Marburg Virus Disease

formation and transduction mechanisms are in dispute and remain to be investigated witlh renewed vigor. Lysogenic conversion may be operative in the myco-bacteria. Six of the papers are devoted to the study of lysogenic mycobacteria, whiclh exlhibit plhenotypic clhanges suclh as cell-wall alterations (expressed as chaniges in eitlher cell or colony morplhology), altered enzymatic activity, and increased virulence of lysogenized strains. The authors are careful to point out that these alterations in phenotype may arise by nonhereditary mechanisms. The natture of the gene interactions remains to be elucidated. Transformation events in mycobacteria have been sporadically reported but lhave lacked confirmation. Three excellent papers in these proceedings are devoted to the study of the related phenomenon of transfection (infection of a competent lhost cell by isolated plhage of viral nucleic acid). The ability of Myco-bactcriu1m srnegniatis to take up isolated phage DNA and other (syntlhetic) poly-nucleoti(les is plromoted by calcium ioIns, and a hiigh transfecting ability of plhage DNA may be accomplished by increasing the competent state of Al. smegmatis by exposure of hiost cells to selected amino acidls or to a well-defined acid medium, pH rainge 3.8-4.0. Seven of the papers (a tlhird of the material presented) wvere tlle work of Margaret Sellers and colleagtues. These inclutled suclh diverse studies as lhost-range mtutaints and temperatuire-sensitive mutants of Mycobacteriophage D29, (crmg-iinduticed clhainges by phage D29 infections of Al. smegmatis and a study of phage receptor sites on the same host. The experimental designs employed in these stucdies are descriled precisely and carefully documented, and slhould pro-vidle otlher investigators witlh excellent models for furtlher studies of lhost-virus relationslhips. In general, the participants presented a sclholarly overview of the "current state of the art," as it applied to the mycobacteria, and the editors should be credite(l for compiling the proceedings in a highlly readable manner. The excellent referenices after eaclh paper add to the value of each presentation. However, in the opinion of this reviewer, the major ftunction of a report of a symposium is for the experts to lead the rest of us into unclharted areas and illuminate tllem.