Enhancing Secretion of Endoglucanase in Zymomonas mobilis by Disturbing Peptidoglycan Synthesis.

Zymomonas mobilis (Z. mobilis) is a potential candidate strain for consolidated bioprocessing (CBP) in lignocellulosic biorefinery. However, the low-level secretion of cellulases limits this CBP process, and the mechanism of protein secretion that is affected by cell wall peptidoglycan is also not well understood. Here, we constructed several penicillin-binding protein (PBP)-deficient strains derived from Z. mobilis S192 to perturb the cell wall peptidoglycan network and then investigated the effects of peptidoglycan on the endoglucanase secretion. The results showed that extracellular recombinant endoglucanase production was significantly enhanced in PBP mutant strains, notably, Δ1089/0959 (4.09-fold) and Δ0959 (5.76-fold) in comparison to parent strains. For PBP-deficient strains, the growth performance was not significantly inhibited, but cell morphology was altered. In addition, enhanced antibiotic sensitivity and reduced inhibitor tolerance were also detected in our study. The concentration of intracellular soluble peptidoglycan was increased, especially for single-gene deletion. Outer membrane permeability of PBP-deficient strains was also improved, notably, Δ1089/0959 (1.14-fold) and Δ0959 (1.07-fold), which might explain the increased endoglucanase extracellular secretion. Our findings indicated that PBP-deficient Z. mobilis was capable of increasing endoglucanase extracellular secretion via cell wall peptidoglycan disturbance, and it will provide a foundation for the development of CBP technology in Z. mobilis in the future.