Carbon:Nitrogen Ratio Affects Differentially the Poly-β-hydroxybutyrate Synthesis in Bacillus thuringiensis Isolates...

Poly-β-hydroxybutyrate (P(3HB)) represents a suitable alternative for plastic replacement, since it consists of intracellularly produced polyesters by different microorganisms including Bacillus thuringiensis (Bt). P(3HB) conserves most of the properties of petroleum-derived plastics; however, some drawbacks are the production costs, processing times, and bioseparation techniques, limiting its extended use. Bt has production advantages over other microorganisms, such as those growing in conventional or non-conventional substrates, with short periods of fermentation, which make it an interesting candidate to develop optimized production processes. In this work, we identified P(3HB) producers from 72 isolates of Bt, from which we selected four potential candidates. These isolates were cultivated under different carbon:nitrogen (C:N) ratios of 3, 7, 30, and 50 in a complex medium named (CM). Here, the best conditions for growth in Bt isolates were C:N 3 and 7 ratios, whereas for P(3HB) production they were C:N 7 and 30. Following this, an experiment in a bioreactor was conducted with isolate 81C with the selected C:N ratio of 30, where the produced P(3HB) achieved a maximum at 10 h. Fourier transform infrared spectroscopy (FTIR)was used to characterize flask and bioreactor cultures. It must be mentioned that although a higher concentration of medium was used, this did not improve P(3HB) accumulation. This research demonstrates that C:N ratios can differentially influence growth and P(3HB) accumulation in Bt isolates, which can serve as a reference to develop P(3HB) production processes using Bt as a microbial production platform.