Development of in silico strategies to photoautotrophically produce poly-β- hydroxybutyrate (PHB) by cyanobacteria

LASRY TESTA, R.; DELPINO, C.; ESTRADA, V.; DIAZ, M.S.

Algal Research

Elsevier

Año: 2022

2211-9264

Poly(3-hydroxybutyrate) (PHB), a biopolymer similar to polypropylene, is currentlyproduced by heterotrophic bacteria. However, the elevated cost of raw material usedas carbon and energy sources are promoting the development of new sustainablebioprocess based on photoautotrophic routes. costs. In unbalanced growth conditions,some cyanobacteria can accumulate PHB using CO 2 as the sole carbon source,becoming an option for PHB production. In this work, we study in silico PHBproduction with the model cyanobacterium Synechocystis sp. PCC 6803 (Synechocystis ). We consider two different strategies for in silico strain design:coupled growth-PHB production and a two-stage fermentation strategy. For bothstrategies we consider a GEnome-scale Model (GEM) of Synechocystis , which wasmodified to account for PHB production. The coupled approach relies on a bileveloptimization problem that identifies gene knock-outs needed to obtain a mutant thatcouples PHB production with biomass formation. For this case, two mutants thatsuccessfully achieve the required coupling are obtained, and the best one is analyzedin terms of intervention strategies, flux distributions and productivities. For the twostagefermentation strategy, we consider two bioreactors in series. The first one isoptimized for biomass production under balanced growth conditions, and the secondone is optimized for PHB production under nitrogen starvation conditions. Both stagesare simulated within dfba, a python tool for solving the Dynamic Flux Balance Analysis(DFBA) problem which provides the solution of a bioreactor model subject to the massbalances of the GEM. Numerical results for the two-stage approach provide a PHBconcentration of 4.764 g PHB/L while the mutant provides a lower concentration of0.391 g PHB/L. Nevertheless, both strategies provide high PHB content per cell dryweight (cdw), which makes results attractive for photosynthetic PHB production.