Intracellular accumulation of c-di-GMP and its regulation on
self-flocculation of the bacterial cells from Zymomonas mobilis
Abstract
Zymomonas mobilis is an emerging chassis for being engineered to
produce bulk products due to 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 limitation associated with strong flocculation.
Herewith we explored the regulation of cyclic diguanosine monophosphate
(c-di-GMP) on self-flocculation of the 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 activities catalyzes c-di-GMP
degradation, but ZMO1055 and ZMO0401 contain the dual domains with
phosphodiesterase activities predominated. Since c-di-GMP is synthesized
from GTP, the intracellular accumulation of this signal molecule through
deactivating the activity of phosphodiesterase is preferred for
activating cellulose biosynthesis to flocculate the bacterial cells,
since such a strategy exerts less perturbance on intracellular processes
regulated by GTP. These discoveries are significant not only for
engineering unicellular Z. mobilis strains with the
self-flocculating morphology to boost production, but also for
understanding mechanism underlying c-di-GMP biosynthesis and degradation
in the bacterium.