Pigment characteristics of melanin produced by Streptomyces glaucescens NEAE-H

Melanin which is the black pigments assists the bacteria by protesting they from chemical and biochemical stresses.

Figure 2: (A) Image of Streptomyces glaucescens strain NEAE-H cultured on a peptone yeast agar plate. (B) An Image of Streptomyces glaucescens strain NEAE-H grown in a culture broth showing the pigment produced.

Melanin producing bacteria are fairly common as this pigment provides a significant advantage to the bacterium. However Streptomyces glaucescens strain NEAE-H is particularly important as it has the ability to produce a much larger quantity of extracellular melanin. Melanin is formed by oxidative polymerization of phenolic or indolic compounds which produces the black pigment. Melanin already has many know functions that have been exploited to benefit humanity. Extracellular Melanin has anticancer and antioxidant activity. It prevents the damaging effect of UV light on bacterium by preventing the oxidative reactions that occur with in the cells which cause damage.

The production of black pigments in bacteria was discovered more than a century ago and related to tyrosine metabolism. However, their diverse biological roles and the control of melanin synthesis in different bacteria have only recently been investigated. The broad distribution of these pigments suggests that they have an important role in a variety of organisms. Melanins protect microorganisms from many environmental stress conditions, ranging from ultraviolet radiation and toxic heavy metals to oxidative stress. Melanins can also affect bacterial interactions with other organisms and are important in pathogenesis and survival in many environments. Bacteria produce several types of melanin through dedicated pathways or as a result of enzymatic imbalances in altered metabolic routes. The control of the melanin synthesis in bacteria involves metabolic and transcriptional regulation, but many aspects remain still largely unknown. The diverse properties of melanins have spurred a large number of applications, and recent efforts have been done to produce the pigment at biotechnologically relevant scales.

Synthetic pigments have been widely used in various applications since the 1980s. However, the hyperallergenicity or carcinogenicity effects of synthetic dyes have led to the increased research on natural pigments. Among the natural resources, bacterial pigments are a good alternative to synthetic pigments because of their significant properties. Bacterial pigments are also one of the emerging fields of research since it offers promising opportunities for different applications. Besides its use as safe coloring agents in the cosmetic and food industry, bacterial pigments also possess biological properties such as antimicrobial, antiviral, antioxidant and anticancer activities. This review article highlights the various types of bacterial pigments, the latest studies on the discovery of bacterial pigments and the therapeutic insights of these bacterial pigments which hopefully provides useful information, guidance and improvement in future study.

Researchers have developed a melanin-enhanced cancer immunotherapy technique that can also serve as a vaccine, based on early experiments done in a mouse model. The technique is applied via a transdermal patch. Melanin is a natural pigment that can efficiently transform absorbed sunlight energy into heat," says Zhen Gu, corresponding author of a paper on the work and an associate professor in the joint biomedical engineering program at North Carolina State University and the University of North Carolina at Chapel Hill. "We demonstrated that melanin, which is found at high levels in melanoma, can actually be used to help treat melanoma. We do this by shining near infrared (IR) light on a therapeutic skin patch, which promotes the systemic immune response that fights cancer."

Exposure to the shortest wavelengths in sunlight, ultraviolet light, constitutes a deleterious ecological factor for many microorganisms. The use of secondary metabolites as sunscreens has emerged as an important photoprotective mechanism in certain groups of large-celled microorganisms, such as cyanobacteria, fungi and many protists. In this Review, we describe our current understanding of microbial 'sunscreen' compounds, including scytonemin, the mycosporines and the naphthalene-based melanins. Study of these sunscreens has led to the discovery of new classes of compounds, new metabolic pathways, a deeper understanding of microbial photobiology and the potential for dermatological or biomedical applications.