Associative cyanobacteria isolated from the roots of epiphytic orchids

Abstract

Associative cyanobacteria were isolated from the rhizoplane and velamen of the aerial roots of the epiphytic orchids Acampe papillosa, Phalaenopsis amabilis, and Dendrobium moschatum and from the substrate roots of Acampe papillosa and Dendrobium moschatum. Cyanobacteria were isolated on complete and nitrogen-free variants of BG-11 medium. On all media and in all samples, cyanobacteria of the genus Nostoc predominated. Nostoc, Anabaena, and Calothrix were isolated from the surface of the A. papillosa aerial roots, whereas the isolates from the substrate roots were Nostoc, Oscillatoria, and representatives of the LPP-group (Lyngbia, Phormidium, and Plectonema, incapable of nitrogen fixation). On the D. moschatum substrate roots, Nostoc and LPP-group representatives were also found, as well as Fischerella. On the aerial roots of P. amabilis and D. phalaenopsis grown in a greenhouse simulating the climate of moist tropical forest, cyanobacteria were represented by Nostoc, LPP-group, and Scytonema in the D. phalaenopsis and by Nostoc, Scytonema, Calothrix, Spirulina, Oscillatoria, and the LPP-group in P. amabilis. For D. moschatum, the spectra of cyanobacteria populating the substrate root zhizophane and the substrate (pine bark) were compared. In the parenchyma of the aerial roots of P. amabilis, fungal hyphae and/or their half-degraded remains were detected, which testifies to the presence of mycorrhizal fungi this plant. This phenomenon is attributed to the presence of a sheath formed by cyanobacteria and serving as a substrate for fungi.