Arid lands, which cover some 40 percent of Earth's terrestrial surface, are too dry to sustain much in the way of vegetation. But far from being barren, they are home to diverse communities of microorganisms -- including fungi, bacteria, and archaea -- that dwell together within the uppermost millimeters of soil. These biological soil crusts, or biocrusts, can exist for extended periods in a desiccated, dormant state. When it does rain, the microbes become metabolically active, setting in motion a cascade of activity that dramatically alters both the community structure and the soil chemistry.
Biocrust amongst one of its many natural habitats, taken about 20 miles from the sampling site (near the Corona Arch, Moab, UT) [Credit: Tami Swenson] |
In a paper published in Nature Communications, Berkeley Lab researchers led by the Northen lab report that specific compounds are transformed by and strongly associated with specific bacteria in native biological soil crust (biocrust) using a suite of tools Northen calls "exometabolomics." Understanding how microbial communities in the biocrusts adapt to their harsh environments could provide important clues to help shed light on the roles of soil microbes in the global carbon cycle.
The work follows a 2015 study that examined how specific small molecule compounds called "metabolites" were transformed in a mixture of bacterial isolates from biocrust samples cultured in a milieu of metabolites from the same soil. "We found that the microbes we investigated were 'picky' eaters," Northen said. "We thought we could use this information to link what's being consumed to the abundance of the microbes in the intact community, thereby linking the biology to the chemistry."
"When we compare the patterns of metabolite uptake and production for isolated bacteria that are related to the most abundant microbes found in the biocrusts, we find that, excitingly, these patterns are maintained," said Northen. That is, increased abundance of a given microbe is negatively correlated with the metabolites that they consume and positively correlated with metabolites that they release.
When active, biocrusts take up atmospheric carbon dioxide and fix nitrogen, contributing to the ecosystem's primary productivity. They also process organic matter in soil, modifying key properties related to soil fertility and water availability.
Northen's group is currently working on expanding these studies to capture a greater fraction of microbial diversity. Ultimately, this may enable the prediction of nutrient cycling in terrestrial microbial ecosystems, and perhaps even manipulation by adding specific metabolites.
Source: Lawrence Berkeley National Laboratory [January 04, 2018]