The role of AbrB from plate to bioreactor: implications of induced expression on physiological and metabolic responses in Bacillus thuringiensis.

Transition state regulators from Bacillus can control diverse physiological responses such as growth, metabolism, motility, virulence, and sporulation. The AbrB protein is a transcriptional regulator involved in multiple functions during exponential phase and intricated regulatory pathways that control adaptive states differentially. Despite its importance, the AbrB role has not been well characterized during the growth cycle, and its implication in metabolic functions remains elusive, especially in the Bacillus cereus group. In this work, we characterized the role of AbrB on phenotypes such as spreading motility, growth profiles, sporulation, and on activity of core metabolic pathways of Bacillus thuringiensis. For this, a strain with inducible abrB expression was generated in the wild type Bt HD73 background. In vitro evaluations of phenotypic traits demonstrated differences in sporulation and motility, where induction of abrB presumably affected these functions under nutrient-limited media. In addition, AbrB induction during bioreactor fermentations led to higher biomass production and changes dissolved oxygen (DO) profile, which was also accompanied with a delay in sporulation. Based on these results, metabolic pathways such as glycolysis and the Krebs cycle were explored to address the effect of AbrB overproduction on transcription of genes coding for pyruvate dehydrogenase (pdHA), lactate dehydrogenase (ldH), citrate synthase (citZ) and aconitase (citB). Our findings suggest variations in the carbon-flux in the central carbon metabolism due to abrB overexpression. This work contributes to the elucidation of AbrB involvement in regulatory networks of B. thuringiensis, to develop engineering-based strategies to use these bacteria in other biotechnological applications besides as biological control agent.