My lab addresses the process of bacterial cell cycle progression and its modification in response to a variety of cues. As a model system, we study the Gram-negative bacterium Sinorhizobium meliloti, which establishes a nitrogen-fixing symbiosis within the roots of leguminous plants. S. meliloti gain entry to host tissues, are endocytosed, and then establish a persistent infection within the host cell cytoplasm where they differentiate into a morphologically distinct 澱acteroidform uniquely capable of nitrogen fixation. One remarkable aspect of bacteroid differentiation is a filamentous cell morphology that is accompanied by several rounds of genomic endoreduplication. This is a particularly striking observation given that S. meliloti appears to strictly limit the initiation of DNA replication to once per cell cycle during free-living growth. My lab is interested in determining the molecular events that underlie the choice cells make during exit from S-phase as they transition into either G2-phase (during free-living growth), back to G1-phase (during bacteroid endoreduplication) or into G0-phase as they finally exit the cell cycle during terminal bacteroid differentiation. To this end, my lab is characterizing several components of the cell cycle regulatory pathway whose function is also required for symbiosis.