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Bacillus coagulans : A superior probiotic

L. sporogenes* was first isolated and described in 1933 by L.M. Horowitz-Wlassowa and N.W. Nowotelnow and the name was accepted in the fifth edition of " Bergey’s Manual of Determinative Bacteriology". However, it was transferred to Bacillus coagulans in the seventh edition of Bergey’s manual due to simplification in cataloging. However, in honor of the original discoverers, the name Lactobacillus sporogenes* is used widely, except for taxonomical purposes. According to the Eighth Edition of Bergey’s Manual of Determinative Bacteriology, "Various spore-bearing rods which produce lactic acid, are facultative or aerobic and catalase positive, have generally and correctly been assigned to the genus Bacillus."

The characteristics of L. sporogenes* as cited in Bergey’s Manual (Seventh Edition) and other sources are: "Gram - positive spore-forming rods 0.9 by 3.0 to 5.0 micron size, aerobic to microaerophilic, producing L(+)-(dextrorotatory) lactic acid homofermentatively." Since L. sporogenes* exhibits characteristics typical of both genera Lactobacillus and Bacillus, its taxonomic position between the families Lactobacillaceae and Bacillaceae has often been discussed. This, along with the fact that there is no universally accepted official classification leaves room for controversy in the nomenclature. The differentiation characteristics of L. sporogenes* are indicated in Table 2.4:

L. sporogenes

                                                    Table 2.4 : L. sporogenes* - key characteristics for differentiation:

Property Bacillus Lactobacillus Sporolactobacillus L. sporogenes*

It is often very difficult to distinguish between two species of bacteria which are morphologically similar and possess similar physiological and biochemical characteristics. DNA-DNA homology is an useful technique in resolving this difficulty. The nucleotide sequence in the DNA of various bacteria differs. Additionally, DNA from closely related bacteria bind to each other more efficiently. These facts are used in the typing and classification of bacteria and have been effectively employed to recognize the innate resemblance between L. sporogenes* and members of the genus Lactobacillus. The results of a detailed study prove conclusively that L. sporogenes* is closer to Lactobacillus than to Bacillus, irrespective of its taxonomical placement under genus Bacillus in the Bergey’s manual.

The characteristics by which L. sporogenes* resembles the genus Bacillus are as listed:

  1. Cells are long and slender (0.3 to 0.8 mM), some are bent and all the cells have rounded ends.
  2. Motile with peritrichous flagellas
  3. Gram positive
  4. Colonies are usually 2.5 mm in diameter, convex, smooth, glistening and do not produce any pigment.
  5. Extremely fastidious organisms requiring complex organic substrates for growth such as fermentable carbohydrate, peptone, meat and yeast extract. MRS medium supplemented with tomato juice, manganese, acetate and Tween-80 is a suitable medium for growth.
  6. Grow optimally at 30° C to 37° C and the optimum pH in the range 5.5 to 6.2.
  7. Microaerophilic, exhibit fermentative metabolism and are facultatively aerobic.
  8. Produce acid from arabinose, xylose, glucose, galactose, mannose, fructose, maltose, sucrose and trehalose.
  9. Do not hydrolyse starch or casein.
  10. Do not liquefy gelatin
  11. Are indole negative and do not produce hydrogen sulfide or gas.
  12. Produce dextro-rotatory lactic acid from glucose, fructose, sucrose, trehalose and inulin.
  13. Menaquinones are absent.

The characteristics by which L. sporogenes* differs from the genus Bacillus are as listed:

  • Species of Bacillus are always rod-shaped and straight but lactic acid bacteria also appear as bent rods and exhibit very little motility.
  • The spores present are terminal in position and are not centrally located as in Bacillus.
  • Lactic Acid Bacteria are oxidase negative (OXIDASE TEST)
  • Do not reduce nitrate to nitrite while most Bacilli reduce nitrate.
  • The mole % G+C of DNA in Bacillus ranges from 32 to 69% whereas in Lactobacillus it does not exceed 53%.

L. sporogenes* was assigned to genus Lactobacillus based on the above characteristics by Nakayama and Yanoshi (1967).

L. sporogenes* grows in the temperature range of 35° C to 50° C; the optimum pH range is 5.5-6.5. Unlike other lactobacilli currently in clinical use, L. sporogenes* can form spores. Sporulation is the development in microorganisms of bodies each wrapped in a protective coat (a natural process of microencapsulation in a calcium-dipicolinic acid- peptidoglycan complex). Under favorable conditions, the spores germinate into viable bacilli and carry on their life activities. The spores of L.sporogenes* are ellipsoidal bodies measuring 0.9 to 1.2 by 1.0 to 1.7 microns. Their morphology and formation are schematically represented in Figures 2.6 and 2.7:

Bacterial Spore

Bacterial Spore

This property of spore formation by L. sporogenes* is the main characteristic that makes it the probiotic of choice in clinical applications. On oral administration, these spores survive the acidic gastric environment and are activated due to the low pH, mechanical churning action of the stomach and the water in the gastric environment. The spore coats imbibe water, swell, and the increased water content causes a rise in the metabolic rate of the sporulated bacilli. Outgrowths begin to protrude from the spore-coats. The spores pass on to the duodenum where the outgrown cells germinate and transform into viable vegetative cells. They begin to proliferate in the small intestine, multiplying rapidly. Usually, germination takes place about four hours after ingestion. A large supply of viable L. sporogenes* is thereby ensured in the small intestine. These cells settle in the intestinal tract and continue their metabolic activities, producing lactic acid and probably bacteriocins, which render the intestinal environment non-conducive for the growth of harmful pathogenic bacteria. The maintenance of a low, constant level of lactic acid on the inner surface of the intestinal tract helps restore the microecological balance after antibiotic therapy. Antibiotic therapy may kill beneficial microbes which help in the synthesis of vitamins B and digestive enzymes. Since L. sporogenes* produces only L (+)-lactic acid, it does not cause metabolic acidosis.

Morphological and physiological characteristics of L. sporogenes*

The vegetative cells are rods occurring singly, rarely in short chains, the filaments varying with cultural conditions. The cells are motile by means of flagella.

Carbohydrate fermentation:

Carbohydrate Acid production Gas production

Inulin

              -

              -

Maltose

              +

              -

Mannitol

              +

              -

Raffinose

              +

              -

Sorbitol

              -

              -

Sucrose

              +

              -

Trehalose

              +

              -

Properties of the spores:

The spores of L. sporogenes*74 are resistant to heat and other adverse environmental conditions, surviving even under a temperature of 100° C for twenty minutes in phosphate buffer at pH 7. The spores germinate in malt broth even in the presence of dilute hydrochloric acid (at pH 4.6 to 5.6), caustic soda solution (pH 7.6-9.6), saline solution (5%, 10%, 20% concentration), a 2.5% solution of boric acid as well as distilled water. The spores are two to eight times more resistant to antibiotics than the vegetative cells.

* The taxonomical classification was revised in 1939 in the seventh edition of the Bergey’s Manual of Determinative Bacteriology to B. coagulans, although some researchers continued to use the original name.