Some effects of ethyl alcohol on the growth of rumen bacteria

The effects of ethyl alcohol on the growth rate and yield of representative isolates of obligately anaerobic rumen bacteria were studied. Yield was monitored as turbidity at 600 nm until stationary phase was obtained and quantitated as protein per milliter. Rate was determined as the fastest rate of turbidity doubling. With very few exceptions, within the concentration range allowing growth, no effects of alcohol concentration were observed on rate, but substantial effects were found on yield. Growth of most of the organisms studied was completely inhibited at an alcohol concentration between 3% and 7% vol/vol, but the growth ofBacteroides amylophilus andRuminococcus flavefaciens was drastically reduced or eliminated at a 1% alcohol concentration. It is likely that major physiological and biochemical differences exist among anaerobic rumen bacteria, and taxonomically similar organisms, as a function of alcohol exposure.