Evolution and Genetic Engineering - Bioprocess Engineering: Kinetics, Biosystems, Sustainability and Reactor Design - page 723

TABLE 14.7 Characteristics of Selected Host Systems for Protein Production from Recombinant DNA
(E ¼ Excellent; VG ¼ Very Good; G ¼ Good; F ¼ Fair; P ¼ Poor)

Organism

Characteristic E. coli S. cerevisiae Pichia pastoris Insect Mammalian

High growth rate E VG VG P-F P-F

Availability of genetic systems E G F F-G F-G

Expression levels E VG E G-E P-G

Low-cost media available E E E P P

Protein folding F F-G F-G VG-E E

Simple glycosylation No Yes Yes Yes Yes

Complex glycosylation No No No Yes * Yes

Low levels of proteolytic
degradation

F-G G G VG VG

Excretion or secretion P normally,

VG in special cases

VG VG VG E

Safety VG E VG E G

* Glycosylation patterns differ from mammalian cells.

product. In some cases, edible portions of transgenic plants can be used to deliver vaccines or
therapeutic proteins.

14.7.1. Escherichia coli
If posttranslational modifications are not necessary, E. coli is most often the first choice as
the host. The main reason for the popularity of E. coli is the broadly available knowledge base
for it. E. coli physiology and its genetics are probably far better understood than any other
living organisms. Awide range of host backgrounds (i.e. combinations of specific mutations)
are available, as well as vectors and promoters. This large knowledge base helps to facilitate
sophisticated genetic manipulations. The well-defined vectors and promoters greatly speed
the development of an appropriate biological catalyst.
The relatively high growth rates for E. coli coupled with the ability to grow E. coli to high
cell concentrations (

50 g/L) and with the high expression levels possible from specific
vector-promoter combinations (about 25 e 50% or more of total protein) can lead to extremely
high volumetric productivities. Also, E. coli will grow on simple and inexpensive media.
These factors give E. coli many economic advantages.
An important engineering contribution was the development of strategies to grow
cultures of E. coli to high cell densities. The build-up of acetate and other metabolic by-
products can significantly inhibit the growth of E. coli . Controlled feeding of glucose so as
to prevent the accumulation of large amounts of glucose in the medium prevents overflow
metabolism and the formation of acetate. Glucose feeding can be coupled to consumption

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