Signal beyond nutrient, fructose, exuded by an arbuscular mycorrhizal fungus triggers phytate mineralization by a phosphate solubilizing bacterium

Abstract

Cooperation is a prevalent phenomenon in nature and how it originates and maintains is a fundamental question in ecology. Many efforts have been made to understand cooperation between individuals in the same species, while the mechanisms enabling cooperation between different species are less understood. Here, we investigated under strict in vitro culture conditions if the exchange of carbon and phosphorus is pivotal to the cooperation between the arbuscular mycorrhizal fungus (AMF) Rhizophagus irregularis and the phosphate solubilizing bacterium (PSB) Rahnella aquatilis. We observed that fructose exuded by the AMF stimulated the expression of phosphatase genes in the bacterium as well as the rate of phosphatase release into the growth medium by regulating its protein secretory system. The phosphatase activity was subsequently increased, promoting the mineralization of organic phosphorus (i.e., phytate) into inorganic phosphorus, stimulating simultaneously the processes involved in phosphorus uptake by the AMF. Our results demonstrated for the first time that fructose not only is a carbon source, but also plays a role as a signal molecule triggering bacteria-mediated organic phosphorus mineralization processes. These results highlighted the molecular mechanisms by which the hyphal exudates play a role in maintaining the cooperation between AMF and bacteria.

Arbuscular mycorrhiza and soil organic nitrogen: network of players and interactions

“…The distinction between saprotrophic and hypersymbiotic microbes in this regards is the origin of C the microbes live on-either from the SOM or from the AMF hyphae, respectively. A nice example of a tight cooperation between the AMF hyphae and a soil bacterium Rahnella aquatilis with regards to organic P (phytate) mineralization has recently been described by Zhang et al [136]. Although mineralization of organic N is at least equally important process as organic P mineralization, and microbial communities in AMF hyphosphere amended with organic N have been analyzed previously [16,43,96], there is as yet no specific information about the identity of primary organic N decomposers teaming directly with the AMF hyphae.…”

Dual‐mycorrhizal plants: their ecology and relevance

“…By contrast, whereas AM fungi can take up and transfer N from organic matter to their host plant (Hodge et al, 2001;Fellbaum et al, 2012;Thirkell et al, 2016), the weight of evidence is that AM fungi take up N or P primarily after mineralization by other soil microbes (Joner & Jakobsen, 1995;Leigh et al, 2009;Whiteside et al, 2012;Wang et al, 2017). Indeed, there is increasing evidence that AM hyphae can stimulate mineralization of organic matter by influencing the metabolism of soil bacteria (Zhang et al, 2018) and compete effectively with soil microbes for those nutrients (Bukovsk a et al, 2018).…”

Arbuscular Mycorrhizal Fungi Co-Colonizing on A Single Plant Root System Recruit Distinct Microbiomes

“…In recent years, mycorrhizal genome sequencing studies have found that mycorrhizal fungi have lost many saprophytic genes in the longterm co-evolution process with plants [16]. Cooperating with functional microbiomes, such as phosphatase releasing bacteria [6,41] is considered an important strategy for AM fungi to compensate their lack of ability to utilize organic P. We find for the first time that different living AM fungi species that colonized single plant root recruit active microbiomes which are distinct from each other. The research not only provides direct evidence for understanding the biophysical process that AM fungal hyphae exudates drive the formation of soil bacteria diversity heterogeneity, but also reveals the potential division of labor may exist in plant-AM fungi-bacteria system that still remains to be understood fully.…”