Characterization of the Bacterial Diversity of the Fruit Carposphere

Abstract

Specialty crop horticulture is a multi-billion-dollar industry in the United States. Everyone has eaten an apple, orange, peach, or melon at some point in their life. In 2020, domestic production alone produced 5 million tons of apples in the United States, whereas melons brought in 2.7 million tons. However, little research has been done at the point of harvest characterizing their surface bacterial composition. Understanding these surface bacteria on fruits is critical for the food industry, growers, processors, as well as the consumer. Characterizing the carposphere microbiome of tree fruit like apples, peaches, and oranges or ground fruit like melons at point of harvest can inform the fruit industry in making decisions on post-harvest processing and storage procedures. The overall goal of these studies was to characterize the bacterial diversity and composition of different fruit carpospheres at the point of harvest to gain a better understanding of the fruit microbiome entering post-harvest. Whole fruits were sampled at point of harvest in the United States and 16S rRNA gene amplicon sequencing was conducted to characterize the bacterial diversity. Apples, oranges, and peaches had bacterial communities that clustered by the season and the harvesting point in the growing season that they were collected. Beta-dissimilarity of apple carpospheres had bacterial communities that were nested over the harvesting points, while orange carpospheres had bacterial communities that were nested and turning over consistently. Lastly, peach carposphere had bacterial communities that were turning over at each harvesting point. Melons that were collected from different regions around the United States, showed differences in bacterial diversity based on region of growth and less on type of melon or netting of melon rind. The two main agricultural growing regions, Arizona, and California, exhibit bacterial turnover and bacterial nestedness for netted melons over the four years sampled, respectively. This study lays the foundation for the produce industry to have a better understanding of the bacteria entering post-harvest processing to eventually improve methods that will impact food safety, storage time, and fruit quality.