Abiotic stressors impact outer membrane vesicle composition in a beneficial rhizobacterium: Raman spectroscopy characterization

Abstract

Outer membrane vesicles (OMVs) produced by Gram-negative bacteria have roles in cell-to-cell signaling, biofilm formation, and stress responses. Here, the effects of abiotic stressors on OMV contents and composition from biofilm cells of the plant health-promoting bacterium Pseudomonas chlororaphis O6 (PcO6) are examined. Two stressors relevant to this root-colonizing bacterium were examined: CuO nanoparticles (NPs)-a potential fertilizer and fungicide- and H2O2-released from roots during plant stress responses. Atomic force microscopy revealed 40–300 nm diameter OMVs from control and stressed biofilm cells. Raman spectroscopy with linear discriminant analysis (LDA) was used to identify changes in chemical profiles of PcO6 cells and resultant OMVs according to the cellular stressor with 84.7% and 83.3% accuracies, respectively. All OMVs had higher relative concentrations of proteins, lipids, and nucleic acids than PcO6 cells. The nucleic acid concentration in OMVs exhibited a cellular stressor-dependent increase: CuO NP-induced OMVs > H2O2-induced OMVs > control OMVs. Biochemical assays confirmed the presence of lipopolysaccharides, nucleic acids, and protein in OMVs; however, these assays did not discriminate OMV composition according to the cellular stressor. These results demonstrate the sensitivity of Raman spectroscopy using LDA to characterize and distinguish cellular stress effects on OMVs composition and contents.

Label-Free Classification of Bacterial Extracellular Vesicles by Combining Nanoplasmonic Sensors With Machine Learning

“…To date, only one recent study demonstrated the use of conventional Raman spectroscopy for characterising bacterial EVs, where changes in the chemical profiles of Pseudomonas chlororaphis O6 (PcO6) cells and resultant EVs were identified according to different abiotic stressors. In addition, they showed that the bacterial EVs had higher relative concentrations of proteins, lipids, and nucleic acids than PcO6 cells [53]. However, to the best of our knowledge, no studies to date have examined whether bacterial EVs could be successfully fingerprinted or classified using SERS.…”

Biochemical and metabolic signatures are fundamental to drought adaptation in PGPR Enterobacter bugandensis WRS7

“…These vesicles might serve some specialized function, such as nutrient acquisition or biofilm formation, and play an important role in host-microbe interactions, hence, offering stress tolerance under stressful environmental conditions. 26,27 McMillian et al, 2021 reported that outer membrane vesicles from Pseudomonas syringae and Pseudomonas fluorescens activate plant immune response in Arabidopsis thaliana against pathogenic bacteria. 28 Membrane vesicles play an essential defense function in mitigating osmotic and oxidative stress.…”

Outer Membrane Vesicles as Mediators of Plant–Bacterial Interactions

“…Bacteria cultured under unfavorable conditions may also produce OMVs with a cargo composition different from the control bacteria. The plant growth-promoting bacterium Pseudomonas chlororaphis O6 (PcO6) was exposed to CuO nanoparticles, and H 2 O 2 released OMVs that contained higher relative concentrations of proteins, lipids, and nucleic acids than PcO6 cells ( Potter et al, 2020 ).…”