Applied Microbiology and Beneficial Microbes

Biography

Biography: Tian Jin

Abstract

How eukaryotic cells find and interact with bacteria is a fundamental question in biology.  Eukaryotic phagocytes and their interactions with bacteria began when single-celled life forms, protozoans, appeared about 2.5 billion years ago. Since then, multicellular organisms endowed with increasingly complex genomes gradually formed, and phagocytic cells from these organisms, such as invertebrates and vertebrates, patrol in a host body to detect, recognize, and eliminate invading pathogenic bacteria for host immunity. The current dogma is that phagocytic cells use at least two types of receptors for defense against invading pathogens: one for detecting and chasing pathogens via chemotaxis and another for recognizing and eliminating them via phagocytosis. Detection and chasing is facilitated by G-protein-coupled-receptors which sense diffusible chemoattractants derived from bacteria. Recognition and elimination employs pattern-recognition receptors (PRRs), such as Toll-like receptors, for recognizing microbial-associated molecular pattern (MAMPs) and/or phagocytic receptors for bacterial surface-bound complements or immunoglobulins. However, the social amoeba Dictyostelium discoideum does not encode orthologs of any known PRRs or phagocytic receptors; yet, they are highly evolved as professional phagocytes that chase bacteria via chemotaxis and consume them as food through phagocytosis. We find that this stereotypical phagocyte, breaking the dogma, assembles a simple and elegant molecular machinery to detect a diffusible chemoattractant and recognize an immobile component on the bacterial coat for both chasing and engulfing bacteria.  Our studies on the social amoeba Dictyostelium discoideum sheds new light on the origin of bacterial recognition by eukaryotic phagocytes, the path through which PRRs evolved, and the unexpectedly close mechanistic connection between chemotaxis and phagocytosis.