Culturable Bacterial Community Compositions From Seeds Of Tomato And Rice And Function Of Plant Growth Promoting Endophytic Bacteria

Endophytic bacteria are the microorganisms that colonize the interior of plants and do no harm to the plant tissues, and they may show beneficial effects on plant growth, disease-resistant, stress-resistant and phytoremediation. The symbiotic relationship between plant and versatile endophytes becomes a hot research topic recently.In this study, seeds of different tomato (Lycopersicum esculent.um Mill.) and rice (Oiyza sativa L.) cultivars were used to analyze and compare the bacterial community compositions of endophytic bacteria. On basis of the16S rRNA PCR-RFLP analysis,84strains isolated from seeds of four tomato cultivars (Red cherry, Pink lady, Yellow angel and Green pearl) showed similarity to five Bacillus species: B. altitudinis, B. amyloliquefaciens, B. atrophaeus, B. pumilus and B. subtilis. B. subtilis and B. amyloliquefaciens were the mutual dominant speices. And48strains isolated from seeds of four rice cultivars (Zhengdao18, Xudao16, Suijing4and Shangyu397) were grouped into10genera, which were closely matched to y-Proteobacteria, α-Proteobacteria, Actinobacteria and Firmicutes. y-Proteobacteria (Enterobacter, Pantoea, Xanthomonas and Pseudomonas) was predominant in the community, and Pantoea was the mutual dominant genus.Nitrogen fixation, phosphate solubilization, production of IAA, siderophore and ACC (1-aminocyclopropane-l-carboxylic acid) deaminase are the characteristics of plant growth-promoting bacteria. Most of strains obtained from tomato and rice seeds were able to grow in nitrogen-free culture medium. Almost50%of the isolates showed the capability of IAA production or phosphate solubilization. Majority of strains exhibited two or more plant growth-promoting traits. Among six ACC deaminase producing bacteria, the enzyme activities of HYT-12-1and NA-397-SYM-1were higher than others, and their ACC deaminase activities were quantified as112.02and131.88nmol a-ketobutyrate mg-1protein h-1. HYT-151-1, LZZ-133and LB-Z-FJ-1had better ability of IAA production, and the IAA contents were5.12,5.49and6.53μg/mL. HYT-12-1, HYT-151-1and LZZ-133were identified as Bacillus subtilis, LB-Z-FJ-1was belonged to Enterobacter, and NA-397-SYM-1was affiliated to Curtobacterium luteum. This is the first report that Curtobacterium bacterium could produce ACC deaminase. These five isolates had self-generated nitrogen-fixing ability.ACC deaminase producing strains (HYT-12-1and NA-397-SYM-1) and IAA producing strains (LB-Z-FJ-1, HYT-151-1and LZZ-133) could colonize in roots, stems and leaves of tomato, rape, radish and rice seedlings, and promoted the growth of seedlings. Treatments with strains significantly improved the length and weight of roots and stems, chlorophyll content, root activity and element content. The plant growth promoting effects were more conspicuous, when treated with HYT-12-1and LZZ-133on tomato seedlings.Besides, these five strains could enhance the disease-resistance and defense function against Botrytis cinerea Pers. and cause the induced systemic resistance (ISR) response by soaking seeds treatments. The elicitation of ISR response by different strains may involve different signal transduction pathway. In Bacillus (HYT-12-1, HYT-151-1and LZZ-133) strains-treated tomato seedlings, resistance was likely to associate with JA signalling, but C. lutuem NA-397-SYM-1and Enterobacter sp. LB-Z-FJ-1treatments maybe induced both SA-and JA-dependent pathways.In conclusion, this study indicated the diversity of endophytic bacterial community compositions of plant seeds, and demonstrated the plant growth-promoting effects of endophytic bacteria on several plants and enhancement of disease resistance on tomato seedlings.