T. A. Cherdyntseva

Microbial producers of plant growth stimulators and their practical use: A review

The ability of pro-and eukaryotic microorganisms to synthesize growth-stimulating phytohormones is reviewed, with emphasis on the pathways of biosynthesis of these compounds and their effects on the physiological and biochemical properties of the producers. Phytohormones are viewed as specific mediators in interactions between various organisms inhabiting the same ecological niche, the biological role of which is not limited to processes taking place in plants. In addition to setting forth the theoretical aspects of this problem, the review underscores the need to utilize such producer microorganisms in plant cultivation and biotechnology

Auxin production by bacteria associated with orchid roots

Bacteria associated with the roots of greenhouse tropical orchids were shown to produce indole-3-acetic acid (IAA) and to excrete it into the culture liquid. The presence and activity of IAA were demonstrated colorimetrically, by thin-layer chromatography, and by biotests. The associated bacteria varied in their ability to excrete indole compounds (1–28 µg/ml nutrient broth). Addition of tryptophan to the growth medium enhanced phytohormone production. Upon addition of 200 µg/ml tryptophan, the bacteria isolated from Dendrobium moschatum roots (Sphingomonas sp. 18, Microbacterium sp. 23, Mycobacterium sp. 1, Bacillus sp. 3, and Rhizobium sp. 5) produced 50.2, 53.1, 92.9, 37.6, and 60.4 µg IAA/ml, respectively, while the bacteria isolated from Acampe papillosa roots (Sphingomonas sp. 42, Rhodococcus sp. 37, Cellulomonas sp. 23, Pseudomonas sp. 24, and Micrococcus luteus) produced 69.4, 49.6, 53.9, 31.0, and 39.2 µg IAA/ml. Auxin production depended on cultivation conditions and on the growth phase of the bacterial cultures. Treatment of kidney bean cuttings with bacterial culture liquid promoted formation of a “root brush” with a location height 7.4- to 13.4-fold greater than the one in the control samples. The ability of IAA-producing associated bacteria to act as stimulants of the host plant root development is discussed.

Hormones and hormone-like substances of microorganisms: A review

Data from the literature on the ability of microorganisms to form plant hormones have been reviewed. The substances covered include abscisic acid, ethylene and other compounds with phytohormone-like properties (brassinosteroids, oligosaccharines) and analogues of animal neurotransmitters (biogenic amines). Pathways whereby the substances are metabolized and their effects on the development and activity (physiological and biochemical) of the microorganisms are considered. The role of phytohormones and hormone-like substances in the formation of association (microorganism-host) interactions are analyzed. The potential utilities of microorganisms producing hormones and hormone-like substances are discussed.

Microbiota of the Orchid Rhizoplane

Six bacterial strains isolated from the underground roots of the terrestrial orchid Calanthe vestitavar. rubro-oculatawere found to belong to the genera Arthrobacter, Bacillus, Mycobacterium, and Pseudomonas.Strains isolated from the aerial roots of the epiphytic orchid Dendrobium moschatumwere classified into the genera Bacillus, Curtobacterium, Flavobacterium, Nocardia, Pseudomonas, Rhodococcus, and Xanthomonas.The rhizoplane of the terrestrial orchid was also populated by cyanobacteria of the genera Nostocand Oscillatoria, whereas that of the epiphytic orchid was populated by one genus, Nostoc.In orchids occupying different econiches, the spectra of the bacterial genera revealed differed. The microbial complex of the terrestrial orchid rhizoplane differed from that of the surrounding soil.

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.

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 the 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 the 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.

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 A. papillosa and D. 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 Calothrixwere 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 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 rhizoplane 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 in this plant. This phenomenon is attributed to the presence of a sheath formed by cyanobacteria and serving as a substrate for fungi.

[Surviving Forms in Antibiotic-Treated Pseudomonas aeruginosa].

Survival of bacterial populations treated with lethal doses of antibiotics is ensured by very small numbers of persister cells. Unlike antibiotic-resistant cells, antibiotic tolerance of persisters is not inheritable and reversible. The present work provides evidence supporting the hypothesis on transformation (maturation) of persisters of an opportunistic pathogen Pseudomonas aeruginosa, revealed by ciprofloxacin (CF) treatment (25–100 μg/mL), into dormant cystlike cells (CLC) and nonculturable cells (NC), as was described previously for a number of non-spore-forming bacteria. Subpopulations of type 1 and type 2 persisters, which survived antibiotic treatment and developed into dormant forms, were heterogeneous in their capacity to form colonies or microcolonies upon germination as resistance to heating at 70°C and in cell morphology. Type 1 persisters, which were formed after 1-month incubation of the stationary-phase cultures grown in the medium with decreased C and N concentrations, developed in several types of surviving cells, including those similar to CLC in cell morphology. In the course of 1-month incubation of type 2 persisters, which were formed in exponentially growing cultures, other types of surviving cells developed: immature CLC and L-forms. Unlike P. aeruginosa CLC formed in the control post-stationary phase cultures without antibiotic treatment, most of 1-month persisters, especially type 2 ones, were characterized by the loss of colony-forming capacity, probably due to transition into an nonculturable state with relatively high numbers of live intact cells (Live/Dead test). Another survival strategy of P. aeruginosa populations was ensured by a minor subpopulation of CF-tolerant and CF-resistant cells able to grow in the form of microcolonies or regular colonies of decreased size in the presence of the antibiotic. The described P. aeruginosa dormant forms may be responsible for persistent forms in bacteria carriers and latent infections and, together with antibiotic-resistant cells, are important as components of test systems to assay the efficiency of potential pharmaceuticals against resistant infections.

Biological effect of extracellular peptide factor from Luteococcus japonicus subsp. casei on probiotic bacteria

The biological effect of the extracellular peptide reactivating factor (RF) from Luteococcus casei on cells of probiotic cultures was studied. The RF showed the protective and reactivating effects on the Bifidobacterium bifidum cells under the action of bile salts and an acidic stress. Also, it acted as a cryoprotector during lyophilisation and long-term culture storage. The RF and the L. casei culture liquid (CL) were shown to have bifidogenic properties. The degree of protection and reactivation of lactic-acid bacteria under the action of bile salts depended on the particular strain properties. The maximum degree of protection (more than thirteen-fold) and reactivation (close to three-fold) was found in Lactobacillus casei, while the minimum values were characteristic of Lactobacillus reuterii. The resistance of lactobacilli to bile was increased in the row of L. acidophilus, L. casei, L. plantarum, L. rhamnosus, and L. reuterii correlating with the RF protection degree.

New approaches for the isolation of bifidobacterial strains, their molecular characterization, and assessment of their probiotic potential

Six stably growing strains of bifidobacteria possessing probiotic properties were isolated from the feces of newborn children and animals. According to the results of molecular analysis, one strain was classified as Bifidobacterium bifidum, while five belonged to Bifidobacterium animalis. Initial identification of the strains was carried out using the primer pairs for the 16S rRNA gene (g-Bifid—F/R, Bif164/662) and for the xfp gene specific for bifidobacteria. Subsequent sequencing of complete genes encoding 16S rRNA synthesis in the isolates confirmed their species affiliation. The cultures exhibited high resistance to gastroenterological stress (5 ≤ RD ≤ 10) and may therefore be recommended as potential probiotics.