The closing date for public comments is rapidly approaching. This is
one chance to say keep GM microbes out of Organic Food Crops!
Field-testing Bacterial Pathogens with Antibiotic Resistance Genes
Prof. Joe Cummins objects on behalf of Independent Science Panel, so
should you
The University of Wisconsin is preparing to release genetically
modified (GM) Erwinia carotovora bacteria containing antibiotic
resistance marker genes in environmental field tests. The United
States department of Agriculture (USDA) Animal and Plant Health
Inspection Service (APHIS) has prepared a docket with background
information on the release and there is a public comment period ending
15 September 2005 [1]. The tests are to be conducted at the University
of Wisconsin Experiment Station near Hancock, Wisconsin. The
environmental release of bacterial strains each containing a different
antibiotic should be a matter of grave concern and a strong public
response is in order.
The purpose of the field trial seems to be simply experimental with no
potential commercial application of the genetically modified bacteria.
Erwinia carotovora causes a rot disease in potatoes. The experiment is
designed to test the fitness of bacteria that have had genes known to
be associated with pathogenesis that have been disrupted by inserting
in those genes the antibiotic resistance genes. The antibiotic
resistance genes not only eliminate the function of the pathogenesis
gene but they also serve as selectable markers to identify the
modified bacteria. The antibiotic resistance genes are precisely
inserted into the target pathogenesis gene by adding short DNA tails
to the resistance genes that are homologous to the target pathogenesis
gene. The pathogenesis gene targeted is hrp, which controls secretion
of virulence proteins into the host plant. Green fluorescence protein
was inserted as a visual marker to identify potatoes with the modified
bacteria [2].
The field test involves four GM mutant strains, WPP60,WPP198, WPP195
and WPP40. WPP60 was created by inserting the streptomycin/spectomycin
genes into the hrpC, while WPP98 had chloramphenicol resistance gene
inserted into hrpL. WPP195 was created by deleting the hrpN gene and
inserting the choramphenicol resistance gene in its place. WPP40 has
the kanamycin resistance gene inserted into the outD gene required for
protein secretion, so it cannot secrete plant cell-wall degrading
enzymes. Inserting antibiotic resistance genes into the hrp genes
interferes with pathogenesis. However, only strain WPP40 that
inactivates the outD gene is reduced in virulence in a direct assay,
nevertheless, the researchers decided to carry out the field
experiment [2].
They claim that the field tests are not expected to impact
agricultural practice because “the test is solely for research
purposes” even though Erwinia carotovora affects potato, cucumber,
capsicum, turnip, brussel sprouts, carrots and celery, all of which
are grown in the general area of the test site. Because the antibiotic
resistance genes are not being selected by antibiotic application,
they are not deemed to be a cause for concern, according to the
applicants. The proposal believes that the antibiotic resistance genes
cannot be transferred to bacteria affecting humans; justifying that
position by referring to the US Food and Drug Administration’s
judgment that antibiotic resistance is already prevalent in bacteria
affecting humans and in soil-borne bacteria. Even though the soil is
sandy and porous in the test site, the applicants claim that the
spread of the GM bacteria is not expected, nor has it been tested for
[2]. In general, the application focuses on the benefits of the
experiments and ignores any evidence that might delay the experiment.
Apart from the release of antibiotic resistance genes, the most
obvious question is why release so many strains that are genetically
modified as well as still virulent? That procedure provides high risk
with little or no benefit.
1
The belief expressed in the proposal, that GM Erwinia carotovora would
not transfer antibiotic resistance genes to other soil bacteria, is
inconsistent with the scientific literature. Horizontal gene transfer
is commonplace in Erwinia and Klebsiella and transfer could extend to
Salmonella, Shigella and E. coli [3]. The GM bacteria contaminating
surfaces of food crops may also transfer antibiotic resistance gene to
enteric bacteria when ingested by humans or animals. Bacteria phage
were found to transfer genes between Erwinia species [4]. Transposons
capable of mobilizing antibiotic resistance genes have been identified
in Erwinia carotovora [5]. There is thus clear evidence that Erwinia
is capable of moving resistance genes among soil Erwinia species,
between other soil bacterial species and among enteric bacteria.
A number of GM microbes bearing antibiotic resistance markers have
been released commercially in the United States, these include
Sinorhizobium, Agrobacterium and Psuedomonas [6]. Little effort
appears to have been made to monitor the consequences of these
releases. Mae-Wan Ho has discussed the hazards of horizontal gene
transfer in some detail [7, 8].
The main problem with the proposed field test of GM Erwinia carotovara
is the failure to monitor the spread of the modified bacteria and the
horizontal spread of transgenes. The release of virulent GM Erwinia
does not appear to provide any benefit that would justify the risks of
spreading the antibiotic genes.
This article has been submitted to the US EPA on behalf of the
Independent Science Panel. Please add your support by registering your
opposition in the docket by referring to this article.
Reference
1. University of Wisconsin-Madison Availability of Environmental
Assessment for Field Tests of Genetically Engineered Erwinia
carotovora Agency Document Number APHIS-2005-0069-0001 Comment Period
End Date (mm/dd/yyyy): 09-12-2005
http://docket.epa.gov/edkfed/do/EDKStaffCollectionDetailView?objectId=0b0007d48094780b
2. USDA/APHIS Environmental Assessment in response to permit
application (05-097-01r) received from University of Wisconsin for
field testing of genetically engineered strains of bacterium, Erwinia
carotovora subsp. Carotovora 2005
http://docket.epa.gov/edkfed/do/EDKStaffAttachDownloadPDF?objectId=090007d48094780e
3 Mulec J, Starcic M and Zgur-Bertok D. F-like plasmid sequences in
enteric bacteria of diverse origin, with implication of horizontal
transfer and plasmid host range. Curr Microbiol. 2002, 44, 231-5.
4. Chatterjee AK, Ross LM, McEvoy JL and Thurn KK. pULB113, an
RP4::mini-Mu plasmid, mediates chromosomal mobilization and R-prime
formation in Erwinia amylovora, Erwinia chrysanthemi, and subspecies
of Erwinia carotovora. Appl Environ Microbiol. 1985, 50(1),1-9.
5. Kotoujansky A, Lemattre M and Boistard P. Utilization of a
thermosensitive episome bearing transposon TN10 to isolate Hfr donor
strains of Erwinia carotovora subsp. Chrysanthemi. J Bacteriol. 1982,
150(1),122-31.
6. Cummins J. GM microbes invade North America. Science in Society
2003, 19, 39.
2
7. Ho MW Horizontal gene transfer – The hidden hazards of genetic
engineering. ISIS Report http://www.i-sis.org.uk/full/HGTFull.php;
also Biotechnology Series, Third World Network, Penang 2001.
8. Ho MW Recent evidence confirms risks of horizontal gene transfer.
ISIS contribution to ACNFP/Food Standards Agency open meeting 2002
http://www.i-sis.org.uk/FSAopenmeeting.php
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