Continuous enrichment strategies for biobutanol production

New national and international policies are pushing for a more sustainable production landscape. Once seen as waste, many resources are now the focus of valorization and recovery [1]. Mixed culture biotechnology is held as promising solution for producing valuable biofuels and chemicals from such low-value substrates and waste streams [2]. In this context, butanol is a biofuel of particular attention. With an energy density 50% higher than ethanol and properties similar to gasoline, it is a qualified substitute for fossil transport fuels [3]. Biobutanol is currently produced by Clostridia pure cultures with strict glucose requirement [4]. However, reports from Junicke et al. [5] and Steinbusch et al. [6] lead to suggest an alternative production pathway using butyrate and hydrogen as the sole substrates and with an improved environmental balance.
This work presents a novel strategy for butanol production based on microbial mixed cultures. Starting from non-defined methanogenic communities fed on butyrate and hydrogen, butanol-producing microorganisms are enriched through directed ecological selection in a continuously stirred tank reactor. Defined operating conditions are key to obtaining a stable microbial population of desired function and suitable design criteria are discussed. This strategy is entirely different from the pure culture approach as it engineers the environment rather than the organism. Key advantages include the absence of contamination risks and the ability to use low-value feedstock for the recovery of valuable chemicals such as butanol. The presented work thus contributes to a wider adoption of sustainable production concepts in a circular economy.