118 • Impacts of Applied Genetics— Micro-Organisms, Plants, and Animals 
grams (kg) of uranium oxide were obtained 
from the water. Thereafter, water was circu- 
lated through the mines as part of the mining 
operation. It has been suggested that extending 
this practice to most mines would have signifi- 
cant environmental benefits because of the 
minimal disruption of the land surface. 
Although the process is slower than the technol- 
ogy currently employed, the operating costs 
might be lower because of the simplicity of the 
system, since no grinding machinery is needed. 
Furthermore, deeper and lower grade deposits 
could be mined more readily. 
Bacterial leaching can also extract sulfur-con- 
taining compounds, such as pyrite, from coal, 
producing coal with a lower sulfur content. 
Sulfur-containing coals from such areas as Ohio 
and the Appalachian Mountains are now less de- 
sirable than other coals because of the sulfur 
dioxide they release during burning. They often 
contain up to 6 percent sulfur, of which 70 per- 
cent can be in the form of pyrite. According to 
recent data, mixed populations of different bac- 
teria, rather than a single species, are respon- 
sible for the most effective removal of sulfur— a 
finding that may lead to the genetic engineering 
of a single sulfur-removing bacterium in the 
future. 
Applied genetics in strain improvement 
The bacterium most studied for its leaching 
properties has been Thiobacillus ferroo^idans 
(which leaches copper), but others have also 
been identified in natural leaching systems. 
Although leaching ability is probably under 
genetic control in these organisms, practically 
nothing is known about the precise mecha- 
nisms. This is largely because little information 
exists in two critical areas: the chemistry of in- 
teraction between the bacteria and rock sur- 
faces; and the genetic structure of the micro- 
organisms. The finding that mixed populations 
of bacteria interact to increase leaching efficien- 
cy complicates the investigation. 
Because of the lack of genetic and biochemi- 
cal information about these bacteria, the appli- 
cation of genetic technologies to mineral leach- 
ing remains speculative. Progress in obtaining 
more information is slow because less than a 
dozen laboratories in the Nation are actively 
performing research. 
But even when the scientific knowledge is 
gathered, two obstacles to the use of genetically 
engineered micro-organisms will remain. The 
first is the need to develop engineered systems 
on a scale large enough to exploit their biologi- 
cal activities. A constant interchange must take 
place between microbial geneticists, geologists, 
chemists, and engineers. E.g., the geneticists 
must understand the needs identified by the 
geologists as well as the problems faced by the 
engineers, who must scale-up laboratory-scale 
processes. The complex nature of the problem 
can be approached most successfully by an 
interdisciplinary group that recognizes the 
needs and limitations of each discipline. 
The second obstacle is en\ironmental. In- 
troducing large numbers of genetically engi- 
neered micro-organisms into the en\ii'onment 
raises questions of possible ecological disrup- 
tion, and liability if damage occurs to the ('ini- 
ronrnent or human health. 
In summary, the present lack of sufficient 
scientific knowledge, scientists, and interdis- 
ciplinary teams, and the concei'iis for ec'ological 
safety present the major obstacles to the use of 
genetic engineering in microbial leaching. 
Metal recovery 
The use of micro-organisms to concentrate* 
metals from dilute solutions suc'h as individual 
waste streams has two goals: to re-cover metals 
as part of a recycling process: and to ('liminate* 
any metal that may lie a pollutant, I he process 
makes use of the ability of micro-organisms to 
bind metals to their surfaces and then concen- 
trate them internally. 
Studies at the Oak Kidge National l.ahoratory 
in Tennessee have shown that micio-organisms 
can he used to remove heavy metals from indus- 
trial effluents. Metals sucli as cohalt, nickel, 
silver, gold, uranium, and plutonium in concen- 
trations of less than 1 j)art |)er million (ppm) can 
be recovered. The process is particularly usetui 
for recovering metals fi'om dilute solutions ol 
