The different roles of hcp 1 and hcp 2 of the type VI secretion system in Escherichia coli strain CE129.

Type VI secretion system (T6SS) is a secretory system found in Gram-negative bacteria. One of the main structures for T6SS is Hcp (hemolysin co-regulation protein) pipeline. To investigate the role of Hcp major sub-unit genes hcp(1) and hcp(2), we deleted hcp(1) and hcp(2) genes for constructing the in-frame gene deletion mutants. The properties of biofilm formation and the adhesion to chicken embryo fibroblasts cells (DF1 cells) were reduced in the hcp(2) mutant. The knockout of hcp(1) and hcp(2) genes reduced the ability of the avian pathogenic Escherichia coli (APEC) strain CE129 to infect developing chicken embryos. The expression of quorum sensing (QS)-associated genes luxS, lsrR, and pfs were down-regulated in the hcp(1) mutant, and the expression of type 1 fimbriae gene fimA and the adhesion-related genes fimC and papC were decreased in the hcp(2) mutant, as well as the expression of anti-serum survival factor genes ompA and iss were inhibited in both hcp(1) and hcp(2) mutants. These results described above from this study help to further elaborate the role of HCP in APEC.