Biomedical Engineering Reference
In-Depth Information
to 25 mg/g dry weight (Murillo et al. 1978, Murillo et al. 1982). In other
fungi, such as
M. circinelloides
, some carotenoid overproducing strains have
been isolated by mutagenesis processes (An et al. 1991, An 1997, Ciegler
1965, Velayos et al. 1997). Different approaches have been developed to
adapt the fungal growth and carotenoid syntheses to the most industrial
requirements. In
P. blakesleeanus
surface cultures have been shown to be
more productive than shaken cultures. In
B. trispora
and in
P. blakesleeanus
temperature conditions also infl uence carotenoid production, the synthesis
being more effi cient below 25ºC. In
M. circinelloides
monomorphic mutants
that grow exclusively as yeast in aerobic conditions may be preferred
by the fermentation industry because they allow growth in submerged
conditions, the biomass production is usually higher and the cells are more
easily separated from the culture media (Iturriaga et al. 2000). One of the
newest applications of the synthesis of carotenoids is the development of
new experimental techniques to produce carotenoids in different types of
organisms that lack this biosynthetic pathway. For instance, the phytoene
synthase gene from daffodil was introduced into rice, obtaining transgenic
rice that accumulates phytoene as a source of provitamin A (Burkhardt
et al. 1997). For a review of metabolic engineering of carotenoids see
Namitha and Negi 2010.
As we have seen, potential alternatives to
Blakeslea
may be
Mucor
and
Phycomyces
. The advantage of
Phycomyces
lies in the large amount of
information accumulated regarding its biology. The disadvantages are the
small production of carotenoids in shaken cultures and the failure to obtain
stable transformants. For the time being
Mucor circinelloides
produces less
β-carotene than
Phycomyces
or
Blakeslea
, but the existence of a transformation
system opens new possibilities for increasing the production of carotenoids.
Carotenoids and their derivatives are playing an increasing role in the
biotechnological industry of the developed world. This is a multimillion
dollar market established during the last 20 years. Today, chemical synthesis
is fulfi lling most of this demand. The lower yield, longer production
time, lack of indoor mass production facilities of microbial sources and
poor exploitation of biosynthetic pathways are the major obstacles in the
implementation of microbial technology (Iturriaga et al. 2000). Nevertheless,
the recent research carried out on the synthesis and regulation of
carotenogenesis in fungi has made possible the determination of the nature
of the genes and enzymes responsible for this synthesis, which is allowing
the development of different strategies to boost industrial production of
these compounds. In recent years the availability of genomic sequences of
several of these organisms is permitting the discovery of new genes involved
in this process, which will undoubtedly lead, in the near future, to the
development and improvement of technology that will increase industrial
effi ciency in the production of carotenoids in fungi.
