STREPTOMYCES GRISEUS: CHARACTERISTICS, LIFE CYCLE AND USES - BIOLOGY - 2025

Streptomyces griseus is a species of aerobic, Gram positive bacteria. It belongs to the group of Actinobacteria, within the Actinomycetales order and the Streptomycetaceae family.

They are common bacteria in the soil. They have been found in association with plant roots in the rhizosphere. Some strains have also been isolated in samples of deep marine waters and sediments and in coastal ecosystems.

Streptomyces griseus seen with a Scanning Electron Microscope. Author: Docwarhol, from Wikimedia Commons. The ability of this species to adapt to a great diversity of ecosystems has generated significant genetic variation that has been attempted to be classified into ecovars.

This species, like other Streptomyces species, produces a large number of secondary metabolites, which gives it great commercial importance. Among them, streptomycin (aminoglycoside antibiotic) stands out, the first antibiotic used effectively against tuberculosis.

characteristics

S. griseus is a Gram positive aerobic bacterium that produces mycelia. The cell wall is thick, made up mainly of peptidoglycan and lipids.

This species develops both substrate and aerial mycelia. Both types of mycelium have a different morphology. The hyphae of the substrate mycelium can be 0.5 - 1 µm in diameter. The aerial mycelium is filamentous and little branched.

In culture medium, these mycelia present different shades of gray. The reverse side of the colony is gray-yellowish. They do not produce melanin pigments.

The spore chains are rectiflexible and consist of 10-50 spores. The surface of these is smooth.

The species uses glucose, xylose, mannitol or fructose as a carbon source. In culture media with arabinose or rhamnose, no colony growth is observed.

The optimum temperature for its development ranges from 25 - 35 ° C.

They grow in a wide range of pH, between 5 and 11. However, its growth is optimal in alkaline environments with pH 9, which is why it is considered alkaline.

Genetics

The genome of S. griseus has been completely sequenced. It has a linear chromosome with more than eight million base pairs. The presence of plasmids has not been observed.

The chromosome has more than 7000 ORFs (open frame RNA sequences). For more than 60% of these sequences, the function they fulfill is known. The GC content for S. griseus is approximately 72%, which is considered high.

Secondary metabolites

Most Streptomyces species produce a large number of secondary metabolites. Among these we find antibiotics, immunosuppressants and enzyme inhibitors.

Likewise, these bacteria are capable of producing some industrially important enzymes, such as glucose isomerase or transglutaminase.

In the case of S. griseus, the most important secondary metabolite is streptomycin. However, this organism produces other compounds, such as certain types of phenols that are very effective in controlling various phytopathogenic fungi.

Taxonomy

The species was first described from soil isolates from an area of ​​Russia. The researcher Krainsky in 1914 identifies it as Actinomyces griseus.

Later, Waskman and Curtis were able to isolate the species in various soil samples in the United States. In 1943 Waskman and Henrici proposed the genus Streptomyces based on the morphology and cell wall type of their species. These authors place the species in this genus in 1948.

Phylogeny and synonyms

Three subspecies had been proposed for S. griseus. However, molecular studies have revealed that two of these taxa correspond to the species S. microflavus.

From a phylogenetic point of view, S. griseus forms a group with S. argenteolus and S. caviscabies. These species have great similarity in relation to ribosomal RNA sequences.

Based on the comparison of RNA sequences, it has been possible to establish that some taxa considered species other than S. griseus have the same genetic composition.

Therefore, these names have become synonymy with the species. Among these we have S. erumpens, S. ornatus and S. setonii.

Biological cycle

Streptomyces species produce two types of mycelium during their development. The substrate mycelium that makes up the vegetative phase and the aerial mycelium that will give rise to the spores

Formation of substrate mycelium

This originates after the germination of the spore. The hyphae are 0.5-1 µm in diameter. These grow from the apices and develop ramifications, producing a complex matrix of hyphae.

Few compartmentalized septa are present that can present multiple copies of the genome. During this phase, the bacteria take advantage of the nutrients present in the environment to accumulate biomass.

As this mycelium develops, there is cell death of some septa. In the mature substrate mycelium, live and dead segments alternate.

When the bacteria develop in the soil or in submerged crops, the vegetative phase is predominant.

Formation of aerial mycelium

At one point in the development of the colonies, a mycelium with fewer branches begins to form. In S. griseus long filaments are formed that are very little branched.

The nutrition necessary for the formation of this mycelium is obtained from the lysis of the substrate mycelium cells. In this phase the species produces the different secondary metabolites.

Spore formation

In this phase, the hyphae stop their growth and begin to fragment transversely. These fragments quickly transform into rounded spores.

Spore chains are formed consisting of approximately fifty cells. The spores are spherical to oval, 0.8-1.7 µm in diameter and with a smooth surface.

Applications

The main use associated with S. griseus is the production of streptomycin. This is a bactericidal antibiotic. It was first detected in 1943 by Albert Schatz in strains of the species.

Streptomycin is one of the most effective treatments for treating tuberculosis caused by Mycobacterium tuberculosis.

However, S. griseus has other uses. The species produces other antibiotics, among which are some that attack tumors. It also produces commercially used proteolytic enzymes, such as pronases. These enzymes block the inactivation of sodium channels.

On the other hand, in recent years it has been determined that S. griseus produces volatile substances from the group of phenols called carvacrol. This substance has the ability to inhibit the growth of spores and mycelia of various phytopathogenic fungi.

References

1. Anderson A and E Wellington (2001) The taxonomy of Streptomyces and related genera. International Journal of Systematic and Evolutionary Microbiology 51: 797-814.
2. Danaei M, A Baghizadeh,, S Pourseyedi, J Amini and M Yaghoobi (2014) Biological control of plant fungal diseases using volatile substances of Streptomyces griseus. European Journal of Experimental Biology 4: 334-339.
3. Horinouchi S (2007) Mining and polishing of the treasure in bacterial genus Streptomyces. Biosci. Biotechnol. Biochem. 71: 283-299.
4. Ohnishi Y, J Ishikawa, H Hara, H Suzuki, M Ikenoya, H Ikeda, A Yamashita, M Hattori and S Horinouchi (2008) Genome sequence of the streptomycin-producing microorganism Streptomyces griseus IFO 13350 Journal of Bacteriology 190: 4050 - 4060.
5. Rong X and Y Huang (2010) Taxonomic evaluation of the Streptomyces griseus clade using multilocus sequence analysis and DNA-DNA hybridization with proposal to combine 29 species and three subspecies as 11 genomic species. International Journal of Systematic and Evolutionary Microbiology 60: 696-703.
6. Yepes A (2010) Two-component systems and regulation of antibiotic production from Streptomyces coelicolor. Thesis to obtain the title of Doctor from the University of Salamanca, Spain. 188 pp.