A team of researchers from the Boyce Thompson Institute (BTI) discovered a distinct group of bacteria that can help fungi and plants acquire soil nutrients. In summary, the findings may pave the way for economical and ecological methods to enrich the soil and improve yields, while reducing farmers' dependence on conventional fertilizer.
Farmers know that arbuscular mycorrhizal (AM) fungi establish symbiotic, positive relationships with the roots of 70% of all land plants. Plants exchange fatty acids for nitrogen and phosphorus from fungi. Unfortunately, AM fungi lack the enzymes needed to liberate nitrogen and phosphorus from complex organic molecules.
A trio of scientists led by the professor Mary Harrison he wondered if other soil microbes could help fungi access those nutrients. The research has been described in an article recently published on The ISME Journal.
A microbiome for fungi
The team looked at bacteria that live on the surfaces of long filament-like structures called hyphae. These are structures that fungi extend into the soil away from their host plant. On hyphae of two species of fungi, the team discovered very similar bacterial communities whose composition was distinct from those of the surrounding soil.
“This tells us that, just like the human gut or plant roots, the hyphae of mushrooms AMs have their own unique microbiomes,” Harrison said. “We're already testing some interesting predictions about what these bacteria might do, such as help with phosphate acquisition.”
If we're right, enriching the soil for some of these bacteria could increase crop yields and ultimately reduce the need for fertilizer. Less costs, zero environmental impact.
Mary Harrison, Boyce Thompson Institute
Mushrooms that can replace conventional fertilizer
In the study, the team used two species of AM mushrooms. This is the Glomus versiforme and Irregular Rhizophagus. The researchers cultivated them in three different soil types in symbiosis with Brachypodium distachyon, a herbaceous species related to wheat. After letting the mushroom grow with the herb for 65 days, the researchers used the gene sequencing to identify bacteria that attached themselves to hyphae surfaces.
The team found remarkable consistency in the composition of the bacterial communities of the two fungal species. The function of these bacteria is still unclear, but their composition has already raised some interesting possibilities, says Professor Harrison.
We expect some of these bacteria to release phosphorus ions in the immediate vicinity of the filaments, giving the fungus the best chance of capturing those ions. Learning which bacteria have this function could be the key to improving the phosphate acquisition process by the fungi for the benefit of plants, which would receive a fertilizing action.
Harrison's team is finally studying the factors that control which bacteria assemble on filaments. AM fungi could secrete molecules that attract these bacteria and, in turn, bacterial communities could affect the molecules secreted by the fungus.
