Center: Tangled filaments of the cyanobacterium Nostoc sp. isolated from the glands of specialized plant tissue, the “bracts” or “stipules” of Ecuadorian wet-highland flowering plant Gunnera manicata. The book The Microbe’s Contribution to Biology (Harvard Univ. Press, 1956), celebrated in this issue, presented the unified theory of photosynthesis and thereby put the photosynthetic process in an evolutionary context. Cyanobacteria altered the Earth and its life throughout all subsequent history by unabated release of oxygen to soil, waters and atmosphere. (Nomarski differential interference light micrograph, by Rita Kolchinski Berson and Lynn Margulis, University of Massachusetts-Amherst.) (Size of the individual cells: 3–5 mm).

Upper left: Negatively stained transmission electron micrograph of Hibiscus latent ringspot virus (HLRSV) particles identified on Hibiscus cannabinus plants (kenaf). Photographed by Concepció Rúbies and Gian Franco Filippini (DISTA, University of Bologna, Italy). (Magnification, ca. 100,000×)

Upper right: Scanning electron micrograph of Helicobacter felis isolated from the gastric mucosa of a cat. The characteristic spiral morphology and periplasmic fibers are shown. Micrograph courtesy of Lucinda Thompson (presently at Stanford University, USA), made at The University of New South Wales, Australia. (Magnification, ca. 10,000×)

Lower left: Phase-contrast micrograph of the tachyzoite phase of the protist (Apicomplexan) Toxoplasma gondii. Photographed by Braúlia Costa Caetano and Óscar Bruña-Romero (Departments of Biochemistry & Immunology, and Microbiology, Federal University of Minas Gerais, Belo Horizonte, MG, Brazil). (Magnification, ca. 10,000×)

Lower right: Conidiospores of Alternaria alternata, a fungus of the Family Dematiaceae, in which several special forms produce specific phytotoxins against the host. The toxins give the fungus high specific pathogenicity against apple and pear trees, tobacco plant and citrics. This strain was isolated and photographed by Jordi Cabrefiga (Institute of Food and Agricultural Technology, University of Girona). (Magnification, ca. 7500×)