SUMMARY: Strain 9956 (minimum temperature for growth about 20°) formed clumps in cultures or suspensions of bacteria from these cultures, when grown at 30° and rapidly cooled to 15° with fast stirring. Electron microscopy showed whole organisms to be connected by an adhesive material. Electron micrographs of thin sections showed that clumps appeared to be formed by single layers of bacteria collecting round gas bubbles. The extent of clumping was greatest around pH 3, and increased as the temperature was decreased from 30° to 15°. Substitution of nitrogen or oxygen for air as gas phase had little effect on the clumping. The clumping ability increased with the age of the culture from the mid-exponential to the late-exponential phase of growth, but thereafter declined. Salts were necessary for clump formation. The relative effects of different monovalent cations and anions depended on the positions of the ions in the Hofmeister series. Incubation of bacteria in buffered solutions of proteolytic enzymes decreased their clumping ability. The extent of clumping also decreased when bacteria were incubated in buffered solutions of guanidine HCl (5 ), urea (8 ) or in a solution of uranyl nitrate (10 m) and NaCl (0.1 ). Isolated walls of the organism formed clumps when suspensions in phosphate buffer (pH 7.0) were incubated at temperatures between 35° and 5° with fast stirring. Pretreatment of walls with trypsin decreased clumping ability. The ability to form clumps when cultures were cooled to 5° with fast stirring was demonstrated with several but not all of the strains of tested.


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