54 • Impacts of Applied Genetics — Micro-Organisms, Plants, and Animals 
nomically, and new enzymes must be added for 
each production cycle. Furthermore, the en- 
zymes are difficult to separate from the end 
product and constitute a potential contaminant. 
Because enzymes used in the continuous meth- 
od are reusable and tend not to be found in the 
product, the continuous method is the method 
of choice for most processes. Depending on the 
desired conversion, the immobilized micro- 
organisms of figure 18 could be replaced by an 
appropriate immobilized enzyme. 
Although more than 2,000 enzymes have 
been discovered, fewer than 50 are currently of 
industrial importance. Nevertheless, two major 
features of enzymes make them so desirable: 
their specificity and their ability to operate 
under relatively mild conditions of temperature 
and pressure. (The most frequently used en- 
zymes are listed in table 2.) 
Comparative advantages of 
fermentations using whole cells 
and isolated enzymes 
At present, it is still uncertain whether the 
use of whole cells or isolated enzymes will be 
more useful in the long run. There are advan- 
tages and disadvantages to each. The role of ge- 
netic engineering in the future of the industry. 
Table 2.— Enzyme Products 
Source/name 
Commercially 
available before: 
Current 
production 
tons/yr 
1900 
1950 
1980 
Animal 
Rennet 
X 
2 
Trypsin 
X 
15 
Pepsin 
X 
5 
Plant 
Malt amylase 
X 
10,000 
Papain 
X 
100 
Microbial 
Koji 
X 
? 
Fungal protease 
X 
10 
Bacillus protease .... 
X 
500 
Amyloglucosidase . . . 
X 
300 
Fungal amylase 
X 
10 
Bacterial amylase .... 
X 
300 
Pectinase 
X 
10 
Glucose isomerase. . . 
X 
50 
Microbial rennet 
X 
10 
however, will be partly determined by which 
method is chosen. With isolated enzymes, ge- 
netic manipulation can readily increase the sup- 
ply of enzymes, while with whole organisms, a 
wide variety of manipulations is possible in con- 
structing more productive strains. 
The relationship of genetics 
to fermentation 
Applied genetics is intimately tied to fermen- 
tation technology, since finding a suitable spe- 
cies of micro-organism is usually the first step in 
developing a fermentation technique. Until re- 
cently, geneticists have had to search for an 
organism that already produced the needed 
product. However, through genetic manipula- 
tion a totally new capability can be engineered; 
micro-organisms can be made to produce sub- 
stances beyond their natural capacities. The 
most striking successes have been in the phar- 
maceutical industry, where human genes have 
been transferred to bacteria to produce insulin, 
growth hormone, interferon, thymosin a-1, and 
somatostatin. (See ch. 4.) 
In general, once a species is found, coinen- 
tional methods have been used to intluce muta- 
tions that can produce even more of the d(\sired 
compound. The geneticist searches fi-om among 
hundreds of mutants for the one micro-orga- 
nism that produces most efficiently. Most of th(’ 
many methods at the microbiologist’s disposal 
involve trial-and-error. Newer g(Mi(!ti(' t('('h- 
nologies, such as the use of recombinant DNA 
(rDNA), allow approaches in which us(’ful genet- 
ic traits can be inserted dir(u;lly into the? micro- 
organism. 
The current industrial approach to lermenta- 
tion technologies therefore consid(>i's two prob- 
lems: First, whether a biological process can 
produce a particular product: and second, w hat 
micro-organism has the gr(;aU‘st potential lor 
production and how the cUisircnl characlei islies 
can be engineered for it. Finding the desii-ed 
micro-organism and improving its capability is 
so fundamental to the lernu'ntation industry, 
that geneticists have hec'onu^ im|)oi tant mem- 
bers of fermentation i'(!S(Nirch teams. 
SOURCE: Office of Technology Assessmerrt. 
