Butyric acid generation by clostridium tyrobutyricum from low moisture anhydrous ammonia (LMAA) pretreated sweet sorghum bagasse

Authors: Stoklosa, Ryan; MOORE, CARRINGTON - Clemson University; Latona, Renee; Nghiem, Nhuan

Submitted to: Applied Biochemistry and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/8/2020
Publication Date: 3/1/2021
Citation: Stoklosa, R.J., Moore, C., Latona, R.J., Nghiem, N.P. 2021. Butyric acid generation by clostridium tyrobutyricum from low moisture anhydrous ammonia (LMAA) pretreated sweet sorghum bagasse. Applied Biochemistry and Biotechnology. 193(3):761-776. https://doi.org/10.1007/s12010-020-03449-w.
DOI: https://doi.org/10.1007/s12010-020-03449-w

Interpretive Summary: The agricultural feedstock sweet sorghum is similar to sugarcane. Sweet sorghum that is crushed produces liquid juice with high contents of fermentable sugars, while the leftover stalks (known as bagasse) are a valuable co-product for other applications. Recovered sweet sorghum bagasse (SSB) is an attractive feedstock for biochemical conversion processes that produce biofuels or high-value chemicals. In this work SSB was pretreated using ammonia and the resulting sugars obtained after pretreatment were fermented to butyric acid by the microbial strain Clostridium tyrobutyricum. The chemical butyric acid is considered a promising product that can be produced by fermentation and applied to a wide range of industries such as pharmaceuticals or for the production of liquid transportation fuels. Media containing dissolved glucose and xylose with supplemented nitrogen showed that butyric acid output was achieved compared to media without nitrogen. The fermentable sugars from pretreated SSB after detoxification produced up to 11.38 g/L of butyric acid. Larger volume fermentation trials were conducted on the fermentable sugars from SSB. At larger fermentation scale with pH control a similar output of butyric acid at 11.3 g/L was achieved. However, the butyric acid productivity increased, and the overall butyric acid yield compared to lower volume fermentation without pH control. Improvements in butyric acid output can be achieved with processing options such as fed-batch fermentation.

Technical Abstract: Sweet sorghum bagasse (SSB) is an under-utilized feedstock that can contribute to an expansion of the bioeconomy for the production of biofuels or high value chemicals. One such chemical that can be produced biochemically and applied to a wide array of industries from pharmaceuticals to production of liquid transportation fuels is butyric acid. This work investigated cultivating the butyric acid producing strain Clostridium tyrobutyricum ATCC 25755 on low moisture anhydrous ammonia (LMAA) pretreated SSB. Defined media with supplemented urea indicated that butyric acid output could be increased compared to defined media without urea. Pretreated SSB hydrolysate was detoxified and supplemented with urea to show that up to 11.38 g/L butyric acid could be produced with a selectivity of 87% compared to other organic acids. Bioreactor fermentation with pH control showed high biomass growth, but a similar output of 11.3 g/L butyric acid was achieved. However, the butyric acid productivity increased to 0.251 g/L·hr with a butyric acid yield of 0.350 g/g sugar consumed. In order to improve butyric acid fermentation of pretreated SSB processing options such as fed-batch operations should be considered.