Biomedical Engineering Reference
In-Depth Information
INTRODUCTION
Over 1.5 million different fungi are estimated to be present in nature,
living in very diverse natural environments as dry soils, rotting fruit
and salty oceans, appearing in different forms ranging from single cells
to mushrooms. This implies that fungi have a wide range of enzymes
enabling consumption of, but also protecting from and competing against
competitors for, the diverse and sometimes scarce set of available nutrients.
It is for this that mankind has been using fungi for a long time in the
production of beverages, fl avors and fermented vegetables like maize and
cabbage. Since the 20th century, fungi and their isolated enzymes have also
been successfully developed as selective biocatalysts. Screening for fungi
and enzymes is relatively simple, allowing the evaluation of thousands of
candidates in a short time. Moreover, fungi and enzymes can be produced
at large scale using inexpensive media and short fermentation cycles. This
has lead to a multi-billion dollar industry in which hundreds of products
are being made using fungal enzymes. Familiar processes as penicillin
production, the depolymerization of (ligno)cellulose, phosphate liberation
in animal feed and lactose degradation in dairy products, are therefore
economically dependent on the functioning of fungal enzymes.
In this chapter, we will focus on the use of fi lamentous fungal enzymes
in food, bio-based and pharmaceutical applications.
ORIGIN OF FILAMENTOUS FUNGAL ENZYMES
Filamentous fungal enzymes used in industry can originate from any
type of fungus, but historically most are obtained from ascomycete fungi
as
Aspergillus
,
Trichoderma
and
Penicillium
. For these, well established
large scale production systems have been developed (see below) and
as expression of homologous enzymes is often easier than heterologous
enzymes it is more advantageous to produce host-originated enzymes
and metabolites. Recently, the genome sequences of all important
fi lamentous fungal production hosts have been deciphered (
A. niger
,
Pel et al. 2007,
A. oryzae
, Machida et al. 2005,
T. reesei
, Martinez et al.
2008,
A. terreus
,
http://www.broadinstitute.org/annotation/genome/
aspergillus_group/GenomesIndex.html,
P. chrysogenum
, van den Berg
et al. 2008,
Chrysosporium lucknowense
, Visser et al. 2011). Only in the
single genome of
A. niger
already 171 carbohydrases and 198 proteins
involved in proteolytic degradation, including 9 aspartyl endoproteases,
10 serine carboxypeptidases and 9 di- and tripeptidylaminopeptidases,
were identifi ed. This wealth of new sequences led to the identifi cation and
development of new fungal biocatalysts such as prolyl specifi c proteases
