COS 153-5 - Microbial food webs involved in utilization of chitin and proteins in arbuscular mycorrhizal hyphosphere

Abstract: Arbuscular mycorrhizal (AM) fungi are important players in mineral nutrition of majority of plant species on Earth. Yet, unlike other mycorrhizal fungi forming ecto- or ericoid mycorrhizal symbioses, the AM fungi do not have the capacity to degrade and utilize organic nutrients in soil on their own. It seems well established now that for this they rely on soil microbes inhabiting the zone close to the AM hyphae exploring soil, the hyphosphere. Many of such microbes produce potent exoenzymes and mineralize various organic nutrients such as proteins, nucleic acids and aminosugars. We have recently shown (Rozmoš et al. 2022 ISME Journal 16: 676-685), using ¹⁵N labelling and tracing, that some (but not all) chitinolytic bacteria facilitate utilization of nitrogen (N) from chitin in the AM fungal hyphosphere, and that this is further enhanced upon including a bacteriovorous protist (Polysphondylium sp.) into our simplified experimental system. Recently, we aimed at elucidating, using a similar approach, which microbes were key to utilize proteins in AM fungal hyphosphere. To our surprise, the bacteria we used were fairly ineffective in gaining access to the N contained in the proteins, but including the protist, with the bacteria or not, actually facilitated efficient recycling of N from proteins to AM fungi and the associated root organ cultures of Cichorium sp. These results indicate that very different microbial guilds could potentially participate in nutrient recycling in AM fungal hyphosphere, advocating carefully designed studies and attention to multiple microbial groups inhabiting this elusive soil zone.