Abstract
The ability to colonize the host plants’ rhizospheres is a crucial feature to study in the case of Plant Growth Promoting Rhizobacteria (PGPRs) with potential agricultural applications. In this work, we have created GFP-tagged derivatives of three candidate PGPRs: Bacillus subtilis MB73/2, Pseudomonas sp. P482 and Ochrobactrum sp. A44. The presence of these strains in the rhizosphere of soil-grown potato (Solanum tuberosum L.) was detected with a classical fluorescence microscope and a confocal laser scanning microscope (CLSM). In this work, we have used a broad-field-of-view CLMS device, dedicated to in vivo analysis of macroscopic objects, equipped with an automated optical zoom system and tunable excitation and detection spectra. We show that features of this type of CLSM microscopes make them particularly well suited to study root colonization by microorganisms. To facilitate the detection of small and scattered bacterial populations, we have developed a fast and user-friendly enrichment method for root sample preparation. The described method, thanks to the in situ formation of mini-colonies, enables visualization of bacterial colonization sites on large root fragments. This approach can be easily modified to study colonization patterns of other fluorescently tagged strains. Additionally, dilution plating of the root extracts was performed to estimate the cell number of MB73/2, P482 and A44 in the rhizosphere of the inoculated plants.
Highlights
The plant rhizosphere supports a large microbial population by providing it with nutrients present in the root exudates [1]
The aim of this study was to investigate the potential of three candidate plant growth-promoting rhizobacteria (PGPR)—Bacillus subtilis
Despite the extensive research conducted on the biology of PGPRs, the concept of ‘efficient colonization’ is not uniformly defined
Summary
The plant rhizosphere supports a large microbial population by providing it with nutrients present in the root exudates [1]. In the resident microflora of the rhizosphere, harmless or beneficial commensals can be found, and plant pathogens. The commensals may provide the roots with a basal level of protection against pathogens by occupying the niche [2]. Direct growth stimulation can be mediated by facilitated acquisition of nutrients, mainly phosphorus and nitrogen, or by modulation of the phytohormone equilibrium [2]. The indirect effect stems from increased plant resistance to diseases. This can result either from induction of the defense system of the plant or from antagonism shown by PGRPs towards plant pathogens (for review see [3,4])
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