Microbial Ecology

Soil sampling in undisturbed forest soils near the Indiana Dunes State Park. Photo credit: USGS

Soil sampling in undisturbed forest soils near the Indiana Dunes State Park. Photo credit: USGS

In previous, independent studies, genotypically-distinct, yet diverse E. coli populations have been recovered in soils in subtropical (Hawaii) and temperate (Great Lakes basin) biomes. In the current study, using rep-PCR DNA fingerprint and multivariate statistical analyses, U.S. Geological Survey Great Lakes Science Center scientists and their collaborators from the Universities of Minnesota and Hawaii investigated whether the E. coli populations from subtropical and temperate soils were different or shared certain genotypes that are likely specific to soil environments.

Analyses of unique E. coli DNA fingerprints from subtropical and temperate soils showed that the E. coli isolates formed tight, cohesive groups, clustering mainly by location.  While some nearly identical E. coli strains were shared between locations, the vast majority of soil E. coli strains were nonetheless genotypically different, suggesting that they were most likely derived from different lineages.  In summary, the current findings are consistent with the hypothesis that the soil-borne E. coli bacteria are not unique: multiple (E. coli) genotypes can readily adapt to become part of the autochthonous microflora.

For more information contact Murulee Byappanahalli at the U.S. Geological Survey Great Lakes Science Center.

See also Ecosystem Function: Soil >>

back to top

An intact sagebrush plot in eastern Oregon. Photo credit: Nicole M. DeCrappeo, USGS Image Gallery

A site that has been invaded by cheatgrass in eastern Oregon. Photo credit: Nicole M. DeCrappeo, USGS Image Gallery

Non-native invasive plant species can become “ecosystem engineers” in their new environments, directly or indirectly controlling resource availability by modifying physical state factors. Cheatgrass (Bromus tectorum) is one such exotic grass that has transformed landscapes in the northern Great Basin from biologically diverse big sagebrush/perennial bunchgrass ecosystems to homogenous annual grasslands. Cheatgrass invasion greatly increases fire return intervals, reduces native plant diversity, alters nutrient inputs and cycling rates, and degrades economically important rangelands. The changes in soil physical and chemical properties wrought by cheatgrass invasion also have the potential to affect soil biological communities, including bacteria, fungi, nematodes, and biological soil crusts. Soil organisms play vital roles in carrying out ecosystem processes such as decomposition and nitrogen cycling, and soil community composition may be particularly important in semi-arid ecosystems where resource availability fluctuates dramatically throughout the year. The aim of our research is to characterize changes in soil microbial community structure and composition with cheatgrass invasion into the sagebrush steppe. We also work to determine the consequences of those changes for important ecosystem processes. Ultimately, we hope to use this knowledge to aid in native plant restoration efforts in the Great Basin.

For more information contact Nicole M. DeCrappeo at the Forest and Rangeland Ecosystem Science Center.

See also Ecosystem Function: Soil >>

back to top