Moselio Schaechter

Escherichia coli and Salmonella 2000: the View From Here

SUMMARY Five years after the publication of the second edition of the reference book Escherichia coli and Salmonella: Cellular and Molecular Biology, and on the eve of launching a successor venture, the editors and colleagues examine where we stand in our quest for an understanding of these organisms. The main areas selected for this brief inquiry are genomics, evolution, molecular multifunctionality, functional backups, regulation of gene expression, cell biology, sensing of the environment, and ecology.

A brief history of bacterial growth physiology

Arguably, microbial physiology started when Leeuwenhoek became fascinated by observing a Vorticella beating its cilia, my point being that almost any observation of microbes has a physiological component. With the advent of modern microbiology in the mid-19th century, the field became recognizably distinctive with such discoveries as anaerobiosis, fermentation as a biological phenomenon, and the nutritional requirements of microbes. Soon came the discoveries of Winogradsky and his followers of the chemical changes in the environment that result from microbial activities. Later, during the first half of the 20th century, microbial physiology became the basis for much of the elucidation of central metabolism. Bacterial physiology then became a handmaiden of molecular biology and was greatly influenced by the discovery of cellular regulatory mechanisms. Microbial growth, which had come of age with the early work of Hershey, Monod, and others, was later pursued by studies on a whole cell level by what became known as the “Copenhagen School.” During this time, the exploration of physiological activities became coupled to modern inquiries into the structure of the bacterial cell. Recent years have seen the development of a further phase in microbial physiology, one seeking a deeper quantitative understanding of phenomena on a whole cell level. This pursuit is exemplified by the emergence of systems biology, which is made possible by the development of technologies that permit the gathering of information in huge amounts. As has been true through history, the research into microbial physiology continues to be guided by the development of new methods of analysis. Some of these developments may well afford the possibility of making stunning breakthroughs.

What makes a virus a virus

(Redefining viruses: lessons from mimivirus. Nature Rev. Microbiol. 6, 315–319 (2008)1) proposed a dichotomy of the biological world, dividing it into ‘organisms’, those entities that encode a functional translational machinery, and viruses, those entities that have capsid shells instead. The implied definition of viruses, although highly relevant, does not rely on the most fundamental aspect of what makes a virus a virus: it breaks up and loses its bodily integrity, with its progeny becoming reconstituted after replication from newly synthesized parts. We propose that the defining attribute of all viruses is their disintegration and reconstitution, from the tiny geminiviruses (15–20 nm diameter; 2.5 kb DNA genome) to the colossal Mimivirus (400 nm diameter; 800 kb DNA genome). Importantly, disintegration and reconstitution are totally independent of time, with reconstitution occurring minutes, days, years or centuries after disintegration. This is true for no other cellular organism. One aspect of this cycle, the reassembly of viral constituents to make a virion, mimics many other biological assembly processes, but the dual nature of the process is what makes it unique. Capsids are essential, but they can be relegated to a list of other viral properties. This definition is pragmatic and is based not on phylogeny but on the distinctive nature of viruses. Imagine examining a particle that is surrounded by what looks like a capsid. One might suspect it to be a virus, but with no other information it could also be some other subcellular structure. If, during an infection experiment, the particle was to lose its integrity but keep its genetic information intact, and later reassemble into progeny, there would be no doubt, however, that it is a virus. We are surprised from our own experience that the world of virology has not fully embraced this outlook. A definition of viruses that is based on their disintegration and reconstitution requires knowledge of the reproductive cycle of the biological entity to be studied. We recognize that on an operational level it is easier to examine particles under the electron microscope than it is to carry out a viral growth curve, which in fact is not achievable unless the host organism of the virus is available. In trying to define viruses, we cannot escape a consideration of viroids and other infectious naked nucleic acids, which might have evolved from viruses that lost their capsid (thus acquiring their ‘oid’) or directly from nucleic acid molecules. Neither capsids nor the loss of integrity are attributes of viroids, and therefore they must be relegated to a separate category.

Lynn Margulis (1938–2011)

A biologists innovative theoretical syntheses provided the intellectual scaffolding for endosymbiotic theory, a cornerstone of mainstream evolutionary biology. Science progresses mainly through experimentation, but to become useful, experimental results have to be scrutinized, interpreted, and placed on a proper intellectual scaffold. These two activities are not always carried out evenly by the same person. Some scientists become known for their impressive experiments, others for innovative theoretical syntheses. Lynn Margulis, who died on 22 November 2011 at the age of 73, was a striking example of the latter group. She is responsible for the transformative idea that eukaryotic cells evolved by the acquisition and exploitation of other, smaller cells, a process known as endosymbiosis. Accordingly, essential components of eukaryotic cells—the organelles mitochondria and, in photosynthetic cells, plastids—are derived from bacteria that some ancestral cell had ingested. These events are thought to have taken place early in the history of life on Earth.

Integrative microbiology--the third Golden Age.

I am taking advantage of advancing age to unravel myself from the narrow confines of my field of research and present a broad personal view of my science, microbiology. Before commenting on my views of present-day microbiology, let me disclose some of the personal experiences that may have had a defining role in my scientific development. I mention them with circumspection because the relationship between early events and later actions may be misleading. Still, sharing aspects of what I experienced in my early days may help to set the stage for my present-day musings. Those eager to get to the message should skip this section.

Microbe, Second Edition

Instructors – Get your examination copy now! Visit http://asmscience.org/instructors for more information. Help your students save on textbooks! Email us and receive a coupon to share with your students for 20% off of the purchase of a print copy. Brings the excitement, breadth, and power of the modern microbial sciences to the next generation of students and scientists. This new edition of Microbe is an eloquent and highly readable introduction to microbiology that will engage and excite science majors and pre-health professionals. The authors, all prominent scientists, have carefully crafted this lively narrative to bring key microbiology concepts to life and promote a lifelong passion for the microbial sciences. Far more than a comprehensive reference book, Microbe is replete with case studies, ranging from sauerkraut fermentation to the cholera outbreak in Haiti, that illustrate the impact of key microbiology concepts on real-world scenarios. To further engage students and deepen their understanding of both the principles and practice of science, each chapter includes multiple active learning exercises that encourage students to demonstrate their understanding and application of concepts, as well as video, spoken, and written resources. Questions are posed throughout the book to introduce the next key concept and to prompt students to actively participate in the learning experience. An equally valuable tool for instructors who teach a traditional lecture format and those who emphasize active learning in their classroom, Microbe integrates key concepts, learning outcomes, and fundamental statements directly from the ASM Recommended Curriculum Guidelines for Undergraduate Microbiology Education. “This is a fantastic text! Written in a comfortable, conversational style, it grabs the readers’ attention immediately, sparking their curiosity and keeping them engaged throughout each chapter while they seek and find answers to questions posed at the beginning of each section. A true joy to read. I recommend it highly for both traditional and flipped classrooms.” --Peggy Cotter, PhD, Professor, Department of Microbiology and Immunology, UNC School of Medicine Watch authors Michele Swanson and Elio Schaechter discuss the new Microbe, 2e during ASM Microbe 2016. Interested in purchasing this title as an electronic publication? Click here for the electronic version on Vital Source! Click here for the electronic version on RedShelf! Hardcover, 846 pages, full-color illustrations, index.