Effects of other microbes and the host on the interaction and ecological function of Pseudomonas and Sphingomonas isolates with plants

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The most common bacterial genera in leaves of wild Arabidopsis thaliana plants in Southwest Germany are Pseudomonas and Sphingomonas. While there are many pathogenic Pseudomonas, there are few, if any, Sphingomonas pathogens, but both taxa include strains that can protect plants from the effects of pathogens. Despite the ubiquity of both genera, they exhibit contrasting distribution patterns across wild A. thaliana plants: The abundances of Sphingomonas populations in individual plants are very uniform, whereas those of Pseudomonas greatly vary, and only Pseudomonas is a strong predictor of overall microbial load in these plants. We will investigate simplified Pseudomonas and Sphingomonas communities to learn about interactions between Pseudomonas and Sphingomonas strains inside plants and their effects on the host. Specific questions that we will ask are: (i) What ecologically relevant genes underlie plant protection by commensal Pseudomonas strains? (ii) How do traits, niches and functions, including interaction with Pseudomonas and a simplified microbial community, differ among individual Sphingomonas strains? (iii) How are Sphingomonas communities established, how do their diversity and composition affect plant health, and how do they interact with other microbes?