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. 2014 Jan 9;9(1):e84574.
doi: 10.1371/journal.pone.0084574. eCollection 2014.

Melanin from the nitrogen-fixing bacterium Azotobacter chroococcum: a spectroscopic characterization

Aulie Banerjee  1 , Subhrangshu Supakar  1 , Raja Banerjee  1
Affiliations

Melanin from the nitrogen-fixing bacterium Azotobacter chroococcum: a spectroscopic characterization

Aulie Banerjee et al. PLoS One. .

Abstract

Melanins, the ubiquitous hetero-polymer pigments found widely dispersed among various life forms, are usually dark brown/black in colour. Although melanins have variety of biological functions, including protection against ultraviolet radiation of sunlight and are used in medicine, cosmetics, extraction of melanin from the animal and plant kingdoms is not an easy task. Using complementary physicochemical techniques (i.e. MALDI-TOF, FTIR absorption and cross-polarization magic angle spinning solid-state (13)C NMR), we report here the characterization of melanins extracted from the nitrogen-fixing non-virulent bacterium Azotobacter chroococcum, a safe viable source. Moreover, considering dihydroxyindole moiety as the main constituent, an effort is made to propose the putative molecular structure of the melanin hetero-polymer extracted from the bacterium. Characterization of the melanin obtained from Azotobacter chroococcum would provide an inspiration in extending research activities on these hetero-polymers and their use as protective agent against UV radiation.

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Conflict of interest statement

Competing Interests: The authors have declared that no competing interests exist.

Figures

Figure 1
Figure 1. Partial MALDI-TOF MS [M+H]+ and [M+Na]+ spectrum of the dark brown compound(s) obtained from the bacterium Azotobacter chroococcum.
Figure 2
Figure 2. FTIR absorption spectrum (in KBr pellet under complete dry conditions in a nitrogen atmosphere) of the dark brown compound(s) obtained from Azotobacter chroococcum.
Figure 3
Figure 3. Natural abundance CPMAS solid-state 13C-NMR 1D-spectrum of the dark brown compound(s) obtained from bacterium Azotobacter chroococcum.
Figure 4
Figure 4. m/z values of the compound(s) obtained from the bacterium Azotobacter chroococcum in MALDI-TOF MS spectrum representing molecular ions corresponding to two sets of [M+H]+ and [M+Na]+ having difference of 191amu (one unit 5,6-dihydroxyindole-2-carboxylic acid).
Figure 5
Figure 5. Proposed putative structure(s) of the protomolecules of melanin hetero-polymers, obtained from the nitrogen-fixing soil bacterium Azotobacter chroococcum.
See this image and copyright information in PMC

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