RNA chaperone that binds small regulatory RNA (sRNAs) and mRNAs to facilitate mRNA translational regulation in response to envelope stress, environmental stress and changes in metabolite concentrations. Also binds with high specificity to tRNAs (By similarity). Plays a central regulatory role in the microbial response to space flight conditions. Is essential for virulence and is required for efficient invasion of non-phagocytic cells. Homohexamer. Cells display drastically reduced virulence in vitro and in vivo. Mice infected with the deletion mutant show no signs of illness during the course of the experiment. This suggests that the mutation results in defects in either invasion of intestinal epithelial cells, macrophage survival, or both. Hfq expression was decreased during the space flight and expression of 64 genes of the hfq regulon was altered. Likewise, several small RNAs that interact with hfq were differentially regulated during the flight (PubMed:17901201). Belongs to the Hfq family.