UC Berkeley

Of the three domains of life, bacteria are by far the most ancient and most diverse.Bacteria thus have evolved creative and varied solutions to different biochemical, structural, and cellular problems. One representation of this diversity is the catalog of different intracellular compartments that bacterial species produce to store excess nutrients, make biochemical reactions more efficient, and/or coordinate cellular processes. The number of bacterial organelles identified has greatly expanded in the last few decades, owing to the development of high-resolution imaging technology. However, many questions regarding the cell biology of these organelles still remain unanswered. How does the bacterial cell regulate the production and function of their organelles? What mechanisms are in place to control the spatial distribution of organelles, and are there any similarities to those in eukaryotic systems? In species that produce multiple types of compartments, is there any coordination in their activity? To address these unknowns, this dissertation features new research that advances our knowledge of how magnetotactic bacteria (MTB) organize their organelles. I start with a literature review of known organelle positioning systems in Chapter 1. The best-studied models of bacterial organelle localization - featuring the carboxysome and the magnetosome - are discussed in detail. Additionally, the current knowledge on the organization of polyhydroxybutyrate and polyphosphate granules is discussed. This chapter also explores the future outlook on the bacterial organelle biology field. Chapter 2 features original research conducted to understand how magnetosomes, lipid membrane-bound compartments where a magnetite crystal is biomineralized [3], are organized in MTB. I focus on how two proteins, McaA and McaB, create subchains of magnetite in the model MTB Magnetospirillum magneticum AMB-1. Using biochemical and microscopy methods, we discovered that McaA and McaB control the dynamics of a bacterial actin-like protein MamK to arrange magnetosomes into a complex pattern.Chapter 3 contains the preliminary findings of how different organelles may be co-regulated in bacteria. In eukaryotic cells, many organelles undergo interorganelle communication to coordinate their activity and physical position in the cell [4–6]. To uncover whether bacteria also have interorganelle communication, we tested whether the absence of any magnetosome genes impacts a second organelle, the polyhydroxybutyrate granule (PHBG). We discovered that MamA regulates both the total number of magnetite crystals in a cell and PHBG size. We use biochemical and genetic experiments to characterize the PHBG and its relationship with MamA. This work provides the foundation for further studies on how magnetosomes and PHBGs are coordinated by a single protein in MTB. Finally, Chapter 4 summarizes the work and states the major conclusions of this thesis. I finish with how this work contributes to the field of bacterial cell biology and directions for future studies in this area.