but that alternative respiratory pathways can contribute significantly to energy conservation under oxygen-limited conditions, as might be found in vivo.

scholarly journals Formate Metabolism in Shewanella oneidensis Generates Proton Motive Force and Prevents Growth without an Electron Acceptor

2016 ◽  
Vol 198 (8) ◽  
pp. 1337-1346 ◽  
Author(s):  
Aunica L. Kane ◽  
Evan D. Brutinel ◽  
Heena Joo ◽  
Rebecca Maysonet ◽  
Chelsey M. VanDrisse ◽  
...  
Keyword(s):  
Formate Dehydrogenase ◽  
Carbon Sources ◽  
Shewanella Oneidensis ◽  
Gene Clusters ◽  
Proton Motive Force ◽  
Motive Force ◽  
Content Type ◽  
Formate Oxidation ◽  
Dehydrogenase Gene

ABSTRACTShewanella oneidensisstrain MR-1 is a facultative anaerobe that thrives in redox-stratified environments due to its ability to utilize a wide array of terminal electron acceptors. Conversely, the electron donors utilized byS. oneidensisare more limited and include products of primary fermentation such as lactate, pyruvate, formate, and hydrogen. Lactate, pyruvate, and hydrogen metabolisms inS. oneidensishave been described previously, but little is known about the role of formate oxidation in the ecophysiology of these bacteria. Formate is produced byS. oneidensisthrough pyruvate formate lyase during anaerobic growth on carbon sources that enter metabolism at or above the level of pyruvate, and the genome contains three gene clusters predicted to encode three complete formate dehydrogenase complexes. To determine the contribution of each complex to formate metabolism, strains lacking one, two, or all three annotated formate dehydrogenase gene clusters were generated and examined for growth rates and yields on a variety of carbon sources. Here, we report that formate oxidation contributes to both the growth rate and yield ofS. oneidensisthrough the generation of proton motive force. Exogenous formate also greatly accelerated growth onN-acetylglucosamine, a carbon source normally utilized very slowly byS. oneidensisunder anaerobic conditions. Surprisingly, deletion of all three formate dehydrogenase gene clusters enabled growth ofS. oneidensisusing pyruvate in the absence of a terminal electron acceptor, a mode of growth never before observed in these bacteria. Our results demonstrate that formate oxidation is a fundamental strategy under anaerobic conditions for energy conservation inS. oneidensis.IMPORTANCEShewanellaspecies have garnered interest in biotechnology applications for their ability to respire extracellular terminal electron acceptors, such as insoluble iron oxides and electrodes. While much effort has gone into studying the proteins for extracellular electron transport, how electrons generated through the oxidation of organic carbon sources enter this pathway remains understudied. Here, we quantify the role of formate oxidation in the anaerobic physiology ofShewanella oneidensis. Formate oxidation contributes to both the growth rate and yield on a variety of carbon sources through the generation of proton motive force. Advances in our understanding of the anaerobic metabolism ofS. oneidensisare important for our ability to utilize and engineer this organism for applications in bioenergy, biocatalysis, and bioremediation.

scholarly journals Phenazines Regulate Nap-Dependent Denitrification inPseudomonas aeruginosaBiofilms

2018 ◽  
Vol 200 (9) ◽  
Author(s):  
Yu-Cheng Lin ◽  
Matthew D. Sekedat ◽  
William Cole Cornell ◽  
Gustavo M. Silva ◽  
Chinweike Okegbe ◽  
...  
Keyword(s):  
Pseudomonas Aeruginosa ◽  
Nitrate Reductase ◽  
Electron Acceptor ◽  
Bacterial Infections ◽  
Redox State ◽  
Reductase Activity ◽  
Anaerobic Growth ◽  
Bet Hedging ◽  
Terminal Electron Acceptor ◽  
Content Type

ABSTRACTMicrobes in biofilms face the challenge of substrate limitation. In particular, oxygen often becomes limited for cells inPseudomonas aeruginosabiofilms growing in the laboratory or during host colonization. Previously we found that phenazines, antibiotics produced byP. aeruginosa, balance the intracellular redox state of cells in biofilms. Here, we show that genes involved in denitrification are induced in phenazine-null (Δphz) mutant biofilms grown under an aerobic atmosphere, even in the absence of nitrate. This finding suggests that resident cells employ a bet-hedging strategy to anticipate the potential availability of nitrate and counterbalance their highly reduced redox state. Consistent with our previous characterization of aerobically grown colonies supplemented with nitrate, we found that the pathway that is induced in Δphzmutant colonies combines the nitrate reductase activity of the periplasmic enzyme Nap with the downstream reduction of nitrite to nitrogen gas catalyzed by the enzymes Nir, Nor, and Nos. This regulatory relationship differs from the denitrification pathway that functions under anaerobic growth, with nitrate as the terminal electron acceptor, which depends on the membrane-associated nitrate reductase Nar. We identified the sequences in the promoter regions of thenapandniroperons that are required for the effects of phenazines on expression. We also show that specific phenazines have differential effects onnapgene expression. Finally, we provide evidence that individual steps of the denitrification pathway are catalyzed at different depths within aerobically grown biofilms, suggesting metabolic cross-feeding between community subpopulations.IMPORTANCEAn understanding of the unique physiology of cells in biofilms is critical to our ability to treat fungal and bacterial infections. Colony biofilms of the opportunistic pathogenPseudomonas aeruginosagrown under an aerobic atmosphere but without nitrate express a denitrification pathway that differs from that used for anaerobic growth. We report that the components of this pathway are induced by electron acceptor limitation and that they are differentially expressed over the biofilm depth. These observations suggest that (i)P. aeruginosaexhibits “bet hedging,” in that it expends energy and resources to prepare for nitrate availability when other electron acceptors are absent, and (ii) cells in distinct biofilm microniches may be able to exchange substrates to catalyze full denitrification.

scholarly journals Secreted Flavin Cofactors for Anaerobic Respiration of Fumarate and Urocanate byShewanella oneidensis: Cost and Role

2019 ◽  
Vol 85 (16) ◽  
Author(s):  
Eric D. Kees ◽  
Augustus R. Pendleton ◽  
Catarina M. Paquete ◽  
Matthew B. Arriola ◽  
Aunica L. Kane ◽  
...  
Keyword(s):  
Reductase Activity ◽  
Inorganic Compounds ◽  
Shewanella Oneidensis ◽  
Model Organism ◽  
Fitness Cost ◽  
Fumarate Reductase ◽  
Anaerobic Growth ◽  
Metal Reduction ◽  
Content Type ◽  
Dissimilatory Metal Reduction

ABSTRACTShewanella oneidensisstrain MR-1, a facultative anaerobe and model organism for dissimilatory metal reduction, uses a periplasmic flavocytochrome, FccA, both as a terminal fumarate reductase and as a periplasmic electron transfer hub for extracellular respiration of a variety of substrates. It is currently unclear how maturation of FccA and other periplasmic flavoproteins is achieved, specifically in the context of flavin cofactor loading, and the fitness cost of flavin secretion has not been quantified. We demonstrate that deletion of the inner membrane flavin adenine dinucleotide (FAD) exporter Bfe results in a 23% slower growth rate than that of the wild type during fumarate respiration and an 80 to 90% loss in fumarate reductase activity. Exogenous flavin supplementation does not restore FccA activity in a Δbfemutant unless the gene encoding the periplasmic FAD hydrolase UshA is also deleted. We demonstrate that the small Bfe-independent pool of FccA is sufficient for anaerobic growth with fumarate. Strains lacking Bfe were unable to grow using urocanate as the sole electron acceptor, which relies on the periplasmic flavoprotein UrdA. We show that periplasmic flavoprotein maturation occurs in careful balance with periplasmic FAD hydrolysis, and that the current model for periplasmic flavin cofactor loading must account for a Bfe-independent mechanism for flavin transport. Finally, we determine that the metabolic burden of flavin secretion is not significant during growth with flavin-independent anaerobic electron acceptors. Our work helps frame the physiological motivations that drove evolution of flavin secretion byShewanella.IMPORTANCEShewanellaspecies are prevalent in marine and aquatic environments, throughout stratified water columns, in mineral-rich sediments, and in association with multicellular marine and aquatic organisms. The diversity of niches shewanellae can occupy are due largely to their respiratory versatility.Shewanella oneidensisis a model organism for dissimilatory metal reduction and can respire a diverse array of organic and inorganic compounds, including dissolved and solid metal oxides. The fumarate reductase FccA is a highly abundant multifunctional periplasmic protein that acts to bridge the periplasm and temporarily store electrons in a variety of respiratory nodes, including metal, nitrate, and dimethyl sulfoxide respiration. However, maturation of this central protein, particularly flavin cofactor acquisition, is poorly understood. Here, we quantify the fitness cost of flavin secretion and describe how free flavins are acquired by FccA and a homologous periplasmic flavoprotein, UrdA.

scholarly journals Insights into the Physiology and Metabolism of a Mycobacterial Cell in an Energy-Compromised State

2019 ◽  
Vol 201 (19) ◽  
Author(s):  
Varsha Patil ◽  
Vikas Jain
Keyword(s):  
Oxidative Phosphorylation ◽  
Atp Synthase ◽  
Drug Targets ◽  
Energy State ◽  
Β Subunit ◽  
Wild Type ◽  
Content Type ◽  
Substrate Level Phosphorylation ◽  
Substrate Level ◽  
Physiological Differences

ABSTRACT Mycobacterium tuberculosis, a bacterium that causes tuberculosis, poses a serious threat, especially due to the emergence of drug-resistant strains. M. tuberculosis and other mycobacterial species, such as M. smegmatis, are known to generate an inadequate amount of energy by substrate-level phosphorylation and mandatorily require oxidative phosphorylation (OXPHOS) for their growth and metabolism. Hence, antibacterial drugs, such as bedaquiline, targeting the multisubunit ATP synthase complex, which is required for OXPHOS, have been developed with the aim of eliminating pathogenic mycobacteria. Here, we explored the influence of suboptimal OXPHOS on the physiology and metabolism of M. smegmatis. M. smegmatis harbors two identical copies of atpD, which codes for the β subunit of ATP synthase. We show that upon deletion of one copy of atpD (M. smegmatis ΔatpD), M. smegmatis synthesizes smaller amounts of ATP and enters into an energy-compromised state. The mutant displays remarkable phenotypic and physiological differences from the wild type, such as respiratory slowdown, reduced biofilm formation, lesser amounts of cell envelope polar lipids, and increased antibiotic sensitivity compared to the wild type. Additionally, M. smegmatis ΔatpD overexpresses genes belonging to the dormancy operon, the β-oxidation pathway, and the glyoxylate shunt, suggesting that the mutant adapts to a low energy state by switching to alternative pathways to produce energy. Interestingly, M. smegmatis ΔatpD shows significant phenotypic, metabolic, and physiological similarities with bedaquiline-treated wild-type M. smegmatis. We believe that the identification and characterization of key metabolic pathways functioning during an energy-compromised state will enhance our understanding of bacterial adaptation and survival and will open newer avenues in the form of drug targets that may be used in the treatment of mycobacterial infections. IMPORTANCE M. smegmatis generates an inadequate amount of energy by substrate-level phosphorylation and mandatorily requires oxidative phosphorylation (OXPHOS) for its growth and metabolism. Here, we explored the influence of suboptimal OXPHOS on M. smegmatis physiology and metabolism. M. smegmatis harbors two identical copies of the atpD gene, which codes for the ATP synthase β subunit. Here, we carried out the deletion of only one copy of atpD in M. smegmatis to understand the bacterial survival response in an energy-deprived state. M. smegmatis ΔatpD shows remarkable phenotypic, metabolic, and physiological differences from the wild type. Our study thus establishes M. smegmatis ΔatpD as an energy-compromised mycobacterial strain, highlights the importance of ATP synthase in mycobacterial physiology, and further paves the way for the identification of novel antimycobacterial drug targets.

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