(251d) Exploring Sustainable n-Butanol Production By Rhodopseudomonas Palustris TIE-1

Producing fuels sustainably using native or engineered autotrophic microbes that can fix carbon dioxide is an attractive idea, given the rising CO₂ concentration on our planet¹. Using autotrophic microbes, a carbon-neutral to a carbon-sequestering process for biofuel production can be realized¹. Among the various biofuels that have been successfully produced using microbes, n-butanol is arguably the most attractive substitute because it shares many properties with gasoline². However, most current studies generate n-butanol from sugars ², which represent fixed carbon that can also serve as a food source. With an imminent food shortage as Earth’s population increases³, using sugars for fuel production is far from ideal.

In the present study, we build a butanol production pathway in a photoautotrophic bacterium, Rhodopseudomonas palustris TIE-1(TIE-1). TIE-1 is very metabolically versatile⁴. To begin with, R. palustris TIE-1 can grow either autotrophically or heterotrophically, using light as an energy source⁴. Unlike algae and cyanobacteria, TIE-1 can use many different sources of electrons (e.g., hydrogen, Fe (II), a poised electrode) and nitrogen for photoautotrophy⁴,⁵ and n-butanol production. In addition to this metabolic diversity, TIE-1 can fix carbon dioxide without generating oxygen⁴, which has been proved to be harmful to the bio-butanol production pathway⁶. By introducing a synthetic pathway with codon-optimized genes into TIE-1, we showed that n-butanol can be produced from TIE-1 under various growth conditions. Among these growth conditions, the most attractive one is using electricity (generated using solar energy) as the electron source, carbon dioxide (CO₂) as the carbon source and dinitrogen gas (N₂) as the nitrogen source. Under this growth condition, all the substrates we use are from renewable and abundant resources, making it a very attractive sustainable bioproduction platform. To improve the butanol production, we generated a genetic mutants in genes that encode critical enzymes that act as potential electron sinks. By calculating the carbon conversion rate and the electron conversion rate of each mutant under different growth conditions, we conclude that all the photoautotrophic conditions tested are more efficient for butanol production and that electron availability is crucial for butanol production in TIE-1.

References:

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