The bacterial cell wall represents a very complex structure disconnecting the interior of single-cell organisms from the environment, thus protecting, but also enabling, them to interact with the surrounding milieu and to exchange both substances and information. Knowledge of the biochemistry of the cell wall (components) and the genetic background helps to understand their significance with regard to microbiology and immunology of bacteria. This book represents the second edition of a publication which was presented nearly 20 years ago in the German language (Die bakterielle Zellwand). Since that time our knowledge in this field has been significantly enlarged. Therefore, the manuscript had to be completely revised and updated. To maintain both the size and the introductory character of the book at least to a great extent, the authors had to restrict the presented material to that which appears basic and most important. This requirement must inevitably bring about many subjective factors. As pointed out in the first edition, the term cell wall was not taken too strictly. Since the constituents located outside the cytoplasmic membrane are frequently difficult to divide in structure, localisation, and/or function into true cell wall components and supplementary substances, they are all at least briefly mentioned.

This book provides an up-to-date overview of the architecture and biosynthesis of bacterial and archaeal cell walls, highlighting the evolution-based similarities in, but also the intriguing differences between the cell walls of Gram-negative bacteria, the Firmicutes and Actinobacteria, and the Archaea. The recent major advances in this field, which have brought to light many new structural and functional details, are presented and discussed. Over the past five years, a number of novel systems, e.g. for lipid, porin and lipopolysaccharide biosynthesis have been described. In addition, new structural achievements with periplasmic chaperones have been made, all of which have revealed amazing details on how bacterial cell walls are synthesized. These findings provide an essential basis for future research, e.g. the development of new antibiotics. The book’s content is the logical continuation of Volume 84 of SCBI (on Prokaryotic Cytoskeletons), and sets the stage for upcoming volumes on Protein Complexes.

Studies of the bacterial cell wall emerged as a new field of research in the early 1950s, and has flourished in a multitude of directions. This excellent book provides an integrated collection of contributions forming a fundamental reference for researchers and of general use to teachers, advanced students in the life sciences, and all scientists in bacterial cell wall research. Chapters include topics such as: Peptidoglycan, an essential constituent of bacterial endospores; Teichoic and teichuronic acids, lipoteichoic acids, lipoglycans, neural complex polysaccharides and several specialized proteins are frequently unique wall-associated components of Gram-positive bacteria; Bacterial cells evolving signal transduction pathways; Underlying mechanisms of bacterial resistance to antibiotics.

It is a common statement that because of its simplicity the bacterial cell makes an ideal model for the study of a wide variety of biological systems and phenomena. While no-one would dispute that much of our under standing of biological function derives from the study of the humble bacterium, the concept of a simple life-form would be hotly disputed by any scientist engaged in the determination of the relationship between structure and function within the bacterial cell. Bacteria are particularly amenable to intensive study; their physiology can be probed with powerful biochemical, genetical and immunological techniques. Each piece of information obtained inevitably raises as many questions as answers, and can lead to a highly confused picture being presented to the lay reader. Nowhere is this more evident than in the study of the surface layers of the bacterial cell. Examination of the early electron micrographs suggested that the bacterial cytoplasm was surrounded by some sort of semi-rigid layer, possessing sufficient intrinsic strength to protect the organism from osmotic lysis. The belief that the surface layers were rather passive led to their neglect, while researchers concentrated on the superficially more exciting cytoplasmic components. Over the last twenty years our view of the bacterial envelope has undergone extensive revision, revealing a structure of enormous complexity.

Welcome to the wonderful world of microbiology! Yay! So. What is microbiology? If we break the word down it translates to "the study of small life," where the small life refers to microorganisms or microbes. But who are the microbes? And how small are they? Generally microbes can be divided in to two categories: the cellular microbes (or organisms) and the acellular microbes (or agents). In the cellular camp we have the bacteria, the archaea, the fungi, and the protists (a bit of a grab bag composed of algae, protozoa, slime molds, and water molds). Cellular microbes can be either unicellular, where one cell is the entire organism, or multicellular, where hundreds, thousands or even billions of cells can make up the entire organism. In the acellular camp we have the viruses and other infectious agents, such as prions and viroids. In this textbook the focus will be on the bacteria and archaea (traditionally known as the "prokaryotes,") and the viruses and other acellular agents.

Bacterial cells are encased in a cell wall, which is required to maintain cell shape and to confer physical strength to the cell. The cell wall allows bacteria to cope with osmotic and environmental challenges and to secure cell integrity during all stages of bacterial growth and propagation, and thus has to be sufficiently rigid. Moreover, to accommodate growth processes, the cell wall at the same time has to be a highly dynamic structure: During cell enlargement, division, and differentiation, bacteria continuously remodel, degrade, and resynthesize their cell wall, but pivotally need to assure cell integrity during these processes. Finally, the cell wall is also adjusted according to both environmental constraints and metabolic requirements. However, how exactly this is achieved is not fully understood. The major structural component of the bacterial cell wall is peptidoglycan (PG), a mesh-like polymer of glycan chains interlinked by short-chain peptides, constituting a net-like macromolecular structure that has historically also termed murein or murein sacculus. Although the basic structure of PG is conserved among bacteria, considerable variations occur regarding cross-bridging, modifications, and attachments. Moreover, different structural arrangements of the cell envelope exist within bacteria: a thin PG layer sandwiched between an inner and outer membrane is present in Gram-negative bacteria, and a thick PG layer decorated with secondary glycopolymers including teichoic acids, is present in Gram-positive bacteria. Furthermore, even more complex envelope structures exist, such as those found in mycobacteria. Crucially, all bacteria possess a multitude of often redundant lytic enzymes, termed “autolysins”, and other cell wall modifying and synthesizing enzymes, allowing to degrade and rebuild the various structures covering the cells. However, how cell wall turnover and cell wall biosynthesis are coordinated during different stages of bacterial growth is currently unclear. The mechanisms that prevent cell lysis during these processes are also unclear. This Research Topic focuses on the dynamics of the bacterial cell wall, its modifications, and structural rearrangements during cell growth and differentiation. It pays particular attention to the turnover of PG, its breakdown and recycling, as well as the regulation of these processes. Other structures, for example, secondary polymers such as teichoic acids, which are dynamically changed during bacterial growth and differentiation, are also covered. In recent years, our view on the bacterial cell envelope has undergone a dramatic change that challenged old models of cell wall structure, biosynthesis, and turnover. This collection of articles aims to contribute to new understandings of bacterial cell wall structure and dynamics.

In 1968 when Cell Walls and Membranes was published it was still reasonable to attempt to write a book covering the whole subject. Accordingly this edition of the book had something to say about walls from micro-organisms and plants as well as about membranes from bacteria and animal cells. A decade later this is manifestly impossible. Knowledge about almost all the subjects has grown explosively, par ticularly about membranes and the biosynthesis of macromolecules. Moreover aspects of the subject that were still in a relatively primitive state ten years ago have grown into highly sophisticated subjects worthy of extended treatment. The result is that the present book has had to be confined to structures and functions relating to only one division of the biological kingdom, namely micro-organisms. Even then severe limitations have had to be made to keep the task within the time available to the authors and their expertise. A few of the titles of chapters such as those on the isolation of walls and membranes, the structure of the components of bacterial and micro-fungal walls and their biosynthesis remain from the earlier book. These chapters have been almost completely rewritten and a number of quite new chapters added on topics such as the action of the antibiotics that inhibit bacterial wall syn thesis, on the function of bacterial membranes, and the bacterial autolysins.