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Microbes in the Soil Environment
Major research activities undertaken in the area of soil microbiology
are profiled below. More detailed information is given at the Rhizobium Research laboratory and at the Rep-PCR
Web site.
Coevolution of Phaseolus host and bean Rhizobium (Graham)
- Post colonial spread
-From Mesoamerica to Caribbean and thence Brazil
-From Andean South America to Europe and thence Africa
-From Mexico to Northern America
-From Andean South America to the Caribbean
- We are studying the transport of bean- rhizobia as contaminants on
seed, and how this impacts the diversity of these organisms in soil
and their interactions with the bean host.
From Bernal (2000).
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- Because they have coevolved with beans over time in the Mesoamerican
center of origin, bean rhizobia from Mexico show differences in
diversity and specificity with those from the Andean area.
- The panel at left shows a principal component analysis of PCR-banding
patterns for strains of rhizobia from the different regions, with
grouping of the rhizobia into four distinct groups evident
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Improving the nitrogen fixation of beans and soybeans (Graham)
From Elisondo et al. (1999)
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- N2 fixation in beans is often considered weak, but
genetic variation exists and nodulat-ion and N2 fixation
can be improved by breeding
- We have used a recurrent selection program to achieve this,
as shown below
| Cycle |
Seed
Yield* |
Seed
Nitrogen* |
Days to flower |
Days to mature |
| C0 parents |
140.2 |
4.8 |
51.7 |
97.1 |
| C1 parents |
138.9 |
4.8 |
51.5 |
97.5 |
| C2 parents |
156.7 |
5.2 |
50.1 |
96.9 |
| *g per four plants |
| Regressions slopes calculated
from C0 to C2 data: |
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12.4*** |
0.3*** |
-1.0* |
-0.4 |
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Studies on microbial tolerance to acidity (Graham)
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- Our laboratory was first to identify acid pH tolerance in Rhizobium
tropici UMR1899, and to study the basis for this
- Because of its acid tolerance UMR1899 has been widely used as
an inoculant strain in the acid soils of Brazil and Africa.
- We are currently collaborating in acid tolerance studies with
Australian and Argentine groups
- The panels at left show the acid tolerance of UMR1899 cf normal
bean rhizobia, and the change in protein production with exposure
to acidity.
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Biodiversity, selection and use of rhizobia from prairie legumes
(Graham)
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- We have been funded by MnDOT to study the rhizobia associated
with prairie legumes such as Dalea purpurea.
- Activities include:
- Selection of inoculant strains for Astragalus, Chamaechrista
and Dalea
- Phylogenetic studies to characterize the rhizobia from Dalea.The
top panel on the left shows differences in FAME profile among
the rhizobia.The Dalea rhizobia are circled
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E. coli source tracking by Rep-PCR DNA fingerprinting
Despite the fact that elevated levels of are correlated with increased
risk of several diseases, fecal contamination of water is a widespread
problem in the United States. A 1996 report to Congress stated that 47%
of the river miles assessed in Minnesota could not be used for swimming
due to high levels of fecal coliform bacteria. For some rivers the problem
is pervasive; the fecal coliform counts for more than 90% of the Minnesota
River and its tributaries are consistently elevated. More detailed information
is given at the Rep-PCR Web site.
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