The biosynthesis of gibberellic acids by the transformants of orchid-associated <Emphasis Type="Italic">Fusarium oxysporum</Emphasis>

The genus Fusarium, including multiple strains in the Gibberella fujikuroi species complex (GFC), is well known for its production of diverse secondary metabolites. F. fujikuroi, associated with the “bakanae” disease of rice, is an active producer of gibberellins (GAs), a wide class of plant hormones. In addition to some members of the GFC, the GA biosynthetic gene cluster, or parts of it, occurs also in some isolates of the closely related species of F. oxysporum, which does not belong to the GFC. However, production of GAs has never been observed in any F. oxysporum strain. In this study, we report on the GA biosynthetic activity in an orchid-associated F. oxysporum strain by transforming a cosmid with the entire F. fujikuroi GA gene cluster. Southern and Northern blot analyses confirmed not only the integration of the entire gene cluster into the genome but also the active expression of the seven GA biosynthetic genes under nitrogen-limiting conditions. The transformants produced GAs at levels similar to those of F. fujikuroi. These data show that the regulatory network for expression of GA genes is fully active in the F. oxysporum background.     

Bacteria associated with orchid roots and microbial production of auxin

Associative bacteria of terrestrial (Paphiopedilum appletonianum) and epiphytic (Pholidota articulata) tropical orchids were investigated. Microbial community of epiphytic plant differed from that of the terrestrial one. Streptomyces, Bacillus, Pseudomonas, Burkholderia, Erwinia and Nocardia strains populated Paphiopedilum roots, whereas Pseudomonas, Flavobacterium, Stenotrophomonas, Pantoea, Chryseobacterium, Bacillus, Agrobacterium, Erwinia, Burkholderia and Paracoccus strains colonized Pholidota roots. Endophytic bacteria populations were represented with less diversity: Streptomyces, Bacillus, Erwinia and Pseudomonas genera were isolated from P. appletonianum, and Pseudomonas, Bacillus, and Flavobacterium genera were isolated from Ph. articulata. Microorganisms produced indole-3-acetic acid (IAA). Variations in its biosynthesis among the strains of the same genus were also observed. The highest auxin level was detected during the stationary growth phase. Biological activity of microbial IAA was proved by treatment of kidney bean cuttings with bacterial supernatants, revealing considerable stimulation of root formation and growth.     

Bacteria associated with the roots of epiphytic orchids

This work is the first to report the isolation and identification of bacteria colonizing the roots of tropical epiphytic orchids Acampe papillosa (Lindl.) Lindl. and Dendrobium moschatum (Buch.-Ham.) Swartz. and bacteria inhabiting inner layers of the aerial and substrate roots of A. papillosa. We showed by the example of this epiphyte that associative bacteria are present in large amounts on the aerial but not substrate roots. We isolated and identified bacteria from the substrate roots of D. moschatum and from its growth substrate (pine bark). The structure of the intercellular matrix of the associative bacteria was studied.     

Localization of Associative Cyanobacteria on the Roots of Epiphytic Orchids

This work is the first study of the localization of phototrophic microorganisms in the rhizoplane and velamen of epiphytic orchids, namely, on the aerial and substrate roots of Acampe papillosa and Dendrobium moschatum and on the aerial roots of Phalaenopsis amabilis and Dendrobium phalaenopsis. The composition of the bacterial community on the plant roots depended on the conditions of plant growth. Under conditions simulating the climate of moist tropical forests, the aerial roots proved to be populated with phototrophic microorganisms, among which cyanobacteria predominated. Interlaced fungal hyphae and filamentous cyanobacteria formed a sheath on the surface of the aerial roots. The nitrogen-fixing capacity of the sheath of the aerial roots was studied on the example of P. amabilis.     

Anaerobic Microbial Degradation of Polypropylene and Polyvinyl Chloride Samples

Microbiology - Resistance to biodegradation, which is among the most advantageous features of synthetic polymers, is also the reason for their accumulation in the environment and therefore...     

Localization of associative cyanobacteria on the roots of epiphytic orchids

This work is the first study of the localization of phototrophic microorganisms in the rhizoplane and velamen of epiphytic orchids, namely on the aerial and substrate roots of Acampe papillosa and Dendrobium moschatum and on the aerial roots of the Phalaenopsis amabilis and Dendrobium phalaenopsis. The composition of the bacterial community on the plant roots depended on the conditions of plant growth. Under conditions simulating climate of moist tropical forests, the aerial roots proved to be populated with phototrophic microorganisms among which cyanobacteria predominated. Interlaced fungal hyphae and filamentous cyanobacteria formed a sheath on the surface of aerial roots. The nitrogen-fixing capacity of the sheath of aerial roots was studied by the example of P. amabilis.     

Associative cyanobacteria isolated from the roots of epiphytic orchids

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.     

Production of gibberellic acids by an orchid-associated Fusarium proliferatum strain

The rice pathogen Fusarium fujikuroi is well known for its ability to produce the plant hormones gibberellins (GAs). However, the majority of closely related Fusarium species is unable to produce GAs although the GA gene cluster is present in their genomes. In this study, we analyzed five orchid-associated Fusarium isolates for their capacity to produce GAs. Four of them did not produce any GAs and were shown not to contain any GA biosynthetic genes. However, the fifth isolate, which has been identified as F. proliferatum based on five molecular markers, produced significant amounts of GAs in contrast to previously characterized F. proliferatum strains. We focused on the molecular characterization of two GA-specific genes, ggs2 and cps/ks, both inactive in F. proliferatum strain D-02945. Complementation of a F. fujikuroi Deltaggs2 mutant with the ET1 ggs2 gene fully restored GA biosynthesis, confirming that the orchid-associated isolate contains an active gene copy. A possible correlation between GA production and their role in plant-fungal interactions is discussed.