Summary In response to nutrient limitation in the environment, the global transcriptional regulator CodY modulates various pathways in low G+C Gram‐positive bacteria. In Bacillus subtilis CodY triggers adaptation to starvation by secretion of proteases coupled to the expression of amino acid transporters. Furthermore, it is involved in modulating survival strategies like sporulation, motility, biofilm formation, and CodY is also known to affect virulence factor production in pathogenic bacteria. In this study, the role of CodY in Bacillus cereus ATCC 14579, the enterotoxin‐producing type strain, is investigated. A marker‐less deletion mutant of codY (ΔcodY) was generated in B. cereus and the transcriptome changes were surveyed using DNA microarrays. Numerous genes involved in biofilm formation and amino acid transport and metabolism were upregulated and genes associated with motility and virulence were repressed upon deletion of codY. Moreover, we found that CodY is important for efficient production of toxins and for adapting from nutrient‐rich to nutrient‐limited growth conditions of B. cereus. In contrast, biofilm formation is highly induced in the ΔcodY mutant, suggesting that CodY represses biofilm formation. Together, these results indicate that CodY plays a crucial role in the growth and persistence of B. cereus in different environments such as soil, food, insect guts and the human body.

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The sensitivity of microorganisms to low pH can be utilized in food protection by preparing coatings based on macromolecular acids. Due to limited diffusivity of macromolecules low pH occurs primarily at the surface, while the interior parts of the food remain unaffected. This principle is demonstrated using food approved alginic acid in various types of coatings (aqueous, emulsions, dispersions, dry coating) on a wide range of foods including meat, fish, chicken, shrimp and boiled rice. Significant delay or inhibition of the natural flora is generally demonstrated, particularly when exposed to 'temperature abuse'. Specifically, we show that the coatings reduce or inhibit regrowth of pathogens (Bacillus cereus, B. weihenstephanensis, Listeria monocytogenes serotype 1 and Staphylococcus aureus). In special cases like boiled rice, alginic acid may largely replace acetic acid for acidification and preservation, as demonstrated studying regrowth of added spores of B. cereus. Most formulations allow easy removal prior to further processing (cooking, frying). Temporary side effects such as 'acid cooking' obtained for high acid concentrations on sensitive surfaces (e.g. salmon) disappear during processing, recovering the normal taste and texture. The coating is hence suitable for a large variety of foods.

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