a) \s Preface For the purposes of this encyclopedia, microbiology has been understood to embrace the study of ‘‘micro- organisms,’’ including the basic science and the roles of these organisms in practical arts (agriculture and technology) and in disease (public health and medicine). Microorganisms do not constitute a well- defined taxonomic group; they include the two king- doms of Archaebacteria and Eubacteria, as well as protozoa and those fungi and algae that are predomi- nantly unicellular in their habit. Viruses are also an important constituent, albeit they are not quite ‘‘or- ganisms.’’ Whether to include the mitochondria and chloroplasts of higher eukaryotes is a matter of choice, since these organelles are believed to be descended from free-living bacteria. Cell biology is practiced extensively with tissue cells in culture, where the cells are manipulated very much as though they were autonomous microbes; however, we shall exclude this branch of research. Microbiol- ogy also is enmeshed thoroughly with biotechno- logy, biochemistry, and genetics, since microbes are the canonical substrates for many investigations of genes, enzymes, and metabolic pathways, as well as the technical vehicles for discovery and manufac- ture of new biological products, for example, recom- binant human insulin. Within these arbitrarily designated limits, let us consider the overall volume of published literature in microbiology, where to find its core, and strategies for searching for current information on particular topics. Most of the data for this preface are derived from the 1988 Journal Citation Reports Current Contents (T) of the Institute for Scientific Information (ISI). Table I lists the 50 most conse- quential journals in microbiology, assessed by cita- tion impact factor, the average number of literature citations per article published in a given journal. Table II presents that list sorted by the total number of articles printed in each journal in 1988. Table II shows the distribution of journals citing the Journal of Bacteriology and the distribution of journals cited in it. Obviously, the publications of the American Soci- ety for Microbiology (indicated by AMS in the ta- bles) play a commanding role. The society is now making its journals available in electronically searchable form (on optical disks), which will greatly facilitate locating and retrieving the most up-to-date information on any given subject. In ad- dition, interdisciplinary journals such as Nature (London), Science, and the Proceedings of the Na- tional Academy of Sciences, U.S.A. are important sources of prompt news of scientific developments in microbiology. It is difficult to assess how much of their total publication addresses microbiology. As seen in Table III, the bibliographies in the Journal of Bacteriology cite half as many articles from the Proceedings (2348) as from the Journal of Bacteriol- ogy itself (5708). The 7038 articles indicated in Table II probably reach some 10,000 per year when these interdisciplinary and other dispersed sources are taken into account. An equal number might be added from overlapping aspects of molecular biol- ogy and genetics. To find and read all these titles would tax any scholar, although it could be done as a near full-time occupation with the help of the weekly Current Contents (T) of the ISI. To start afresh, with perhaps a decade’s accumulation of timely back- ground, would be beyond reasonable human com- petence. No one person would intelligently peruse more than a small fraction of the total texts. The *‘Encyclopedia of Microbiology” is intended to survey the entire field coherently, complementing material that would be included in an advanced un- dergraduate and graduate major course of university study. Particular topics should be accessible to tal- ented high school and college students, as well as graduates involved in teaching, research, and tech- nical practice of microbiology. Even these hefty volumes cannot embrace all cur- rent knowledge in the field. Each article does pro- vide key references to the literature available at the time of writing. Acquisition of more detailed and up-to-date knowledge depends on (1) exploiting the review and monographic literature and (2) biblio- graphic retrieval of the preceding and current re- search literature. To make greatest use of review literature and monographs, the journals listed in Ta- ble IT are invaluable. Titles such as Annual Reviews should not be misunderstood: these journals appear at annual intervals, but 5 or 10 years of accumulated research is necessary for the inclusion of a focused treatment of a given subject. To access bibliographic materials in microbiol- vii viii Preface ogy, the main retrieval resources are Medline, spon- sored by the U.S. National Library of Medicine, and the Science Citation Index of the ISI. With govern- mental subsidy, Medline is widely available at mod- est cost: terminals are available at every medical school and at many other academic centers. Med- line provides searches of the recent literature by author, title, and key word, and offers on-line dis- plays of the relevant bibliographies and abstracts. Medical aspects of microbiology are covered ex- haustively; general microbiology is covered in rea- sonable depth. The Science Citation Index must recover its costs from user fees, but is widely avail- able at major research centers. It offers additional search capabilities, especially by citation linkage. Therefore, starting with the bibliography of a given encyclopedia article, one can quickly find (1) all arti- cles more recently published that have cited those bibliographic reference starting points and (2) all other recent articles that share bibliographic infor- mation with the others. With luck, one of these arti- cles may be identified as another comprehensive review that has digested more recent or broader primary material. On a weekly basis, services such as Current Con- tents on Diskette (ISI) and Reference Update offer still more timely access to current literature as well as abstracts with a variety of useful features. Under the impetus of intense competition, these services are evolving rapidly, to the great benefit of a user community desperate for electronic assistance in coping with the rapidly growing and intertwined net- works of discovery. The bibliographic services of Chemical Abstracts and Biological Abstracts would also be potentially invaluable; however, their cover- age of microbiology is rather limited. In addition, major monographs have appeared from time to time—‘‘The Bacteria,’ ‘‘The Pro- karyotes,’’ and many others. Your local reference library should be consulted for these volumes. Valuable collections of reviews also include Criti- cal Reviews for Microbiology, Symposia of the Soci- ety for General Microbiology, Monographs of the ASM, and Proceedings of the International Con- gresses of Microbiology. The articles in this encyclopedia are intended to be accessible to a broader audience, not to take the place of review articles with comprehensive bibliog- raphies. Citations should be sufficient to give the reader access to the latter, as may be required. We do apologize to many individuals whose contribu- tions to the growth of microbiology could not be adequately embraced by the secondary bibliogra- phies included here. The organization of encyclopedic knowledge is a daunting task in any discipline; it is all the more complex in such a diversified and rapidly moving domain as microbiology. The best way to anticipate the rapid further growth that we can expect in the near future is unclear. Perhaps more specialized se- ries in subfields of microbiology would be more ap- propriate. The publishers and editors would wel- come readers’ comments on these points, as well as on any deficiencies that may be perceived in the current effort. My personal thanks are extended to Kathryn Linenger at Academic Press for her diligent, patient, and professional work in overseeing this series; to my coeditors Martin Alexander, David A. Hop- wood, Barbara H. Iglewski, and Allan I. Laskin; above all, to the many very busy scientists who took time to draft and review each of these articles. Joshua Lederberg