Bacillus species present a major concern in the dairy industry as they can form biofilms within pipelines and on surfaces of equipment. These biofilms represent a continuous hygiene problem and can lead to serious economic losses due to food spoilage and equipment impairment. Biofilm formation by Bacillus species is apparently dependent on LuxS quorum sensing (QS) by Autoinducer-2 (AI-2). However, the link between sensing environmental cues and AI-2 induced biofilm formation remains largely unknown. The aim of this study is to investigate the role of lactose, the primary sugar in milk, on biofilm formation by Bacillus species and its possible link to QS process.
Biofilm formation was tested using the chemical defined agar (CDA), with or without lactose, for colony type biofilm, while the confocal laser scanning microscopy (CLSM) was used for biofilm bundle formation analysis as well as for examining the expression of major operons involved in the biofilm formation. In order to test the level of AI-2 production by B. subtilis in response to lactose, reporter strain assay Vibrio harveyi MM77 (AI-2-/-) was used.
We found that lactose highly induced biofilm formation in bundle as well as in colony type biofilms. Furthermore, we observed an increase in AI-2 production by B. subtilis in response to lactose in a dose dependent manner. Finally, we found that expression of eps and tapA operons, responsible for extracellular matrix, was highly up-regulated in response to lactose. Our results suggest that lactose may induce biofilm formation by Bacillus species through the LuxS pathway.
