The community composition and growth-promoting activities of the cultivable epiphytic bacteria from the dimorphic fruits of Suaeda glauca Bunge

Abstract:

[Background] Seeds can harbor a lot of microorganisms and may influence a range of seed traits. The interactions between seed type and microorganisms are important for understanding seed germination and seedling growth. However, the interaction between different type seeds and seed-associated microorganisms in seed-heteromorphic plant is poor characterized. [Objective] To isolate and analyze community composition and growth-promoting activities of the epiphytic bacteria of two distinct types of fruits present on the same plant, Suaeda glauca Bunge., which mainly distributed in saline-alkaline soil. [Methods] Conventional culture dependent method was used to isolate the epiphytic bacteria from dimorphic fruits of S. glauca. The identification of the isolated strains was done based on 16S rRNA gene sequencing. The growth-promoting activities of isolated strains were also analyzed qualitatively. [Results] The epiphytic bacterial community composition of the type A fruits clearly differed from those of type B fruits. The results showed that, 67 epiphytic bacteria were isolated from type A fruits, which belonged to 3 classes, and 15 genus with Curtobacterium (34.33%), Bacillus (13.43%) and Pantoea (10.45%) as the most dominant genus; whereas 47 epiphytic bacteria were isolated from type B fruits, which belonged to 4 classes, 20 genus with Curtobacterium (12.77%), Bacillus (17.02%) and Frigoribacterium (14.89%) as the most dominant genus. The diversity of isolates were analyzed and compared using different diversity index, the shannon index, margalef index and evenness index which showed type A fruits were lower than those of type B fruits; but the Berger-Parker dominance index of type A fruits was higher than that of type B fruits. The percentage of the isolates with nitrogen-fixing, phosphate-solubilizing, potassium-dissolving, siderophore-producing and IAA-producing activity showed different changing trend in the dimorphic fruits of S. glauca. The high-proportioned nitrogen-fixing activity and the low-proportioned phosphate-solubilizing activity presented in strains which isolated from the type A and type B fruits of S. glauca. In addition, the percentage of potassium-dissolving activity in strains isolated from type A fruits showed higher than that of type B fruits, whilethe IAA-producing activity in strains isolated from type A fruits showed lower than that of type B fruits. [Conclusion] Our results show thatthe diversity, the community composition and growth-promoting activities of epiphytic bacterial communities in the dimorphic fruits of S. glauca arevaries.