Microscopic studies of the phytoplasma infection effect on the symbiotic system Medicago sativa – Rhizobium meliloti in simulated conditions

Aim. Aim of the study was to microscopically investigate the interaction of Acholeplasma laidlawii var. granulum 118 with the target plant Medicago sativa, as well as to determine the role of Rhizobium meliloti strains with natural and defective polysaccharides in the plant’s resistance occurrence. Methods. Cultivation of plants and their inoculation with bacteria was performed under conditions of microvegetation experiment. The study of the ultrastructure of alfalfa roots and nodules was carried out with both light and electron microscopy. Results. The rhizobial mutant strain, defective in the synthesis of lipopolysaccharides, more often formed atypical nodules on M. sativa, which aged faster. In the variant with double inoculation of alfalfa with rhizobia together with acholeplasma changes in the morphology of the lateral roots of plants, as well as deformation of the nodules were observed. Conclusions. Results of this study indicate not only the ability of phytoplasmas to penetrate the root system and migrate to plant aboveground organs, but also demonstrate the possibility of their presence in the nodules formed by rhizobia. Keywords: Mollicutes, acholeplasma, rhizobia, mutant, lipopolysaccharides.

Archaea, bacteria and termite, nitrogen fixation and sustainable plants production

Certain bacteria and archaea are responsible for biological nitrogen fixation. Metabolic pathways usually are common between archaea and bacteria. Diazotrophs are categorized into two main groups namely: root-nodule bacteria and plant growth-promoting rhizobacteria. Diazotrophs include free living bacteria, such as Azospirillum, Cupriavidus, and some sulfate reducing bacteria, and symbiotic diazotrophs such Rhizobium and Frankia. Three types of nitrogenase are iron and molybdenum (Fe/Mo), iron and vanadium (Fe/V) or iron only (Fe). The Mo-nitrogenase have a higher specific activity which is expressed better when Molybdenum is available. The best hosts for Rhizobium legumiosarum are Pisum, Vicia, Lathyrus and Lens; Trifolium for Rhizobium trifolii; Phaseolus vulgaris, Prunus angustifolia for Rhizobium phaseoli; Medicago, Melilotus and Trigonella for Rhizobium meliloti; Lupinus and Ornithopus for Lupini, and Glycine max for Rhizobium japonicum. Termites have significant key role in soil ecology, transporting and mixing soil. Termite gut microbes supply the enzymes required to degrade plant polymers, synthesize amino acids, recycle nitrogenous waste and fix atmospheric nitrogen. The positive effects of Arbuscular mycorrhizal (AM) fungi such as growth promotion, increased root length, leaf area, stem diameter, transplant performance and tolerance to stresses have been reported previously.

Evaluation of meliloti rhizobium activity effectiveness on quantitative properties of alfalfa by bacterial inoculation in the south-east of Iran

In order to investigate the effect of bacterial inoculation on yield, chlorophyll and protein content of alfalfa to obtain economically experimental products in Shahid Zande Rouh Agricultural Training Center in Kerman as a split plot in time based on a completely randomized block design with four replications on the ground Which had not been done before, was done. Bacterial inoculation was at three levels (Rhizobium meliluti, Rhizobium leguminasarum and no inoculation as a control). Bacterial inoculation had a significant effect on all studied traits and caused an increase in chlorophyll content, yield and protein percentage. In terms of fresh forage weight, the first and third crops had the highest yield with the application of Rhizobium meliloti (6 tons per hectare). The highest percentage of protein related to inoculation of Rhizobium meliloti was observed in the second Picking. According to the results of this study, inoculation with Rhizobium meliloti bacteria increases the ability of nitrogen fixation 3 to 4 times compared to the control and improved the alfalfa traits of Bami cultivar in southeastern Iran.

A model bioassay for influence of heavy metal salts toxicity on the viability of nodule-forming bacteria Rhizobium meliloti

The study consists of a bioassay of a medium experimentally contaminated with heavy metals using Rhizobium meliloti microorganisms as a test object. In vitro, the viability reaction of clover and alfalfa nodule bacteria to lead, cadmium, copper and zinc was established. The effect of the studied metals on the number of colonies depends on the concentration of the chemical element, physiological action of the microelement and biological characteristics of the strains used. The studies performed have determined a direct relationship of reducing the growth in the rhizobia colonies number of clover and alfalfa with an increase in the concentration of salts of heavy metals. Inhibition of the colonies number had a high regularity when the environment was contaminated with lead, copper and cadmium at a concentration of 0,3%; with a subsequent increase, complete death of microorganisms was observed. With the introduction of zinc into the nutrient medium in small concentrations, a positive resistance tendency of the clover and alfalfa bacteria was observed: thus, at 0,01-0,1% of the zinc salt content, the number of grown colonies was above the control level and amounted to 714-987 pcs. at the control value of 578 pcs. In an environment with a concentration of zinc 0,5%, a significant decrease in the growth of clover rhizobia was noted up to 65 pieces of colonies. At the same time, in the alfalfa rhizobia colonies in these concentrations a lower degree of survival was observed and the environment of zinc 0,3% became critical.

Bio-chemical characterization of rhizobia isolated from root nodules of Velvet bean (Mucuna pruriens L.)

Rhizobia are the symbiotic bacteria found in the soil which have potential ability to convert atmospheric di-nitrogen into usable form. A total of ten rhizobial strains were isolated from the root nodules of a medicinal legume Mucuna pruriens (L.) that commonly grow in the foothills of the Himalaya. All the ten strains isolated from different locations of same area were morphologically, biochemically and physiologically characterized based on the Bergey’s Manual of systematic Bacteriology. They were tested for the antibiotics sensitivity. The isolates showed high sensitivity to amoxicillin and least to erythromycin. Authentication test was done in eleven legumes but shown nodulations only in Trigonella foenum-graecum, Mucuna pruriens and Medicago sativa. The morphology, physiology, biochemical and infection test studies carried out justifies that the bacteria isolated belonged to the species of Rhizobium meliloti.

Diversity of root nodule bacteria from leguminous crops

In the present study, a total of 353 nodule-associated bacteria were isolated from 220 legume plant samples belonging to Cicer arietinum (85), Glycine max (74), Vigna radiata (21) and Cajanus cajan (40). A total of 224 bacteria were identified as fast-growing Rhizobium spp. on the basis of differential staining (Gram staining and carbol fuchsin staining) and biochemical tests. All the isolates were tested for indole acetic acid production (IAA), phosphate solubilization and siderophore production on plate assay. To examine the effect of volatile organic metabolites (VOM) and water soluble soil components (WSSC) on nodule bacteria, culture conditions were optimized by observing the effects of various parameters such as pH, salt content and temperatures on the growth of bacteria. Selected rhizobia were subjected to random amplified polymorphic DNA (RAPD) and amplified ribosomal DNA restriction analysis (ARDRA) analysis to identify their species. On the basis of RAPD and ARDRA, 10 isolates were identified as Rhizobium meliloti. In this study, Rhizobium GO4, G16, G20, G77, S43, S81, M07, M37, A15 and A55 were observed as the best candidates among the tested bacteria and can be further used as potent bioinoculants.