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James T. Hollibaugh - One of the best experts on this subject based on the ideXlab platform.
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Transcriptional response of the Obligate Anaerobe Desulfuribacillus stibiiarsenatis MLFW‐2T to growth on antimonate and other terminal electron acceptors
Environmental microbiology, 2019Co-Authors: Christopher A. Abin, James T. HollibaughAbstract:Enzymes of the dimethyl sulfoxide reductase (DMSOR) family catalyse two-electron redox reactions pivotal to the dissimilatory metabolism of a variety of organic and inorganic compounds. The draft genome of the Obligately anaerobic bacterium Desulfuribacillus stibiiarsenatis MLFW-2T contains 14 genes that are predicted to encode catalytic subunits of DMSOR family enzymes. We quantified transcription of these genes during growth on antimonate, arsenate, nitrate and selenate, with the goal of identifying the respiratory antimonate reductase. Transcription of BHU72_10330, BHU72_03635 and BHU72_07355 was enhanced during growth on arsenate, nitrate and selenate, respectively, implicating these genes as encoding the catalytic subunits of a respiratory arsenate reductase (arrA), periplasmic nitrate reductase (napA) and membrane-bound selenate reductase (srdA) respectively. Transcription of BHU72_07145 increased markedly when MLFW-2T was grown on antimonate, suggesting that this gene encodes the catalytic subunit of a respiratory antimonate reductase, designated anrA. We also compared the transcriptomes of MLFW-2T during growth on antimonate and arsenate to examine the broader physiological response of the organism to growth on these substrates. Relative to arsenate, antimonate was found to induce transcription of genes involved in pathways for dealing with oxidative stress, including those involved in repairing damaged cellular biomolecules and scavenging reactive oxygen species.
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transcriptional response of the Obligate Anaerobe desulfuribacillus stibiiarsenatis mlfw 2t to growth on antimonate and other terminal electron acceptors
Environmental Microbiology, 2018Co-Authors: Christopher A. Abin, James T. HollibaughAbstract:Enzymes of the dimethyl sulfoxide reductase (DMSOR) family catalyse two-electron redox reactions pivotal to the dissimilatory metabolism of a variety of organic and inorganic compounds. The draft genome of the Obligately anaerobic bacterium Desulfuribacillus stibiiarsenatis MLFW-2T contains 14 genes that are predicted to encode catalytic subunits of DMSOR family enzymes. We quantified transcription of these genes during growth on antimonate, arsenate, nitrate and selenate, with the goal of identifying the respiratory antimonate reductase. Transcription of BHU72_10330, BHU72_03635 and BHU72_07355 was enhanced during growth on arsenate, nitrate and selenate, respectively, implicating these genes as encoding the catalytic subunits of a respiratory arsenate reductase (arrA), periplasmic nitrate reductase (napA) and membrane-bound selenate reductase (srdA) respectively. Transcription of BHU72_07145 increased markedly when MLFW-2T was grown on antimonate, suggesting that this gene encodes the catalytic subunit of a respiratory antimonate reductase, designated anrA. We also compared the transcriptomes of MLFW-2T during growth on antimonate and arsenate to examine the broader physiological response of the organism to growth on these substrates. Relative to arsenate, antimonate was found to induce transcription of genes involved in pathways for dealing with oxidative stress, including those involved in repairing damaged cellular biomolecules and scavenging reactive oxygen species.
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desulfuribacillus stibiiarsenatis sp nov an Obligately anaerobic dissimilatory antimonate and arsenate reducing bacterium isolated from anoxic sediments and emended description of the genus desulfuribacillus
International Journal of Systematic and Evolutionary Microbiology, 2017Co-Authors: Christopher A. Abin, James T. HollibaughAbstract:A novel anaerobic, Gram-stain-negative, endospore-forming bacterium, designated strain MLFW-2T, was isolated from anoxic sediments collected from the drainage area of a geothermal spring near Mono Lake, CA, USA. Optimal growth was achieved at 34 °C and pH 8.25–8.50 in medium containing 0.75 % (w/v) NaCl. Catalase, but not oxidase, was produced. Strain MLFW-2T was an Obligate Anaerobe capable of respiring with nitrate, nitrite, DMSO, arsenate, antimonate, selenate and selenite as terminal electron acceptors. Lactate, pyruvate, formate and H2 could serve as electron donors to support growth. The isolate was incapable of fermentation. The predominant fatty acids were C16 : 0, C16 : 1ω9c, C16 : 1ω7c, C18 : 1ω9c and C18 : 1ω7c. The major polar lipids were phosphatidylglycerol and phosphatidylethanolamine. The only isoprenoid quinone detected was menaquinone 7 (MK-7). The DNA G+C content was 38.2 mol%. Phylogenetic analysis based on the 16S rRNA gene sequence demonstrated that strain MLFW-2T was a member of the order Bacillales and was most closely related to Desulfuribacillus alkaliarsenatis AHT28T (93.9 % similarity). On the basis of phenotypic and phylogenomic evidence, strain MLFW-2T represents a novel species of the genus Desulfuribacillus , for which the name Desulfuribacillus stibiiarsenatis sp. nov. is proposed. The type strain is MLFW-2T (=DSM 28709T=JCM 30866T). An emended description of the genus Desulfuribacillus is also provided.
Christopher A. Abin - One of the best experts on this subject based on the ideXlab platform.
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Transcriptional response of the Obligate Anaerobe Desulfuribacillus stibiiarsenatis MLFW‐2T to growth on antimonate and other terminal electron acceptors
Environmental microbiology, 2019Co-Authors: Christopher A. Abin, James T. HollibaughAbstract:Enzymes of the dimethyl sulfoxide reductase (DMSOR) family catalyse two-electron redox reactions pivotal to the dissimilatory metabolism of a variety of organic and inorganic compounds. The draft genome of the Obligately anaerobic bacterium Desulfuribacillus stibiiarsenatis MLFW-2T contains 14 genes that are predicted to encode catalytic subunits of DMSOR family enzymes. We quantified transcription of these genes during growth on antimonate, arsenate, nitrate and selenate, with the goal of identifying the respiratory antimonate reductase. Transcription of BHU72_10330, BHU72_03635 and BHU72_07355 was enhanced during growth on arsenate, nitrate and selenate, respectively, implicating these genes as encoding the catalytic subunits of a respiratory arsenate reductase (arrA), periplasmic nitrate reductase (napA) and membrane-bound selenate reductase (srdA) respectively. Transcription of BHU72_07145 increased markedly when MLFW-2T was grown on antimonate, suggesting that this gene encodes the catalytic subunit of a respiratory antimonate reductase, designated anrA. We also compared the transcriptomes of MLFW-2T during growth on antimonate and arsenate to examine the broader physiological response of the organism to growth on these substrates. Relative to arsenate, antimonate was found to induce transcription of genes involved in pathways for dealing with oxidative stress, including those involved in repairing damaged cellular biomolecules and scavenging reactive oxygen species.
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transcriptional response of the Obligate Anaerobe desulfuribacillus stibiiarsenatis mlfw 2t to growth on antimonate and other terminal electron acceptors
Environmental Microbiology, 2018Co-Authors: Christopher A. Abin, James T. HollibaughAbstract:Enzymes of the dimethyl sulfoxide reductase (DMSOR) family catalyse two-electron redox reactions pivotal to the dissimilatory metabolism of a variety of organic and inorganic compounds. The draft genome of the Obligately anaerobic bacterium Desulfuribacillus stibiiarsenatis MLFW-2T contains 14 genes that are predicted to encode catalytic subunits of DMSOR family enzymes. We quantified transcription of these genes during growth on antimonate, arsenate, nitrate and selenate, with the goal of identifying the respiratory antimonate reductase. Transcription of BHU72_10330, BHU72_03635 and BHU72_07355 was enhanced during growth on arsenate, nitrate and selenate, respectively, implicating these genes as encoding the catalytic subunits of a respiratory arsenate reductase (arrA), periplasmic nitrate reductase (napA) and membrane-bound selenate reductase (srdA) respectively. Transcription of BHU72_07145 increased markedly when MLFW-2T was grown on antimonate, suggesting that this gene encodes the catalytic subunit of a respiratory antimonate reductase, designated anrA. We also compared the transcriptomes of MLFW-2T during growth on antimonate and arsenate to examine the broader physiological response of the organism to growth on these substrates. Relative to arsenate, antimonate was found to induce transcription of genes involved in pathways for dealing with oxidative stress, including those involved in repairing damaged cellular biomolecules and scavenging reactive oxygen species.
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desulfuribacillus stibiiarsenatis sp nov an Obligately anaerobic dissimilatory antimonate and arsenate reducing bacterium isolated from anoxic sediments and emended description of the genus desulfuribacillus
International Journal of Systematic and Evolutionary Microbiology, 2017Co-Authors: Christopher A. Abin, James T. HollibaughAbstract:A novel anaerobic, Gram-stain-negative, endospore-forming bacterium, designated strain MLFW-2T, was isolated from anoxic sediments collected from the drainage area of a geothermal spring near Mono Lake, CA, USA. Optimal growth was achieved at 34 °C and pH 8.25–8.50 in medium containing 0.75 % (w/v) NaCl. Catalase, but not oxidase, was produced. Strain MLFW-2T was an Obligate Anaerobe capable of respiring with nitrate, nitrite, DMSO, arsenate, antimonate, selenate and selenite as terminal electron acceptors. Lactate, pyruvate, formate and H2 could serve as electron donors to support growth. The isolate was incapable of fermentation. The predominant fatty acids were C16 : 0, C16 : 1ω9c, C16 : 1ω7c, C18 : 1ω9c and C18 : 1ω7c. The major polar lipids were phosphatidylglycerol and phosphatidylethanolamine. The only isoprenoid quinone detected was menaquinone 7 (MK-7). The DNA G+C content was 38.2 mol%. Phylogenetic analysis based on the 16S rRNA gene sequence demonstrated that strain MLFW-2T was a member of the order Bacillales and was most closely related to Desulfuribacillus alkaliarsenatis AHT28T (93.9 % similarity). On the basis of phenotypic and phylogenomic evidence, strain MLFW-2T represents a novel species of the genus Desulfuribacillus , for which the name Desulfuribacillus stibiiarsenatis sp. nov. is proposed. The type strain is MLFW-2T (=DSM 28709T=JCM 30866T). An emended description of the genus Desulfuribacillus is also provided.
James A. Imlay - One of the best experts on this subject based on the ideXlab platform.
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endogenous superoxide is a key effector of the oxygen sensitivity of a model Obligate Anaerobe
Proceedings of the National Academy of Sciences of the United States of America, 2018Co-Authors: Ramakrishnan Sethu, James A. ImlayAbstract:It has been unclear whether superoxide and/or hydrogen peroxide play important roles in the phenomenon of Obligate anaerobiosis. This question was explored using Bacteroides thetaiotaomicron, a major fermentative bacterium in the human gastrointestinal tract. Aeration inactivated two enzyme families—[4Fe-4S] dehydratases and nonredox mononuclear iron enzymes—whose homologs, in contrast, remain active in aerobic Escherichia coli. Inactivation-rate measurements of one such enzyme, B. thetaiotaomicron fumarase, showed that it is no more intrinsically sensitive to oxidants than is an E. coli fumarase. Indeed, when the E. coli enzymes were expressed in B. thetaiotaomicron, they no longer could tolerate aeration; conversely, the B. thetaiotaomicron enzymes maintained full activity when expressed in aerobic E. coli. Thus, the aerobic inactivation of the B. thetaiotaomicron enzymes is a feature of their intracellular environment rather than of the enzymes themselves. B. thetaiotaomicron possesses superoxide dismutase and peroxidases, and it can repair damaged enzymes. However, measurements confirmed that the rate of reactive oxygen species production inside aerated B. thetaiotaomicron is far higher than in E. coli. Analysis of the damaged enzymes recovered from aerated B. thetaiotaomicron suggested that they had been inactivated by superoxide rather than by hydrogen peroxide. Accordingly, overproduction of superoxide dismutase substantially protected the enzymes from aeration. We conclude that when this Anaerobe encounters oxygen, its internal superoxide levels rise high enough to inactivate key catabolic and biosynthetic enzymes. Superoxide thus comprises a major element of the oxygen sensitivity of this Anaerobe. The extent to which molecular oxygen exerts additional direct effects remains to be determined.
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An anaerobic bacterium, Bacteroides thetaiotaomicron, uses a consortium of enzymes to scavenge hydrogen peroxide
Molecular Microbiology, 2013Co-Authors: Surabhi Mishra, James A. ImlayAbstract:Abstract Obligate Anaerobes are periodically exposed to oxygen, and it has been conjectured that on such occasions their low-potential biochemistry will predispose them to rapid ROS formation. We sought to identify scavenging enzymes that might protect the Anaerobe Bacteroides thetaiotaomicron from the H2 O2 that would be formed. Genetic analysis of eight candidate enzymes revealed that four of these scavenge H2 O2 in vivo: rubrerythrins 1 and 2, AhpCF, and catalase E. The rubrerythrins served as key peroxidases under anoxic conditions. However, they quickly lost activity upon aeration, and AhpCF and catalase were induced to compensate. The AhpCF is an NADH peroxidase that effectively degraded low micromolar levels of H2 O2 , while the catalytic cycle of catalase enabled it to quickly degrade higher concentrations that might arise from exogenous sources. Using a non-scavenging mutant we verified that endogenous H2 O2 formation was much higher in aerated B. thetaiotaomicron than in Escherichia coli. Indeed, the OxyR stress response to H2 O2 was induced when B. thetaiotaomicron was aerated, and in that circumstance this response was necessary to forestall cell death. Thus aeration is a serious threat for this Obligate Anaerobe, and to cope it employs a set of defences that includes a repertoire of complementary scavenging enzymes.
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how does oxygen inhibit central metabolism in the Obligate Anaerobe bacteroides thetaiotaomicron
Molecular Microbiology, 2001Co-Authors: Ning Pan, James A. ImlayAbstract:The molecular basis of Obligate anaerobiosis is not well established. Bacteroides thetaiotaomicron is an opportunistic pathogen that cannot grow in fully aerobic habitats. Because microbial niches reflect features of energy-producing strategies, we suspected that aeration would interfere with its central metabolism. In anaerobic medium, this bacterium fermented carbohydrates to a mixture of succinate, propionate and acetate. When cultures were exposed to air, the formation of succinate and propionate ceased abruptly. In vitro analysis demonstrated that the fumarase of the succinate–propionate pathway contains an iron–sulphur cluster that is sensitive to superoxide. In vivo, fumarase activity fell to < 5% when cells were aerated; virtually all activity was recovered after extracts were chemically treated to rebuild iron–sulphur clusters. Aeration minimally affected the remainder of this pathway. However, aeration reduced pyruvate:ferredoxin oxidoreductase (PFOR), the first enzyme in the acetate fermentation branch, to 3% of its anaerobic activity. This cluster-containing enzyme was damaged in vitro by molecular oxygen but not by superoxide. Thus, aerobic growth is precluded by the vulnerability of these iron–sulphur cluster enzymes to oxidation. Importantly, both enzymes were maintained in a stable, inactive form for long periods in aerobic cells; they were then rapidly repaired when the bacterium was returned to anaerobic medium. This result explains how this pathogen can easily recover from occasional exposure to oxygen.
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How does oxygen inhibit central metabolism in the Obligate Anaerobe Bacteroides thetaiotaomicron.
Molecular Microbiology, 2001Co-Authors: Ning Pan, James A. ImlayAbstract:The molecular basis of Obligate anaerobiosis is not well established. Bacteroides thetaiotaomicron is an opportunistic pathogen that cannot grow in fully aerobic habitats. Because microbial niches reflect features of energy-producing strategies, we suspected that aeration would interfere with its central metabolism. In anaerobic medium, this bacterium fermented carbohydrates to a mixture of succinate, propionate and acetate. When cultures were exposed to air, the formation of succinate and propionate ceased abruptly. In vitro analysis demonstrated that the fumarase of the succinate–propionate pathway contains an iron–sulphur cluster that is sensitive to superoxide. In vivo, fumarase activity fell to
Alain Dolla - One of the best experts on this subject based on the ideXlab platform.
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RESEARCH ARTICLE Growth of the Obligate Anaerobe Desulfovibrio vulgaris Hildenborough under Continuous Low Oxygen Concentration Sparging: Impact of the Membrane-Bound Oxygen Reductases
2016Co-Authors: Fanny Ramel, Gael Brasseur, Laetitia Pieulle, Odile Valette, Agnès Hirschler-réa, Marie Laure Fardeau, Alain DollaAbstract:Although Obligate Anaerobe, the sulfate-reducing bacterium Desulfovibrio vulgaris Hilden-borough (DvH) exhibits high aerotolerance that involves several enzymatic systems, includ-ing two membrane-bound oxygen reductases, a bd-quinol oxidase and a cc(b/o)o3 cytochrome oxidase. Effect of constant low oxygen concentration on growth and morpholo-gy of the wild-type, single (Δbd, Δcox) and double deletion (Δcoxbd) mutant strains of the genes encoding these oxygen reductases was studied. When both wild-type and deletion mutant strains were cultured in lactate/sulfate medium under constant 0.02 % O2 sparging, they were able to grow but the final biomasses and the growth yield were lower than that ob-tained under anaerobic conditions. At the end of the growth, lactate was not completely con-sumed and when conditions were then switched to anaerobic, growth resumed. Time-lapse microscopy revealed that a large majority of the cells were then able to divide (over 97%) but the time to recover a complete division event was longer for single deletion mutant Δbd than for the three other strains. Determination of the molar growth yields on lactate sug-gested that a part of the energy gained from lactate oxidation was derived toward cells pro
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Growth of the Obligate Anaerobe Desulfovibrio vulgaris Hildenborough under Continuous Low Oxygen Concentration Sparging: Impact of the Membrane-Bound Oxygen Reductases
PloS one, 2015Co-Authors: Fanny Ramel, Gael Brasseur, Laetitia Pieulle, Odile Valette, Agnès Hirschler-réa, Marie Laure Fardeau, Alain DollaAbstract:Although Obligate Anaerobe, the sulfate-reducing bacterium Desulfovibrio vulgaris Hildenborough (DvH) exhibits high aerotolerance that involves several enzymatic systems, including two membrane-bound oxygen reductases, a bd-quinol oxidase and a cc(b/o)o3 cytochrome oxidase. Effect of constant low oxygen concentration on growth and morphology of the wild-type, single (Δbd, Δcox) and double deletion (Δcoxbd) mutant strains of the genes encoding these oxygen reductases was studied. When both wild-type and deletion mutant strains were cultured in lactate/sulfate medium under constant 0.02% O2 sparging, they were able to grow but the final biomasses and the growth yield were lower than that obtained under anaerobic conditions. At the end of the growth, lactate was not completely consumed and when conditions were then switched to anaerobic, growth resumed. Time-lapse microscopy revealed that a large majority of the cells were then able to divide (over 97%) but the time to recover a complete division event was longer for single deletion mutant Δbd than for the three other strains. Determination of the molar growth yields on lactate suggested that a part of the energy gained from lactate oxidation was derived toward cells protection/repairing against oxidative conditions rather than biosynthesis, and that this part was higher in the single deletion mutant Δbd and, to a lesser extent, Δcox strains. Our data show that when DvH encounters oxidative conditions, it is able to stop growing and to rapidly resume growing when conditions are switched to anaerobic, suggesting that it enters active dormancy sate under oxidative conditions. We propose that the pyruvate-ferredoxin oxidoreductase (PFOR) plays a central role in this phenomenon by reversibly switching from an oxidative-sensitive fully active state to an oxidative-insensitive inactive state. The oxygen reductases, and especially the bd-quinol oxidase, would have a crucial function by maintaining reducing conditions that permit PFOR to stay in its active state.
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Growth of the Obligate Anaerobe Desulfovibrio vulgaris Hildenborough under Continuous Low Oxygen Concentration Sparging: Impact of the Membrane-Bound Oxygen Reductases
PLoS ONE, 2015Co-Authors: Fanny Ramel, Gael Brasseur, Laetitia Pieulle, Odile Valette, Agnès Hirschler-réa, Marie Laure Fardeau, Alain DollaAbstract:Although Obligate Anaerobe, the sulfate-reducing bacterium Desulfovibrio vulgaris Hilden-borough (DvH) exhibits high aerotolerance that involves several enzymatic systems, including two membrane-bound oxygen reductases, a bd-quinol oxidase and a cc(b/o)o(3) cytochrome oxidase. Effect of constant low oxygen concentration on growth and morphology of the wild-type, single (Delta bd,Delta cox) and double deletion (Delta coxbd) mutant strains of the genes encoding these oxygen reductases was studied. When both wild-type and deletion mutant strains were cultured in lactate/sulfate medium under constant 0.02% O-2 sparging, they were able to grow but the final biomasses and the growth yield were lower than that obtained under anaerobic conditions. At the end of the growth, lactate was not completely consumed and when conditions were then switched to anaerobic, growth resumed. Time-lapse microscopy revealed that a large majority of the cells were then able to divide (over 97%) but the time to recover a complete division event was longer for single deletion mutant Delta bd than for the three other strains. Determination of the molar growth yields on lactate suggested that a part of the energy gained from lactate oxidation was derived toward cells protection/repairing against oxidative conditions rather than biosynthesis, and that this part was higher in the single deletion mutant Delta bd and, to a lesser extent, Delta cox strains. Our data show that when DvH encounters oxidative conditions, it is able to stop growing and to rapidly resume growing when conditions are switched to anaerobic, suggesting that it enters active dormancy sate under oxidative conditions. We propose that the pyruvate-ferredoxin oxidoreductase (PFOR) plays a central role in this phenomenon by reversibly switching from an oxidative-sensitive fully active state to an oxidative-insensitive inactive state. The oxygen reductases, and especially the bd-quinol oxidase, would have a crucial function by maintaining reducing conditions that permit PFOR to stay in its active state.
Jeffrey C Smith - One of the best experts on this subject based on the ideXlab platform.
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characterization of the primary starch utilization operon in the Obligate Anaerobe bacteroides fragilis regulation by carbon source and oxygen
Journal of Bacteriology, 2006Co-Authors: Cheryl Spence, Greg W Wells, Jeffrey C SmithAbstract:The opportunistic pathogen Bacteroides fragilis is a commensal organism in the large intestine, where it utilizes both dietary and host-derived polysaccharides as a source of carbon and energy. In this study, a four-gene operon required for starch utilization was identified. The operon also was found to be oxygen responsive and thus was designated osu for oxygen-induced starch utilization. The first three genes in the operon were predicted to encode outer membrane proteins involved in starch binding, and a fourth gene, osuD, encoded an amylase involved in starch hydrolysis. Insertional mutation of the osuA gene (ΩosuA) resulted in the inability to utilize starch or glycogen and an insertional mutation into the osuD gene (ΩosuD) was severely impaired for growth on starch media. Transcriptional studies indicated that maltose, maltooligosaccharides, and starch were inducers of osu expression and that maltose was the strongest inducer. A transcriptional activator of osuABCD, OsuR, was identified and found to mediate maltose induction. The ΩosuA and ΩosuD mutants were able to grow on maltose but not starch, whereas a mutation in osuR abolished growth on both substrates, indicating that additional genes under the control of OsuR are needed for maltose utilization. The osuABCD operon also was induced by exposure to oxygen and was shown to be part of the oxidative stress response important for aerotolerance of B. fragilis. Transcriptional analyses showed that osuA was induced 20-fold by oxygen, but OsuR was not required for this activation. Analysis of osu mutants suggested that expression of the operon was important for survival during oxygen exposure but not to hydrogen peroxide stress.
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role of the alkyl hydroperoxide reductase ahpcf gene in oxidative stress defense of the Obligate Anaerobe bacteroides fragilis
Journal of Bacteriology, 1999Co-Authors: Edson R Rocha, Jeffrey C SmithAbstract:In this study we report the identification and role of the alkyl hydroperoxide reductase (ahp) gene in Bacteroides fragilis. The two components of ahp, ahpC, and ahpF, are organized in an operon, and the deduced amino acid sequences revealed that B. fragilis AhpCF shares approximately 60% identity to orthologues in other gram-positive and gram-negative bacteria. Northern blot hybridization analysis of total RNA showed that the ahpCF genes were transcribed as a polycistronic 2.4-kb mRNA and that ahpC also was present as a 0.6-kb monocistronic mRNA. ahpC and ahpCF mRNAs were induced approximately 60-fold following H2O2 treatment or oxygen exposure of the parent strain but were constitutive in a peroxide-resistant strain. Further investigation using an ahpCF′::β-xylosidase gene transcriptional fusion confirmed that ahpCF had lost normal regulation in the peroxide-resistant strain compared to the parent. The ahpCF mutant was more sensitive to growth inhibition and mutagenesis by organic peroxides than the parent strain, as determined by disk inhibition assays and the frequency of mutation to fusidic acid resistance. This finding suggests that the ahp genes play an important role in peroxide resistance in B. fragilis. Under anaerobic conditions, we observed increases in the number of spontaneous fusidic acid-resistant mutants of five- and sevenfold in ahpCF and ahpF strain backgrounds, respectively, and eightfold in the ahpCF katB double mutant strain compared to the parent and katB strains. In addition, ahpCF, ahpF, and ahpCF katB mutants were slightly more sensitive to oxygen exposure than the parent strain. Moreover, the isolation of a strain with enhanced aerotolerance and high-level resistance to alkyl hydroperoxides from an ahpCF katB parent suggests that the physiological responses to peroxide toxicity and to the toxic effects of molecular oxygen are overlapping and complex in this Obligate Anaerobe.