CodY-Dependent Regulation of Sporulation in Clostridium difficile

Adenine Addition Restores Cell Viability and Butanol Production in Clostridium saccharoperbutylacetonicum N1-4 (ATCC 13564) Cultivated at 37°C

We have developed butanol-producing consolidated bioprocessing from cellulosic substrates through coculture of cellulolytic clostridia and butanol-producing Clostridium saccharoperbutylacetonicum strain N1-4. However, the butanol fermentation by strain N1-4 (which has an optimal growth temperature of 30°C) is sensitive to the higher cultivation temperature of 37°C; the nature of this deleterious effect remains unclear. Comparison of the intracellular metabolites of strain N1-4 cultivated at 30°C and 37°C revealed decreased levels of multiple primary metabolites (notably including nucleic acids and cofactors) during growth at the higher temperature. Supplementation of the culture medium with 250 mg/liter adenine enhanced both cell growth (with the optical density at 600 nm increasing from 4.3 to 10.2) and butanol production (increasing from 3.9 g/liter to 9.6 g/liter) at 37°C, compared to those obtained without adenine supplementation, such that the supplemented 37°C culture exhibited growth and butanol production approaching those observed at 30°C in the absence of adenine supplementation. These improved properties were based on the maintenance of cell viability. We further showed that adenine supplementation enhanced cell viability during growth at 37°C by maintaining ATP levels and inhibiting spore formation. This work represents the first demonstration (to our knowledge) of the importance of adenine-related metabolism for clostridial butanol production, suggesting a new means of enhancing target pathways based on metabolite levels.IMPORTANCE Metabolomic analysis revealed decreased levels of multiple primary metabolites during growth at 37°C, compared to 30°C, in C. saccharoperbutylacetonicum strain N1-4. We found that adenine supplementation restored the cell growth and butanol production of strain N1-4 at 37°C. The effects of adenine supplementation reflected the maintenance of cell viability originating from the maintenance of ATP levels and the inhibition of spore formation. Thus, our metabolomic analysis identified the depleted metabolites that were required to maintain cell viability. Our strategy, which is expected to be applicable to a wide range of organisms, permits the identification of the limiting metabolic pathway, which can serve as a new target for molecular breeding. The other novel finding of this work is that adenine supplementation inhibits clostridial spore formation. The mechanism linking spore formation and metabolomic status in butanol-producing clostridia is expected to be the focus of further research.

CodY Promotes Sporulation and Enterotoxin Production by Clostridium perfringens Type A Strain SM101

Clostridium perfringens type D strains cause enterotoxemia and enteritis in livestock via epsilon toxin production. In type D strain CN3718, CodY was previously shown to increase the level of epsilon toxin production and repress sporulation. C. perfringens type A strains producing C. perfringens enterotoxin (CPE) cause human food poisoning and antibiotic-associated diarrhea. Sporulation is critical for C. perfringens type A food poisoning since spores contribute to transmission and resistance in the harsh food environment and sporulation is essential for CPE production. Therefore, the current study asked whether CodY also regulates sporulation and CPE production in SM101, a derivative of C. perfringens type A food-poisoning strain NCTC8798. An isogenic codY-null mutant of SM101 showed decreased levels of spore formation, along with lower levels of CPE production. A complemented strain recovered wild-type levels of both sporulation and CPE production. When this result was coupled with the earlier results obtained with CN3718, it became apparent that CodY regulation of sporulation varies among different C. perfringens strains. Results from quantitative reverse transcriptase PCR analysis clearly demonstrated that, during sporulation, codY transcript levels remained high in SM101 but rapidly declined in CN3718. In addition, abrB gene expression patterns varied significantly between codY-null mutants of SM101 and CN3718. Compared to the levels in their wild-type parents, the level of abrB gene expression decreased in the CN3718 codY-null mutant strain but significantly increased in the SM101 codY-null mutant strain, demonstrating CodY-dependent regulation differences in abrB expression between these two strains. This difference appears to be important since overexpression of the abrB gene in SM101 reduced the levels of sporulation and enterotoxin production, supporting the involvement of AbrB repression in regulating C. perfringens sporulation.

Effect of tcdR Mutation on Sporulation in the Epidemic Clostridium difficile Strain R20291

C. difficile infects thousands of hospitalized patients every year, causing significant morbidity and mortality. C. difficile spores play a pivotal role in the transmission of the pathogen in the hospital environment. During infection, the spores germinate, and the vegetative bacterial cells produce toxins that damage host tissue. Thus, sporulation and toxin production are two important traits of C. difficile. In this study, we showed that a mutation in tcdR, the toxin gene regulator, affects both toxin production and sporulation in epidemic-type C. difficile strain R20291.

Clostridium difficile is an important nosocomial pathogen and the leading cause of hospital-acquired diarrhea. Antibiotic use is the primary risk factor for the development of C. difficile-associated disease because it disrupts normally protective gut flora and enables C. difficile to colonize the colon. C. difficile damages host tissue by secreting toxins and disseminates by forming spores. The toxin-encoding genes, tcdA and tcdB, are part of a pathogenicity locus, which also includes the tcdR gene that codes for TcdR, an alternate sigma factor that initiates transcription of tcdA and tcdB genes. We created a tcdR mutant in epidemic-type C. difficile strain R20291 in an attempt to identify the global role of tcdR. A site-directed mutation in tcdR affected both toxin production and sporulation in C. difficile R20291. Spores of the tcdR mutant were more heat sensitive than the wild type (WT). Nearly 3-fold more taurocholate was needed to germinate spores from the tcdR mutant than to germinate the spores prepared from the WT strain. Transmission electron microscopic analysis of the spores also revealed a weakly assembled exosporium on the tcdR mutant spores. Accordingly, comparative transcriptome analysis showed many differentially expressed sporulation genes in the tcdR mutant compared to the WT strain. These data suggest that regulatory networks of toxin production and sporulation in C. difficile strain R20291 are linked with each other.

IMPORTANCEC. difficile infects thousands of hospitalized patients every year, causing significant morbidity and mortality. C. difficile spores play a pivotal role in the transmission of the pathogen in the hospital environment. During infection, the spores germinate, and the vegetative bacterial cells produce toxins that damage host tissue. Thus, sporulation and toxin production are two important traits of C. difficile. In this study, we showed that a mutation in tcdR, the toxin gene regulator, affects both toxin production and sporulation in epidemic-type C. difficile strain R20291.

Chemical and Stress Resistances of Clostridium difficile Spores and Vegetative Cells

Clostridium difficile is a Gram-positive, sporogenic and anaerobic bacterium that causes a potentially fatal colitis. C. difficile enters the body as dormant spores that germinate in the colon to form vegetative cells that secrete toxins and cause the symptoms of infection. During transit through the intestine, some vegetative cells transform into spores, which are more resistant to killing by environmental insults than the vegetative cells. Understanding the inherent resistance properties of the vegetative and spore forms of C. difficile is imperative for the development of methods to target and destroy the bacterium. The objective of this study was to define the chemical and environmental resistance properties of C. difficile vegetative cells and spores. We examined vegetative cell and spore tolerances of three C. difficile strains, including 630Δerm, a 012 ribotype and a derivative of a past epidemic strain; R20291, a 027 ribotype and current epidemic strain; and 5325, a clinical isolate that is a 078 ribotype. All isolates were tested for tolerance to ethanol, oxygen, hydrogen peroxide, butanol, chloroform, heat and sodium hypochlorite (household bleach). Our results indicate that 630Δerm vegetative cells (630 spo0A) are more resistant to oxidative stress than those of R20291 (R20291 spo0A) and 5325 (5325 spo0A). In addition, 5325 spo0A vegetative cells exhibited greater resistance to organic solvents. In contrast, 630Δerm spores were more sensitive than R20291 or 5325 spores to butanol. Spores from all three strains exhibited high levels of resistance to ethanol, hydrogen peroxide, chloroform and heat, although R20291 spores were more resistant to temperatures in the range of 60-75°C. Finally, household bleach served as the only chemical reagent tested that consistently reduced C. difficile vegetative cells and spores of all tested strains. These findings establish conditions that result in vegetative cell and spore elimination and illustrate the resistance of C. difficile to common decontamination methods. These results further demonstrate that the vegetative cells and spores of various C. difficile strains have different resistance properties that may impact decontamination of surfaces and hands.

CodY, a master integrator of metabolism and virulence in Gram-positive bacteria

A growing body of evidence points to CodY, a global regulator in Gram-positive bacteria, as a critical link between microbial physiology and pathogenesis in diverse environments. Recent studies uncovering graded regulation of CodY gene targets reflect the true nature of this transcription factor controlled by ligands and reveal nutrient availability as a potentially critical factor in modulating pathogenesis. This review will serve to update the status of the field and raise new questions to be answered.

Clostridium difficile colitis: pathogenesis and host defence

Clostridium difficile is a major cause of intestinal infection and diarrhoea in individuals following antibiotic treatment. Recent studies have begun to elucidate the mechanisms that induce spore formation and germination and have determined the roles of C. difficile toxins in disease pathogenesis. Exciting progress has also been made in defining the role of the microbiome, specific commensal bacterial species and host immunity in defence against infection with C. difficile. This Review will summarize the recent discoveries and developments in our understanding of C. difficile infection and pathogenesis.

Coinfection and Emergence of Rifamycin Resistance during a Recurrent Clostridium difficile Infection

Clostridium difficile (Peptoclostridium difficile) is a common health care-associated infection with a disproportionately high incidence in elderly patients. Disease symptoms range from mild diarrhea to life-threatening pseudomembranous colitis. Around 20% of patients may suffer recurrent disease, which often requires rehospitalization of patients. C. difficile was isolated from stool samples from a patient with two recurrent C. difficile infections. PCR ribotyping, whole-genome sequencing, and phenotypic assays were used to characterize these isolates. Genotypic and phenotypic screening of C. difficile isolates revealed multiple PCR ribotypes present and the emergence of rifamycin resistance during the infection cycle. Understanding both the clinical and bacterial factors that contribute to the course of recurrent infection could inform strategies to reduce recurrence. (This study has been registered at ClinicalTrials.gov under registration no. NCT01670149.).

Importance of Glutamate Dehydrogenase (GDH) in Clostridium difficile Colonization In Vivo

Clostridium difficile is the principal cause of antibiotic-associated diarrhea. Major metabolic requirements for colonization and expansion of C. difficile after microbiota disturbance have not been fully determined. In this study, we show that glutamate utilization is important for C. difficile to establish itself in the animal gut. When the gluD gene, which codes for glutamate dehydrogenase (GDH), was disrupted, the mutant C. difficile was unable to colonize and cause disease in a hamster model. Further, from the complementation experiment it appears that extracellular GDH may be playing a role in promoting C. difficile colonization and disease progression. Quantification of free amino acids in the hamster gut during C. difficile infection showed that glutamate is among preferred amino acids utilized by C. difficile during its expansion. This study provides evidence of the importance of glutamate metabolism for C. difficile pathogenesis.