Metabolomics Analyses Reveal Metabolites Affected by Plant Growth-Promoting Endophytic Bacteria in Roots of the Halophyte Mesembryanthemum crystallinum

Abstract

Mesembryanthemum crystallinum L. (common ice plant) is an edible halophyte. However, if ice plants are used to phytoremediate salinity soil, there are problems of slow initial growth, and a long period before active NaCl uptake occurs under higher salinity conditions. Application of endophytic bacteria may improve the problem, but there remain gaps in our understanding of how endophytic bacteria affect the growth and the biochemical and physiological characteristics of ice plants. The aims of this study were to identify growth-promoting endophytic bacteria from the roots of ice plants and to document the metabolomic response of ice plants after application of selected endophytic bacteria. Two plant growth-promoting endophytic bacteria were selected on the basis of their ability to promote ice plant growth. The two strains putatively identified as Microbacterium spp. and Streptomyces spp. significantly promoted ice plant growth, at 2-times and 2.5-times, respectively, compared with the control and also affected the metabolome of ice plants. The strain of Microbacterium spp. resulted in increased contents of metabolites related to the tricarboxylic acid cycle and photosynthesis. The effects of salt stress were alleviated in ice plants inoculated with the endobacterial strains, compared with uninoculated plants. A deeper understanding of the complex interplay among plant metabolites will be useful for developing microbe-assisted soil phytoremediation strategies, using Mesembryanthemum species.

Cadmium-Tolerant Rhizospheric Bacteria of the C3/CAM Intermediate Semi-Halophytic Common Ice Plant (Mesembryanthemum crystallinum L.) Grown in Contaminated Soils

“…Elevated soil salinity is yet another serious worldwide problem caused by excessive human activities such as deforestation, improper irrigation and fertilization ( Ashraf et al, 2010 ; Liang et al, 2017 ). Approximately 20% of irrigated areas are affected with salinization caused by irrigation not only with seawater but also with water considered as good quality, which may still contain up to 500 mg⋅dm –3 of soluble salts ( Zhang et al, 2018 ; Kataoka et al, 2021 ). Salinity is regarded as a common primary cause of stress in plants leading to increased osmotic pressure and water deficit, nutritional imbalance and accumulation of toxic ions in plant organs, mostly roots, and has strong negative influence on plant growth and development ( Zanetti et al, 2019 ; Nosek et al, 2020 ).…”

“…No significant toxic effect is visible up to 40% of salt content in plant dry mass ( Amari et al, 2014 ). That unique feature makes the common ice plant a perfect model in saline phytoremediation ( Kataoka et al, 2021 ). In turn, Ghnaya et al (2005) first suggested that it may also be a perfect candidate in cadmium decontamination due to accumulation capabilities of considerable amounts of this element in tissues.…”

“…They can also produce PGP hormones such as indole-3-acetic acid (IAA). Tissues or rhizosphere of M. crystallinum were shown to be colonized with microorganisms resistant to high saline concentrations and exhibiting PGP-traits, capable of N-fixation or P-solubilization ( Zhang et al, 2018 ; Yaprak et al, 2019 ; Kataoka et al, 2021 ). Some of these strains were identified as belonging to genera Halomonas, Bacillus, Planococcus , Microbacterium , and Streptomyces ( Zhang et al, 2018 ; Kataoka et al, 2021 ).…”

“…Tissues or rhizosphere of M. crystallinum were shown to be colonized with microorganisms resistant to high saline concentrations and exhibiting PGP-traits, capable of N-fixation or P-solubilization ( Zhang et al, 2018 ; Yaprak et al, 2019 ; Kataoka et al, 2021 ). Some of these strains were identified as belonging to genera Halomonas, Bacillus, Planococcus , Microbacterium , and Streptomyces ( Zhang et al, 2018 ; Kataoka et al, 2021 ). The plant-beneficial effect of these microorganisms was manifested by significant root elongation and shoot mass increase ( Yaprak et al, 2019 ), promotion of initial growth of seedlings ( Kataoka et al, 2021 ) and improvement of salinity resistance of non-halophytic plant ( Zhang et al, 2018 ).…”

“…Some of these strains were identified as belonging to genera Halomonas, Bacillus, Planococcus , Microbacterium , and Streptomyces ( Zhang et al, 2018 ; Kataoka et al, 2021 ). The plant-beneficial effect of these microorganisms was manifested by significant root elongation and shoot mass increase ( Yaprak et al, 2019 ), promotion of initial growth of seedlings ( Kataoka et al, 2021 ) and improvement of salinity resistance of non-halophytic plant ( Zhang et al, 2018 ).…”