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). Contributes to long-term survival under nutrient deprivation, to stationary phase-dependent hydrogen peroxide and acid stress resistance and is required for prolonged survival in the intracellular environment of the host macrophage. Therefore, contributes not only to a generalized stress response in stationary phase but also to pathogenesis in mice, allowing the brucellae to adapt to the harsh conditions encountered within macrophages. Cells show increased sensitivity to hydrogen peroxide and decreased survival at pH 4.0 during stationary phase growth. It is less able to withstand prolonged starvation. It fails to replicate in cultured murine macrophages and is completely cleared from spleens and livers of infected mice 10 weeks after infection. Belongs to the Hfq family.