The 1st volume of our Research Topic "The Bacterial Cell: Coupling between Growth, Nucleoid Replication, Cell Division and Shape” was published as an eBook in May 2016 (see: http://journal.frontiersin.org/researchtopic/2905/the-bacterial-cell-coupling-between-growth-nucleoid-replication-cell-division-and-shape). As a sign of growing interest to the topic, two workshops followed the same year: "Stochasticity in the Cell Cycle" in Jerusalem (Israel) by the Hebrew University’s Institute of Advanced Studies and EMBO's "Cell Size Regulation" in Joachimsthal (Germany). From the time of launching the first edition, several new groups have entered the field, and many established groups have made significant advances using state-of-the-art microscopy and microfluidics. Combining these approaches with the techniques pioneered by quantitative microbiologists decades ago, these approaches have provided remarkable amounts of numerical data. Most of these data needed yet to be put into a broader theoretical perspective. Moreover, the molecular mechanisms governing coordination and progression of the main bacterial cell cycle processes have remained largely unknown. These outstanding fundamental questions and the growing interest to the field motivated us to launch the next volume titled “The Bacterial Cell: Coupling between Growth, Nucleoid Replication, Cell Division, and Shape, Volume 2” shortly after completion of the first edition in October 2016. The issue contains 17 contributions from a diverse array of scientists whose field of study spans microbiology, biochemistry, genetics, experimental and theoretical biophysics. The specific questions addressed in the issue include: What triggers initiation of chromosome replication? How is cell division coordinated with replication both spatially and temporally? How is cell size controlled and linked to the rate of mass growth? What role plays physical organization of the chromosomes in their segregation and in regulation of cell division? The publications covering these questions are divided into three topical areas: 1) Cell Cycle Regulation, 2) Growth and Division, and 3) Nucleoid Structure and Replication. New ideas and techniques put forward in these articles bring us closer to understand these fundamental cellular processes, but the quest to resolve them is far from being complete. Plans for the next edition are under way along with further meetings and workshops, e.g., an EMBO Workshop on Bacterial cell biophysics: DNA replication, growth, division, size and shape in Ein Gedi (Israel), May 2020. We hope that via such interdisciplinary exchange of ideas we will come closer to answering the above-mentioned complex and multifaceted questions.

Bacterial Physiology was inaugurated as a discipline by the seminal research of Maaløe, Schaechter and Kjeldgaard published in 1958. Their work clarified the relationship between cell composition and growth rate and led to unravel the temporal coupling between chromosome replication and the subsequent cell division by Helmstetter et al. a decade later. Now, after half a century this field has become a major research direction that attracts interest of many scientists from different disciplines. The outstanding question how the most basic cellular processes - mass growth, chromosome replication and cell division - are inter-coordinated in both space and time is still unresolved at the molecular level. Several particularly pertinent questions that are intensively studied follow: (a) what is the primary signal to place the Z-ring precisely between the two replicating and segregating nucleoids? (b) Is this coupling related to the structure and position of the nucleoid itself? (c) How does a bacterium determine and maintain its shape and dimensions? Possible answers include gene expression-based mechanisms, self-organization of protein assemblies and physical principles such as micro-phase separations by excluded volume interactions, diffusion ratchets and membrane stress or curvature. The relationships between biochemical reactions and physical forces are yet to be conceived and discovered. This e-book discusses the above mentioned and related questions. The book also serves as an important depository for state-of-the-art technologies, methods, theoretical simulations and innovative ideas and hypotheses for future testing. Integrating the information gained from various angles will likely help decipher how a relatively simple cell such as a bacterium incorporates its multitude of pathways and processes into a highly efficient self-organized system. The knowledge may be helpful in the ambition to artificially reconstruct a simple living system and to develop new antibacterial drugs.

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.

Bacterial Physiology focuses on the physiology and chemistry of microorganisms and the value of bacterial physiology in the other fields of biology. The selection first underscores the chemistry and structure of bacterial cells, including the chemical composition of cells, direct and indirect methods of cytology, vegetative multiplication, spores of bacteria, and cell structure. The text then elaborates on inheritance, variation, and adaptation and growth of bacteria. The publication reviews the physical and chemical factors affecting growth and death. Topics include hydrogen ion concentration and osmotic pressure; surface and other forces determining the distribution of bacteria in their environment; dynamics of disinfection and bacteriostasis; bacterial resistance; and types of antibacterial agents. The text also ponders on the anaerobic dissimilation of carbohydrates, bacterial oxidations, and autotrophic assimilation of carbon dioxide. The selection is a dependable reference for readers interested in bacterial physiology.

How small can a free-living organism be? On the surface, this question is straightforward-in principle, the smallest cells can be identified and measured. But understanding what factors determine this lower limit, and addressing the host of other questions that follow on from this knowledge, require a fundamental understanding of the chemistry and ecology of cellular life. The recent report of evidence for life in a martian meteorite and the prospect of searching for biological signatures in intelligently chosen samples from Mars and elsewhere bring a new immediacy to such questions. How do we recognize the morphological or chemical remnants of life in rocks deposited 4 billion years ago on another planet? Are the empirical limits on cell size identified by observation on Earth applicable to life wherever it may occur, or is minimum size a function of the particular chemistry of an individual planetary surface? These questions formed the focus of a workshop on the size limits of very small organisms, organized by the Steering .Group for the Workshop on Size Limits of Very Small Microorganisms and held on October 22 and 23, 1998. Eighteen invited panelists, representing fields ranging from cell biology and molecular genetics to paleontology and mineralogy, joined with an almost equal number of other participants in a wide-ranging exploration of minimum cell size and the challenge of interpreting micro- and nano-scale features of sedimentary rocks found on Earth or elsewhere in the solar system. This document contains the proceedings of that workshop. It includes position papers presented by the individual panelists, arranged by panel, along with a summary, for each of the four sessions, of extensive roundtable discussions that involved the panelists as well as other workshop participants.

Extensive and up-to-date review of key metabolic processes in bacteria and archaea and how metabolism is regulated under various conditions.