Abstract

Bacterial fruit blotch (BFB), caused byAcidovorax citrulli, severely damages watermelon, melon, and other cucurbit crops worldwide. Nitrogen, one of the most important limiting elements in the environment, is necessary for the growth and reproduction of bacteria. As a nitrogen-regulating gene,ntrCplays an important role in maintaining bacterial nitrogen utilization and biological nitrogen fixation. However, the role ofntrChas not been determined forA. citrulli. In this study, we constructed antrCdeletion mutant and a corresponding complementary strain in the background of theA. citrulliwild-type strain, Aac5. Through phenotype assays and qRT-PCR analysis, we investigated the role ofntrCinA. citrulliin nitrogen utilization, stress tolerance, and virulence against watermelon seedlings. Our results showed that theA. citrulliAac5ntrCdeletion mutant lost the ability to utilize nitrate. ThentrCmutant strain also exhibited significantly decreased virulence, in vitro growth, in vivo colonization ability, swimming motility, and twitching motility. In contrast, it displayed significantly enhanced biofilm formation and tolerance to stress induced by oxygen, high salt, and copper ions. The qRT-PCR results showed that the nitrate utilization genenasS; the Type III secretion system-related geneshrpE, hrpX, andhrcJ; and the pili-related genepilAwere significantly downregulated in thentrCdeletion mutant. The nitrate utilization genenasT, and the flagellum-related genesflhD, flhC, fliA, andfliCwere significantly upregulated in thentrCdeletion mutant. The expression levels ofntrCgene in the MMX-q and XVM2 media were significantly higher than in the KB medium. These results suggest that thentrCgene plays a pivotal role in the nitrogen utilization, stress tolerance, and virulence ofA. citrulli.Keywords:Acidovorax citrulli;ntrC;virulence;nitrogen;nitrate;stress