Effects of feeding strategy on cathodic electro-fermentation of xylose with mixed microbial cultures

Xylose fermentation is sometimes hindered by unbalanced redox states, limiting its efficiency in industrial biotechnology applications. Recent advancements in cathodic electro-fermentation (CEF) technologies have addressed this issue by regulating the metabolic states of microorganisms and modulating intercellular electron transfer using a cathode electrode. However, the feasibility of mixed culture CEF using xylose as the feedstock has not been studied. This study investigated feeding strategies in mixed culture CEF systems to enhance the production rates and yields of carboxylic acids, namely propionate and butyrate, using xylose as the substrate over runs lasting ca. 25 days. The results compared the repeated batch and continuous cathodic electrofermentation systems (poised cathode potential -0.40 V vs. standard hydrogen electrode) and analyzed their microbial community compositions. The repeated batch CEF systems demonstrated rapid and consistent steered metabolism towards propionate and butyrate, achieving higher yields for propionate (1.57-fold) and butyrate (1.64-fold) compared to the open-circuit controls. In contrast, continuous systems did not exhibit cathodeassisted metabolism. The microbial community analyses suggested that Clostridium, in both biofilm and planktonic cells, played a pivotal role in cathodic xylose electro-fermentation. These findings highlight the potential of repeated batch CEF systems for enhancing carboxylic acid production.