Screening of Gas Substrate and Medium Effects on 2,3-Butanediol Production with C. ljungdahlii and C. autoethanogenum Aided by Improved Autotrophic Cultivation Technique

Gas fermentation by acetogens of the genus Clostridium is an attractive technology since it affords the production of biochemicals and biofuels from industrial waste gases while contributing to mitigate the carbon cycle alterations. The acetogenic model organisms C. ljungdahlii and C. autoethanogenum have already been used in large scale industrial fermentations. Among the natural products, ethanol production has already attained industrial scale. However, some acetogens are also natural producers of 2,3-butanediol (2,3-BDO), a platform chemical of relevant industrial interest. Here, we have developed a lab-scale screening campaign with the aim of enhancing 2,3-BDO production. Our study generated comparable data on growth and 2,3-BDO production of several batch gas fermentations using C. ljungdahlii and C. autoethanogenum grown on different gas substrates of primary applicative interest (CO2 center dot H-2, CO center dot CO2, syngas) and on different media featuring different compositions as regards trace metals, mineral elements and vitamins. CO center dot CO2 fermentation was found to be preferable for the production of 2,3-BDO, and a fair comparison of the strains cultivated in comparable conditions revealed that C. ljungdahlii produced 3.43-fold higher titer of 2,3-BDO compared to C. autoethanogenum. Screening of different medium compositions revealed that mineral elements, Zinc and Iron exert a major positive influence on 2,3-BDO titer and productivity. Moreover, the CO2 influence on CO fermentation was explored by characterizing C. ljungdahlii response with respect to different gas ratios in the CO center dot CO2 gas mixtures. The screening strategies undertaken in this study led to the production of 2.03 +/- 0.05 g/L of 2,3-BDO, which is unprecedented in serum bottle experiments.

Automated summary

Gas fermentation by acetogens of the genus Clostridium is a promising technology for producing biochemicals and biofuels from industrial waste gases. Among acetogenic organisms, C. ljungdahlii shows higher efficiency in producing 2,3-butanediol compared to C. autoethanogenum. The presence of mineral elements Zinc and Iron has a significant positive influence on the titer and productivity of 2,3-butanediol.