Proteolysis produced within biofilms of bacterial isolates from raw milk tankers

In this study, six bacterial isolates that produced thermo-resistant enzymes isolated from the internal surfaces of raw milk tankers were evaluated for their ability to produce proteolysis within either single culture biofilms or co-culture biofilms. Biofilms were formed in an in vitro model system that simulated the upper internal surface of a raw milk tanker during a typical summer's day of milk collection in New Zealand. The bacterial isolates were further evaluated for their ability to form biofilms at 25, 30 and 37 °C. Mutual and competitive effects were observed in some of the co-culture biofilms, with all isolates being able to form biofilms in either single culture or co-culture at the three temperatures. The proteolysis was also evaluated in both biofilms and corresponding planktonic cultures. The proteolysis per cell decreased as the temperature of incubation (20–37 °C) increased. Furthermore, mutualistic interactions in terms of proteolysis were observed when cultures were grown as co-culture biofilms. This is the first study to show that proteolytic enzymes can be produced in biofilms on the internal surfaces of raw milk tankers. This has important implications for the cleaning and the temperature control of raw milk transport tankers.

► We examined proteolysis in biofilms and their corresponding planktonic cultures in an in vitro model simulating a raw milk tanker.
► All isolates in this study formed biofilms.
► Proteolysis in biofilms were higher compared with their corresponding planktonic cultures.
► Proteolytic enzymes produced by biofilm bacteria in a raw milk tanker may have important implications for the dairy industry.