Ectomycorrhizal Helper Bacteria: The Third Partner in the Symbiosis

In natural conditions, mycorrhizal fungi are surrounded by complex microbial communities, which may trigger various responses, from enhancement of the establishment of mycorrhizal symbiosis to mycelial growth inhibition or cell death. The symbiosis between mycorrhizal soil fungi and higher plants takes advantage of active collaboration with specific helper bacteria. Thus, a symbiosis so far thought of involving two components could be the result of the interaction among at least three different partners. This chapter focuses on the relationship between edible ectomycorrhizal mushrooms and soil bacteria, in particular nitrogen-fixing bacteria associated with Tuber species. The ability of these bacteria to modify nutrient availability during the fructification phase is very important to truffle development. This chapter will also discuss perspectives on the beneficial use of ectomycorrhizal symbiosis with nitrogen-fixing bacteria to develop predictive models that could be used to improve the mycorrhization processes with the further aim of obtaining plants infected with Tuber magnatum Pico, the most economically important truffle species that remains difficult to cultivat