Kit J. Pogliano
Department of Biology
University of California, San Diego
9500 Gilman Drive, 0349
La Jolla, CA 92093-0349
1998 Searle Scholar
Phagocytosis and Sporulation in Bascillus subtilis
Bacillus subtilis is a gram positive bacterium with a simple developmental pathway leading to spore formation under conditions of nutrient limitation. Shortly after the formation of the two cells required for spore formation, the septum between them begins to migrate around the forespore, ultimately pinching it off as a free protoplast within the mother-cell cytoplasm (see Figure 1). This process, known as engulfment, demonstrates that B. subtilis is capable of moving macromolecules (in this case the cell envelope) from one region of the cell to another. Such abilities are not normally considered part of the bacterial repertoire, but it has recently been recognized that bacterial chromosomes are actively pulled apart prior to division, suggesting the existence of a mitotic apparatus in bacteria. The nature of this apparatus, like that used to drive the phagocytosis-like process of engulfment, is entirely unclear.
My lab seeks to understand the mechanism of engulfment, as a model system for understanding how bacteria move macromolecules within their cells. We have developed methods to allow the observation of engulfment in living bacteria (Figure 1). Our research is focused on three main questions: What is the mechanism of engulfment? A crucial first step towards understanding the mechanism of engulfment is the identification of the proteins required for engulfment, a careful dissection of the effects of their absence, and the identification of proteins with which they interact. We are therefore searching for additional engulfment proteins using both genetic and biochemical approaches.
How do bacteria catalyze membrane fusion? The final step of engulfment is the fusion of the engulfing membranes at the distal side of the forespore. We have developed an in vivo assay for membrane fusion during engulfment, and have isolated mutants that inhibit membrane fusion. We predict that in bacterial cells, as in eukaryotic cells, membrane fusion will be both tightly regulated and catalyzed.
How are bacterial cells organized? Subcellular protein targeting is crucial for many essential processes in bacteria, and is also crucial for engulfment. We are investigating the subcellular localization of engulfment and membrane fusion proteins.
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