Isolation and analysis of bacteria associated with spores of Gigaspora margarita

Aims: The aim of this work was to observe bacteria associated with the spores of Gigaspora margarita, an arbuscular mycorrhizal fungus (AMF). Methods and Results: First, a direct analysis of DNA from sterilized spores indicated the bacteria belonging to the genus Janthinobacterium. In the second assay, two bacterial strains were isolated by osmosis from protoplasts, which were derived from spores by using two particular enzymes: lysing enzymes and yatalase. After isolation, cultivation and identification by their DNA as performed in the first experiment, the species with the closest relation were Janthinobacterium lividum (KCIGM01) and Paenibacillus polymyxa (KCIGM04) isolated with lysing enzymes and yatalase respectively. Morphologically, J. lividum was Gram negative and oval, while P. polymyxa was also oval, but Gram positive. Both strains had antagonistic effects to the pathogenic fungi Rosellimia necatrix, Pythium ultimum, Fusarium oxysporum and Rhizoctonia solani. In particular, J. lividum was much stronger in this role. However, in phosphorus (P) solubilization P. polymyxa functioned better than J. lividum. Conclusions: This experiment had revealed two new bacteria species (P. polymyxa and J. lividum), associated with AMF spores, which functioned to suppress diseases and to solubilize P. Significance and Impact of the Study: AMF spores could be a useful source for bacterial antagonists to soil-borne diseases and P solubilization.