|Spore arrangement in Streptomyces griseus. Grey spores arranged in straight chains, as is typical of these strains.|
Waksman and Henrici 1948
Streptomyces griseus is a species of bacteria in the genus Streptomyces commonly found in soil. A few strains have been also reported from deep-sea sediments. It is a Gram positive bacterium with high GC content. Along with most other streptomycetes, S. griseus strains are well known producers of antibiotics and other such commercially significant secondary metabolites. These strains are known to be producers of 32 different structural types of bioactive compounds. The first antibiotic ever reported from a bacterium comes from strains of S. griseus. Recently, the whole genome sequence of one of its strains had been completed. The taxonomic history of S. griseus and its phylogenetically related strains have been turbulent. S. griseus was first described by Waksman and Henrici in 1948. The interest towards these strains was sought because of their ability to produce streptomycin, a compound which demonstrated significant bactericidal activity against organisms such as Yersinia pestis (the causative agent of plague) and Mycobacterium tuberculosis (the causative agent of tuberculosis). For his work on these strains of bacteria and the antibiotic they produce, Waksman would later be awarded a Nobel Prize.
Streptomyces is the largest genus of the Actinobacteria and is the type genus of the family Streptomycetaceae. These are Gram positive bacteria with high GC content and are characterised by a complex secondary metabolism. They produce over two-thirds of the clinically useful antibiotics of natural origin . Streptomycetes are found predominantly in soil and in decaying vegetation, and most produce spores. Streptomycetes are noted for their distinct "earthy" odor which results from production of a volatile metabolite, geosmin.
Like other streptomycetes, S. griseus has a high GC content in its genome, with an average of 72.2%. The species was first described by Waksman and Henrici in 1948. The taxonomy of S. griseus and its evolutionarily related strains have been a considerable source of confusion for microbial systematists. 16S rRNA gene sequence data have been used to recognise the related strains, and are called S. griseus 16S rRNA gene clade. The strains of this clade have homogeneous phenotypic properties but show substantial genotypic heterogenecity based on genomic data. Several attempts are still made to solve this issue using techniques such as DNA:DNA homology and multilocus sequence typing. A whole genome sequence was recently carried out on the IFO 13350 strain of S. griseus.
Physiology and morphology 
S. griseus and its related strains have recently been shown to be alkaliphilic, i.e., they grow best at alkaline pH values. Although these organisms grow in a wide pH range (from 5 to 11), they show a growth optimum at pH 9. They produce grey spore masses and grey-yellow reverse pigments when they grow as colonies. The spores have smooth surfaces and are arranged as straight chains.
Streptomyces griseus strains have been isolated from various ecologies, including stell waste tips, rhizosphere, deep sea sediments and coastal beach and dune sand systems. Recent studies have indicated the strains of S. griseus might be undergoing ecology-specific evolution, giving rise to genetic variation with the specific ecology, termed ecovars.
Antibiotic production 
Interest in the genus Streptomyces for antibiotics came after the discovery of the antibiotic streptomycin in a S. griseus strain in 1943. The discovery of streptomycin, an antituberculosis antibiotic, earned Waksman the Nobel Prize in 1952. The strains of this species are now known to be rich sources of antibiotics and to produce 32 different structural types of commercially significant secondary metabolites. Furthermore, the genomic studies have revealed a single strain of S. griseus IFO 13350 has the capacity to produce 34 different secondary metabolites.
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