Research Article: Type VI secretion system contributes to Enterohemorrhagic Escherichia coli virulence by secreting catalase against host reactive oxygen species (ROS)

Date Published: March 13, 2017

Publisher: Public Library of Science

Author(s): Baoshan Wan, Qiufen Zhang, Jinjing Ni, Shuxian Li, Donghua Wen, Jun Li, Haihan Xiao, Ping He, Hong-yu Ou, Jing Tao, Qihui Teng, Jie Lu, Wenjuan Wu, Yu-Feng Yao, Dario S. Zamboni.


Enterohemorrhagic Escherichia coli (EHEC) is one major type of contagious and foodborne pathogens. The type VI secretion system (T6SS) has been shown to be involved in the bacterial pathogenicity and bacteria-bacteria competition. Here, we show that EHEC could secrete a novel effector KatN, a Mn-containing catalase, in a T6SS-dependent manner. Expression of katN is promoted by RpoS and OxyR and repressed by H-NS, and katN contributes to bacterial growth under oxidative stress in vitro. KatN could be secreted into host cell cytosol after EHEC is phagocytized by macrophage, which leads to decreased level of intracellular reactive oxygen species (ROS) and facilitates the intramacrophage survival of EHEC. Finally, animal model results show that the deletion mutant of T6SS was attenuated in virulence compared with the wild type strain, while the deletion mutant of katN had comparable virulence to the wild type strain. Taken together, our findings suggest that EHEC could sense oxidative stress in phagosome and decrease the host cell ROS by secreting catalase KatN to facilitate its survival in the host cells.

Partial Text

Enterohemorrhagic Escherichia coli (EHEC) is a globally important zoonotic pathogen capable of causing diarrhea, hemorrhagic colitis and hemolytic–uremic syndrome (HUS) [1]. A prominent feature of EHEC infection is its low infectious dose. A dose of 50–100 colony forming units (CFUs) of EHEC is sufficient to cause disease in healthy individuals [2]. EHEC consists of multiple serotypes, among which O157:H7 is the one most commonly linked to epidemic and sporadic diseases in humans throughout China, Japan, North America, and Europe.

T6SS has been shown to be widely distributed in up to 25% of Gram-negative bacteria [21]. Although most of these bacteria possess only one single T6SS gene cluster, some species harbor multiple distinct T6SS copies. For example, five phylogenetically distinct T6SS loci have been identified in S. enterica [52], Burkholderia pseudomallei and Burkholderia thailandensis display six and five T6SSs, respectively [53], and P. aeruginosa possesses three T6SS clusters [54]. The distribution and copy number of T6SS in E. coli are various. APEC and EAEC contain up to 3 phylogenetically distinct T6SS clusters [55], while UPEC strain CFT037 only harbors one set of T6SS locus. There is one T6SS gene cluster in EHEC strains of Sakai and EDL933. Although the number of T6SS gene cluster is identical in UPEC and EHEC, the sequence and organization of their T6SS genes are distinct, suggesting the origin of T6SS is highly complicated.




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