Enzymes of glucose and pyruvate catabolism in cells, spores, and germinated spores of Clostridium botulinum

Effects of carbon dioxide on germination of Clostridium botulinum spores

Clostridium botulinum is a Gram -positive, strict anaerobic, rod -shaped, spore -forming, SOD -positive and catalase -negative bacterium. Its antioxidant defenses are not suited to chronic oxidative stress. H₂O₂ and reactive oxygen species have deleterious effects on C. botulinum. Spore germination is one of the key steps in its development. However, the mechanisms that trigger this germination have yet to be described. To manage C. botulinum growth, it is essential to understand the mechanisms that underlie the germination process. In this article, a series of complementary cascade reactions with water -dissolved CO₂ as an initiating germinant, and bicarbonate is suggested. It seems clear that ATP production is achieved through the use of various anaplerotic reactions with dissolved CO₂ as the carbon source. In addition to the production of oxaloacetate, an intermediate metabolite pyruvate would also be synthesized. Pyruvate would initiate the second phase of germination by producing hydrogen, which is a powerful reducing agent, via two enzymes (pyruvate -ferredoxin oxidoreductase and ferredoxin hydrogenase). These conditions would activate proteolytic enzymes and would reduce and would break the disulfide bridges of the proteins that make up the spore coats, thereby opening them. Thus, the phosphoenolpyruvate -pyruvate -acetyl -CoA pathway, in the presence of CO₂, would play a major role in the germination of spores of C. botulinum.

Identity, Abundance, and Reactivation Kinetics of Thermophilic Fermentative Endospores in Cold Marine Sediment and Seawater

Cold marine sediments harbor endospores of fermentative and sulfate-reducing, thermophilic bacteria. These dormant populations of endospores are believed to accumulate in the seabed via passive dispersal by ocean currents followed by sedimentation from the water column. However, the magnitude of this process is poorly understood because the endospores present in seawater were so far not identified, and only the abundance of thermophilic sulfate-reducing endospores in the seabed has been quantified. We investigated the distribution of thermophilic fermentative endospores (TFEs) in water column and sediment of Aarhus Bay, Denmark, to test the role of suspended dispersal and determine the rate of endospore deposition and the endospore abundance in the sediment. We furthermore aimed to determine the time course of reactivation of the germinating TFEs. TFEs were induced to germinate and grow by incubating pasteurized sediment and water samples anaerobically at 50°C. We observed a sudden release of the endospore component dipicolinic acid immediately upon incubation suggesting fast endospore reactivation in response to heating. Volatile fatty acids (VFAs) and H2 began to accumulate exponentially after 3.5 h of incubation showing that reactivation was followed by a short phase of outgrowth before germinated cells began to divide. Thermophilic fermenters were mainly present in the sediment as endospores because the rate of VFA accumulation was identical in pasteurized and non-pasteurized samples. Germinating TFEs were identified taxonomically by reverse transcription, PCR amplification and sequencing of 16S rRNA. The water column and sediment shared the same phylotypes, thereby confirming the potential for seawater dispersal. The abundance of TFEs was estimated by most probable number enumeration, rates of VFA production, and released amounts of dipicolinic acid during germination. The surface sediment contained ∼105-106 inducible TFEs cm-3. TFEs thus outnumber thermophilic sulfate-reducing endospores by an order of magnitude. The abundance of cultivable TFEs decreased exponentially with sediment depth with a half-life of 350 years. We estimate that 6 × 109 anaerobic thermophilic endospores are deposited on the seafloor per m2 per year in Aarhus Bay, and that these thermophiles represent >10% of the total endospore community in the surface sediment.

Immobilized anaerobic fermentation for bio-fuel production by Clostridium co-culture

Clostridium thermocellum/Clostridium thermolacticum co-culture fermentation has been shown to be a promising way of producing ethanol from several carbohydrates. In this research, immobilization techniques using sodium alginate and alkali pretreatment were successfully applied on this co-culture to improve the bio-ethanol fermentation performance during consolidated bio-processing (CBP). The ethanol yield obtained increased by over 60 % (as a percentage of the theoretical maximum) as compared to free cell fermentation. For cellobiose under optimized conditions, the ethanol yields were approaching about 85 % of the theoretical efficiency. To examine the feasibility of this immobilization co-culture on lignocellulosic biomass conversion, untreated and pretreated aspen biomasses were also used for fermentation experiments. The immobilized co-culture shows clear benefits in bio-ethanol production in the CBP process using pretreated aspen. With a 3-h, 9 % NaOH pretreatment, the aspen powder fermentation yields approached 78 % of the maximum theoretical efficiency, which is almost twice the yield of the untreated aspen fermentation.

PHYSIOLOGY OF THE SPORULATION PROCESS IN CLOSTRIDIUM BOTULINUM. I. CORRELATION OF MORPHOLOGICAL CHANGES WITH CATABOLIC ACTIVITIES, SYNTHESIS OF DIPICOLINIC ACID, AND DEVELOPMENT OF HEAT RESISTANCE

Day, Lawrence E. (Michigan State University, East Lansing), and Ralph N. Costilow. Physiology of the sporulation process in Clostridium botulinum. I. Correlation of morphological changes with catabolic activities, synthesis of dipicolinic acid, and development of heat resistance. J. Bacteriol. 88:690-694. 1964.-A reasonable degree of synchrony in the sporulation of Clostridium botulinum 62-A was attained by using a large inoculum of a young culture into a medium containing 4% Trypticase and 1 ppm of thiamine. Sporulation was complete within 24 to 36 hr. Cells harvested at various intervals were studied for their fermentative activity with l-alanine and l-proline as substrates. The Q values (microliters of gas per hour per milligram of dry cells) were maximal at the time a large percentage of the cells had initiated sporulation as indicated by swelling. They declined to a plateau at about the same level as found in vegetative cells by the time 10% of the cells had completed sporulation, and finally to a much lower level when sporulation was completed. The rates of accumulation of volatile acids (acetic, valeric, and propionic acids) corresponded closely with the catabolic potential observed. However, in the case of acetic acid, there was a significant decrease in the total acid present as the number of mature spores increased to over 50% of the final number. The total acetic acid then increased at a slow rate. The production of basic compounds during growth and sporulation more than balanced the rate of acid production, because the hydrogen ion concentration decreased exponentially throughout the period as indicated by the steady increase in pH. The synthesis of dipicolinic acid coincided closely with the development of heat resistance. Refractility developed 3 to 5 hr in advance of heat resistance.

COMPARISION OF SOLUBLE REDUCED NICOTINAMIDE ADENINE DINUCLEOTIDE OXIDASES FROM CELLS AND SPORES OF CLOSTRIDIUM BOTULINUM

Green, J. H. (Michigan State University, East Lansing), and H. L. Sadoff. Comparison of soluble reduced nicotinamide adenine dinucleotide oxidases from cells and spores of Clostridium botulinum. J. Bacteriol. 89:1499-1505. 1965.-The properties of purified reduced nicotinamide adenine dinucleotide (NADH(2)) oxidases from cells and spores of Clostridium botulinum 62-A have been studied to determine whether they are the same or different proteins. The spore NADH(2) oxidase was very heat-stable, whereas the vegetative enzyme was readily denatured at 70 C. The spore oxidase exhibited less affinity for the substrate than did the vegetative protein, but possessed a tightly bound cofactor. Atabrine was a noncompetitive inhibitor for both enzymes, but was less inhibitory to the spore NADH(2) oxidase. The enzymes could be separated from each other by gel filtration or chromatography on a diethylaminoethyl-cellulose column. The molecular weight of the spore oxidase was estimated to be 200,000 or greater, whereas that of the vegetative enzyme was 100,000 or less. Neither NADH(2) oxidase would cross-react with its heterologous antibody in a precipitation reaction. The conclusion drawn from this investigation is that the two NADH(2) oxidases are distinctly different proteins.

Use of microbial spores as a biocatalyst

Endospores of a bacterium Bacillus subtilis and ascospores of a yeast Saccharomyces cerevisiae contained almost all the activities for the same enzymes as vegetative cells. The biotechnological potential of spores was studied by selecting adenosine 5'-triphosphatase and alkaline phosphatase in bacterial and yeast spores, respectively, as model enzymes. The activity of both enzymes was efficiently expressed when the spores were treated by physical (sonication or electric field pulse) and chemical (organic solvents or detergents) methods. The yeast spores were immobilized in polyacrylamide gel without any appreciable loss of activity. The immobilized spores were packed in a column and used successfully for the continuous reactions of alkaline phosphatase and glyoxalase I. The microbial spores were confirmed to be promising as a biocatalyst for the production of useful chemicals in bioreactor systems.

Inactivation of clostridial ferredoxin and pyruvate-ferredoxin oxidoreductase by sodium nitrite

Clostridial ferredoxin and pyruvate-ferredoxin oxidoreductase activity was investigated after in vitro or in vivo treatment with sodium nitrite. In vitro treatment of commercially available Clostridium pasteurianum ferredoxin with sodium nitrite inhibited ferredoxin activity. Inhibition of ferredoxin activity increased with increasing levels of sodium nitrite. Ferredoxin was isolated from normal C. pasteurianum and Clostridium botulinum cultures and from cultures incubated with 1,000 micrograms of sodium nitrite per ml for 45 min. The activity of in vivo nitrite-treated ferredoxin was decreased compared with that of control ferredoxin. Pyruvate-ferredoxin oxidoreductase isolated from C. botulinum cultures incubated with 1,000 micrograms of sodium nitrite per ml showed less activity than did control oxidoreductase. It is concluded that the antibotulinal activity of nitrite is due at least in part to inactivation of ferredoxin and pyruvate-ferredoxin oxidoreductase.

The physiology of Clostridium sporogenes NCIB 8053 growing in defined media

The physiology of Clostridium sporogenes was investigated in defined, minimal media. In batch culture, the major end products of glucose dissimilation were acetate, ethanol and formate. When L-proline was present as an electron acceptor, acetate production was strongly enhanced at the expense of ethanol. As judged by assay of the relevant enzymes, glucose was metabolized via the Embden-Meyerhof-Parnas pathway. The growth energetics of Cl. sporogenes were investigated in glucose- or L-valine-limited chemostat cultures. In the former case, the addition of L-proline to the medium caused a significant increase in the molar growth yield (as calculated by extrapolation to infinite dilution rate). This finding adds weight to the view that the reduction of L-proline by Cl. sporogenes is coupled to the conservation of free energy.

Dependence of Clostridium botulinum gas and protease production on culture conditions

Reports that Clostridium botulinum toxin can sometimes be detected in the absence of indicators of overt spoilage led to a systematic study of this phenomenon in a model system. Media with various combinations of pH (5.0 to 7.0) and glucose (0.0 to 1.0%) were inoculated with vegetative cells of C. botulinum 62A and incubated anaerobically at 35 degrees C. Although growth and toxin production occurred at all pH and glucose combinations, accumulation of gas was delayed or absent in media with low pH, low glucose levels, or both. Other proteolytic C. botulinum strains gave similar results. Trypsin activation was required to detect toxin in some low pH cultures. The trypsinization requirement correlated with low proteolytic activity in the cultures. Proteolytic activity of the strains examined was 5- to 500-fold lower in botulinal assay medium than in cooked meat medium. The results indicate that the absence of gas accumulation does not preclude the presence of botulinal toxin and that proteolytic cultures grown under adverse conditions may require trypsinization for the detection of toxin.

Arginine and ornithine catabolism by Clostridium botulinum

Clostridium botulinum 62-A was shown to catabolize l-arginine via citrulline to ornithine, NH(3), and CO(2). The individual enzymes of the dihydrolase system were all demonstrated in extracts of cells, spores, and germinated spores. There was no liberation of urea from l-arginine, so no functional arginase enzyme is present, but there was some transamidinase activity in cell extracts. l-Ornithine was degraded at a significant rate by cells grown in an l-ornithine-supplemented medium; it was partially decarboxylated to putrescine and partially fermented to NH(3), CO(2), volatile acids, and delta-aminovaleric acid. Results from the fermentation of l-ornithine-C(14), -1-C(14), and -2-C(14) demonstrated that essentially all of the CO(2) was derived from carbon 1, and volatile acids from carbons 2 to 5. Assays for the products of l-ornithine-C(14) fermentation revealed that the volatile acids consisted of acetate, propionate, valerate, and butyrate (in order of decreasing concentrations), and that delta-amino-valerate was the primary reduced product. A small amount of citrulline was formed during the fermentation. The carbon and redox balances indicated that l-ornithine is fermented as a single substrate. Preliminary experiments demonstrated that the fermentation of l-ornithine is carried out by cell extracts with the production of volatile acids.