Tuesday , 16 October 2018

Novel mushroom pigment discovered in Goa

Dr. Nandkumar M. Kamat


We at Goa University are thankful to the Mycological Society Of China (https://goo.gl/kjP9Zs) for publishing our internationally peer reviewed research (purification and characterisation of a sulphur rich melanin from edible mushroom Termitomyces albuminosus Heim) on a novel pigment (due to its high sulphur content) found in local mushrooms.

Having done most exhaustive literature survey possible on microbial pigments we concluded that this is world’s first edible sulphur rich melanin with immense industrial and biomedical potential with hundreds of potential economic applications. It automatically means that any scientist in future working on this genus i.e. Termitomyces Heim, systematically researched over past 125 years, having more than 90 different taxa, examining the black pigment in any other species in field or laboratory would have to refer to our historic, pioneer publication.

But it’s a strange situation in Goa where people are more interested in consuming these species rather than understanding their ecological and scientific importance. Without any concerns for their conservation, Goans would buy the local wild, edible termite hill mushrooms, ‘roenchi alami’, belonging to genus Termitomyces at astronomical prices from this week without understanding their crucial role in the ecosystems (50 percent forest litter is converted by these species to rich soil) and the immense scientific value (these mushroom have many useful enzymes, acids and new molecules).

One of the local species, Termitomyces albuminosus screened by my PhD student, a Government of India , DST Inspire, SRF, Rosy de Souza gave her a culture which produced a nature alike black pigment and it served as a starting point for its controlled production and chemical identification. In the whole world, only we at Goa University today have this precious melanin producing culture obtained after years of efforts and the special techniques used by us. Work by de Souza as first author is published in Mycology a Journal published by USA based Taylor & Francis for Mycological society Of China.

What was the impulse behind this work? When my PhD candidate and first author Rosy de Souza approached me for her research proposal I told her about the huge contributions made on melanins by Italian chemist Rodalfo A Niolaus. I told her that during my own PhD work I had found the melanic nature of the pigment and knew the importance of studying it in detail. My guiding light was Nicolaus. In 2000 we perfected the techniques to work on tropical fungal melanins when Davina Fernandes Solomon screened hundreds of dark fungal cultures and zeroed on a superior melanin producing strain which could tightly bind iron.

It was inspiration from University of Western Ontario, Canadian fungal biochemist, MJ Butler who showed us the right direction by sending his important 1998 review paper on melanins. All natural black pigments are melanins. These are very recalcitrant, insoluble pigments. For 32 years, we have been studying the black pigment found in local mushrooms and had identified it on basis of simple chemical tests as melanin. Rosy de Souza went a step further and characterized it spectroscopically and matched it with standard pure melanin. So the presence of melanin in wild mushroom tissues was confirmed.

Her next challenge was to produce it artificially in lab under controlled conditions and then using standard techniques determine its structure. After several attempts she identified a strain which consistently gave the black pigment on growth medium. Then followed the time-consuming work of its production and purification. She prepared a far better protocol then used by many other researchers. Finally she succeeded in getting a crude melanin using shaken submerged culture conditions and the purified product was studied using  scanning electron microscopy (SEM), elemental analysis, ultraviolet and visible (UV-VIS), Fourier transformed infrared spectroscopy (FTIR), electron paramagnetic resonance (EPR) and 13C (CP/MAS) NMR spectra. Chemical tests indicated that sulphur was present. So finally the mystery of the dark, brownish-black pigment found in these species was solved. Elemental analysis of our melanin sample indicated by weight 54.6 percent carbon, 3.5 percent hydrogen, 2.4 percent nitrogen, 26.9 percent oxygen, and 12 percent sulphur.

Natural product chemists, biochemists frequently report many novel natural pigments – so what is so special about this new mushroom pigment? First – it is produced by a pure culture unlike the mushrooms of the same species in nature. Thus we have resources now to understand its full biochemistry under lab conditions. Second- there are very few sulphur rich melanins among fungal world. And this is the only sulphur rich, non toxic, edible melanin which we believe Goans have been consuming from wild mushrooms for centuries. It did not escape our notice that in strengthening the natural rubber, sulphur is added in a thermal curative process. So we suspected that the incorporation of upto 12 percent sulphur by a similar biocurative process in the complex biopolymeric scaffold of the melanin molecule would give considerable biomechanical strength to melanized mushroom tissues. Polymer chemist Professor Vishnu Nadkarni co-author from the chemistry department also contributed actively in solving the mystery of the intricate elemental composition of this recalcitrant novel molecule.

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