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 broccoli collected from 22 farms in four farming regions of Jeju Island, South Korea, using 454 pyrose-quencing of 16S rRNA amplicons, and we determined their relationships 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 operational taxonomic units (OTUs) assigned to Pseudomonas, Acinetobacter, 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 communities on 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. IMPORTANCE Fresh vegetables harbor diverse and complex bacterial populations on their surfaces. These indigenous bacteria may play a role in human and crop health; however, the diversity and variability of bacterial communities on fresh vegetables require further study. A popular crop of leafy vegetables, broccoli, is of great agricultural and industrial importance. This study provides a detailed description of the bacterial community composition and diversity on the surfaces of broccoli florets. The variability of bacterial communities is associated with the geographic location of farming sites and is affected by host growth and health. The bacterial communities specific to broccoli were identified and showed greater similarity to those found on ground vegetables than to those found on tree fruits/vegetables. This study presents novel data on the impact of environmental and host-associated conditions on the variability of floret-associated bacterial populations present on field-grown broccoli.