Microscale interactions between immigrant bacteria and plant leaf microbiota as revealed by live imaging

Abstract The phyllosphere – the aerial parts of plants – is an important microbial habitat that is home to diverse microbial communities. The spatial organization of bacterial cells on leaf surfaces is non-random and correlates with leaf microscopic features. Yet the role of microscale interactions between cells therein is not well-understood. Here, we ask how interactions between immigrant bacteria and resident microbiota affect the spatial organization of the combined population. By means of live imaging on a simplified in vitro system, we studied the microscale spatial organization of the plant pathogen Pseudomonas syringae B728a and the bio-control agent P. fluorescens A506 when introduced to both native and non-native leaf microbiota (bean and pear). We revealed that both strains preferentially attach to the surface in locations adjacent to microbiota aggregates. Interestingly, preferential attachment of microbiota cells near newly formed P. fluorescens aggregates was also observed. Our results indicate that two-way immigrant bacteria – resident microbiota interactions affect the microscale spatial organization of leaf microbial communities; and that preferential attachment – previously suggested as a general strategy that increases fitness under periodic stress – is a common surface colonization strategy. The implications of this study are likely relevant to other surface-associated microbial habitats.