9 
becomes available, use it as a basis for the review of the pathogen listing 
in Appendix B of the Guidelines. He added that the working group would 
also consider the advisability of eliminating opportunistic pathogens 
from Appendix B. 
Dr. Barkley said the working group would in addition also evaluate strat- 
egies for dealing with nonhuman pathogens. No listing of such pathogens 
is available and these pathogens are not currently listed in the Guidelines. 
CT. Barkley said the 1974 National Cancer Institute (NCI) listing of onco- 
genic viruses entitled "Safety Standards for Research Involving Oncogenic 
Viruses" which appears in Appendix B as Appendix B-II is out of date. The 
data base on which recommended safeguards can be constructed has signifi- 
cantly increased over the last decade. He said the NCI, in collaboration 
with the NIH Division of Safety, is planning to revise that document. The 
revised document, when available, will be distributed to the working group 
and the classification of oncogenic viruses in the NIH Guidelines for 
Research Involving Recombinant DNA t Molecules will be considered. 
VI. REQUEST TO RELEASE STRAINS OF PSEUDOMONAS SYRINGAE AND ERWIN IA HERBICOLA 
Dr. Brill introduced the request (tab 1081) of Drs. Nickolas Panopoulos and 
Steven Lindow of the University of California, Berkeley, for permission to 
construct and release in the environment Pseudomonas syringae pv. syringae 
and Erwinia herbicola to biologically control frost damage in plants. The 
strains would be carrying deletions of all or part of the genes involved 
in ice nucleation. 
Dr. Brill said that when freezing occurs on plant tissues, the tissues are 
damaged on thawing. Bacteria then enter through the damaged tissue and 
destroy the plant or at least destroy the tissue. Certain bacteria, such 
as Pseud omonas syringae (various pathovars under the current taxoncmic 
classification) , Erwinia herbicola , and, occasionally, isolates of Pseudo- 
monas fluorescens , serve as nuclei for ice crystal formation in supercooled 
water at temperatures slightly below 0°C (threshold nucleation temperature 
about -1.8°C). These bacteria are common plant epiphytes found in substan- 
tial numbers on above-ground plant surfaces (leaves, twigs, buds, flowers), 
with seasonal fluctuations from undetectable levels up to 10^ cells/gram 
tissue fresh weight. A causal relationship between frost damage on frost 
sensitive crop plants at relatively warm subzero temperatures (down to -5°C) 
and these organisms has been established. For instance, the degree of damage 
after exposure to low temperatures either in the field or in controlled 
environments (growth chambers) is directly related to the populations of 
ice nucleation active (Il& + ) bacteria present in or on the surfaces of 
abcve-ground parts. Plants grown aseptically can tolerate temperatures of 
several (ca. 6) degrees Celsius below zero without apparent damage. They 
are rendered sensitive to such temperatures by spraying with suspensions 
of INA + bacteria prior to low temperature exposure. 
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