Natural hosts for biochemical productions are often limited by the type of resources that can be used. Development of novel microbial factories for utilization of various resources for biochemical production require delicate cellular control and properly engineered metabolic pathways. Succinate is a top value-added chemical from biomass identified by the U.S. Department of Energy and has been commercialized using sugars as feedstock. However, as sugar based bio-succinate production matures, attention is shifted towards utilization of non-food based resources such as lignocellulosic biomass and CO2. Currently, all demonstrations of succinate production using CO2 by cyanobacteria require either dark anoxic treatment or nutrient limitation, prohibiting the development of an effective process. Here, we systematically engineered cyanobacteria for simultaneous photoautotrophic growth and succinate production. Four different metabolic pathways leading to succinate were evaluated based on their thermodynamics and enzyme availability and compatibility. Introduction of the most thermodynamically favorable pathway with heterologous α-ketoglutarate decarboxylase and succinate semialdehyde dehydrogenase enabled direct photosynthetic CO2 based succinate production, but caused severe growth retardation. Subsequently, we restored the growth deficiency with step-wise carbon flux enhancement into citrate biosynthesis. The resulting strain also achieved significant improvement in succinate productivity.

Systematic development of direct photosynthetic succinate production from CO2

253rd National Meeting (2017)

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