Development of a self-flocculating Zymomonas mobilis biocatalyst for efficient bioethanol production from lignocellulosic biomass

Jung, Won-Gyeom; Lim, Jung-In; Choi, Seong Seok; Heo, Hye-Sook; Jang, Mi-Seon; Tsang, Yiu Fai; Jeon, Young Jae

doi:.0..

DOI: https://doi.org/10.4491/eer.2025.223

Development of a self-flocculating Zymomonas mobilis biocatalyst for efficient bioethanol production from lignocellulosic biomass

Won-Gyeom Jung¹, Jung-In Lim¹, Seong Seok Choi^1,2, Hye-Sook Heo¹, Mi-Seon Jang¹, Yiu Fai Tsang³, and Young Jae Jeon^1,4^†

¹Department of Microbiology, Pukyong National University, Busan 48513, Republic of Korea
²Industry-University Cooperation Foundation, Pukyong National University, Busan 48513, Republic of Korea
³Department of Science and Environmental Studies and State Key Laboratory in Marine Pollution, The Education University of Hong Kong, Tai po, New Territories 999077, Hong Kong Special Administrative Region
⁴School of Marine and Fisheries Life Science, Pukyong National University, Busan 48513, Republic of Korea

Corresponding Author: Young Jae Jeon ,Tel: +82-51-629-5612, Fax: +82-51-629-5619, Email: youngjaejeon@pknu.ac.kr

Received: April 24, 2025; Accepted: May 8, 2025.

ABSTRACT

Flocculation represents a promising biological strategy to enhance biomass recovery and improve process efficiency in bioethanol production. In this study, we engineered a self-flocculating strain of Zymomonas mobilis, designated ZAM2, by inactivating the EAL domain (phosphodiesterase region) of the regulatory gene ZMO_1055. This targeted genetic modification led to enhanced cell aggregation and improved stress tolerance against common fermentation inhibitors, including acetic acid, furfural, and vanillin, which are typically generated during lignocellulosic biomass pretreatment. Compared to its parental strain ZM401, ZAM2 accumulated higher levels of intracellular c-di-GMP, exhibited reduced PDE activity, and upregulated cellulose biosynthesis genes. These changes contributed to enlarged floc size and superior fermentation performance. Notably, ZAM2 completed glucose consumption and ethanol production more rapidly than ZM401 under inhibitor-rich conditions, resulting in increased ethanol productivity. Our results demonstrate a rational genetic strategy for enhancing microbial robustness and process efficiency, offering a viable approach for sustainable, high-gravity bioethanol fermentation from lignocellulosic feedstocks.

Keywords: c-di-GMP signaling | EAL domain inactivation | Lignocellulosic ethanol fermentation | Self-flocculation | Zymomonas mobilis