The ultimate objectives of the proposed research are: i. to understand the hierarchical relationship between individual bacterial cell growth and the morphogenesis of multicellular bacterial macrofibers, and ii. to characterize the fiber state. Macrofibers are helical structures that twist and writhe as they grow and thus provide a unique opportunity to study fundamental aspects of twist and supercoiling. The health relatedness of these studies pertain to issues dealing with the behavior of DNA and chromosomes, to the use of twist and supercoiling as potential molecular motors in cells, and to the properties of multicellular bacterial states. There are seven specific aims all related to new discoveries: i. wire drag, and ii. micromanipulator approaches will be used to study half-fiber behavior and to measure forces associated with twist, supercoiling and motions associated with fiber self-assembly. Newly discovered fiber motions: iii. pivoting, and iv. walking will be characterized and their relationship to twist and writhe will be sought. v. The dragging of structures by macrofibers undergoing a twist to writhe conversion will be examined and the work accomplished measured. The power generated by fibers will be estimated and its relationship to fiber growth, and ultimately individual cell growth will be determined. vi. Macrofiber helix hand reversal will be studied in terms of structural constraints and the relationship of helix hand to pivoting, walking and dragging. vi. Two engineering and four modeling projects will be undertaken. Instruments that can measure forces associated with fiber motions will be designed and built. A dual-image microscope will be constructed for use in studying fiber motions that involve interactions with the floor of the growth chamber. Theory will focus on: fiber models that examine how the two halves of a fiber influence one another, examination of the significance of constraint on fiber morphogenesis caused by interactions with the floor of the growth chamber, the development of a theory of walking caused by twist and writhe, and the properties of a twist/writhe machine that can do work. All seven projects included in this proposal represent the continuation of lines of investigation underway currently in the laboratory using experimental approaches developed here. They build upon foundations established by our long term study of the bacterial macrofiber system and seek to consolidate what is know into a comprehensive overview of how the system works.
