Screening analysis of light-responsive phenotype of leaf bacteria

The phyllosphere is a harsh environment in which microorganisms experience various stresses, many of which are attributed to sunlight. To understand the adaptation strategy of bacteria to the phyllospheric environment under sunlight, we examined light-responsive phenotypes by cultivating leaf bacterial isolates under light. Seven bacterial strains belonging to the genera Massilia, Kocuria, Gordonia, Agromyces, Microbacterium , and Arthrobacter were identified to enhance the production of yellow or red carotenoid pigments under light exposure. Light-responsive phenotypes were further analyzed in Massilia sp. ST22. This bacterium was confirmed to have the ability to colonize as well as produce pigments on plants. Analysis of several forms of stress resistance revealed that light positively affected UV resistance and negatively affected resistance to osmotic pressure and oxidative stress. These results uncover the light-responsive phenotypes of the leaf bacteria and indicate that light regulates several bacterial abilities necessary for plant colonization.