Optimization of secondary metabolites production by Bacillus subtilis strain 30BB6

Details

Supervisors

Stenuit, Benoît

Faculty

Faculté des bioingénieurs

Degree label

Master [120] : bioingénieur en sciences agronomiques, à finalité spécialisée

Abstract

Pesticides are vital for maintaining food security in a growing global population. However, the increased use of pesticides has raised concerns regarding their adverse effects on human health, the environment and biodiversity. In response, there is a growing interest in biopesticides, derived from natural organisms or their products, are increasingly recognized as sustainable alternatives to chemical pesticides, which offer effective pest management with minimal environmental impact. The microbial biopesticides are one of the categories with a great potential, often held back by poor industrial scale production, resulting in too high costs for a product for agricultural use. Thus, this master's thesis explores the optimization and scale-up of production of three secondary metabolites, bacilysin, plipastatin and bacillibactin by Bacillus subtilis 30BB6, with a particular focus on bacilysin. The research objectives focus on maximizing bacilysin yield by manipulating nitrogen sources, particularly L-glutamate and L-aspartate, and varying phosphate buffer concentrations. The study also investigates the effect of dissolved oxygen levels and scaling up the production process to ensure consistency across different experimental conditions. Additionally, the impact of these variables on the production of plipastatin and bacillibactin is explored, providing a comprehensive understanding of how media composition and environmental factors influence secondary metabolite production. Through a series of experiments in both shake flasks and 5 L bioreactor, it was found that specific growth rates and bacilysin yields varied significantly depending on the nitrogen source and dissolved oxygen levels. The results suggest that L-glutamate as a nitrogen source under low dissolved oxygen conditions enhances bacilysin production, while high dissolved oxygen favors ammonium as a nitrogen source. Furthermore, this work revealed that phosphate concentration plays a crucial role in regulating secondary metabolism. The findings suggest that phosphate starvation triggers bacilysin biosynthesis, potentially through the PhoR-PhoP regulatory system. Overall, this research contributes to the understanding of the metabolic pathways involved in secondary metabolite production by Bacillus subtilis and provides valuable insights for optimizing bacilysin production to make it a more competitive alternative to synthetic pesticides.