Biomedical Engineering Reference
In-Depth Information
2000b). In this fungus both genes are 446 bp apart, 612 bp in
Blakeslea
and
1381 bp in
Phycomyce
s. The presence of several putative light-controlling
motifs called APE in these short promoters are believed to be important for
the photoregulation of gene expression (Ruiz-Hidalgo e al. 1997, Rodríguez-
Romero and Corrochano 2004, Velayos et al. 2000a, b).
In
Phycomyces
, specifi c binding complexes were formed between the
carB-carRA
intergenic region and protein extracts from the wild type grown
in the dark or 8 minutes after irradiation. These two conditions correspond
to the points at which the expression of both genes are minimal, supporting
the hypothesis that these binding complexes are involved in the down-
regulation of the photocarotenogenesis (Sanz et al. 2010). Protein extracts
from carotene mutants disturbed in the
carRA
,
carB
,
carC
,
carS
and
carD
genes failed to form the dark retardation complex, suggesting a role of these
gene products in the regulation of the photocarotenogenesis (Sanz et al.
2010). The majority of the regulatory genes have been identifi ed only from
classical genetics, this explains the relative lack of detailed knowledge of
the complex regulation mediating carotene synthesis in
Phycomyces
and in
the rest of Mucorales. In the absence of effi cient transformation, the recent
sequencing of the
Phycomyces
genome by the Joint Genome Institute (JGI)
should facilitate the identifi cation of the genes and the understanding of the
regulatory processes. The
M. circinelloides
genome has also been sequenced
by the JGI. This fungus can be efficiently transformed and different
molecular biology approaches that can be applied which should provide
a more complete and complementary picture of the different regulatory
circuits operating in this biosynthetic pathway in Mucorales.
INDUSTRIAL PRODUCTION AND BIOTECHNOLOGY
Despite the broad range of carotenoids with interesting industrial
properties, to date only the industrial production of β-carotene from
Blakesleea trispora
mated cultures has been well established. This process
was developed in the USA (Ciegler 1965), then improved in France (Ninet
and Renaut 1979, Filkenstein et al. 1993) and is now employed in Russia.
The opposite sex strains are cultured with aeration and agitation as well
as other different factors affecting the production (Lampila et al. 1985).
In fungi the carotenoid production is still too small to attract attention
at a large-scale industrial level, but researchers are carrying out different
approaches to increase the carotenoid production by fungi, such as the
employment of chemical enhancers, improved culture media or the
development of genetic techniques to obtain overproducing strains. In
P.
blakesleeanus
,
carS
strains have an increased β-carotene production of 3-5
mg/g dry weight and the use of intersexual
carS
heterokaryons carrying
balanced lethal mutations has allowed β-carotene overproductions of up
