The sugar beets' health followed the typical arc of plants in disease-suppressive soil: they enjoyed a few good years, then they succumbed to disease, followed by healthy beets again as pathogen-fighting microbes were activated and the soil became hostile to R. solani. To return the favor, the sugar beets funnel about a fifth of their photosynthetically captured carbon through their roots into the soil to fuel the microbes.
Disease-suppressive soils are quite common, and scientists have identified some of the microbes involved in this underground immune system. But they don't know all of the microbes that participate.
To find out, the scientists used the PhyloChip, which is a credit-card sized chip that can detect the presence of 59,000 species of bacteria and archaea in samples of air, water, and soil without the need of culturing. It was developed at Berkeley Lab to rapidly identify not only the most common and abundant organisms in an environmental sample, but also very rare types that are present in extremely small numbers. It does this by comparing a DNA sequences unique to each bacterial species with over one million reference DNA targets on the chip. The PhyloChip has shed light on many environmental mysteries, such as what's killing coral reefs near Puerto Rico and what degraded much of the oil from the Gulf of Mexico's Deepwater Horizon spill.
In this case, soil samples from the sugar beet field were modified to exhibit six levels of disease suppression. DNA was isolated from the samples and sent to Berkeley Lab for analysis. The PhyloChip detected more than 33,000 bacterial and archaeal species in the samples, with all six having more or less the same types of bacteria.
But when the scientists looked at the abundance of bacteria in each sample, they found that each had a unique fingerprint. All of the samples in which disease was suppressed had a greater abundance of 17 unique types of bac
|Contact: Dan Krotz|
DOE/Lawrence Berkeley National Laboratory