Truffle-Associated Bacteria: Extrapolation from Diversity to Function

A third partner in the symbiosis between the fungus and plant root is represented by natural bacterial communities, which seem to play pivotal role in the complex biological processes of exchange involving nutrients and signaling from the soil hyphae, ectomycorrhizas, ascomata, and stromata. This review summarizes the recent evidence reported in literature showing that ascoma provides a habitat to complex microbial communities that are clearly differentiated from those of the soil and the ectomycorrhizosphere. Although the traditional plate isolation and the culture of microbes are indispensable for vegetative compatibility and/or functional assays, these techniques do not let a real in vivo picture the truffle ecosystem. Advent of the next-generation sequencing methods and recent advances in microarray technologies have increased culture-independent studies. Indeed, most microbiota remains uncultivable in laboratory conditions, and these novel technologies have greatly improved the understanding of microbial diversity and its functioning. This is particularly important for the ectomycorrhizal fungi of Tuber genus, since specific uncultivable-associated prokaryotes may play important roles in the biological system and ontogenetic cycle of these fungi. Success of truffle cultivation may be achieved with co-inoculum of specific bacteria with Tuber spp. upon establishment of commercial plantations; this is particularly relevant to the Tuber species with a high agronomic value

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