Aggregation of Lactobacillus brevis associated with decrease in pH by glucose fermentation

Some Lactobacillus brevis strains were found to aggregate upon the addition of glucose, which resulted in glucose fermentation and pH decrease. Surface layer proteins (Slp) that represented the outermost layer of the bacteria decreased under these low pH conditions, probably because of the partial detachment of Slp from the cell surface triggered by the acidic environment. Similar observations of decreased Slp and aggregation were observed under the culture conditions, confirming that L. brevis aggregation was due to the partial Slp detachment under the acidic conditions of glucose fermentation. Such Slp detachment might affect the electrostatic nature of L. brevis cells by initiating the formation of irregular charge across the L. brevis cell surface, thereby leading to aggregation. These observations would be useful for elucidating the aggregation mechanism of lactic acid bacteria, which was considered to be involved in the probiotic effect of the bacteria.