Isolation of Clostridium absonum and its cultural and biochemical properties

The acquisition of Clostridium tyrobutyricum mutants with improved bioproduction under acidic conditions after two rounds of heavy-ion beam irradiation

End-product inhibition is a key factor limiting the production of organic acid during fermentation. Two rounds of heavy-ion beam irradiation may be an inexpensive, indispensable and reliable approach to increase the production of butyric acid during industrial fermentation processes. However, studies of the application of heavy ion radiation for butyric acid fermentation engineering are lacking. In this study, a second ¹²C⁶⁺ heavy-ion irradiation-response curve is used to describe the effect of exposure to a given dose of heavy ions on mutant strains of Clostridium tyrobutyricum. Versatile statistical elements are introduced to characterize the mechanism and factors contributing to improved butyric acid production and enhanced acid tolerance in adapted mutant strains harvested from the fermentations. We characterized the physiological properties of the strains over a large pH value gradient, which revealed that the mutant strains obtained after a second round of radiation exposure were most resistant to harsh external pH values and were better able to tolerate external pH values between 4.5 and 5.0. A customized second round of heavy-ion beam irradiation may be invaluable in process engineering.

First Insights into the Draft Genome of Clostridium colicanis DSM 13634, Isolated from Canine Feces

Clostridium colicanis DSM 13634 is a strictly anaerobic, rod-shaped, and spore-forming bacterium. It produces acids from common sugars such as glucose and fructose. The draft genome consists of one chromosome (2.6 Mbp) and contains 2,159 predicted protein-encoding genes.

Radiation induces acid tolerance of Clostridium tyrobutyricum and enhances bioproduction of butyric acid through a metabolic switch

BACKGROUND

Butyric acid as a renewable resource has become an increasingly attractive alternative to petroleum-based fuels. Clostridium tyrobutyricum ATCC 25755T is well documented as a fermentation strain for the production of acids. However, it has been reported that butyrate inhibits its growth, and the accumulation of acetate also inhibits biomass synthesis, making production of butyric acid from conventional fermentation processes economically challenging. The present study aimed to identify whether irradiation of C. tyrobutyricum cells makes them more tolerant to butyric acid inhibition and increases the production of butyrate compared with wild type.

RESULTS

In this work, the fermentation kinetics of C. tyrobutyricum cultures after being classically adapted for growth at 3.6, 7.2 and 10.8 g·L-1 equivalents were studied. The results showed that, regardless of the irradiation used, there was a gradual inhibition of cell growth at butyric acid concentrations above 10.8 g·L-1, with no growth observed at butyric acid concentrations above 3.6 g·L-1 for the wild-type strain during the first 54 h of fermentation. The sodium dodecyl sulfate polyacrylamide gel electrophoresis also showed significantly different expression levels of proteins with molecular mass around the wild-type and irradiated strains. The results showed that the proportion of proteins with molecular weights of 85 and 106 kDa was much higher for the irradiated strains. The specific growth rate decreased by 50% (from 0.42 to 0.21 h-1) and the final concentration of butyrate increased by 68% (from 22.7 to 33.4 g·L-1) for the strain irradiated at 114 AMeV and 40 Gy compared with the wild-type strains.

CONCLUSIONS

This study demonstrates that butyric acid production from glucose can be significantly improved and enhanced by using 12C6+ heavy ion-irradiated C. tyrobutyricum. The approach is economical, making it competitive compared with similar fermentation processes. It may prove useful as a first step in a combined method employing long-term continuous fermentation of acid-production processes.

Increasing ursodeoxycholic acid in the enterohepatic circulation of pigs through the administration of living bacteria

We investigated the feasibility of increasing ursodeoxycholic acid (UDCA) in the enterohepatic circulation of pigs by administering living bacteria capable of epimerising endogenous amidated chenodeoxycholic acid (CDCA) to UDCA. We first demonstrated that combining Bifidobacterium animalis DN-173 010, as a bile salt-hydrolysing bacterium, and Clostridium absonum ATCC 27555, as a CDCA to UDCA epimerising bacterium, led to the efficient epimerisation of glyco- and tauro-CDCA in vitro, with respective UDCA yields of 55·8 (se 2·8) and 36·6 (se 1·5)%. This strain combination was then administered to hypercholesterolaemic pigs over a 3-week period, as two daily preprandial doses of either viable (six experimental pigs) or heat-inactivated bacteria (six controls). The main effects of treatment were on unconjugated bile acids (P=0·035) and UDCA (P<0·0001) absorbed into the portal vein, which increased 1·6–1·7- and 3·5–7·5-fold, respectively, under administration of living compared with inactivated bacteria. In bile, UDCA did not increase significantly, but the increase in biliary lithocholic acid with time in the controls was not observed in the experimental pigs (P=0·007), and the same trend was observed in faeces. All other variables (biliary lipid equilibrium, plasma lipid levels and partition of cholesterol between the different lipoprotein classes) remained unaffected by treatment throughout the duration of the experiment. In conclusion, it is feasible to increase the bioavailability of UDCA to the intestine and the liver by administering active bacteria. This may represent an interesting new probiotic activity, provided that in future it could be expressed by a safe food micro-organism.

Clostridium sardiniense Prévot 1938 and Clostridium absonum Nakamura et al. 1973 are heterotypic synonyms: evidence from phylogenetic analyses of phospholipase C and 16S rRNA sequences, and DNA relatedness

Clostridium sardiniense Prévot 1938 and Clostridium absonum Nakamura et al. 1973 have long been considered similar in terms of their biological and biochemical properties, but their taxonomic positions have not been clarified by DNA-DNA hybridization studies or rigorous analysis of 16S rRNA genes. In the present study, DNA-DNA hybridization analysis revealed that C. absonum strains DSM 599(T), DSM 600 and KZ 1544 shared 83.0-86.3 % DNA relatedness with C. sardiniense DSM 2632(T). 16S rRNA gene sequence analysis showed that the C. absonum strains also shared high identity with C. sardiniense DSM 2632(T) (99.7, 99.3 and 99.8 % for DSM 599(T), DSM 600 and KZ 1544, respectively), implying that C. absonum and C. sardiniense are synonyms. In addition, alignment of the inferred amino acid sequences for phospholipase C (PLC) indicated 96.5 % identity between PLCs from C. sardiniense and C. absonum, but relatively low identity with other clostridial species. These results strongly suggest that the species C. sardiniense and C. absonum should be united, with the name C. sardiniense having priority.

Transformation of chenodeoxycholic acid to ursodeoxycholic acid in patients with Crohn's disease

In vivo 7 beta-epimerization of chenodeoxycholic acid to ursodeoxycholic acid and the role of 7-ketolithocholic acid as an intermediate in this biotransformation were studied in 11 patients with Crohn's disease and in 5 healthy volunteers. The incorporation of deuterium into biliary ursodeoxycholic acid and 7-ketolithocholic acid was determined by computed gas chromatography-mass fragmentography after ingestion of a dideuterated chenodeoxycholic acid, chenodeoxycholic-11,12-d2 acid. The incorporation of deuterium into ursodeoxycholic acid increased to a peak level at 48 h in the patients with Crohn's disease, but was delayed in healthy volunteers. In 8 patients and 2 healthy controls there were small amounts of 7-ketolithocholic acid in bile. The incorporation of deuterium into 7-ketolithocholic acid was confirmed in only 2 patients and the peak level was noted at 48 h. These observations suggest that 7-ketolithocholic acid is an intermediate of this biotransformation in patients with Crohn's disease.

Biochemical differentiation between enterotoxigenic heat-sensitive and heat-resistant Clostridium perfringens strains

Some biochemical characteristics of 37 enterotoxigenic Clostridium perfringens strains isolated from human feces, ground beef, and soil samples by heat-selection methods and of two NCTC strains were studied. Two different biochemical patterns closely related to the heat resistance of the strains were found. The strains placed into group 1 were trehalose, inositol, and sorbitol negative and synthesized heat-resistant spores, while those placed into group 2 were trehalose and inositol positive and synthesized heat-sensitive spores. Sorbitol fermentation was variable among the strains of this last group. The strains of group 1 were more cellobiose, melibiose, and salicin fermentative than those of group 2. Only the strains placed into group 2 synthesized toxins of sufficient levels for typing. In spite of having been isolated by mild heat treatment of the specimens, two strains showed the same biochemical and toxigenic characteristics of the strains of group 1. The heating of these two strains did not modify their characteristics. We conclude that enterotoxigenic C. perfringens strains showing the two different toxigenic and biochemical patterns are present in the human gut, ground beef, and, probably, in soil. These strains may be differentiated on the basis of their capacity to produce acid from trehalose, inositol, and sorbitol, heat resistance of the spores and grade of toxigenicity. The heat-selection methods used for isolation of C. perfringens strains from different sources exerted a selection of strains from one or another group, but had no influence on their toxigenic and biochemical properties.

The suitability of Tórtora's medium for the production of enterotoxin in Clostridium perfringens strains

Examination of 200 samples from soil and the same number of samples from healthy human feces yielded 49 (24.5%) and 105 (52.5%) strains of heat-resistant Clostridium perfringens respectively. Fourteen (7.0%) strains isolated from soil and 37 (18.5%) from feces synthesized enterotoxin, as demonstrated by Tórtora's method, at sufficient levels to permit its detection by mouse lethality, microslide double gel diffusion or counterimmunoelectrophoresis tests. By using the Duncan-Strong (DS) method, only four (2%) enterotoxigenic strains from soil and 14 (7.0%) from feces were obtained. The supernatant fluid from two enterotoxigenic-negative strains grown in DS medium gave a false-positive reaction when they were injected intravenously into mice. Tórtora's medium was preferable because a larger number of isolated strains produced spores and enterotoxin to permit their recognition as enterotoxigenic strains.

Formation of ursodeoxycholic acid from chenodeoxycholic acid by a 7 beta-hydroxysteroid dehydrogenase-elaborating Eubacterium aerofaciens strain cocultured with 7 alpha-hydroxysteroid dehydrogenase-elaborating organisms

A gram-positive, anaerobic, chain-forming, rod-shaped anaerobe (isolate G20-7) was isolated from normal human feces. This organism was identified by cellular morphology as well as fermentative and biochemical data as Eubacterium aerofaciens. When isolate G20-7 was grown in the presence of Bacteroides fragilis or Escherichia coli (or another 7 alpha-hydroxysteroid dehydrogenase producer) and chenodeoxycholic acid, ursodeoxycholic acid produced. Time course curves revealed that 3 alpha-hydroxy-7-keto-5 beta-cholanoic acid produced by B. fragilis or E. coli or introduced into the medium as a pure substance was reduced by G20-7 specifically to ursodeoxycholic acid. The addition of glycine- and taurine-conjugated primary bile acids (chenodeoxycholic and cholic acids) and other bile acids to binary cultures of B. fragilis and G20-7 revealed that (i) both conjugates were hydrolyzed to give free bile acids, (ii) ursocholic acid (3 alpha, 7 beta, 12 alpha-trihydroxy-5 beta-cholanoic acid) was produced when conjugated (or free) cholic acid was the substrate, and (iii) the epimerization reaction was at least partially reversible. Corroborating these observations, an NADP-dependent 7 beta-hydroxysteroid dehydrogenase (reacting specifically with 7 beta-OH-groups) was demonstrated in cell-free preparations of isolate G20-7; production of the enzyme was optimal at between 12 and 18 h of growth. This enzyme, when measured in the oxidative direction, was active with ursodeoxycholic acid, ursocholic acid, and the taurine conjugate of ursodeoxycholic acid (but not with chenodeoxycholic, deoxycholic, or cholic acids) and displayed an optimal pH range of 9.8 to 10.2

Epimerization versus dehydroxylation of the 7 alpha-hydroxyl- group of primary bile acids: competitive studies with Clostridium absonum and 7 alpha-dehydroxylating bacteria (Eubacterium sp.)

Primary bile acids, chenodeoxycholic (3 alpha,7 alpha-dihydroxy-5 beta-cholan-24-oic) and cholic (3 alpha,7 alpha,12 alpha-trihydroxy-5 beta-cholan-24-oic) were included in cultures of (a) Clostridium absonum alone (b) a mixture of C. absonum and a 7-dehydroxylating organism, Eubacterium sp. (c) a mixture of C. absonum and fecal bacteria, and (d) fecal bacteria alone. C. absonum, when added to Eubacterium sp. cultures totally prevented lithocholic acid formation when the substrate was chenodeoxycholic acid and halved deoxycholic acid formation when the substrate was cholic acid. As expected, formation of 7 beta-hydroxy- and 7-keto-bile acids took precedence over formation of 7 alpha-dehydroxylated bile acids. However, the addition of C. absonum to mixed fecal cultures containing chenodeoxycholic acid did not alter production of lithocholic (3 alpha-hydroxy-5 beta-cholan-24-oic) acid; instead it enhanced formation of ursodeoxycholic acid (3 alpha,7 beta-dihydroxy-5 beta-cholan-24-oic acid) at the expense of 7-keto-lithocholic acid (3 alpha-hydroxyl-7-oxo-5 beta-cholan-24-oic acid). Similarly, the addition of C. absonum to mixed fecal cultures containing cholic acid promoted production of ursocholic acid (3 alpha,7 beta,12 alpha-trihydroxy-5 beta-cholan-24-oic acid) which did not take place when C. absonum was not added. Surprisingly, deoxycholic acid formation was somewhat enhanced when C. absonum was added to fecal cultures. These studies suggest that successful introduction of "foreign" 7 alpha-epimerizing organisms into animal or human intestines may influence bile acid metabolism in vivo.

Bile induction of 7 alpha- and 7 beta-hydroxysteroid dehydrogenases in Clostridium absonum

Eight strains of Clostridium absonum grown in the presence of 4 . 10(-4) M deoxycholate contained both NADP-dependent 7 alpha- and 7 beta-hydroxysteroid dehydrogenase activities. In one strain studied in detail, significant amounts of NADP-dependent 7 alpha- and 7 beta-hydroxysteroid dehydrogenase and NAD-dependent 7 alpha-hydroxysteroid dehydrogenase activities were demonstrated only when cells were grown in the presence of deoxycholate or chenodeoxycholate, both optimal at 4 . 10(-4) M. When the bile salt was deleted from the medium, only a trace of 7 alpha-hydroxysteroid dehydrogenase was present and 7 beta-hydroxysteroid dehydrogenase was absent. Other bile salts including cholate, ursodeoxycholate and keto bile salts were less effective as inducers. Addition of cholate to medium already containing deoxycholate at a suboptimal concentration enhanced the induction, while addition of ursodeoxycholate suppressed the induction. Further enhancement of 7 alpha- and 7 beta-hydroxysteroid dehydrogenase could be obtained by additions of deoxycholate (up to a total of 6 . 10(-4) M) during the growth of the organisms (in log phase). As enzyme enhancement is blocked by addition of rifampicin to the medium, the authors conclude that the enzymes are bile salt-inducible. Growth curve studies revealed an optimal enzyme yield at a harvest time of approx. 6-9 h. We have preliminarily characterized several inducible enzyme components: an NADP-dependent 7 beta-hydroxysteroid dehydrogenase as well as both NAD- and NADP-dependent 7 alpha-hydroxysteroid dehydrogenases.