The atypical quorum sensing system of classical <i>Brucella</i> species

<i>Brucella</i> species are notorious pathogens of animals and humans and cause significant morbidity and economic losses globally. These hardy bacteria have evolved to survive and replicate in host cells, particularly macrophages, and have developed a specialized quorum sensing system that is essential for navigating intracellular life. Moreover, successful infection of the host is dependent upon elements of the <i>Brucella</i> quorum sensing system. While quorum sensing is a thoroughly well-defined process in many Gram-negative bacteria, several unique features in the quorum sensing pathway have evolved that set <i>Brucella</i> apart from more established model organisms. The current review is aimed at describing the paradigmatic aspects of <i>Brucella</i> quorum sensing, while also underscoring the nuance and distinctiveness of quorum sensing in the brucellae, and we discuss important questions that remain unanswered in the field.