The Rhizosphere of wild barley across Evolution Canyon

Bacteria and other microorganisms contribute greatly to the Earth’s biomass as they form the bottom of the food chain and orchestrate the cycling of carbon, nitrogen, and flow of other nutrients through the ecosystem. They are the ‘dark matter’ of life and may also hold the key to various global problems facing our society e.g. generating sources of nutrition and energy, developing powerful new pharmaceuticals, and cleaning up the environmental disorder. To date, there are a limited number of microbial species that have been studied in the laboratory. The most well-known of these are perhaps E. coli and B. subtilis. However even their wild relatives differ substantially from the highly subcultured laboratory representatives.

In the study reported in this manuscript, samples were collected from the ecological laboratory called Evolution Canyon (EC) which is found in northern Israel. The ‘African’ or south-facing slopes in canyons north of the equator receive higher solar radiation than on the adjacent ‘European’ or north-facing slopes. This difference in solar radiation is associated with higher maximal and average temperatures and evapotranspirations on the more stressful ‘African’ slope. It causes dramatic physical and biotic interslope divergence, which may have originated several million years ago after mountain uplifts. These canyons are extraordinary, natural, evolutionary laboratories. Rocks, soils, and topography are similar on the opposite slopes (50–100 m apart at the bottom); microclimate remains the major interslope divergent factor. So far the intraspecific interslope divergence has been compared in 2500 species across various life forms from prokaryotes through eukaryotic lower and higher plants, fungi, and animals, unraveling the link between environmental stress and genome evolution in adaptation. This unique ecological situation facilitates the generation of theoretical testable and predictable models of biodiversity and genome evolution.

Timmusk S, Paalme V, Pavlicek T, Bergquist J, Vangala A, et al. 2011 Bacterial Distribution in the Rhizosphere of Wild Barley under Contrasting Microclimates. PLoS ONE 6(3): e17968. doi:10.1371/journal.pone.0017968
Background – All plants in nature harbor a diverse community of rhizosphere bacteria which can affect the plant growth. Our samples are isolated from the rhizosphere of wild barley Hordeum spontaneum at the Evolution Canyon (‘EC’), Israel. The bacteria which have been living in close relationship with the plant root under the stressful conditions over millennia are likely to have developed strategies to alleviate plant stress.
Methodology/Principal Findings – We studied distribution of culturable bacteria in the rhizosphere of H. spontaneum and characterized the bacterial 1-aminocyclopropane-1-carboxylate deaminase (ACCd) production, biofilm production, phosphorus solubilization and halophilic behavior. We have shown that the H. spontaneum rhizosphere at the stressful South Facing Slope (SFS) harbors significantly higher population of ACCd producing biofilm forming phosphorus solubilizing osmotic stress tolerant bacteria.
Conclusions/Significance – The long-lived natural laboratory ‘EC’ facilitates the generation of theoretical testable and predictable models of biodiversity and genome evolution on the area of plant microbe interactions. It is likely that the bacteria isolated at the stressful SFS offer new opportunities for the biotechnological applications in our agro-ecological systems.