Linking plant growth promoting arbuscular mycorrhiza with sulfonate desulfurizing bacteria

Sulfur (S) exists in organically bound complexes (∼95%), predominantly as sulfonates, and are not directly plant available. Specific soil bacteria can mobilize sulfonates (desulfonate) but very little is known about these bacteria in the hyphosphere. Since mycorrhizal fungi support growth of most land plants, hyphospheric desulfonating bacteria may be of substantial benefit to the plant host. This study analyzed the effect of arbuscular mycorrhizal (AM) inoculation with Rhizophagus irregularis (former Glomus intraradices) and a mix of six AM species on plant growth promotion, microbial communities and desulfonating bacteria. Lolium perenne, Agrostis stolonifera and Plantago lanceolata served as plant hosts in bicompartmental microcosms, while A. stolonifera also served as plant host in a pot experiment. AM inoculation significantly increased plant growth (pot experiment), percentage root colonization and the quantity of cultivable desulfonating bacteria in the hyphosphere over noninoculated soil for all plants (microcosm experiment). Community analysis via PCR-DGGE revealed significantly different bacterial and fungal communities postinoculation. Analysis of the desulfonating bacteria via the marker gene asfA revealed an altered community and novel bacterial isolates with this important functional ability postinoculation. This study confirmed that AM inoculation has the potential to increase plant biomass yield and demonstrated that AM root colonization altered bacterial and fungal community dynamics in the hyphosphere and increased the abundance of desulfonating bacteria. These findings suggest that AM inoculation ultimately contributes to plant-S supply through attraction of beneficial bacteria.