AUTHOR=Li Duan You , Liu Ying Li , Liao Xiao Jian , He Tian Tian , Sun Shan Shan , Nie Pin , Xie Hai Xia 

TITLE=Identification and Characterization of EvpQ, a Novel T6SS Effector Encoded on a Mobile Genetic Element in Edwardsiella piscicida

JOURNAL=Frontiers in Microbiology

VOLUME=12

YEAR=2021

URL=https://www.frontiersin.org/journals/microbiology/articles/10.3389/fmicb.2021.643498

DOI=10.3389/fmicb.2021.643498

ISSN=1664-302X

ABSTRACT=<p>In this study, a hypothetical protein (ORF02740) secreted by <italic>Edwardsiella piscicida</italic> was identified. We renamed the ORF02740 protein as EvpQ, which is encoded by a mobile genetic element (MGE) in <italic>E. piscicida</italic> genome. The <italic>evpQ</italic> gene is spaced by 513 genes from type VI secretion system (T6SS) gene cluster. Low GC content, three tRNA, and three transposase genes nearby <italic>evpQ</italic> define this MGE that <italic>evpQ</italic> localizes as a genomic island. Sequence analysis reveals that EvpQ shares a conserved domain of C70 family cysteine protease and shares 23.91% identity with T3SS effector AvrRpt2 of phytopathogenic <italic>Erwinia amylovora.</italic> Instead, EvpQ of <italic>E. piscicida</italic> is proved to be secreted at a T6SS-dependent manner, and it can be translocated into host cells. EvpQ is thereof a novel T6SS effector. Significantly decreased competitive index of Δ<italic>evpQ</italic> strain in blue gourami fish (0.53 ± 0.27 in head kidney and 0.44 ± 0.19 in spleen) indicates that EvpQ contributes to the pathogenesis of <italic>E. piscicida</italic>. At 8-, 18-, and 24-h post-subculture into DMEM, the transcription of <italic>evpQ</italic> was found to be negatively regulated by Fur and positively regulated by EsrC, and the steady-state protein levels of EvpQ are negatively controlled by RpoS. Our study lays a foundation for further understanding the pathogenic role of T6SS in edwardsiellosis.</p>