Fermentation phenomena when different species of micro-organisms are in close association.

Abstract

Conclusions

“Baker's yeast” as obtainable in Ceyloln and in England is not a pure culture of yeast, but is generally composed of two or more species of Saccharomyces an'd one or two or several species of bacteria diving in close association. The whole yeast as a rule gas-fermented more carbohydrates than any of the isolated germs did, either Saccharomyces or bacteria. 4 bacillus, which produced only acidity, not gas, in maltose, would produce gas when Saccharomyces was added to it, was inactive on maltose and was isolated from the same sample.

In recent years I have used for my experiments mostly pathogenic bacteria and also a pathogenic yeast, Cryptococcus graciloides.

Simple acid fermentation of certain carbon compounds caused by micro-organisms which never produce gas may in a number of instances be transformed into fermentation with the productioln of gas by adding a micro-organism which, alone, is inert, viz., produces neither acidity nor gas on those particular carbon compounds. For example :B. dysenteriae Flexner produces acidity, never gas, in maltose and mannitol; B. morgani produces neither acidity nor gas in those two carbohydrates; the mixture B. dysenteriae Flexner + B. morgani producrs, however, acidity and gas. For the phenomenon to take place several conditions are necessary; the most important one seems to be that the added bacillus, though inert on those particular carbon compounds, must be capable of producing fermentation with gas in glucose.