Impact of membrane gene overexpression on endoglucanase secretion in ruminal cellulolytic Escherichia coli

Various protein secretion systems of gram-negative Escherichia coli ( E. coli ) are well known, but the secretion pathway of endoglucanase (BcsZ) is unknown. To further elucidate the secretion mechanism, we analyzed the transcriptome data of five ruminal cellulolytic E. coli strains. Gene Ontology (GO) enrichment analysis revealed that the differentially expressed genes (DEGs) upregulated in all five strains were significantly enriched in the membrane. Nine DEGs related to membrane transporters were overexpressed in E. coli JBZ-DH5α (overexpressing BcsZ in the genome of E. coli DH5α). The results revealed that the overexpression of the b4332 ( yjiJ ), b2142 ( yohK ), and b2377 ( yfdY ) genes significantly reduced the growth and BcsZ concentration of the strain. The overexpression of the genes b3533 ( bcsA ), b3009 ( yghB ), and b3522 ( yhjD ) did not significantly affect strain growth or the BcsZ concentration. The overexpression of the b1859 ( znuB ), b0458 ( ylaC ), and b1195 ( ymgE ) genes increased the secretion of BcsZ but had no significant effect on strain growth. In conclusion, the yjiJ , yohK , yfdY , znuB , ylaC , and ymgE genes are involved in the secretion of E. coli BcsZ. These findings provide insight into the secretion mechanism of E. coli BcsZ.