Streptomyces is the largest genus of Actinobacteria and the type genus of the family Streptomycetaceae. Over 500 species of Streptomyces bacteria have been described. As with the other Actinobacteria, Streptomyces are gram-positive and have genomes with high GC content. Found predominantly in soil and decaying vegetation, most Streptomyces produce spores and are noted for their distinct "earthy" odor that results from the production of a volatile metabolite, geosmin. Streptomyces are characterized by a complex secondary metabolism. They produce over two-thirds of the clinically useful antibiotics of natural origin (e.g., neomycin, capreomycin, grisemycin, bottromycins, and chloramphenicol). The now uncommonly used streptomycin takes its name directly from Streptomyces. Streptomycetes are infrequent pathogens, though infections in humans, such as myeloma, can be caused by S. somaliensis and S. sudanensis, and in plants can be caused by S. caviscabies, S. acid scabies, S. turgid scabies, and S. scabies.