Bacillus cereus growth and biofilm formation: the impact of substratum, iron sources, and transcriptional regulator Sigma 54

Biofilms are surface-associated communities of microbial cells embedded in a matrix of extracellular polymers. It is generally accepted that the biofilm growth mode represents the most common lifestyle of microorganisms. Next to beneficial biofilms used in biotechnology applications, undesired biofilms can be formed by spoilage and pathogenic microorganisms in food production environments. <em>Bacillus cereus</em> is a foodborne human pathogen able to cause two types of food poisoning, emetic and diarrheal. <em>B. cereus</em> can persist in factory environments in the form of biofilms, which can become a source of food contamination. This thesis adds to the knowledge about (a)biotic factors and conditions that affect <em>B. cereus</em> biofilm formation, including the effect of type of substratum such as polystyrene and stainless steel, with the latter supporting the highest biofilm formation for all tested strains including two reference strains and 20 food isolates. The ability of <em>B. cereus</em> to use a variety of iron sources was subsequently studied in these 22 strains and linked to the genes encoding iron transport systems present in the respective genomes, revealing significant diversity in the capacity to use complex and non-complex iron sources for growth and biofilm formation. For spore forming <em>Bacilli,</em> biofilm formation and sporulation are two intertwined cellular processes and studies in wet and dry (air-exposed) biofilms revealed differences in sporulation rate and efficacy, with biofilm-derived spores showing higher heat resistance than their planktonic counterparts. Additionally, comparative phenotype and transcriptome analysis of <em>B. cereus</em> wild type and a Sigma 54 deletion mutant provided insight into the pleiotropic role of this transcriptional regulator in <em>B. cereus</em> biofilm formation and physiology in general. Taken together, this knowledge improves our understanding of the biofilm lifecycle of this notorious food-borne human pathogen and provides clues which can help to reduce the domestication of this microorganism in production environments.