302 • Impacts of Applied Genetics— Micro-Organisms, Plants, and Animals 
complex molecules, ready-made, such as amino acids 
and vitamins. 
The more cheaply these nutrient needs can he 
provided, the better. Whenever an organism can be 
given genes from another source by applied biotech- 
nology techniques, there is a possibility that complex 
nutrient requirements can be obviated. However, 
this requires that all the genes in a given pathway be 
located in the source and be made to function in the 
new microbes. The feasibility of this is uncertain, but 
solutions would decrease the cost of producing etha- 
nol with yeast as well as Clostridia. 
• Stain stability.— Many of the suggested ethanol 
processes propose to employ continuous culture. 
Although this offers several advantages over batch 
culture, it is somewhat vulnerable to deleterious mu- 
tations of the microbe used, particularly if the mi- 
crobe has been extensively altered in ways that make 
it less competitive. 
These deleterious genetic changes are almost en- 
tirely catalysed by biological systems in the microbe. 
Alteration of these systems, so that the frequency of 
unwanted genetic changes is decreased, could great- 
ly extend the period of operation that is possible 
before having to shut down and restart the fermen- 
tation. So far, this is a possibility only in microbes 
that have a highly developed genetics. It may be that 
strain stabilization of this sort would not be possible 
in other microbes until their genetics are highly de- 
veloped. 
It is also possible to design strategies using current 
strain development techniques that might lead to 
genetically stable strains, but these are unproven. 
• Cell separations.— Many fermentation schemes 
incorporate cell recycle to boost productivity. This 
requires that cells be separated from effluent broth. 
Others need to separate cells from other residue as a 
byproduct. In addition, some of the low-energy alter- 
natives to distillation, such as adsorption, could re- 
quire separation of the cells from the broth prior to 
ethanol recovery. 
In these cases, microbes that can be made to floe- ’ 
culate and redisperse, or that can be made to rever- 
sibly change their morphology would allow cheap 
gravity separations (settling or flotation). 
• Operating conditions.— An increase in the 
temperature an organism will tolerate is advanta- 
geous for heat removal and in situ ethanol removal 
schemes. The feasibility of accomplishing this is 
uncertain. 
The extreme of productivity improvement via cell 
recycle is an immobilized cell reactor. It is con- 
ceivable that cells could be made less prone to 
degradation under the conditions of immobilization, 
by modifying sensitive components and degradation 
systems, and by adding protective systems. This is 
not at all a near-term possibility. 
• Range and efficiency of substrate utilization.— A 
single-step conversion of a substrate to ethanol is 
highly desirable. This often requires that the ethanol 
fermenting organism possess a degradation capabili- 
ty it does not have. 
As an example, consider ligno-cellulose. It consists 
of hexosans, pentosans, and lignin. All of these com- 
ponents should be used. Assume that one cellulase- 
producing candidate does not use pentoses, while a 
related noncellulase producing organism does, this is 
exactly the situation with clostridia. If the second 
organism can be given the cellulase genes of the first, 
a microbe better-suited to direct conversion could he 
created. The pace at which such a manipulation 
could be developed cannot be predicted with con- 
fidence, although this is not necessarily a long-term 
prospect. 
Another obvious area that merits attention is the 
enhancement of cellulase activity. Classical genetic 
manipulations, employing mutation and selection or 
screening, should result in micro-organisms better 
equipped to degrade cellulose. E.g, it should he possi- 
ble to isolate strains that are deregulated in cellulase 
production (hyperproducers) as well as those in 
which the cellulase is not subject to [jroduct inhibi- 
tion. In addition, it is tempting to think about the 
possibilities of amplifying cellulase genes by im'ans 
of DNA technology and cloning. How(ner, this latter 
approach must await further understanding of the 
biochemistry and genetics of the cellulase .system as 
well as the development of the a|)pi'opriate genetic 
systems in cellulolytic micro-organisms. 
Utilization of fermentation byproducts 
Presently for each gallon of ethanol |)rodueed, ap- 
proximately 14 liters of stillage is formed.'^ If ethanol 
is mixed with gasoline to make gasohol (10 percent 
ethanol), the total stillage pioduci'd annually iti the 
United States would he in tlie billions of liters. Sui ('ly 
a problem of this magnitude d(?sern!s serious atten- 
tion. The utilization of stillage or ferm(>ntation by- 
products could be greatly improved In genetic 
means in several ways. In actuality, only a lational 
long-range genetic approach can increa.se tin* value 
of such a fermentation byproduct. V alue can he in- 
creased in two main ways. The fir st is to increase the 
nutritive value of the fermentation byproduct fol- 
lowed by develoiring economical processing technol- 
*^W. K. Tyner, ' The j^otenlliil ot ( )l)l.iinin/' I .nei \ mm \i;i m ulhi' • 
posium on Biulerhnolof^v: I'lw hlnrri^v Pnuiin tinn ntuf ( tmsri \ (..iilut 
berg, Tenn., 1979. 
