Spatially-explicit depiction of a floral epiphytic bacterial community reveals role for environmental filtering within petals

The microbiome of flowers (anthosphere) is an understudied compartment of the plant microbiome. Within the flower, petals represent a heterogeneous environment for microbes in terms of resources and environmental stress. Yet little is known of drivers of structure and function of the epiphytic microbial community at the within-petal scale. We characterized the petal microbiome in two co-flowering plants that differ in pattern of ultraviolet (UV) absorption along their petals. Bacterial communities were similar between plant hosts, with only rare phylogenetically distant species contributing to differences. The epiphyte community was highly culturable (75% of families) lending confidence to the spatially-explicit isolation and characterization of bacteria. In one host, petals were heterogeneous in UV absorption along their length and in these there was a negative relationship between growth rate and position on the petal, as well as lower UV tolerance in strains isolated from the UV abso...