Biological membranes organize cellular life, from compartmentalizing specialized biochemistry within a single cell to demarking the cell’s very boundary within an organism. No less central are the controlled manipulations of membranes, i.e. their deformation, fission, and fusion. I study the least understood of these, membrane fission, using B. subtilis sporulation as a model system.
Upon environmental stress B. subtilis and most other gram-positive bacteria, including () B. anthracis and C. difficile, transition to a long-lived, metabolically inert state called a “spore”. Spore formation, or “sporulation”, proceeds through a unique, ordered developmental pathway host to several membrane transformations outlined below.
(1) Asymmetric cell division – membrane fission to separate daughter cells – to produce a “mother cell” and prosprective spore cell pair, followed by
(2) forespore engulfment as the mother cell membrane wraps the prospective spore, also known as a “forespore”, and
(3) release of the forespore into the mother cell cytoplasm, which marks completion of engulfment. Like the mammalian processes of endocytosis, multivesicular body biogenesis, and autophagy which sequester cargo into a membrane-bound vesicle, forespore internalization too relies on membrane fission.
The FisB protein has been implicated by the Karatekin and Rudner labs in this last fission step; its mechanism of action is the subject of my research. Through a combination of approaches, including step photo-bleaching, quantitative western blotting, and in vivo fluorescence standards, I aim to determine absolute FisB protein copy number at discrete sites in the cell. Paired with biochemistry from other members of the Karatekin group, my data will inform a descriptive model of FisB’s dynamics during sporulation, and shed light on FisB’s contribution to the mechanism of membrane fission.