Despite their diminutive size and seemingly simple construction, bacteria lead remarkably complex lives. In order to fulfill their biological roles of growth and reproduction, they must integrate a wealth of information about their environment and, depending upon the suitability of the available conditions for survival, they can act to relocate themselves to more preferred locales. Doing so requires that bacteria be able to sense environmental stimuli and relay signals induced by those stimuli to various locomotive apparatuses. Once a cell has fulfilled its nutrient quota to support replication, cell division can occur. Cell division is also intricately timed and regulated in bacterial cells, which are now known to possess intracellular organization, cytoskeletal features, and, in some species, compartmentalization. Therefore, division of a bacterial cell must coordinate disassembly, reassortment, and segregation of these cell biological features. In this work, I investigate the connection between the cell cycle and bacterial organelle formation in the magnetotactic bacterium Magnetospirillum magneticum AMB-1. Magnetotactic bacteria, including AMB-1, are defined by their ability to synthesize chains of intracellular membrane-bounded magnetic minerals, which facilitate bacterial alignments with and responses to geomagnetic fields. To determine the role of the cell cycle in governing the production of these bacterial organelles, called magnetosomes, I disrupted homologs of regulatory factors known to control the progression of the cell cycle as well as polar organelle development in related Alphaproteobacteria. Surprisingly, mutants in the CtrA regulatory pathway were viable, indicating alternative mechanisms of cell cycle progression in AMB-1; in addition, magnetosome formation was also unaffected. Notably, motility was the only feature of AMB-1 disrupted by the CtrA pathway mutations. While subsequent studies to probe upstream regulators of motility in AMB-1 failed to yield additional insight, my results suggest a terminal role for CtrA in the transcription of flagellar biosynthesis genes. This role appears to be ancestral in the Alphaproteobacteria. Further, I have developed protocols which should enable future investigations of the cell cycle in AMB-1 and the temporal changes in gene expression which allow its progression. Preliminary studies indicate that genes involved in signal transduction and possibly magnetosome membrane formation vary their expression throughout the AMB-1 cell cycle. Continued investigation of the connections between the CtrA pathway, magnetosome gene expression, and the cell cycle may elucidate regulation of motility in magnetotactic bacteria and illustrate novel mechanisms of cell cycle progression in these unique organisms.

The size, shape, and subcellular positioning of organelles in eukaryotes are optimized for their function and can dynamically respond to cellular demands (1, 2). Bacteria make a number of membrane-bound organelles but very little is understood about how the size and positioning of membrane-bound bacterial organelles influence their function (3, 4). This work explores the distinct structural features and dynamic properties that are linked to bacterial organelles. Specifically, this work uses Magnetospirillum magneticum AMB-1 as a model system to explores the formation and positioning of membrane-bound organelle, the magnetosome. The first chapter of this dissertation, a published review article written in collaboration with a fellow Komeili lab member Nicole Abreu, introduces the topic of compartmentalization and subcellular organization in bacteria (4). Unlike eukaryotic cells, which share a specific set of organelles, bacteria possess a variety of morphologically and functionally distinct organelles that are not shared amongst all bacteria (3). Rather than describe all the bacterial organelles that have been discovered to date, chapter 1 provides vignettes of model organisms that exemplify different modes of membrane remodeling used to achieve compartmentalization. In addition, chapter 1 discusses the mechanisms that position a membrane-bound organelle and a protein-bound organelle from two model systems, magnetotactic bacteria and cyanobacteria. The second chapter of this dissertation, a published primary research article, uncovers the dynamic nature of a membrane-bound bacterial organelle in the model magnetotactic bacterium. Magnetotactic bacteria make magnetic nanoparticles inside membrane-bound organelles called magnetosomes; however, it is unclear how the magnetosome membrane controls the biomineralization that occurs within this bacterial organelle. In collaboration with Grant Jensen's lab at Caltech, magnetosome formation was placed under inducible control in Magnetospirillum magneticum AMB-1 (AMB-1) and electron cryo-tomography was used to capture magnetosomes in their near-native state as they form de novo. An inducible system provided the key evidence that magnetosome membranes grow continuously unless they have not properly initiated biomineralization. Our finding that the size of a bacterial organelle impacts its biochemical function is a fundamental advance that impacts our perception of organelle formation in bacteria. The third chapter of this dissertation (unpublished work) focuses on magnetosome organization and the positioning of newly formed magnetosomes in wildtype AMB-1. In a wildtype AMB-1, the individual magnetosomes of a chain are at a different stages of formation, suggesting that magnetosomes are being made and added to the chain at different times (5). Indeed, maintaining a chain of magnetosomes over multiple cell generations would require the faithful segregation of the magnetosome chain by the mother cell, as well as the correct positioning of new magnetosomes in the daughter cells. To explore the spatial and temporal dynamics of magnetosome positioning, we developed a pulse-chase system to differentially label pre-existing versus newly formed magnetosomes. The preliminary data presented in chapter 3 provide evidence that this pulse-chase system can be used to identify sites of magnetosome biogenesis in relation to the pre-existing magnetosome chain. In addition, this system can be combined with time-lapse imaging to observe how the magnetosome chain is segregated and maintained over multiple cell divisions.

The Prokaryotes is a comprehensive, multi-authored, peer reviewed reference work on Bacteria and Achaea. This fourth edition of The Prokaryotes is organized to cover all taxonomic diversity, using the family level to delineate chapters. Different from other resources, this new Springer product includes not only taxonomy, but also prokaryotic biology and technology of taxa in a broad context. Technological aspects highlight the usefulness of prokaryotes in processes and products, including biocontrol agents and as genetics tools. The content of the expanded fourth edition is divided into two parts: Part 1 contains review chapters dealing with the most important general concepts in molecular, applied and general prokaryote biology; Part 2 describes the known properties of specific taxonomic groups. Two completely new sections have been added to Part 1: bacterial communities and human bacteriology. The bacterial communities section reflects the growing realization that studies on pure cultures of bacteria have led to an incomplete picture of the microbial world for two fundamental reasons: the vast majority of bacteria in soil, water and associated with biological tissues are currently not culturable, and that an understanding of microbial ecology requires knowledge on how different bacterial species interact with each other in their natural environment. The new section on human microbiology deals with bacteria associated with healthy humans and bacterial pathogenesis. Each of the major human diseases caused by bacteria is reviewed, from identifying the pathogens by classical clinical and non-culturing techniques to the biochemical mechanisms of the disease process. The 4th edition of The Prokaryotes is the most complete resource on the biology of prokaryotes. The following volumes are published consecutively within the 4th Edition: Prokaryotic Biology and Symbiotic Associations Prokaryotic Communities and Ecophysiology Prokaryotic Physiology and Biochemistry Applied Bacteriology and Biotechnology Human Microbiology Actinobacteria Firmicutes Alphaproteobacteria and Betaproteobacteria Gammaproteobacteria Deltaproteobacteria and Epsilonproteobacteria Other Major Lineages of Bacteria and the Archaea

This book describes the structures and functions of active protein filaments, found in bacteria and archaea, and now known to perform crucial roles in cell division and intra-cellular motility, as well as being essential for controlling cell shape and growth. These roles are possible because the cytoskeletal and cytomotive filaments provide long range order from small subunits. Studies of these filaments are therefore of central importance to understanding prokaryotic cell biology. The wide variation in subunit and polymer structure and its relationship with the range of functions also provide important insights into cell evolution, including the emergence of eukaryotic cells. Individual chapters, written by leading researchers, review the great advances made in the past 20-25 years, and still ongoing, to discover the architectures, dynamics and roles of filaments found in relevant model organisms. Others describe one of the families of dynamic filaments found in many species. The most common types of filament are deeply related to eukaryotic cytoskeletal proteins, notably actin and tubulin that polymerise and depolymerise under the control of nucleotide hydrolysis. Related systems are found to perform a variety of roles, depending on the organisms. Surprisingly, prokaryotes all lack the molecular motors associated with eukaryotic F-actin and microtubules. Archaea, but not bacteria, also have active filaments related to the eukaryotic ESCRT system. Non-dynamic fibres, including intermediate filament-like structures, are known to occur in some bacteria.. Details of known filament structures are discussed and related to what has been established about their molecular mechanisms, including current controversies. The final chapter covers the use of some of these dynamic filaments in Systems Biology research. The level of information in all chapters is suitable both for active researchers and for advanced students in courses involving bacterial or archaeal physiology, molecular microbiology, structural cell biology, molecular motility or evolution. Chapter 3 of this book is open access under a CC BY 4.0 license.

Following an introduction to biogenic metal nanoparticles, this book presents how they can be biosynthesized using bacteria, fungi and yeast, as well as their potential applications in biomedicine. It is shown that the synthesis of nanoparticles using microbes is eco-friendly and results in reproducible metal nanoparticles of well-defined sizes, shapes and structures. This biotechnological approach based on the process of biomineralization exploits the effectiveness and flexibility of biological systems. Chapters include practical protocols for microbial synthesis of nanoparticles and microbial screening methods for isolating a specific nanoparticle producer as well as reviews on process optimization, industrial scale production, biomolecule-nanoparticle interactions, magnetosomes, silver nanoparticles and their numerous applications in medicine, and the application of gold nanoparticles in developing sensitive biosensors.

This volume details recent developments in magnetotactic bacteria research. It includes reviews on the formation and organization of magnetosomes, the genes controlling magnetosome biomineralization, and new cryogenic techniques to visualize novel cytoskeleton structures. Coverage also describes potential nanobiotechnological applications of the magnetosome crystals.

The new series "Microbiology Monographs" begins with two volumes on intracellular components in prokaryotes. In this second volume, "Complex Intracellular Structures in Prokaryotes", the components, labeled complex intracellular structures, encompass a multitude of important cellular functions. Continuing and newly initiated research will provide a clearer understanding of the complex intracellular structures known at present and will bring to light surprising new ones as well.