129
Tab. 6.1:
Journal articles dealing with pigments and different organisms.
Key words
Number of journal articles
Pigments
136,705
Plant pigments
14,517
Bacterial pigments
5,752
Microbial pigments
2,230
Fungal pigments
1,551
Microbial natural pigments
261
Database survey conducted on April 2015 (SCOPUS).
Moreover, a variety of strains are well known. This will depend on market and consumer’s
expectations, industrial prices and availability (Dufossé et al., 2014). Another expectative is
to use cheaply available organic residues from industries as substrate (See Babitha, 2009).
6.3 Microbial pigments in natural sites
The high number of ecosystems and plant diversity described worldwide suggest that, most
habitats are underexplored for microbial occurrence. Interest in natural sites to be prospected
is increasing in parallel with the recognition that novel compounds from fungi to obtain
several drugs will valuate the fungal bio-prospecting market. Moreover, researchers have
stressed the urgent need to search for sites and substrates with high fungal richness towards
protection of fungal resources for unique compound detection (Tang et al., 2007). Preserving
ecosystem biodiversity will help to maintain its multifunctionality, which can be decisive to
obtaining new compounds against microorganisms. For example, Dark septate endophytes
(DSE) are frequently associated to roots of numerous endemic and endangered plants, still
more in tropical regions where many fungi remain new to science (Hawksworth, 2001).
The kingdom Fungi (yeasts and filamentous fungi) are a promising source able to produce
different both primary and secondary metabolites, which include peptides, enzymes, acids,
antibiotics and pigments. Fungi called “black fungi” includes different species are able to
produce a mixture of several different pigments to survive adverse conditions (carotenoids,
lycopene and xanthophylls can predominate). For example, carotenoids protect the fungus
from damaging sunlight and UV light; melanin and sporopollenin found in the spores and
hyphal walls protect from radiation and drought (Reviewed by Pagano and Dhar, 2015).
Additionally, fungal pigments have been reported as bioactive compounds with antioxi-
dative, free radical scavenging, anticancer, immunomodulatory, antiviral and antibacterial
activities, many of these pigments are quinones or similar conjugated structures (Velísek and
Cejpek, 2011).
One of the most important pigments produced by fungi are the melanins (Fig. 6.1), which
are high molecular weight pigments and displayed different biological functions (Hill, 1992).
130
6 Microbial Pigments
Several fungal species are able to produce melanin, which seems to confer advantage to
survive in the environment by protecting against environmental predators, heavy metals
toxicity, and physical insults such as UV and solar radiation (Nosanchuk and Casadevall,
2003). Melanized fungi were found on the walls of damaged reactor in Chernobyl, which
were consequently exposed to high levels of radiation (Mironenko et al., 2000). After that,
further studies were made to investigate the radioprotective activity of microbial melanins
(Dadachova et al., 2007).
Researchers have bio-explored for stressed and extreme habitats worldwide. Vaz et al. (2011)
investigated yeasts diversity from different sites in Antarctica. They studied rhizospheric Des-
champsia Antarctica soil, ornithogenic (penguin guano) soil, water from lakes, seawater and
sediments. Besides possible novel species identification, they found that ten yeast isolates
produced mycosporines and that more than 40 % produced pigments and could be considered
adapted to survive in the continent. The adaptation of yeasts to cold habitats reveals struc-
tural and biochemical characteristics, such as the production of photoprotective compounds
(carotenoids and mycosporines), as possible strategy to survive in extreme environments
(Libkind et al., 2009; Thomas-Hall et al., 2010). Mycosporines (watersoluble, UV-absorbing
compounds) in yeasts from high-altitude lakes have been correlated with the survival of some
species adapted to these environments (Libkind et al., 2005; Libkind et al., 2009).
In addition, Fernández et al. (2012) analyzed the yeast and yeast-like fungi present on
Nothofagus nervosa (raulí) dry fruits. In this work, a total of 171 isolates corresponding to
17 species were recovered, most of which belonged to the phylum Ascomycota (78 % of the
isolates and 61 % of the species). All the ascomycetous species were dark pigmented melanin
containing yeast-like fungi, while only one basidiomycetous species was pigmented (Rhodo-
torula colostri, a pink carotenogenic yeast). Besides, most of the species present on N. nervosa
fruits (71 %) were capable of synthesizing mycosporines. It is important to mention that the
three most abundant species (which accounted for 73 % of the isolates) corresponded to
melanin and mycosporine producing yeast-like fungi (Ascomycetous yeast sp. 1, Aureobasi-
dium pullulans and Dothichiza sp. 1), being two of them novel species (Tab. 6.2). It has been
described that mycosporines, as well as pigments such as melanin and carotenes, play an
(a)
(b)
Fig. 6.1:
Fungal colonies isolated from environmental samples showing
different pigments (Photographs by L H Rosa).
6.3 Microbial pigments in natural sites
131
antioxidant role in addition to UV protection (Pagano and Dhar, 2015; Moliné et al. 2011,
Fernández et al. 2012). Altogether, these results highlight how important these components
(carotenes, melanin, mycosporines) are for surviving in harsh environments, usually char-
acterized by reduced access to nutrients, high fluctuations in temperature and exposure
to desiccation and/or high UV radiation. Considering the adaptation strategies (carotenes,
melanin, mycosporines) of different microorganisms to this type of environments together
with the high proportion of novel species present in them, they should be considered one of
the main research targets for looking for species capable of synthetizing molecules of bio-
technological importance, appropriate for the bio-prospecting market.
Tab. 6.2:
Fungal species isolated from Nothofagus nervosa dry fruits surface. % = percentage out of the total
number of isolates, Pig = pigments, M = melanin, C = carotenes, Myc = mycosporines, +/– = presence/
absence.
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