Appendix I-D 
The Impact of Genetics on Ethanol — 
A Case Study 
Objective 
This study examines how genetics can and will af- 
fect the utilization of biomass for liquid fuels produc- 
tion. There are two major areas where genetics are 
applicable. One is in plant breeding to impro\ e avail- 
ability (both quantity and quality) of biomass re- 
sources (with existing and pre\ iously unused land); 
the second is in the application of both classical 
mutation and selection procedures and the new ge- 
netic engineering techniques to develop more effi- 
cient microbial strains for biomass conversion. Ex- 
amples of goals in a plant breeding program would 
include impro\ ements in pbotosynthetic efficiencies, 
increased carbohydrate content, decreased or modi- 
fied lignin content, adaptation of high productixity 
plants to poor quality land, improved disease resist- 
ance, and so forth. However, the focus here is entire- 
ly on the second area, the use of genetics to improve 
microbial-based conversion to produce ethanol. 
In order to assess the type and extent of im- 
provements in micro-organisms that might benefit 
ethanol production, its process technology and 
economics must first be examined. An overview of 
the biomass conversion technology is presented in 
figure I-D-1; processes are defined mainly on the 
basis of the primary raw material and the type of 
pretreatment required to produce mono- or di- 
saccharides prior to fermentation. In addition, there 
are several alternative fermentation routes to pro- 
duce ethanol; these are characterized by the type of 
micro-organisms and will be examined with the in- 
Figure I-D-1. —An Overview of Alternative Routes for Conversion of Biomass to Ethanol 
Primary raw 
material 
Sugar 
(cane or beet) 
Starch 
(corn, wheat 
or tuber 
crop) 
Cellulosic biomass 
(agricultural or 
forest residue) 
Pretreatment 
Extraction 
Gelatiniza- 
tion 
Grinding, possible 
delignification 
Sucrose 
inversion 
Liquefac- 
tion, saccha- 
rifi cation 
Acid or enzymatic 
hydrolysis 
Fermentable 
substrate 
Glucose/ 
fructose 
Glucose/ 
maltose 
Glucose/cellobiose 
xylose/xylobiose 
Fermentation of 
sugar to ethanol 
Yeast 
Zymomonas 
Anaerobic bacteria 
Product 
recovery 
Ethanol and 
for fuel 
Residue 
for feed 
The arrows designate the fermentation substrate used by each type of microorganism. 
SOURCE: Massachusetts Institute ofTechnology. 
293 
