418 STATE BOARD OF AGRICULTURE. 



THE INFLUENCE OF CERTAIN ACID-DESTROYING YEASTS 



UPON LACTIC BACTERIA. 



Technical Bulletin No. 15. 



BY ZAE NORTHRUP. 



During the fall of 1910, a reddening of the soured milk in a sup- 

 posedly pure culture of Bad. lactis acidi was remarked by one of the 

 laboratory assistants. Upon microscopic examination, several types of 

 organisms were found to be present, so plating methods were resorted 

 to for the isolation of this pigment-producing organism ; none of the 

 resulting colonies gave a red chromogenesis. In order to preserve this 

 organism for study, transfers were made into plain milk flasks every 

 month or so. 



It was noted that each time a transfer was made, the milk first 

 curded, then shortly afterwards the characteristic reddening appeared. 

 Further effort was made to isolate the red organism, and dextrose agar 

 was the medium from which the pigmented colony was finally isolated. 

 The cliromogenic organism ])roved to be a yeast (3). The lactic bacteria by 

 propagation in this mixed culture seemed to retain their vitality over 

 a much longer period of time than a pure culture of active lactic bac- 

 teria growing in milk, which soon produce sufficient acid to effect their 

 own destruction.* 



The yeast in this mixed culture seemed to be the most prominent 

 organism involved, so a pure culture each of this red yeast and a lactic 

 bacterium was added to a flask of plain milk to see if the same 

 phenomenon would repeat itself in a pure combined culture. The char- 

 acteristic curding and later reddening of the milk took place and trans- 

 fers from this flask from month to month gave results similar to those 

 obtained in the original culture, the curding and the time of curding 

 were practically constant with each transfer. 



This caused the question to be raised : To what property or proper- 

 ties is this activity of the red yeast due? Two possibilities present them- 

 selves, viz., the revitalizing action of the yeast may be caused directly 

 by the intracellular activity of the yeast, again, it may be due to 

 enzymes which may be either intracellular, liberated by disintegration 

 of the cell, or simply excreted enzymes. 



Tlie most plausible explanation of the retention of the vitality of the 

 lactic bacteria by growth wiih Hi is yeast seems to be that it possesses 

 an acid reducing ])ower, a i)ro})erty common to many yeasts. The next 

 I)ossibility although not considered first is by no mejins subordinate to 

 the preceding, i. e., the possibility of independent enzymic action. 



♦G.Troili-Petersson (9) observed a sim'lnr phenomenon during his studies upon the stereochcmis- 

 trv of fermentation lactic acid. He grew Bad. lactis acidi with Oidium laclis in millv culture and dis- 

 covered that the lactic bacteriaVere still active at the end of 2J months. 



