Sphingomonas sediminicola Dae20 Is a Highly Promising Beneficial Bacteria for Crop Biostimulation Due to Its Positive Effects on Plant Growth and Development

Abstract

Current agricultural practices rely heavily on synthetic fertilizers, which not only consume a lot of energy but also disrupt the ecological balance. The overuse of synthetic fertilizers has led to soil degradation. In a more sustainable approach, alternative methods based on biological interactions, such as plant growth-promoting bacteria (PGPRs), are being explored. PGPRs, which include both symbiotic and free-living bacteria, form mutualistic relationships with plants by enhancing nutrient availability, producing growth regulators, and regulating stress responses. This study investigated the potential of Sphingomonas sediminicola Dae20, an α-Proteobacteria species commonly found in the rhizosphere, as a beneficial PGPR. We observed that S. sediminicola Dae20 stimulated the root system and growth of three different plant species in the Brassicaceae family, including Arabidopsis thaliana, mustard, and rapeseed. The bacterium produced auxin, nitric oxide, siderophores and showed ACC deaminase activity. In addition to activating an auxin response in the plant, S. sediminicola Dae20 exhibited the ability to modulate other plant hormones, such as abscisic acid, jasmonic acid and salicylic acid, which are critical for plant development and defense responses. This study highlights the multifunctional properties of S. sediminicola Dae20 as a promising PGPR and underscores the importance of identifying effective and versatile beneficial bacteria to improve plant nutrition and promote sustainable agricultural practices.

Keywords: Brassicaceae plants; Sphingomonas sediminicola Dae20; growth promotion; plant growth-promoting bacteria (PGPR); root stimulation; sustainable agriculture.

Figure 1

Arabidopsis thaliana root phenotype (a), primary root length (b), lateral root (LR) density (c), root hair (RH) length (d), RH density (e), shoot dry weight (f) and root dry weight (g) of 10-day-old Arabidopsis thaliana not inoculated (NI) or inoculated with different bacterial concentrations expressed as the number of colony-forming units (CFU) of S. sediminicola Dae20. Error bars represent SD. Letters represent a significant difference among modalities.

Figure 2

(a) Primary root, (b) lateral root (LR) density, (c) shoot fresh weight and (d) root fresh weight in 10-day-old Arabidopsis thaliana not inoculated (NI), inoculated with S. sediminicola Dae20 or grown in the presence of volatile organic compounds (VOC) released by the bacterial strain. Error bars represent SD. Letters represent a significant difference among modalities.

Figure 3

DR5::GUS (a) and ARR5::GUS (b) signals in 10-day-old Arabidopsis plants non-inoculated or inoculated with Sphingomonas sediminicola Dae20. Bars = 100 µm. (c) Development of S. sediminicola Dae20 on DF medium in a nitrogen-free medium (negative control), DF with ammonium sulphate (positive control) and DF with ACC as sole nitrogen source.

Figure 4

Relative expression of genes involved in auxin, abscisic acid, and salicylic acid pathways when S. sediminicola Dae20 was inoculated to Arabidospsis seedlings for 10 days. Error bars represent SD. Statistical differences were based on Kruskal–Wallis rank sum tests with Holm’s p-adjust. ***, p < 0.001.

Figure 5

Root of non-inoculated and Sphingomonas sediminicola Dae20-inoculated rapeseed (a) and (b) mustard plants, scale bar = 500 µm. (c) Root hair (RH) length of 7-day-old rapeseed or mustard plants non-inoculated (white bar) or inoculated with S. sediminicola Dae20 (gray bar). Error bars represent SD. Statistical differences were based on Kruskal–Wallis rank sum tests with Holm’s p-adjust. ***, p < 0.001.

Figure 6

Phenotypic traits of non-inoculated (white bar) and Sphingomonas sediminicola Dae20-inoculated (gray bar) mustard (a–d) and rapeseed (e–h) plants. (a,e) Shoot length; (b,f) root length; (c,d) shoot and root dry biomass; (d,h) SPAD values of cotyledons and penultimate leaves. Statistical differences were based on Kruskal–Wallis rank sum tests with Holm’s p-adjust. *, p < 0.05; **, p < 0.01; ***, p < 0.001.