Metabolic footprint of epiphytic bacteria on Arabidopsis thaliana leaves

Abstract

The phyllosphere, which is defined as the parts of terrestrial plants above the ground, is a large habitat for different microorganisms that show a high extent of adaption to their environment. A number of hypotheses were generated by culture-independent functional genomics studies to explain the competitiveness of specialized bacteria in the phyllosphere. In contrast, in situ data at the metabolome level as a function of bacterial colonization are lacking. Here, we aimed to obtain new insights into the metabolic interplay between host and epiphytes upon colonization of Arabidopsis thaliana leaves in a controlled laboratory setting using environmental metabolomics approaches. Quantitative nuclear magnetic resonance (NMR) and imaging high-resolution mass spectrometry (IMS) methods were used to identify Arabidopsis leaf surface compounds and their possible involvement in the epiphytic lifestyle by relative changes in compound pools. The dominant carbohydrates on the leaf surfaces were sucrose, fructose and glucose. These sugars were significantly and specifically altered after epiphytic leaf colonization by the organoheterotroph Sphingomonas melonis or the phytopathogen Pseudomonas syringae pv. tomato, but only to a minor extent by the methylotroph Methylobacterium extorquens. In addition to carbohydrates, IMS revealed surprising alterations in arginine metabolism and phytoalexin biosynthesis that were dependent on the presence of bacteria, which might reflect the consequences of bacterial activity and the recognition of not only pathogens but also commensals by the plant. These results highlight the power of environmental metabolomics to aid in elucidating the molecular basis underlying plantepiphyte interactions in situ.

Environmental Metabolomics of the Tomato Plant Surface Provides Insights on Salmonella enterica Colonization

“…These sugars were the predominant compounds depleted on Arabidopsis thaliana leaf surfaces colonized by Sphingomonas melonis and Pseudomonas syringae pv. tomato (13). In this study, sugar and sugar alcohol quantities in exudates increased with plant age, probably reflecting the higher photosynthesizing capacity of plants as they develop.…”

“…The availability of nutrients on plants is a major determinant of successful bacterial epiphytic colonization (9). Inorganic ions, sugars, amino acids, and organic acids are thought to leach from plant surfaces by passive diffusion (10), providing a source of nutrients sufficient to support bacterial growth (11)(12)(13). In addition, many plants actively exude an enormous range of secondary metabolites, including fatty acids, phenolics, flavonoids, terpenoids, and acyl sugars, through specialized structures known as glandular trichomes (14,15).…”

Systems-level Proteomics of Two Ubiquitous Leaf Commensals Reveals Complementary Adaptive Traits for Phyllosphere Colonization

“…Interestingly, the importance of alanine catabolism for successful in vivo proliferation has been demonstrated for another Pseudomonad, the human pathogen Pseudomonas aeruginosa during infection of the lungs (63). Besides alanine dehydrogenase, enzymes for arginine and valine degradation were among the most up-regulated proteins, in line with the recently acquired metabolic footprint by MALDI-TOF imaging of S. melonis, demonstrating arginine utilization on Arabidopsis leaves (64). We furthermore found a set of transport proteins involved in multidrug resistance, efflux of toxic compounds as well as iron uptake induced in S. melonis Fr1 upon plant colonization, which might contribute to its perseverance in the phyllosphere, also with regard to pathogenic strains invading the habitat.…”

The isolation and characterization of resident yeasts from the phylloplane of Arabidopsis thaliana

“…1b. Dilute (0.2 x) potato dextrose agar (PDA) was selected as a culture medium with the reasoning that a nutrient-poor, plant-based medium lacking high levels of exogenous amino acids would mimic the conditions in the phyllosphere1120. Plates were monitored daily over two weeks and colonies marked and picked as they appeared.…”

“…Physical barriers and multiple chemical factors limit the growth and survival of microbes in the phyllosphere. However, the energy content of leaf surface components and simple sugars leached from the interior tissues1112 make the phyllosphere a considerable microbial habitat. Microbes residing in the phyllosphere can have various lifestyles and modes of interaction with the host, being neutral residents, latent pathogens, or plant-health and -growth promoters.…”