Virulent phase separation in Mycobacterium tuberculosis Protein phosphorylation is a principal mechanism by which Mycobacterium tuberculosis (Mtb) translates extracellular environmental stimuli into cellular responses. In a recent break-through, we discovered that the N-terminal cytoplasmic portion of the Mtb ATP-binding cassette (ABC) transporter Rv1747 undergoes phosphorylation-enhanced phase separation. That is, the isolated protein fragment forms dynamic "liquid droplets" in vitro upon phosphorylation by Mtb kinases. Key to this phenomenon are weak multivalent interactions between two phosphothreonine (pThr)-binding Forkhead-associated (FHA) domains with at least two phospho-acceptor threonines in an intervening intrinsically disordered (ID) linker; collectively these form the postulated regulatory module of Rv1747. In this seminar, I will discuss our biophysical characterization of the regulatory module, including defining its phase diagram for droplet formation in solution and in the context of a model membrane system. I will also present our most recent studies to ascertain the biological role of Rv1747 phase separation in Mtb using super-resolution STORM microscopy.