Pre-requisites for Dextran Production by Streptococcus bovis

Abstract

IN a recent paper¹ we showed that many strains of Streptococcus bovis of rumen origin gave good yields of an unbranched dextran when incubated anaerobically for one day at 38° C. in a liquid sucrose medium. An essential condition for these yields of dextran was either incubation in a 100 per cent carbon dioxide atmosphere or the incorporation of solid calcium carbonate or 0.01 M bicarbonate in the medium. The latter was well buffered with 0.05 M phosphate and also contained 0.5 per cent yeast extract and 1.1 per cent casitone, or an equivalent peptone as sources of organic nitrogen, and growth factors. In the absence of carbon dioxide, cell yields were almost as good as in its presence and, though a normal lactic acid fermentation took place, little or no dextran was produced. No detailed study of the effect of buffer strength and composition on dextran yields nor any attempt to simplify the medium was made at the time.