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OCR for page 123
11
Conclusions and Recommendations
Microorganisms
Mankmd hap a long history of using microorganisms ~ food
processing, agriculture, waste treatment, and in other beneficial am
plications. New molecular methods for genetically modifying m~-
croorg=~srns will expand the range of beneficial applications, for
example, in control of plant disease ~d ~ biodegradation of toxic
pollutants.
In many respects, molecular methods resemble the classical
methods for modifying particular strains of microorganisms, but
many of the new methods have two features that make them even
more useful than the classical methods. Precision allows scientists
to make genetic modifications in ~n~crobial strains that can be cha~-
acter~zed more fully, in some cases to the level of the DNA sequence.
This reduces the degree of Certainty associated with any intended
application. The new methods have greater power because they
enable scientists to isolate genes and transfer them across natured
barriers.
The power of these new techr iques creates the opportunity for
new applications of microorganisms. Despite some initial concerns
over the use of recombinant methods in laboratory research' it is
now clew that these methods in themselves are not intrinsically
dangerous.
The next step after laboratory experunentation is to test modi-
fied microorganisms ~ the field, arid establishing a scientifically based
123
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i24
framework for decisions on field testing has been a primary purpose
in this report. No adverse effects of introductions have been seen
and an extensive body of information documents safe introductions
of some microorganisms, such as the rhizobia, mycorrhizal fungi,
bacuToviruses, Bacillus thuringiensis, and Agrobacterium radiobac-
ter. However, less is known about field tests of microorganisms than
of plants. Thus, for unfamiliar applications, it is prudent to prepare
for the control of the introduced rn~croorganisms.
Questions concerning the effects of an introduced microorgan-
ism arise whenever the intended introduction differs substantially
from those with an established record of safety. Such questions as
unintended persistence and possible adverse effects should be ad-
dressed scientifically, and as the scientific community continues to
accumulate information regarding the safety or risk of environmental
applications of microorganisms in field tests, levels of oversight can
be tuned to the needs of particular situations.
~ the recommendations that follow, a framework has been de-
veloped as a basis for a workable and scientifically based evaluation of
the safety of microorganisms intended for field testing. This frame-
work has been developed from consideration of three criteria: (1)
familiarity with the history of introductions similar to the proposed
introduction (Chapter 7), (2) control over persistence and spread
of the introduced microorganism as well as over exchange of ge-
netic material with the indigenous microflora (Chapters 8 through
10), and (3) environmental effects, including potential adverse effects
associated with the introduction (Chapters 9 and 10).
The framework does not distinguish between classical and molec-
ular methods of genetic manipulation, nor between modified and un-
modified genotypes. The framework is product- rather than pracess-
oriented, focusing on the properties of the microorganism rather
than on the methods by which it is obtained. Knowledge of the
methods used may nonetheless yield useful information concerning
the precision of genetic characterization of the rn~croorganism, which
in turn may be relevant for assessment of its si~nilarity to previous
applications, persistence, and possible effects after introduction.
The framework has not focused on other variables, often sug-
gested as criteria for oversight, because they convey relatively less
scientifically useful information for assessments: the sources of genes,
whether recombinants are intra- or intergeneric, and whether cod-
ing or noncoding regions of the genome have been modified. The
OCR for page 125
125
necessity of using, whenever possible, sunple and readily identifiable
criteria for oversight is recognized.
Terms such as Uncertainty, ~sufficient," and Significant are
used in the framework without precisely defining their quantitative
tenets. Any specific numerical values assigned would be arbitrary
and subject to disagreement, as some underlying variables may be
difficult to quantify precisely. In the final analysis, assignment of
risk categories must mclude a rational examination of the relevant
scientific knowledge for each introduction.
In the framework, assessments of potential risks arising from the
introduction of mucroorganisms into the environment are made ac-
cording to the three major criteria of familiarity, control, and effects.
Upon evaluation of these three criteria, a proposed introduction can
be field-tested according to establisher] practice or it can be assigned
to one of three levels of concern: low, moderate, or high uncertainty
(Fig. 11-13. The framework is inherently flexible, allowing an appli-
cation to be reassigned to a different category as additional scientific
information is obtained that is relevant to any of the three criteria.
Small-scale field tests can proceed according to established prac-
tice if the microorganism used, its intended function, and the target
environment are all sufficiently similar to prior Introductions that
have a safe history of use (Fig. 11-2~. Rhizobium used for enhance-
ment of nitrogen fixation in leguminous crops provides a familiar
example.
If an introduction does not satisfy the farn~liarity criteria, it is
evaluated with respect to both our ability to control the m~croorgan-
ism's persistence and disserrunation and the microorganism' poten-
ti~ for significant adverse effects (Fig. 11-1~. For example, Rhizobium
modified to encode an insecticidal toxin would not be a familiar ~ntro-
duction, even though it might well prove to be safe. An introduction
is considered to be in the low-uncertainty category if it satisfies
appropriate criteria with respect to both controllability =d low po-
tentia] to result In adverse effects. An Introduction ~ considered
to be in the moderate-uncertainty category if it satisfies criteria for
either controllability or potential effects, but not both. An mtroduc-
tion ~ considered to be in the high-uncertainty category if it satisfies
neither the control nor the effects criterion (Fig. 11-1~. The high
uncertainty status implies that potential adverse effects exist and are
coupled with potential inability to control the microorganism, and
hence its potential effects.
OCR for page 126
126
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Specific criteria for evaluating control of the microorganism af-
ter it is introduced must include the potentials for persistence of
the introduced microorganism, genetic exchange between the intros
duced and indigenous microorganisms, and spread of the introduced
microorganism to nontarget environments (Fig. 11-3~. A series of
questions to be addressed in evaluating the potential for unwanted
persistence of an introduced microorganism Is illustrated In Fig. 11-4.
Criteria for evaduat~g ejects must depend, at least in part,
on the intended function of the introduced microorganism in its
target environment (Fig. 11-5~. Thus, a proposed field test of a
bacterium to be used for biodegradation of a toxic poDut ant should be
preceded by definitive laboratory experiments and should be designed
to determine whether toxic by-products of the degradation may be
created and persist.
As the agencies grant permission to introduce genetically mod-
ified microorganisms in field tests, they will receive advice Dom
panels of experts who can utilize the decision framework described
here. With experience, familiarity wiD increase, and we anticipate
this will be accompanied by adjustments in the rigor of oversight.
