Summary: Of 25 isolates of α-haemolytic group D streptococci from the rumens of calves (Mann & Oxford, 1955), 7 produced intracellular iodophilic polysaccharide when grown aerobically or anaerobically in agar media containing starches of various origins, amylopectin, maltose, maltotriose, glycogen, amylose and amylopectin dextrins, or amylose glycollate. The iodophilic polysaccharide was not produced from glucose, sucrose, trehalose, glucose-1-phosphate, glucose-6-phosphate, cellobiose or amylose. These results are discussed in the light of the amylolytic action of the bacteria and known enzymic mechanisms of starch-type polysaccharide formation.

In liquid media the polysaccharide was only produced from maltose when the cells were held at a pH value between 5 and 6, either by adjusting the reaction of the medium after the initial growth period, or by transferring the cells to a maltose solution buffered at the correct pH value and incubating further. Under the correct conditions polysaccharide formation was rapid. The polysaccharide was obtained in a partially purified form from the cells and appears to be unlike most ‘starches’ from bacteria so far reported. A possible explanation of the mode of development of an iodophilic reaction in streptococci in the rumen is given.


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