Jorge Zaldivar1, Catherine Tays1,2, Lisa Stein2, Dominic Sauvageau1.
1Department of Chemical and Materials Engineering, University of Alberta, Edmonton, Alberta, Canada.
2Department of Biological Sciences, University of Alberta, Edmonton, Alberta, Canada.
Plastic pollution creates a demand for economically viable alternative biodegradable polymers. Polyhydroxyalkanes (PHAs), of which polyhydroxybutyrate (PHB) is most common, are natural biodegradable biopolymers with desirable mechanical properties. However, current industrial production relies on fermenting bacteria using sugars as feedstock, leading to high production costs and controversy regarding the food vs. chemicals debate. A promising alternative involves using methanotrophs: a class of bacteria that can convert single-carbon (C1) compounds into PHAs. The use of methane and methanol – two common industrial wastes – as feedstocks reduces the costs of PHA and abates equivalent CO2 emissions from methane. Our work focuses on understanding and optimizing the production of biomass and PHB by methylotrophs.
Experiments were conducted to identify the main factors (carbon source, nitrogen source, nitrogen to carbon ratio, oxygen limitation, inoculum history) affecting biomass growth, PHB yield and PHB cellular content in Methylosinus trichosporium OB3b. Statistical analyses were performed to assess the importance and interactions of these factors. From these results, Response-Surface Analysis optimization studies were performed to determine the conditions leading to optimal biomass and PHB production. Independent optimal conditions were thus identified for the growth of M. trichosporium OB3b, its production of PHB and its PHB cell content. These results are combined with comparative transcriptomic studies to highlight the mechanisms regulating these optimal conditions, allowing for further optimization.
The results obtained guide the development of bioprocessing strategies for the optimal conversion of methane and methanol to biopolymers, making PHB a more economically viable alternative to polymers of petrochemical origin, all while reducing the GHG emissions of methane emitters.