Plant Pathogens Consistently Reduce the Relative Abundance of Bacterial Order Sphingomonadales upon Infection

Abstract

Plants are inhabited by a collection of microorganisms, together called the microbiome. Some of these microorganisms can positively influence plant functioning, while others negatively impact plant health. Therefore, the overall composition of the microbiome is important for the plants’ well-being. Pathogens have been shown to alter the microbiome com- position through microbe-pathogen interactions. Furthermore, plants themselves alter the microbiome upon pathogen detection. There is no knowledge on the generality of the microbial change; infections with different pathogen sources on different plants might affect the microbial community in similar ways. In this study, it was shown that there is a consistent decrease in the relative abundance of bacterial order Sphingomonadales upon pathogen infection. This shift happens irrespective of the present pathogen type and the infected host. Furthermore, the specific shift was localized to the pathogen residence, showing that systemic signalling is not responsible for the Sphingomonadales decrease. It appears that general plant stress invoked by successful pathogen invasion does not necessarily contribute towards the Sphingomonadales reduction. Immune system suppression on the other hand might partially explain the pathogenic ef- fects on the Sphingomonadales, as A. thaliana mutants with altered immune system functioning show a similar shift in the relative abundances of the bacterial order. It is probable that direct microbe-pathogen interactions also play a role in the Sphingomonadales decrease, which should be confirmed in further research.