Creation of an inducible vector system based on the rhizobia nodA gene promoter

Background: The possibility of changing the properties of rhizobial bacteria by giving them the ability to regulate the expression of additionally introduced genes into them is an urgent task both for fundamental science and for applied agrobiology, since this will make it possible to obtain microsymbionts with desired properties. An expression construct using the rhizobia regulatory system was created in this work. The rhizobia nodD gene encodes a regulatory protein that, in the presence of plant inducers, flavonoids, activates the transcription of nod-genes involved in the early stages of the formation of legume-rhizobium symbiosis. Materials and methods: A vector construct containing the nodD gene from Rhizobium leguminosarum bv. trifoli under the regulation of its own promoter and the gfp gene under the regulation of the nodA gene promoter from the same rhizobia was obtained. Neorhizobium galegae CIAM 0702 were transformed with the vector construct. Results: It has been shown that in recombinant strains synthetic flavonoids are capable of inducing expression of gfp gene to varying degrees. Conclusion: In the future, the results can be used to obtain rhizosphere microorganisms with a controlled synthesis of growth-stimulating and protective substances.

Experimental assembly reveals ecological drift as a major driver of root nodule bacterial diversity in a woody legume crop

ABSTRACT Understanding how plant-associated microbial communities assemble and the role they play in plant performance are major goals in microbial ecology. For nitrogen-fixing rhizobia, community assembly is generally driven by host plant selection and soil conditions. Here, we aimed to determine the relative importance of neutral and deterministic processes in the assembly of bacterial communities of root nodules of a legume shrub adapted to extreme nutrient limitation, rooibos (Aspalathus linearis Burm. Dahlgren). We grew rooibos seedlings in soil from cultivated land and wild habitats, and mixtures of these soils, sampled from a wide geographic area, and with a fertilization treatment. Bacterial communities were characterized using next generation sequencing of part of the nodA gene (i.e. common to the core rhizobial symbionts of rooibos), and part of the gyrB gene (i.e. common to all bacterial taxa). Ecological drift alone was a major driver of taxonomic turnover in the bacterial communities of root nodules (62.6% of gyrB communities). In contrast, the assembly of core rhizobial communities (genus Mesorhizobium) was driven by dispersal limitation in concert with drift (81.1% of nodA communities). This agrees with a scenario of rooibos-Mesorhizobium specificity in spatially separated subpopulations, and low host filtering of other bacteria colonizing root nodules in a stochastic manner.

Legume Nodulating Bacterium, Achromobacter xylosoxidans Found in Tropical Shrub Agroecosystem, Sumatera, Indonesia

Legume nodulating bacteria (LNB), known also as rhizobia, are soil bacteria, which are able to form rootnodules and fi x nitrogen in the leguminous plants. The LNB availability in the soil depends on the type ofagroecosystem, where plant grows. In this study, we isolated LNB from the shrub agroecosystem in Sumatera,Indonesia, and obtained four selected bacterial strains. Among them, the isolate UGM48a formed root nodulein Macroptilium atropurpureum and showed highest number of nitrogenase activity. UGM48a also contains nifHand nodA genes. An analysis of the PCR-amplifi ed 16S rDNA and BLASTn analysis showed that UGM48adisplayed 96% similarity with Achromobacter xylosoxidans. In addition, UGM48a were successfully nodulatedGlycine max (L.) merr var. wilis. This is the fi rst report detecting A. xylosoxidans as nodule-forming species forGlycine max possesing the positive copy of nodA gene. Keywords : Legume Nodulating Bacteria, shrub agroecosystem, Achromobacter xylosoxidans, nodA, Glycine max