Characterization of biofilm structures produced by some bacteria that promote plant growth by raman spectroscopy

Plant growth promoting rhizobacteria (PGPR) are common in the rhizosphere. These bacteria increase plant root development and provide plants with maximum nutrient uptake opportunities for better growth. Besides promoting growth, PGPRs have a number of functions including stress tolerance (heat, drought, salinity and disease), bioremediation of heavy metals, biodegradation of complex toxic organic compounds, biocontrol agents and biofilm formation. The interaction between various plant growth promoting rhizobacteria was mainly investigated under the planktonic growth mode. However, studies to understand the behavior of PGPR on root surface and soil in biofilm mode are very recent and it is clear that more research is needed in this area. Therefore, in-depth investigation of biofilm development on root surface and rhizosphere colonization is needed to improve understanding of plant-microorganism interaction. Infrared and Raman spectroscopy are vibration spectroscopy techniques that are used complementary to each other to obtain spectral information about the molecular structure of biofilms. Although infrared spectroscopy (IR) is widely used to characterize biofilms, interference from water has limited its use in the composition of hydrated biofilms. Since the frequencies of scattered photons depend on the types of bonds in the molecule, the Raman spectrum of each molecule is unique and can be thought of as that molecule's fingerprint. The diffraction-limited spatial resolution of Raman spectroscopy is about 1 μm, enabling detailed analysis of complex structures containing various molecules and molecular groups such as proteins, carbohydrates, lipids, and nucleic acids. In this study; The biofilm structures formed by Bacillus drentensis, Bacillus mojavensis, Pseudomonas fluorescens, Pseudomonas putida and Arthrobacter nitroguajacolicus bacteria, which have plant growth promoting properties, were characterized by Raman and FT-IR Spectroscopy. In addition, the biofilm formation capacity of these bacteria on polystyrene surfaces was determined by the crystal violet test, and the colonization of Bacillus drentensis, Pseudomonas fluorescens and Arthrobacter nitroguajacolicus bacteria on Arabidopsis thaliana Columbia ecotype roots was determined by Scanning Electron Microscope (SEM) analysis.