Studies on Capsule Formation

Abstract

A new technique was developed by which the relative viscosity of a culture of encapsulated bacteria was used as a standard to define the relative sizes of capsules. Friedlander''s bacterium was grown in Ostwald viscosity tubes, and, from the determinations of relative viscosity and simultaneous bacterial counts, deductions could be made as to the degree of encapsulation. The largest capsules were obtained by cultivation for about 8 hrs. at 37 [degree]C. in a medium containing 1 to 4% peptone and 1% glucose, initial pH 7.5. Capsule formation took place mainly after the logarithmic phase of growth when the multiplication of the bacteria became restricted. In the absence of sugars, the capsules were very small. The presence either of glucose, maltose, sucrose, mannitol, or to a lesser extent, pyruvate or glycerin, was necessary to ensure the formation of large capsules. The protein source was also important for encapsulation. Neopeptone, Witte peptone or bacto-peptone served equally well as source of protein. However, several media such as yeast extract, Loeffler''s blood serum, and brain-heart infusion contained factors, as yet unknown, which inhibited encapsulation markedly, although they did not affect the growth of the bacteria. In a synthetic medium, capsule formation took place only under special conditions, i.e., when the phosphate conc. was below the limits of optimal bacterial growth.