Geographic and host-associated variations in bacterial communities on the floret surfaces of field-grown broccoli

Fresh vegetables harbor diverse bacterial populations on their surfaces. However, information on this microbiota is limited to a few types of fresh vegetables, and little is known about how it varies with geography and host condition. Here, we analyzed bacterial communities on the floret surfaces of 66 field-grown broccolis collected from 22 farms in four farming regions of Jeju Island using 454 pyrosequencing of 16S rRNA amplicons, and determined their relationship to farming region and host-associated factors. Geographic variations in bacterial community composition and diversity were observed among farming regions, which partly reflected their relative humidity and insolation. The most abundant phyla were Proteobacteria, followed by Actinobacteria, Firmicutes and Bacteroidetes; core OTUs assigned to Pseudomonas, Acinetobacter and Oxalobacteraceae, Comamonadaceae and Enterobacteriaceae contributed to the community differences. Bacterial community composition differed between immature and mature samples, with mature samples harboring higher bacterial diversity. In comparison with other types of fresh vegetables and fruits, bacterial communities on broccoli florets were unique, but more similar to those of ground vegetables than to those of tree fruits/vegetables. This study presents novel data on the variability of floret-associated bacterial populations of field-grown broccoli relative to environmental and host-associated factors.