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legitimately be considered part of an "exchangers" list, and then only 
where more detailed information is available (see below). 
2. Natural rates of exchange have not been taken into account in ar- 
riving at the list of "exchangers". The demonstration of any degree of 
chromosomal DNA exchange is sufficient for membership on the list. Thus, 
while only prokaryotes are on the present list, the consistent application 
of this principle could ultimately place eukaryotes and prokaryotes on the 
same "exchangers" list (that is, exempt from the Guidelines) since some lim- 
ited exchange has undoubtedly occurred between certain pairs (i.e. Agrobac- 
terium tumefaciens and its host plant) . 
3. The rationale for membership on the "exchangers" list completely 
ignores ecological considerations. For example, recombination experiments be- 
tween wild type strains of E. coli (those strains which inhabit the normal hu- 
man large intestine) and Salmonella (some species of which are responsible for 
seveifefood poisoning) are proposed to be exempt from the Guidelines, presum- 
ably because some species of these genera can exchange chromosomal DNA in the 
laboratory. There is no discussion of whether these microorganisms ever occu- 
py the same ecological niche, and thus have the opportunity to exchange in na- 
ture. Fredrickson, in his statement, talks about the lack of success in con- 
verting E. coli K12 into a pathogen by insertion of Salmonella genes (p . 33059). 
Has this been attempted with wild type E. coli ? Under the proposed revised 
Guidelines, such an experiment, with a host with none of the inherent weakness- 
es of K12, could be performed subject to no regulations. 
RECOMMENDATIONS : Members of the "exchangers" list should be designated only 
by species name, and only where exchange can be demonstrated 
in a realistic ecological setting at a non-vanishing rate. 
Furthermore, recombination between members of the list 
should be subject to P2 physical containment and thus remain 
within the Guidelines. 
[A-399] 
