Functional Characterization of Acinetobacter baumannii Lacking the RNA Chaperone Hfq

Abstract

The RNA chaperone Hfq is involved in the riboregulation of diverse genes via small RNAs. Recent studies have demonstrated that Hfq contributes to the stress response and the virulence of several pathogens, and the roles of Hfq vary among bacterial species. Here, we attempted to elucidate the role of Hfq in <i>Acinetobacter baumannii</i> ATCC 17978. In the absence of <i>hfq</i>, <i>A. baumannii</i> exhibited retarded cell growth and was highly sensitive to environmental stress, including osmotic and oxidative pressure, pH, and temperature. Compared to the wild-type, the Hfq mutant had reduced outer membrane vesicles secretion and fimbriae production as visualized by atomic force microscopy. The absence of <i>hfq</i> reduced biofilm formation, airway epithelial cell adhesion and invasion, and survival in macrophage. Further, the <i>hfq</i> mutant induced significantly higher IL-8 levels in airway epithelial cells, which would promote bacterial clearance by the host. In addition to results similar to those reported for other bacteria, our findings demonstrate that Hfq is required in the regulation of the iron-acquisition system via downregulating the <i>bauA</i> and <i>basD</i> genes, the stress-related outer membrane proteins <i>carO</i>, <i>A1S_0820</i>, <i>ompA</i>, and <i>nlpE</i>, and the stress-related cytosolic proteins <i>uspA</i> and <i>groEL</i>. Our data indicate that Hfq plays a critical role in environmental adaptation and virulence in <i>A. baumannii</i> by modulating stress responses, surface architectures, and virulence factors. This study is the first to illustrate the functional role of Hfq in <i>A. baumannii.</i>