Mutualism between Klebsiella SGM 81 and Dianthus caryophyllus in modulating root plasticity and rhizospheric bacterial density

Abstract

Aims Dianthus caryophyllus 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 Klebsiella SGM 81 strain to promote D. caryophyllus 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 Klebsiella SGM 81 as major bacterial trait most likely to enhance growth of D. caryophyllus. Methods ipdC dependent IAA production of SGM 81 was quantified using LC-MS/MS and localised proximal to D. caryophyllus 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 gfp 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 Klebsiella SGM 81 (accession number PRJEB21197) was determined to validate PGP traits and phylogenic relationships. Results Inoculation of D. caryophyllus roots with Klebsiella 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 Klebsiella SGM 81 genome, identified the presence of a canonical ipdC gene in Klebsiella 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 Klebsiella SGM 81 to be a rhizoplane and endophytic coloniser of D. caryophyllus 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. Conclusion Klebsiella SGM 81 effectively improves root traits of D. caryophyllus 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 Klebsiella SGM 81 and carnation that potentially extends to the wider rhizosphere microbiota.

Dual Microbial Inoculation, a Game Changer? – Bacterial Biostimulants With Multifunctional Growth Promoting Traits to Mitigate Salinity Stress in Spring Mungbean

“…Abdel-Salam et al (2013) reported B. licheniformis strain having pqq gene with expected amplified PCR product of 1202 bp for efficient phosphate solubilization. According to Gang et al (2017) Klebsiella SGM81 strain showed the presence of ipdc gene and confirmed bacterial production of IAA with improvement in PGP traits of D. caryophyllus . In addition to acds gene, various strains of Mesorhizobium , Rhizobium , Sinorhizobium , Microbacterium , Klebsiella , Enterococcus , and Pseudomonas etc .…”

Bacterial Indole-3-Acetic Acid Influences Soil Nitrogen Acquisition in Barley and Chickpea

“…The details of K.q. SGM81 sequence (PRJEB21197) are mentioned in our previous manuscript [ 9 ]. K.q.…”

“…The few main mechanisms of the rhizosphere that influence N-uptake efficiency are: root size morphology, root N transporter system, and interaction of root–microorganisms such as plant growth-promoting bacteria (PGPB) [ 7 ]. Many PGPBs are reported to positively improve root system development by manipulating plant hormones such as auxins, cytokinins, or gibberellins [ 8 , 9 ], and hence the acquisition of some nutrients. NO 3 − and NH 4 + uptake systems may be enhanced by the interaction with arbuscular mycorrhizal fungi (AMF), PGPB, and some organic acids [ 7 , 10 ].…”

Analysis of indole-3-acetic acid (IAA) production in Klebsiella by LC-MS/MS and the Salkowski method

“…Again, incubate the plates at 25 °C in 14 h light and 10 h dark cycles in a plant culture room. Salkowski reagent shows a maximum yield to 215 μg•ml -1 detected after 72 h with 0.15% tryptophan (Figure 1a in Gang et al, 2018).…”