Intracellular accumulation of c-di-GMP and its regulation on self-flocculation of the bacterial cells from Zymomonas mobilis
Kai Li, Juan Xia, Chen-Guang Liu*, Feng-Wu Bai11*Corresponding authors. E-mails: cg.liu@sjtu.edu.cn (C. G. Liu) and fwbai@sjtu.edu.cn (F. W. Bai)
State Key Laboratory of Microbial Metabolism, Joint International Research Laboratory of Metabolic & Developmental Sciences, School of Life Sciences and Biotechnology, Shanghai Jiao Tong University, Shanghai 200240, China.
Abstract:Zymomonas mobilis  is an emerging chassis engineered to produce bulk products because of its glycolysis through the Entner-Doudoroff pathway, with less ATP produced for lower biomass accumulation and higher yields with targeted products. When self-flocculated, the bacterial cells are more productive and tolerant to stresses for high product titers, but this morphology needs to be controlled properly to avoid internal mass transfer limitations associated with strong flocculation. In this study, we explored the regulation of cyclic diguanosine monophosphate (c-di-GMP) on self-flocculation of bacterial cells through cellulose biosynthesis. While ZMO1365 and ZMO0919, with GGDEF domains for diguanylate cyclase activities, catalyze c-di-GMP biosynthesis, ZMO1487, with an EAL domain for phosphodiesterase activity, catalyzes c-di-GMP degradation, but ZMO1055 and ZMO0401 contain dual domains with phosphodiesterase activities. Since c-di-GMP is synthesized from GTP, the intracellular accumulation of this signal molecule by deactivating the activity of phosphodiesterase is preferred for activating cellulose biosynthesis to flocculate bacterial cells, since such a strategy exerts less perturbation on intracellular processes regulated by GTP. These discoveries are significant not only for engineering unicellular Z. mobilis  strains with a self-flocculating morphology to boost production but also for understanding the mechanism underlying c-di-GMP biosynthesis and degradation in the bacterium.
Keywords: Zymomonas mobilis ; chassis; self-flocculation; c-di-GMP; microbial cell factories; industrial production