We examined 46 isolates of Borrelia burgdorferi, the etiologic agent of Lyme disease and related disorders, with polyacrylamide gel electrophoresis and monoclonal antibodies. Our attention was on the OspA proteins, which are major proteins of the spirochete. There were at least four discernible phenotypes of the OspA protein. While 25 North American isolates were, with one exception, homogeneous in the type of OspA protein that they produced, 21 European isolates were heterogeneous in the types of OspA proteins represented. Only three European strains resembled North American strains in their OspA phenotype. Application of a deoxyribonucleic acid probe for an ospA gene demonstrated that the arrangement of ospA-associated sequences in the DNA differed between isolates.

In immunofluorescence assays monoclonal antibody H9724 recognized eight species of the spirochetal genus Borrelia but not representatives of the genera Treponema, Leptospira, and Spirochaeta. We examined the reactivity of H9724 against subcellular components of Borrelia hermsii, an agent of relapsing fever, and B. burgdorferi, the cause of Lyme disease. H9724 bound to isolated periplasmic flagella of the two borreliae. In Western blots the antibody reacted with the predominant protein in flageliar preparations from B. hermsii and B. burgdorfferi; the apparent molecular weights of these flagellins were 39,000 and 41,000, respectively.

Plasmavirus MVL2 was propagated on three Acholeplasma laidlawii strains, JA1, S2, or BC1-13. Previously reported host-controlled modification (HCM) of MVL2, as reflected by changes in plating efficiency, was observed. Adsorption rates and one-step growth curves varied according to host used. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the three MVL2 populations revealed differences in polypeptide profiles.

Colonial size and opacity variation were observed in four independently isolated strains of the murine pathogen Mycoplasma pulmonis. Selecting colonial opacity variants of similar size, we identified opaque and transparent stable variants. Opaque colony-derived broth cultures shed transparent colonies at a rate of about 1.2 X 10(-8) per CFU per generation. The reverse conversion was about two orders of magnitude less frequent. Appearance of opacity and plating efficiency of each pure culture were altered by changing the serum source used to supplement the growth medium. Horse or sheep serum was most efficient at accentuating visualization of opacity differences. Fetal bovine serum was least efficient. In two M. pulmonis strains, each opacity variant showed a distinctive polypeptide profile, as displayed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In the same strains, distinctive intrastrain differences were found by agarose gel electrophoresis to display the DNA fragments produced after digestion by several endonucleases. Each pure culture variant retained these differences in DNA even when grown in a medium supplemented with a serum which did not accentuate visualization of the opacity phenotype. Characterization of variants in 30 other M. pulmonis strains is in progress.