Gang Shraddha, Saraf Meenu, Waite Christopher J, Buck Martin, Schumacher Jörg
1Department of Microbiology and Biotechnology, School of Sciences, Gujarat University, Ahmedabad, 380009 India.
2Department of Life Science, Faculty of Natural Sciences, Imperial College, London, SW7 2AZ UK.
Plant Soil. 2018;424(1):273-288. doi: 10.1007/s11104-017-3440-5. Epub 2017 Nov 8.
is a commercially important ornamental flower. Plant growth promoting rhizobacteria are increasingly applied as bio-fertilisers and bio-fortifiers. We studied the effect of a rhizospheric isolate SGM 81 strain to promote growth under sterile and non-sterile conditions, to colonise its root system endophytically and its impact on the cultivatable microbial community. We identified the auxin indole-3-acetic acid (IAA) production of SGM 81 as major bacterial trait most likely to enhance growth of .
dependent IAA production of SGM 81 was quantified using LC-MS/MS and localised proximal to roots and correlated to root growth promotion and characteristic morphological changes. SGM 81 cells were localised on and within the plant root using 3D rendering confocal microscopy of expressing SGM 81. Using Salkowski reagent IAA production was quantified and localised proximal to roots in situ. The effect of different bacterial titres on rhizosphere bacterial population was CFU enumerated on nutrient agar. The genome sequence of SGM 81 (accession number PRJEB21197) was determined to validate PGP traits and phylogenic relationships.
Inoculation of roots with SGM 81 drastically promoted plant growth when grown in agar and soil, concomitant with a burst in root hair formation, suggesting an increase in root auxin activity. We sequenced the SGM 81 genome, identified the presence of a canonical gene in SGM 81, confirmed bacterial production and secretion of IAA in batch culture using LC-MS/MS and localised plant dependent IAA production by SGM 81 proximal to roots. We found SGM 81 to be a rhizoplane and endophytic coloniser of roots in a dose dependent manner. We found no adverse effects of SGM 81 on the overall rhizospheric microbial population unless supplied to soil in very high titres.
SGM 81 effectively improves root traits of in a dose dependent manner, likely through tryptophan dependent IAA production in the rhizoplane and potentially within the intercellular spaces of root tissue. Under optimal plant growth promoting conditions in non-sterile soil, the high total microbial titre in the rhizosphere supports a mutualistic relationship between SGM 81 and carnation that potentially extends to the wider rhizosphere microbiota.
康乃馨是一种具有重要商业价值的观赏花卉。植物促生根际细菌越来越多地被用作生物肥料和生物强化剂。我们研究了一种根际分离菌株SGM 81在无菌和非无菌条件下促进康乃馨生长的效果，其内生定殖于康乃馨根系的情况以及对可培养微生物群落的影响。我们确定了SGM 81产生生长素吲哚 - 3 - 乙酸（IAA）是最有可能促进康乃馨生长的主要细菌特性。
使用液相色谱 - 串联质谱法（LC - MS/MS）对SGM 81依赖色氨酸产生IAA的情况进行定量，并在康乃馨根附近定位，将其与根系生长促进和特征性形态变化相关联。使用表达SGM 81的康乃馨的三维共聚焦显微镜在植物根上和根内定位SGM 81细胞。使用索尔科夫斯基试剂对原位根附近产生的IAA进行定量和定位。在营养琼脂上计数不同细菌浓度对根际细菌种群的影响（以CFU计）。测定SGM 81的基因组序列（登录号PRJEB21197）以验证其植物促生特性和系统发育关系。
用SGM 81接种康乃馨根，在琼脂和土壤中培养时显著促进了植物生长，同时伴随着根毛形成的激增，表明根系生长素活性增加。我们对SGM 81基因组进行了测序，在SGM 81中鉴定出一个典型的生长素基因，使用LC - MS/MS在分批培养中证实了细菌产生和分泌IAA，并在根附近定位了SGM 81依赖植物产生的IAA。我们发现SGM 81以剂量依赖的方式定殖于康乃馨根的根际和内生部位。我们发现除非以非常高的浓度施用于土壤，SGM 81对整个根际微生物种群没有不利影响。
SGM有效地以剂量依赖的方式改善康乃馨的根系特性，可能是通过在根际平面以及可能在根组织细胞间隙内依赖色氨酸产生IAA。在非无菌土壤中最佳植物促生条件下，根际中高的总微生物浓度支持了SGM 81与康乃馨之间的互利关系，这种关系可能扩展到更广泛的根际微生物群。
