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Shareware Overload Trio 2
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1994-07-17
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PLANTS - PATHOGENIC MICROBES MODULE EXAMPLES
test organisms
Xanthomonas campestris pv. campestris
/end
source of donor DNA
V. fischeri - luminescent bacteria
/end
vector(s)
The transposon, Tn4331, was used to construct bioluminescent
strains of the bacterium. This transposon carries the lux
genes in a manner which facilitates transcriptional fusion
of the genes into the bacterial chromosomal DNA.
Vector or vector agent: Organisms or objects used to
transfer genetic material from the donor organism to the
recipient organism. Well-characterized and contain only
non-coding regulatory regions. (e.g. operators, promoters,
origins of replication, terminators and ribosomes binding
regions). The genetic material added to a microorganism in
which the following can be documented about such genetic
material: (a) The exact nucleotide base sequence of the
regulatory region and any inserted flanking nucleotides; (b)
The regulatory region and any inserted flanking nucleotides
do not code for protein or peptide; and (c) The regulatory
region solely controls the activity of other sequences that
code for protein or peptide molecules or act as recognition
sites for the initiation of nucleic acid or protein
synthesis.
/end
other genetic sequences
Another gene complex, besides the luciferase genes and the
transposon, is incorporated into the chromosomal DNA after
transformation. The tetracycline resistance gene complex
functions only as a marker in the initial cell selection
process following transformation. Neither of the marker
genes nor the resultant enzyme products have any inherent
plant pest characteristics.
/end
exact location(s)
The experiment will be conducted on a research farm owned by
(Institution Name). It is located on a secondary road in
(county), (state). This is XX.XX miles from (city), the
nearest population center.
/end
summary statement
Pursuant to regulations in 7 CFR Part 340 we propose to
field test X. campestris pv. campestris which has been
modified to express the luciferase gene complex. The genes
were inserted into the bacterial chromosomal DNA using a
suicide vector system. The field trial wiil take place on a
small plot on agricultural land in (county), (state). The
farm will provide adequate physical security. Site
monitoring of the field trial and agronomic management
practices that create a nonpropogative environment are
expected to provide the necessary degree of both biological
and physical containment.
/end
purpose
X. campestris pv. campestris has been genetically modified
to express the luciferase gene complex. Limited field
testing is necessary so that information can be gathered for
scientific evaluation of the efficacy of the genetic change.
The bacterium has been tested in the greenhouse to obtain
initial data relating to the genetic stability of the
engineered genes and preliminary data on light production.
Field tests are performed after greenhouse testing to
confirm the data, which can only be validated in the
environment using standard agricultural practices.
/end
description of the methods
A detailed description of the transposon Tn4331 delivery
system is described by Shaw et al. (1988). Briefly, Tn4331,
a member of the Tn3 family (Sherratt, 1988), was transferred
to X. campestris pv. campestris 2D520 in a biparental mating
with Escherichia coli containing the suicide transposon
delivery plasmid, pUCD623 (a derivative of pSa235). Plasmid
pSA325 does not replicate in X. campestris pv. campestris,
but can be transferred into X. campestris pv. campestris due
to the fertility functions provided. This fact makes it an
ideal suicide delivery system. Plasmid pUBD623 (Figure
1) was constructed by allowing Tn4331 to insert into pSA325.
Plasmid pUCD623 can be transferred into X. campestris pv.
campestris from E. coli but cannot replicate. Upon
introduction of pUCD623 into X. campestris pv. campestris,
select sequences were introduced into Xanthomonad
chromosomal DNA.
/end
amount and nature
Vector/Donor DNA Remaining Mutants containing these
sequences (i.e. transposon Tn4331, tetracycline resistance
marker, and luciferase) were found (as expected) to be
tetracycline resistant and bioluminescent. To verify that
only the tetracycline resistance marker and the lux gene
complex and no other plasmid sequences retained by the
mutants, a limited number of exconjugants were
demonstrated to be sensitive to ampicillin and
chloramphenicol. A further verification, colony
hybridization of a limited number of exconjugants
demonstrated that the mutants had acquired DNA homologous
to the transposon and had not retained portions of the
plasmid vector pSa325.
/end
containment procedures
Information obtained during studies of the modified pathogenic
organism in containment (e.g. microcosm, greenhouse, growth
chamber) is crucial. Containment conditions that most closely
imitate field situations will provide the best idea as to the
potential field performance of the test organism. For example,
containment studies for soilborne transformed microbes should
include tests using soil from the proposed release site. If the
methods of monitoring and identifying pathogenic biotypes are
well established, provide details (include information on
the previous use of these methods).
Studies conducted under containment conditions comparing the
genetically engineered organism with the non-modified parent
organism are recommended prior to field testing. Some of the
topics you may wish to address include:
1. Phenotype.
2. Physical characteristics, e.g., colony morphology.
3. Serology.
4. What genes do the recombinants express differently from the
parent and what is the manifestation of this expression.
5. Persistence in the environment.
6. Effects on pathogenicity. Provide a brief description.
Example - Studies in Containment
The recombinant has a slower doubling time than its parental
strain. In vegetable, the recombinant is less virulent and
its population levels reached is approximately 100-fold less
than its parental strain. Based on current knowledge on the
genetic basis of host range determinants in Xanthomonads
(Daniels et al., 1987; Turner et al., 1985; Keen and
Staskawicz, 1988), the recombinant X. campestris pv.
campestris could not have a wider host range than the
parental bacterium.
Host and Alternate Hosts. The natural host range of X.
campestris pv. campestris is generally limited to the
Brassica family. Many weeds can harbor the bacterium
including Brassica campestris, B. nigra, B. geniculata,
Lepidium virginicum, and Cardaria pubescens (Sherf and
MacNab, 1986). Schaad and Dianese (1981) demonstrated that
in Georgia, X. campestris pv. campestris was found on the
weeds B. campestris, Lepidium virginicum, Cornopus didymud,
and Raphanus sativus. They also demonstrated that X.
campestris pv. campestris was disseminated up to 12 meters
from infected weeds to cabbage. Laboratory and greenhouse
studies in soil survival at different moisture regimes have
shown that populations of X. campestris pv. campestris
declined very slowly in soils maintained at low moisture
levels (-30 bars). In contrast, populations declined more
rapidly in soils maintained at higher moisture levels and
were quickly eliminated from soils maintained near field
capacity (-0.1 bar). The pathogen could no longer be
recovered from moist soils 6 days after adding the inoculum,
whereas 95 percent of the initial inoculum could be detected
in dry soils after infestation (Alvarez et al., 1987).
/end
transmitted to other species
Stability of Vector and/or Other Genetic Sequences.
The recombinant bacterium has no detectable plasmids,
reducing the likelihood that the lux genes or other
introduced genes could transfer to a conjugal plasmid and
subsequently vectored to new bacterial hosts. This strain
has been refractory to conjugation manipulation under
laboratory conditions. The recombinant has been
demonstrated to be stable in vegetable. Plants were
inoculated with the recombinant, allowed to grow and disease
progressed. Bacteria from this infected plant was used as
inoculum for another plant and this procedure repeated once
again. X. campestris pv. campestris was isolated from the
last infected plant and greater than 99 percent of the
bacterial colonies were bioluminescent and tetracycline
resistant (Shaw, unpublished).
/end
effects on human health
No potential impact on people living in the area of the
field test, or any other human population, can be
identified. Xanthomonads are not known to be human or
animal pathogens (Starr, 1981).
/end
design of the experiment
The main plot will be divided into four subplots. Each
subplot will consist of 4 rows of plants, 18 inches apart,
with each row about 6 feet in length. A disposal area will
be located adjacent to the main plot. An unplanted area
will surround the main plot and disposal areas. Surrounding
the unplanted area will be a single row of cabbage or
cauliflower. These plants will be monitored for the
presence of the recombinant X. campestris pv. campestris
during the growing season. The total plot size, including
the perimeter row, will not exceed 6,000 square feet. The
plant varieties are the susceptible hosts: snowball
cauliflower (B. oleracea L. boytrytis) and perfect ball
cabbage (B. oleracea L. capitata). Plants will be
inoculated by: stabbing or injecting bacterial suspensions
into the petioles, or spraying a bacterial suspension over
the plant with a hand-held spray bottle.
/end
monitoring plan
During the field test, university scientists will monitor
the field plots regularly. Plant parts, debris, and soil
will be sampled periodically for X. campestris pv.
campestris. Samples will be placed in small bags or small
containers and transported to the laboratory under contained
conditions (7 CFR 340.6). At the laboratory they will be
analyzed for light production ability and/or the presence of
viable recombinant X. campestris pv. campestris. The
recombinant X. campestris pv. campestris under appropriate
conditions produces light. This light production ability
allows the movement and spread of the bacterium in the
environment to be monitored. Plant disease index will be
recorded and correlated with the location of the
recombinant.
Procedures for Sample Processing
Soil inoculations with recombinant will involve small
amounts of bacteria (less than 100 ml of stationary
culture). The bacteria will be mixed with soil and then the
mixture will be buried into the soil. Alternately, infected
plant parts (from laboratory or field) will be buried in the
soil. Areas so inoculated will be marked by a flag and
periodically sampled for bacteria and bioluminescence.
/end
Termination of the Experiment
At the conclusion of the experiment, all plant material
remaining at the test site will be incorporated into the
soil and the test site watered thoroughly for 1 week. Plant
parts and soil removed from the test site for laboratory
analysis will be autoclaved prior to disposal. Plant
samples removed during the course of the experiment
and not autoclaved will be returned to the test site and
buried in the disposal area to allow for natural
decomposition. Survival of the recombinant bacterium in
soil will be minimized by irrigating the field after
termination of the experiment. Irrigation of the field will
also encourage decay of plant debris. There is no evidence
showing prolonged survival of Xanthomonads in irrigation
water.
/end