(202f) A Multiscale, Multiphysics Modelling Framework for the Processes Involved in Consolidated Bioprocessing

Current biofuel production in the world is primarily from starch or sugar sources, such as corn and sugar cane. This has led to concerns about competition affecting prices as demand for both fuel and food increases. In order to overcome this, focus has turned to lignocellulose resources. The production of biofuels is currently carried out by processes such as separate hydrolysis and fermentation that convert biomass over a series of stages. These have proven to be inefficient and unattractive in terms of cost effectiveness. In order to make biofuels economically viable and competitive with oil-based equivalents, it is necessary to improve the efficiency and cost effectiveness of these processes. One of the ways to achieve this is by consolidated bioprocessing (CBP). CBP involves utilizing microorganisms to produce the cellulases needed to digest the biomass. whilst simultaneously metabolising the sugars produced into desirable products, such as ethanol, all in one reactor. This removes the need for extra reactors, heaters, pumps and other auxiliary equipment. The metabolism of the sugars as they are produced has the potential to reduce product inhibition of the enzymatic hydrolysis step. However, there is not a single organism that is able to both produce the enzymes to hydrolyse the biomass and ferment the sugars to products at a desirable rate and yield. Therefore, research has focused on engineering desirable traits into organisms to create an ideal CBP microorganism, such as modifying Saccharomyces Cerevisiae to produce hydrolytic enzymes, or adding fermentative pathways to naturally cellulolytic organisms.

We have developed a multiscale, multiphysics model for the production of valuable fuels and chemicals by consolidated bioprocessing. The thermophile, Geobacillus Thermoglucosidasius, has been used as the microorganism for the work. A metabolic reconstruction of the key pathways in a genetically modified strain was carried out. This was then combined with kinetic expressions of intracellular reactions to create a dynamic metabolic flux model that allowed us to visualise fluxes through the organism to products, cell growth and enzyme production. A hydrolysis model describing the breakdown of cellulose into cellobiose using Langmuir adsorption and competitive product inhibition was developed. This, combined with the metabolism model, has allowed us to follow carbon from the biomass through to the end product. A global sensitivity analysis was carried out on model parameters to identify key factors, as well as to locate possible sources of uncertainty in the model. By identifying the most important rate limiting steps we can focus future work on the areas that will have the greatest impact on performance.