AcfA Regulates the Virulence and Cell Envelope Stress Response of Vibrio parahaemolyticus

<i>Vibrio parahaemolyticus</i> is a ubiquitous inhabitant of estuarine and marine environments that causes vibriosis in aquatic animals and food poisoning in humans. Accessory colonizing factor (ACF) is employed by <i>Vibrio</i> to assist in the colonization and invasion of host cells leading to subsequent illnesses. In this work, Δ<i>acfA</i>, an in-frame deletion mutant strain lacking the 4th to the 645th nucleotides of the open reading frame (ORF) of the <i>acfA</i> gene, and the complementary strain <i>acfA</i>⁺ were constructed to decipher the function of AcfA in <i>V. parahaemolyticus</i>. The deletion of <i>acfA</i> had no effect on bacterial growth but resulted in a significant reduction in biofilm formation, hemolytic activity, mucus adhesion, and the accumulated mortality of zebrafish, compared to the wild-type strain and the complementary strain <i>acfA</i>⁺. Additionally, AcfA was involved in adapting to stressors, such as H₂O₂, EDTA, and acid, in <i>V. parahaemolyticus</i>. Furthermore, RNA-Seq transcriptome analysis was conducted to identify global gene transcription alterations resulting from deletion of the <i>acfA</i> gene. A total of 416 differentially expressed genes were identified in the Δ<i>acfA</i> vs. wild-type comparison, with 238 up-regulated genes and 178 down-regulated genes. The expression of genes associated with the type III secretion system, type VI secretion system, and oligopeptide permeases system were significantly reduced, and yet the expression of genes associated with cell envelope biosynthesis and response regulation system were enhanced dramatically in the absence of the <i>acfA</i> gene compared to the wild-type strain. These findings suggest that AcfA may play a role in the overall success of pathogenesis and the cell envelope stress response of <i>V. parahaemolyticus</i>.