Molecular Biology and Pathogenicity of Mycoplasmas Molecular Biology and Pathogenicity of Mycoplasmas Edited by Shmuel Razin The Hebrew University-Hadassah Medical School Jerusalem, Israel and Richard Herrmann University 0/ Heidelberg Heidelberg, Germany Springer Science+Business Media, LLC ISBN 978-1-4757-8232-5 ISBN 978-0-306-47606-8 (eBook) DOI 10.1007/978-0-306-47606-8 ©2002 Springer Science+Business Media New York Originally published by Kluwer Academic I Plenum Publishers, New York in 2002. Softcover reprint ofthe hardcover 1st edition 2002 http://www.wkap.nll W 9 8 765 4 3 2 1 A C.I.P. record for this book is available from the Library of Congress All rights reserved No part of this book may be reproduced, stored in a retrleval system, or transmitted in any form or by any means, electronic, mechanical, photocopying, microfilming, recording, or otherwise, without written permission from the Publisher, with the exception of any material supplied specifically for the purpose of being entered and executed on a computer system, for exclusive use by the purchaser of the work. Foreword: From the Enigmatic Pleuropneumonia-like Organisms to the Paradigmatic Mycoplasma Over a century ago, Edmond Nocard and Pierre Roux were engaged in the study ofinfectious bovine pleuropneumonia. The etiological agents were filterab1e, 1ike the recently discovered viruses but could be cu1tured in sterile growth media simi1ar to bacteria1 culture.I When related taxa were discovered, they were designated p1europneumonia-like organisms (PPLO). The driving force for the first half of the century or more of PPLO research was the interest in a number of anima1 diseases associated with these organismsand the possibility oftheir involvement in human diseases. In 1960, Volume 79 Article 10 ofthe Annals ofthe New York Academy of Sciences' presented the proceedings of a previous year's meeting entitled, "Biology ofthe Pleuropneumonia-like Organisms." Among the authors were several of the pioneers in the description of these still incompletely characterized microbes. The papers in this volume reveal great uncertainty about the relation of the PPLO to bacteria, newly discovered bacterial L forms, viruses, and other infectious agents such as the rickettsia. Of course, 1959 was less than a century after the founding of microbiology by Koch and Pasteur. Most of the papers in the Academy volume focus on pathogenicity with particular reference to animal diseases of importance to agriculture. A few papers began to probe the biochemical characterization ofthese organisms. In the late 1950s, efforts were underway, from the perspective of biophysics, to seek the lower limit of life, the smallest, autonomous, self­ replicating organisms. This began as a search for microbial oddities and seemed to lead relentlessly toward the pleuropneumonia-like organisms, which might therefore have a special role to play in molecular biology . This second domain of interest in the PPLO resulted in the "Conference on the Molecular Biology of the Pleuropneumonia-like Organisms" held June 14-16, 1962, at the Vniversity of Connecticut. The site ofthe meeting v vi Foreword was the result of the efforts of Robert Cleverdon. The rapidly developing discipline of molecular biology and the rapidly expanding knowledge of the PPLO were brought together at this meeting. In addition to the PPLO· specialists, the conference invited Julius Marmur to compare PPLO DNA to DNA of other organisms; David Garfinkel, who was one of the first to develop computer models of metabolism; Cyrus Levinthal to talk about coding; and Henry Quastler to discuss information theory constraints on very small cells. The conference was an announcement ofthe role ofPPLO in the fundamental understanding ofmolecular biology. Looking back 40-some years to the Connecticut meeting, it was a rather bold enterprise. The meeting was international and inter-disciplinary and began aseries of important collaborations with influences resonating down to the present. If I may be allowed a personal remark, it was where I first met Shmuel Razin, .who has been a leading figure in the emerging mycoplasma research and a good friend. This present volume is in some ways the fulfillment of the promise of that early meeting. It is an example of the collaborative work of scientists in building an understanding of fundamental aspects ofbiology. In the three years between the 1959 New York Academy meeting and the University of Connecticut meeting, the problem of establishing the structural nature of PPLO cellularity had been approached in many ways. The first Academy meeting had left uncertainty about whether we were dealing with normal cells, syncitia, or some other form ofbiological organization, perhaps a novel method of structure. In retrospect the uncertainties resulted from small size and absence of a rigid cell wall. From a physiological point of view, we regarded a cell as an aqueous core surrounded by a membrane with limited conductivity for polar molecules and ions, but this required proof. This type of problem could be studied by a biophysical method going back to J. Clerk Maxwell in 1873.3 It involved dielectric dispersion measurements on a packed suspension of cells between two platinum plates. We solicited the collaboration of Herman Schwan of the University of Pennsylvania, who was a specialist in dielectric dispersion studies. This led to the experimental conclusion" that the organization was indeed cellular with membranes having a capacitance of 1.3 pfarad/cm., which is anormal value for other living cells. These results allowed us to speak more definitely of the smallest living cells. In subsequent years, S. Razin and others have carried out detailed characterization of the membrane that gave rise to the electrical properties. Although the dielectric work is seldom cited, the dielectric dispersion studies were to me of enormous significance. They established the nature of the mycoplasma. Robert Cleverdon and I in 1959 had posited another feature of the organism, the small amount of DNA per cell or minimum genome.' Our experimental value was misleadingly small, which I believe was due to errors in our method of determining cell number. In 1962 Mark Tourtellotte and I explored the question, "What are the Foreword VB smallest dimensions compatible with life?,,6 We were driven by the assumption that mycoplasma were primitive organisms. Another mea culpa: Carl Woese, Jack Maniloff, and L. B. Zablen later showed from molecular taxonomie arguments that, rather than being primitive, mycoplasma are the ultimate parasites and saprophytes.' I would now argue that primitive organisms must be autotrophs, and mycoplasma are the ultimate heterotrophs. Nonetheless, I believe that the taxon is of importance in the basic study ofallliving cells. In May 1966, a second meeting of the New York Academy of Seiences brought together a considerably larger group to discuss "Biology of the Mycoplasma''." The impressive volume is 824 pages. In the opening remarks, Leonard Hayflick notes, "Since the first conference dedicated to them seven years ago, taxonomie dignity has been obtained by replacing the name PPLO with proper Linnean terminology." The major subject of the 1966 volume is microbiology and characterization of mycoplasma. Much of what we now call molecular biology was in the seetion called physiology and pathogenicity. It divided according to the host taxon. In any case, from our point of view, the fundamentals ofthe material discussed in this volume had been laid down. The 1966 publication also included areport on Hans Bode's work on unambiguously determining the genome size and configuration of mycoplasma DNA. 9 This was an important normalizing ofthis taxon among the prokaryotes. In the absence ofmethods for determining the sequence of DNA nucleotides, other methods were then undertaken, such as lohn Ryan's analysis of t-RNA and r-RNA coding regions.!" This ultimately led to the studies on gene organization ofMycoplasma capricolum by Akira Muto and his coworkers and by Shmuel Razin and bis coworkers. In the 60s and 70s, mycoplasma also turned out to be a taxon of choice for certain basic membrane studies for two reasons. First, the small size resulted in a high surface-to-volume ratio and a large fraction of the cell's mass as membrane. Secondly, the absence of a cell wall facilitated the preparation ofmembrane. In addition, varying the fatty acid composition of the growth medium permitted considerable control in the membrane fatty acid composition. As a result, aseries of physical chemical studies of bilayer-phase transitions was carried out on purified membrane and whole cells.",12 It is doubtful that these fundamental membrane experiments could have been done with any other taxon . In asense, all ofthis was serendipity. Cells that were being studied for other reasons turned out to be ideal for basic biophysical characterizations of cellularity and fundamentals of membrane structure and function. The science that is the subject ofthis volume has covered about a century from the discovery of the etiological agent ofbovine pleuropneumonia to the sequencing ofthe genome ofMycoplasma genitalium and other species. It is rooted in the bacteriology ofPasteur and Koch, expands in the biochemistry Vlll Foreword ofWatson and Crick, matures into present day genomics and looks ahead to proteomics and physiomics. Starting as a sideshow of early microbiology, mycoplasma have become central to modem computational and theoretical biology and the understanding of infectious disease. To look ahead, I'm confident that the first decade of the 21st century will lead to a complete computer model of mycoplasma cell function. As the biology of the 21sI century unfolds, I suspect that the minimal cell concept as embodied in the mycoplasma will continue to be central to the understanding of life. The publishers and editors have chosen an appropriate moment in time for this volume. HAROLD J. MOROWITZ Robinson Professor, Krasnow Institute for Advanced Studies, George Mason University, Fairfax, Virginia 22030, USA I Nocard, E., E.