The mycosphere constitutes an arena for horizontal gene transfer with strong evolutionary implications for bacterial-fungal interactions

Abstract

In the microhabitat that surrounds fungal hyphae in soil, coined the mycosphere, carbonaceous compounds that are released from the hyphae stimulate the growth of heterotrophic bacteria, and thus activate organism-to-organism contacts through genetic interactions. Therefore, the mycosphere is postulated to constitute a gene transfer arena, in which a plethora of genes, including locally adaptive ones, are swapped across the resident microbial communities. Such genetic transfers may have plasmids, in particular ones with broad host ranges, as the basis. Indeed, evidence is increasing for the contention that plasmids play crucial roles as accelerators of evolution in the mycosphere, serving as a horizontal gene pool and, therefore, providing competence factors to local bacteria as well as fungi. The evidence so far points at mycosphere roles for two major plasmid classes, the IncP-1 and PromA groups. Moreover, recent data indicate that bacterium-to-fungus gene transfers are detectable and have been evolutionarily important. The large gene pool present in the mycosphere, coupled with the chances for cell-to-cell contact between mycosphere dwellers allows enhanced recombination frequencies, and as such, organisms are selected locally for enhanced fitness.

Distinctive Feature of Microbial Communities and Bacterial Functional Profiles in Tricholoma matsutake Dominant Soil

“…Tricholoma matsutake forms its hyphal dominant environment around the fairy ring. Although the hyphal dominant environment can influence microbial communities [55], microbial interaction and functional activity in the Tm -dominant soil remain poorly characterized. In the work reported here, we compared soil communities between soil types ( Tm -dominant and Tm -minor soil) across geographic locations.…”

Exploring interactions of plant microbiomes

“…The first piece of evidence is the high occurrence of transmissible plasmids in the mycosphere (soil region influenced by the fungal hyphae), which carry genes that enable the recipient bacteria to colonize the fungal-driven environment (Zhang et al, 2014). It is likely that something similar is present in the rhizosphere that, furthermore, supplies microbial resources for the host colonization, as evidenced in the manuscript by Tauch et al (2002) for the cryptic plasmid pIPO2.…”

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

“…Fungi, in particular symbiotic mycorrhizal fungi, are prevalent dwellers of the root zone of plants and may be a key driver for the ‘rhizosphere effect’ in HGT40, attributed to high cell densities in the mycosphere14 in response to fungal exudates or the chemotaxis-driven colonization41. Our data emphasize the physical role of mycelia in enabling bacterial transport and concentration.…”

“…Bacterial displacement over longer distances thus requires episodes of water flow or bioturbation13. Mycelial organisms like fungi establish a dense network of thread-like hyphae, which provides ample amounts of nutrients and colonisable surfaces that both are prerequisites for bacterial HGT14. Plasmids of ecological relevance have been discovered in the vicinity of hyphae, such as plasmid-encoded genes for monoaromatics degradation in Pseudomonas fluorescens 15 or elevated levels of IncP-1β plasmids, known to encode a variety of ecological traits1617.…”