From isolation to bioprocess of a novel Bacillus velezensis strain exhibiting antagonistic activity against Gram-negative foodborne pathogens

Nowadays, foodborne illnesses remain a major concern of public health with Campylobacter spp., Salmonella spp., Yersinia spp. and E. coli pathotypes as the most commonly reported bacterial pathogens. Besides their occurrence, the food industries have to cope with the increasing demand from the consumers for less processed and less chemically preserved food. In this context, biopreservation appears as a valuable technology which can be synergistically combined with the traditional food preservation methods. This study aimed to develop a bioactive metabolite against Gram-negative foodborne pathogens. To this end, the Bacillus subtilis group was investigated based on its alleged safety and its ability to synthesize a wide diversity of antimicrobials. First, a collection of strains from the B. subtilis group was screened for antimicrobial activity against a panel of relevant Gram-negative foodborne pathogens. This screening led to the selection of eight Bacil- lus velezensis strains for which the dipeptide bacilysin was specifically involved in their antimicrobial activity against Gram-negative pathogens. The second phase of this project focused on the bioprocess develop- ment of B. velezensis CN026. First, no safety concern was identified from its completely sequenced genome. Then its growth culture conditions were optimised and its activity spectrum was quantified against 95 foodborne pathogens. Finally, its scaling-up was achieved up to a 15L-bioreactor and the resulting supernatant was successfully challenged in milk, artificially contaminated with foodborne pathogens. Altogether, this work revealed the promising biopreservation potential of strain CN026 for which industrial applicative outcomes should be further investigated.(AGRO - Sciences agronomiques et ingénierie biologique) -- UCL, 201