Transformation of the interaction pattern between rhizobia and non-rhizobia of Sophora davidii under different culture conditions

Abstract:

[Objective]In addition to rhizobia,non-rhizobia have been simultaneously isolated from the same root nodules,and the existence of non-rhizobia in root nodules of Fabaceae plants was a universal phenomenon.Their colonization meaning and potential ecological functions have been unknown so far.Moreover,the real relationships between rhizobia and non-rhizobia remain unclear.Therefore,the interactions and mechanism of their co-evolution should be investigated intensively and further studied.This paper was designed to reveal the interactions between rhizobia and non-rhizobia in root nodule microbiome of Sophora davidii and to further explore the shift in the interaction pattern between them under different culture conditions.[Methods] The rhizobia and non-rhizobia isolated from the root nodules of wild Sophora davidii in arid areas of Northern Shaanxi Province was taken as the subjects.The interacting strains were screened based on co-culture,two-compartment culture and pure culture,and were investigated for the tolerance to pH and NaCl and the utilization of various nitrogen sources.The colony diameter,growth curve and polysaccharide production of the rhizobia were used to evaluate the interaction effects,so as to further explore the transformation mechanism underlying the interaction effects of strains under saline-alkali and nutritional stresses.[Results] Under saline-alkali stress,the interaction effects of the non-rhizobia Pseudomonas oryzihabitans BT-147 and Priestia aryabhattai BT-59 on Rhizobium azibense BT-170 changed from inhibition under normal culture conditions to promotion.The colony diameter of R.azibense BT-170 increased by 0.803 mm and 1.034 mm,respectively in test groups as compared with the condition in control group.When Bacillus siamensis BT-9-1was co-cultured with Mesorhizobium metallidurans YC-39 under saline-alkali stress,the interaction pattern changed to promotion from inhibition under normal culture conditions.Compared with control group,the test group had increased colony diameter of M.metallidurans YC-39 by 1.019 mm,and the exopolysaccharide production rose from 1.088 μg/mL to 2.555µg/mL.When Glutamic acid was used as the only nitrogen source,the non-rhizobia Pseudomonas oryzihabitans BT-147 and Priestia aryabhattai BT-59 had promotion effects on R.azibense BT-170,and the difference in colony diameter of R.azibense BT-170 between test group and control group reached 1.348 mm and 2.196 mm,respectively.The exopolysaccharides yield of R.azibense BT-170 increased from 0.559 μg/mL in control group to 0.821 μg/mL and 3.341µg/mL,respectively.[Conclusion] Under saline-alkali and nitrogen source stresses,the interaction effects of the non-rhizobia Pseudomonas oryzihabitans BT-147 and Priestia aryabhattai BT-59 on R.azibense BT-170 changed to promotion from inhibition under normal culture conditions and enhanced the exopolysaccharides production of R. azibense BT-170(P<0.05).The shift in the interaction pattern between rhizobia and non-rhizobia under different culture conditions improved the stress resistance of rhizobia and expanded the range of nitrogen sources available to rhizobia,revealing the role of non-rhizobia in root nodule microbiome and simplifying the complex interactions in root nodule microbiome in vitro.