Axenic growth of the arbuscular mycorrhizal fungus Rhizophagus irregularis and growth stimulation by coculture with plant growth-promoting rhizobacteria
Arbuscular mycorrhizal (AM) fungi are ecologically important for the growth and survival of most vascular plants. These fungi are known as obligate biotrophs that acquire carbon solely from host plants. A 13C-labeling experiment revealed the ability of axenically grown Rhizophagus irregularis DAOM 197198 to derive carbon from axenic culture on a relatively novel medium containing two sources of palmitic acid developed by Ishii (designated IH medium). In a separate experiment, this model fungus grew larger mycelia and produced more daughter spores on the IH medium in the presence of two Variovorax paradoxus strains than in axenic culture. In contrast, a strain of Mycobacterium sp. did not influence the growth of the AM fungus. Rhizophagus irregularis produced branched absorbing structures on the IH medium and, in monoxenic culture with V. paradoxus, sometimes formed densely packed hyphal coils. In this study, we report for the first time the formation of coarse terminal pelotons and of terminal and intercalary very fine (≈ 1 μm diameter) hyphal elongations, which could form daughter spores in the presence of V. paradoxus. This study shows the value of IH medium and certain rhizobacteria in the culture of R. irregularis DAOM 197198 in vitro.
KeywordsArbuscular mycorrhizal fungi Axenic culture Mycorrhiza helper bacteria Plant growth-promoting rhizobacteria Rhizophagus irregularis
Deepest thanks to Dhia Khadri for helping with isotopic calculations, Takaaki Ishii for providing DMPC and DMPE, Michelle Hubbard for reviewing the manuscript, and Keith Hanson for providing technical assistance.
This research was supported by grant 20120091 from the Agriculture Development Fund of the Province of Saskatchewan and grant 20120091 from Saskatchewan Pulse Growers.
Compliance with ethical standards
Conflict of interest
The authors declare that they have no conflicts of interest.
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