Trusha Daya
My adopted bacterium that I would like to share with everyone is Streptomyces elicolor . I have chosen this beautiful, deep blue bacterium as it intrigued me when i found out that the smell from wet soil on a rainy morning does not actually come from the soil alone, but actually from the Streptomyces living within it.
Streptomyces is a genus of Gram-positive bacteria that grows in various environments, and its shape resembles filamentous fungi. The morphological differentiation of Streptomyces involves the formation of a layer of hyphae that can differentiate into a chain of spores. The most interesting property of Streptomyces is the ability to produce bioactive secondary metabolites, such as antifungals, antivirals, antitumorals, anti-hypertensives, immunosuppressants, and especially antibiotics. The production of most antibiotics is species specific, and these secondary metabolites are important for Streptomyces species in order to compete with other microorganisms that come in contact, even within the same genre. Despite the success of the discovery of antibiotics, and advances in the techniques of their production, infectious diseases still remain the second leading cause of death worldwide, and bacterial infections cause approximately 17 million deaths annually, affecting mainly children and the elderly. Self-medication and overuse of antibiotics is another important factor that contributes to resistance, reducing the lifetime of the antibiotic, thus causing the constant need for research and development of new antibiotics.
Streptomyces coelicolor, a filamentous, high G-C, gram-positive bacteria, was first dubbed Streptothrix coelicolor in 1908 by R. Muller after he found it on a potato(2). Later, it became known as Streptomyces coelicolor. The Streptomyces coelicolor
A3(2) strain studied in depth by David A Hopwood and sequenced by the John Innes Center and the Sanger Institute is actually taxonomically a member of the Streptomyces violaceoruber genus, although it retains the former name, and is not the same strain as the Muller strain(25). Streptomyces coelicolor, like the streptomyces genus in general, live in the soil. Streptomyces are responsible for much of the break down of organic material in the soil as well as the “earthy” smell of soil. They also live in colonies and have structural similarities to fungus. Colonies of Streptomyces coelicolor release pigments that are blue/green in alkali and red in acidic conditions, thereby giving the bacterial colonies those colors under the respective conditions. Other differentiating characteristics of Muller's Streptomyces coelicolor are grayish-yellow aerial mycelium, smooth spores, aerial mycelium lacking spirals, and no melanoid pigment(5). Since the A3(2) strain is actually Streptomyces violaceoruber, it looks a bit different. One distinction is that the A3(2) strain has ash gray aerial mycelium with spirals(5). From this point on, I will refer to Streptomyces coelicolor as the A3(2) strain and not Muller's strain because the A3(2) strain was sequenced, and a great deal of information is available about it. Streptomyces coelicolor are important bacteria and were sequenced because of their “adaptability to environmental stress”, “source of bioactive molecules for medicine and industry”, and “relat[ion] to human pathogens”(3). Streptomyces coelicolor has a very similar core genome to Mycobacterium tuberculosis and Corynebacterium diphtheriae, as well as some similarity to Mycobacterium leprae, so it can be used to study these disease causing bacteria(4). The Streptomyces genus is responsible for producing a majority of the antibiotics in use today, as well as some immunosuppressants and anti-tumor agents. Streptomyces coelicolor also has an interesting life-cycle that includes differentiation into aerial mycelium and spore formation(3).
The genetically well-known strain Streptomyces coelicolor A3(2) produces the pH indicator (red/blue) antibiotic actinorhodin, but not all the "blue pigment" produced by this strain is actinorhodin. When the organism was subjected to various nutrient limitations (ammonium, nitrate, phosphate, or trace elements), and also during growth cessation caused by a relatively low medium pH, blue pigment production was initiated but the pigment and its location varied. At pH 4.5 to 5.5, significant formation of actinorhodin occurred and was located exclusively intracellularly. At pH 6.0 to 7.5 a different blue pigment was produced intracellularly as well as extracellularly. It was purified and identified as gamma-actinorhodin (the lactone form of actinorhodin). Analysis of act mutants of S. coelicolor A3(2) confirmed that both pigments are derived from the act biosynthetic pathway. Mutants with lesions in actII-ORF2, actII-ORF3, or actVA-ORF1, previously implicated or suggested to be involved in actinorhodin export, were impaired in production of gamma-actinorhodin, suggesting that synthesis of gamma-actinorhodin from actinorhodin is coupled to its export from the cell. However, effects on the level of actinorhodin production were also found in some mutants.
Expression of specific modifying enzymes in an organism producing a natural product can lead to tailoring of the structure and can be used to enhance the bioactivity. One of the first examples was the introduction of some of the genes for the biosynthesis of the polyketide actinorhodin (a blue antibiotic) from Streptomyces coelicolor into medermycin (a yellow antibiotic) producing Streptomyces AM7161, resulting in the production of hybrid mederrhodins (which had a red color).60 This was found to be caused by the addition of a hydroxyl at position C-6, added by a P450 from the actinorhodin cluster (see Fig. 5A).
Colors from natural sources are gaining popularity because synthetic colors are carcinogenic. Natural colors are obtained from plants or microorganisms. Pigments produced by microorganisms have advantages over plant pigments, due to their ease of use and reliability. In the present study, a blue pigment producing actinomycete klmp33 was isolated from the Gulbarga region in India. The isolate was identified based on morphologic, microscopic, and biochemical characterization, and 16S rRNA sequencing. Phylogenetic analysis of the isolates showed a close relationship with Streptomyces coelicolor. Pigment produced by the isolate was analyzed using UV–visible spectroscopy, thin-layer chromatography, Fourier transform infrared and liquid chromatography/mass spectroscopy analysis, and was identified as γ actinorhodin. γ-Actinorhodin is used as a pH indicator which deviates from acid to non-acid. Moreover, it subrogates synthetic dye.
This deep blue filamentous bacteria produces well-developed vegetative hyphae with branches. They form a complex substrate mycelium that aids in scavenging organic compounds from their substrates.
Streptomycetes are the most widely studied and well known genus of the actinomycete family. Streptomycetes usually inhabit soil and are important decomposers. They also produce more than half of the world's antibiotics, and are consequently invaluable in the medical field.
