Growth-promoting Sphingomonas paucimobilis ZJSH1 associated with Dendrobium officinale through phytohormone production and nitrogen fixation

Abstract

Growth-promoting Sphingomonas paucimobilis ZJSH1, associated with Dendrobium officinale, a traditional Chinese medicinal plant, was characterized. At 90 days post-inoculation, strain ZJSH1 significantly promoted the growth of D. officinale seedlings, with increases of stems by 8.6% and fresh weight by 7.5%. Interestingly, the polysaccharide content extracted from the inoculated seedlings was 0.6% higher than that of the control. Similar growth promotion was observed with the transplants inoculated with strain ZJSH1. The mechanism of growth promotion was attributed to a combination of phytohormones and nitrogen fixation. Strain ZJSH1 was found using the Kjeldahl method to have a nitrogen fixation activity of 1.15 mg l(-1) , which was confirmed by sequencing of the nifH gene. Using high-performance liquid chromatography-mass spectrometry, strain ZJSH1 was found to produce various phytohormones, including salicylic acid (SA), indole-3-acetic acid (IAA), Zeatin and abscisic acid (ABA). The growth curve showed that strain ZJSH1 grew well in the seedlings, especially in the roots. Accordingly, much higher contents of SA, ABA, IAA and c-ZR were detected in the inoculated seedlings, which may play roles as both phytohormones and 'Systemic Acquired Resistance' drivers. Nitrogen fixation and secretion of plant growth regulators (SA, IAA, Zeatin and ABA) endow S. paucimobilis ZJSH1 with growth-promoting properties, which provides a potential for application in the commercial growth of D. officinale.

Fig 1

Effects of strain ZJSH1 on growth-promoting of tissue culture seedlings (A) and on polysaccharide accumulation (B).A. Increasing ratio of treatment versus control.B. Polysaccharide content of D. officinale seedlings (*P < 0.05; **P < 0.01; CK: control).

Fig 2

Growth-promoting effect of strain ZJSH1 on the transplants in pot.A. The plants showing stem and root.B. Increasing ratio 10 months post-transplanting versus pre-transplanting (*P < 0.05; **P < 0.01; IBT: inoculation before transplantation; IDT: inoculation during transplantation; CK: control).

Fig 3

Reproduction dynamics of strain ZJSH1 (A) and their effect on the contents of the four main phytohormones in the culture seedlings (B) (CK: control).