PhD study trip

Bacillus Cereus Biofilms

Bacillus cereus is a common cause of food poisoning and spoilage of different food products, including dairy products and minimally processed foods that require storage at chilled conditions.

Vegetative cells and spores have the ability to attach to the surfaces of processing equipment and to form multicellular structures called biofilms. To the food industry, these biofilms are undesired as cells and spores can detach and become a source of product (re)contamination. Spores of this microorganism are particularly difficult to eradicate by mild heat  treatment. This is why it is important to provide mechanistic insight in the behaviour of Bacillus cereus in biofilms to allow control of biofilm formation and (re) contamination of food products [1].   


The aim of this project is to gain insight in the biofilm life cycle of Bacillus cereus. This life cycle includes attachment of cells to surfaces, biofilm formation and maturation, sporulation, and finally dispersal of cells and spores from the biofilm. The impact of various environmental factors on these processes will be determined.


The biofilm forming capacity of Bacillus cereus type strains ATCC14579 and ATCC10987 originating from different environmental niches was tested in a range of  conditions, including  different media, temperatures and on two types of surface material. Performance was compared to that of B. cereus industrial isolates. Transcriptome analysis of selected strains will be performed to identify  putative key factors and specific responses in biofilm formation.

Mechanistic insight in biofilm formation will be obtained by transcriptome analysis and phenotyping of targeted deletion mutants. Disinfectant resistance, selection of stress resistant variants and biofilm-derived spore characteristics will be determined. This information may provide new leads to prevent domestication and establishment of pathogenic persisters and to develop more effective strategies to eradicate them from factory environments

Future research

For further studies two different directions are planned. B. cereus is able to make spores while growing within the biofilm [2], and the characteristics of these spores will be determined and compared with that of spores derived from planktonic cells.

Due to diversity in microenvironments in the biofilm, cells may evolve differently which can  lead to genotypic heterogeneity and differences in performance including resistance to stresses. The second direction is therefore focused on isolation and characterisation of disinfectant-resistant and general stress-resistant variants that evolved within the biofilm.


So far a static system to study the biofilm formation by B. cereus has been set up and used in a screening to study biofilm formation by model strains and industrial isolates. The effect of different environmental factors has been characterized and will be coupled with transcriptome analysis to identify corresponding gene expression.        


1.    Andersson, A., Ronner, U., Granum, P.E. 1995. What problems does the food industry have with the spore-forming pathogens Bacillus cereus and Clostridium perfringens? Int. J. Food Microbiol. 28, 145-155.

2.    Wijman, J.G.E., de Leeuw, P.P.L.A., Moezelaar, R., Zwietering, M.H. and Abee, T. 2007. Air-Liquid Interface Biofilms of Bacillus cereus: Formation, Sporulation, and Dispersion. Appl. Environ Microbiol. 73, 1481–1488.