Signal molecules and enzymes produced by Rhizobium leguminosarum sv. trifolii strains originating from the subpolar and temperate climate zones as elements of adaptation to low temperature stress

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Rhizobium leguminosarum sv. trifolii is a soil bacterium capable of establishing a nitrogen-fixing symbiosis with Trifolium spp. (clover) plants. In this study, two subpopulations of Rlt strains derived from the subpolar and temperate climate zones were characterized with respect to different physiological and metabolic traits. In addition, the influence of temperature on these processes was examined. Our results indicated that all the rhizobial strains grew at pH 5–9, tolerated salinity, and were sensitive to a majority of antibiotics. Moreover, the subpolar strains proved to be more tolerant to salinity than the temperate strains. A great majority of the strains (83.8 %) produced acyl-homoserine lactones in a wide range of temperatures (10–25 °C). Although no difference in the frequency of this trait between the subpopulations was found, more highly efficient AHL-producers were found among the temperate strains. In terms of the production of iron-chelating compounds and phosphate solubilization, half of the studied Rlt strains exhibited these traits, but more effective isolates were identified within the temperate subpopulation. These rhizobia also synthesized high amounts of indole-3-acetic acid and exhibited ACC deaminase activity, which is important for the regulation of the plant hormone ethylene. Some differences in phenotypic profiles between the individual strains were observed. The temperature range of 20–25 °C was optimal, whereas lower temperatures negatively affected the production of these molecules. In addition, the Rlt population exhibited a large diversity with respect to the auxiliary genetic content and metabolic potential. In conclusion, the Rlt strains produced a large set of signal molecules and enzymes and utilized a variety of carbon, nitrogen, phosphorus, and sulfur sources, which ensures their successful adaptation to various environments. • The Rlt strains from two climate regions synthesized a large set of components that provide them an environmental advantage. • Low temperature negatively affected the synthesis of these bioactive molecules and a large diversity among Rlt was found . • The Rlt strains exhibited a large diversity with respect to the size and number of plasmids. • Rhizobia derived from two climatic zones utilized a wide range of C, N, P, and S sources, indicating their high metabolic potential. • The subpolar strains possessed a higher plasmid DNA content and utilized more compounds than the temperate strains.