Mycelia as a focal point for horizontal gene transfer among soil bacteria, Berthold 2016

Fungus is a key component of healthy soil. It is known to “translocate compounds from nutrient-rich to nutrient-poor regions… facilitate the access of bacteria to suitable microhabitats for growth, enable efficient contaminant biodegradation, and increase the functional stability in systems exposed to osmotic stress” [Berthold 2016: 5]. This study shows that, in addition, mycelia facilitate bacterial evolution, thereby bolstering bacterial diversity and adaptability.

Abstract: Horizontal gene transfer (HGT) is a main mechanism of bacterial evolution endowing bacteria with new genetic traits. The transfer of mobile genetic elements such as plasmids (conjugation) requires the close proximity of cells. HGT between genetically distinct bacteria largely depends on cell movement in water films, which are typically discontinuous in natural systems like soil. Using laboratory microcosms, a bacterial reporter system and flow cytometry, we here investigated if and to which degree mycelial networks facilitate contact of and HGT between spatially separated bacteria. Our study shows that the network structures of mycelia promote bacterial HGT by providing continuous liquid films in which bacterial migration and contacts are favoured. This finding was confirmed by individual-based simulations, revealing that the tendency of migrating bacteria to concentrate in the liquid film around hyphae is a key factor for improved HGT along mycelial networks. Given their ubiquity, we propose that hyphae can act as a focal point for HGT and genetic adaptation in soil.