Growth Tolerance of Rhizobia Isolated from Sand Dune Legumes of the Southwest Coast of India

Diversity and plant growth promoting properties of rhizobia isolated from root nodules of Ononis arvensis

This is the first report describing isolates from root nodules of Ononis arvensis (field restharrow). The aim of this investigation was to describe the diversity, phylogeny, and plant growth promoting features of microsymbionts of O. arvensis, i.e., a legume plant growing in different places of the southern part of Poland. Twenty-nine bacterial isolates were characterized in terms of their phenotypic properties, genome fingerprinting, and comparative analysis of their 16S rRNA, nodC and acdS gene sequences. Based on the nodC and 16S rRNA gene phylogenies, the O. arvensis symbionts were grouped close to bacteria of the genera Rhizobium and Mesorhizobium, which formed monophyletic clusters. The acdS gene sequences of all the isolates tested exhibited the highest similarities to the corresponding gene sequences of genus Mesorhizobium strains. The presence of the acdS genes in the genomes of rhizobia specific for O. arvensis implies that these bacteria may promote the growth and development of their host plant in stress conditions. The isolated bacteria showed a high genomic diversity and, in the BOX-PCR reaction, all of them (except three) exhibited DNA fingerprints specific only for them. Our studies showed that restharrow isolates formed effective symbiotic interactions with their native host (O. arvensis) and Ononis spinosa but not with Trifolium repens and Medicago sativa belonging to the same tribe Trifolieae as Ononis species and not with Lotus corniculatus, representing the tribe Loteae.

Stress tolerance and genetic variability of phosphate-solubilizing fluorescent Pseudomonas from the cold deserts of the trans-Himalayas

Nineteen efficient phosphate-solubilizing fluorescent Pseudomonas from the cold deserts of the trans-Himalayas were screened for stress tolerance against temperature, alkalinity, salinity, calcium salts, and desiccation. Phylogenetic analysis based on 16S rRNA gene sequencing placed these bacteria under three groups with fourteen strains in Group I including Pseudomonas trivialis and P. poae, two strains in Group II together with Pseudomonas kilonensis and P. corrugata, and three strains in Group III along with Pseudomonas jessenii and P. moraviensis. Genetic diversity assessed by ERIC and BOX-PCR revealed variability among strains belonging to the same phylogenetic groups. Cluster analysis based on the growth characteristics under regimes of different stress levels placed the strains into three distinct clusters displaying no correlation to their phylogenetic groups. Stress-tolerant strains differed in the level of decline in phosphate solubilization under increasing intensity of various stress parameters. The highest decrease occurred with 5% CaCO(3,) followed by 2.5% CaCO(3), pH 11, 5% NaCl, temperature of 37 degrees C, 40% PEG, 5% CaSO(4), 2.5% NaCl, 2.5% CaSO(4), pH 9 and temperature of 15 degrees C. Two strains belonging to Phylogenetic Group I exhibited higher phosphate solubilization at lower temperature. The results revealed that stress-tolerance ability was not limited to any particular phylogenetic group. Knowledge about the genetic variants of phosphate-solubilizing fluorescent Pseudomonas with potential for tolerance to desiccation, alkalinity, temperature, and salinity could be useful in understanding their ecological role under stressful environments of low phosphate availability.

Thermo-tolerant phosphate-solubilizing microbes for multi-functional biofertilizer preparation

In order to prepare the multi-functional biofertilizer, thermo-tolerant phosphate-solubilizing microbes including bacteria, actinomycetes, and fungi were isolated from different compost plants and biofertilizers. Except Streptomycesthermophilus J57 which lacked pectinase, all isolates possessed amylase, CMCase, chitinase, pectinase, protease, lipase, and nitrogenase activities. All isolates could solubilize calcium phosphate and Israel rock phosphate; various isolates could solubilize aluminum phosphate, iron phosphate, and hydroxyapatite. During composting, biofertilizers inoculated with the tested microbes had a significantly higher temperature, ash content, pH, total nitrogen, soluble phosphorus content, and germination rate than non-inoculated biofertilizer; total organic carbon and carbon-to-nitrogen ratio showed the opposite pattern. Adding these microbes can shorten the period of maturity, improve the quality, increase the soluble phosphorus content, and enhance the populations of phosphate-solubilizing and proteolytic microbes in biofertilizers. Therefore, inoculating thermo-tolerant phosphate-solubilizing microbes into agricultural and animal wastes represents a practical strategy for preparing multi-functional biofertilizer.