Streptomyces griseoviridis. Coloured scanning electron micrograph of a colony of the bacteria Streptomyces griseoviridis. Streptomyces species are natural producers of various antibiotics, including streptomycin. Streptomyces griseoviridis produces a substance which inhibits the growth of some fungi which parasitize plants. Streptomyces species share many characteristics with fungi. The bacteria commonly grow in the soil as branching networks of filaments, known as mycelia. They also produce aerial mycelia, from the tips of which develop chains of spores. Magnification: x3600 at 6x4.5cm size.