MILK CONSTITUENTS TRIGGER BIOFILM FORMATION OF BACILLUS SPECIES VIA ACTIVATION OF MATRIX GENES EXPRESSION

Bacillus species are prevalent in the milk processing environment where they form biofilms that are a major concern in the dairy industry. Contamination of milk by these bacteria is a serious health hazard, since some strains are highly pathogenic to human. The model organism Bacillus subtilis forms matrix-enclosed biofilms in response to different environmental cues. Biofilm formation depends on the synthesis of an extracellular matrix, which is indirectly regulated by the transcriptional regulator, Spo0A. The activity of Spo0A depends on its phosphorylation state. Low and intermediate levels of phosphorylated Spo0A lead to induction of the epsA-O and tapA operons, which results in production of the extracellular matrix and thus biofilm formation. Here, we report that the biofilm formation of B. subtilis is significantly triggered by milk constituents. We further show that transcription of the major matrix operons is notably enhanced in response to milk constituents. We also find that milk components have a similar biofilm-promoting effect in other Bacillus species, B. licheniformis and B. cereus, indicating that the biofilm-promoting effect of milk is conserved in Bacillus species. In overall, we propose that small signaling molecules found within milk and its products trigger biofilm formation of Bacillus species.