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We isolated a Tn5-induced Rhizobium tropici mutant that has enhanced capacity to oxidize N,N-dimethylp-phenylendiamine (DMPD) and therefore has enhanced respiration via cytochrome oxidase. The mutant had increased levels of the cytochromes c 1 and CycM and a small increase in the amount of cytochrome aa 3 . In plant tests, the mutant increased the dry weight of Phaseolus vulgaris plants by 20 to 38% compared with the control strain, thus showing significantly enhanced symbiotic performance. The predicted product of the mutated gene is homologous to glycogen synthases from several bacteria, and the mutant lacked glycogen. The DNA sequence of the adjacent gene region revealed six genes predicted to encode products homologous to the following gene products from Escherichia coli: glycogen phosphorylase (glgP), glycogen branching enzyme (glgB), ADP glucose pyrophosphorylase (glgC), glycogen synthase (glgA), phosphoglucomutase (pgm), and glycogen debranching enzyme (glgX). All six genes are transcribed in the same direction, and analysis with lacZ gene fusions suggests that the first five genes are organized in one operon, although pgm appears to have an additional promoter; glgX is transcribed independently. Surprisingly, the glgA mutant had decreased levels of high-molecular-weight exopolysaccharide after growth on glucose, but levels were normal after growth on galactose. A deletion mutant was constructed in order to generate a nonpolar mutation in glgA. This mutant had a phenotype similar to that of the Tn5 mutant, indicating that the enhanced respiration and symbiotic nitrogen fixation and decreased exopolysaccharide were due to mutation of glgA and not to a polar effect on a downstream gene.

Aims:  In this study, 10 putative plant growth‐promoting rhizobacteria (PGPR) were assayed for their ability to improve Pinus pinea growth and mycorrhization. Methods and Results:  After an inoculation assay, except for two, all strains stimulated plant growth. All bacteria altered rhizosphere microbial communities as revealed by phospholipid fatty acid analysis; associating plant growth promotion with a decrease in biological diversity. Three strains were tested for their ability to enhance pine mycorrhization with wild fungi species. Only strain BB1 increased the total number of mycorrhizal root tips. Mycorrhizas present in the roots of each treatment were identified by ribosomal RNA sequencing and denaturing gradient gel electrophoresis analysis, detecting specificity between mycorrhizal species colonizing the roots and the inoculated PGPR. Conclusions:  In conclusion, BB1 appears to be a good candidate to be developed into a biofertilizer directed to enhance pine growth and mycorrhization, which should result in a better establishment rate for plants used in reforestation. Significance and Impact of the Study:  This study shows the potential of PGPR to improve fitness of forest tree specie. Moreover, the specificity between the bacteria inoculated and the mycorrhiza that the plant selects involve a potential biotechnological use in production of value‐added fungi.

The effect of a variety factors on the survival of several rhizobia strains on inoculants and inoculated seeds has been evaluated. Since the rhizobia strains showed different cell-density-evolution patterns on peat-based inoculants and on inoculated seeds, several inoculant formulations with highly effective Rhizobium/Bradyrhizobium strains (for Lupinus, Hedysarum, Phaseolus and Glycine max.) were monitored under the following storage conditions: (a) the inoculants were kept refrigerated (at 4 degrees C), or (b) at room temperature (25 degrees C). The effect of water content (30-50%, w/w) in the inoculants as well as that of several seed-coating adhesives were also investigated. Alternative carriers including perlite and vermiculite were tested. For all of the strains, survival on sterile peat-based inoculants was higher than on the corresponding unsterile peat formulation; for the latter, refrigerated storage conditions are recommended to ensure high bacterial densities. The water content of the inoculants had a differential effect on strain survival depending on the sterility of the peat, such that a high water content was more detrimental when unsterilized peat was employed. The best adherent for rhizobia survival was a gum arabic/water solution. Perlite was as effective as peat in maintaining a high population of rhizobia, at least for 6 months of storage.

Several isolates were obtained from sporocarps of Amanita caesarea (Scop.: Fr.) Pers. associated with Quercus suber and Castanea sativa coming from the southwest of Spain. Culture conditions were optimized for these isolates. The largest radial growth was obtained at pH 6-7, and optimal growth temperature was 24-28 degrees C depending on the isolate. Albumin bovine and nitrate produced the largest patch size diameters, but the greatest mycelium dry weight yields were obtained with ammonium. Mannitol produced the largest radial growth, and mannitol and glucose yielded the biggest mycelium dry weights. Although variations in growth behaviour between isolates were observed, only one internal spacer sequence-restriction fragment length polymorphism type was obtained.

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