Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/8/2014
Publication Date: 6/1/2014
Publication URL: http://handle.nal.usda.gov/10113/58886
Citation: McGarvey, J.A., Connell, J., Stanker, L.H., Hnasko, R.M. 2014. Bacterial population structure and dynamics during the development of almond drupes. Journal of Applied Microbiology. 116:1542-1552. Interpretive Summary: We examined the types of bacteria that are present on almond drupes at 3 time points: when the drupes first formed but were immature; when the drupes were just starting to split; and when the drupes were fully mature but before harvesting. At the first time point we observed relatively few types of bacteria; and mostly bacteria that have been associated with plants before. At the second time point we observed more types of bacteria, some of which were not usually associated with plants. At the third time point we observed many more types of bacteria, many of which are not usually associated with plants. At this last time point we also observed Salmonella on the drupes. From these observations we conclude that once the drupes begin to split a burst of microbial diversity occurs and it is at this time point that Salmonella may contaminate the drupes.
Technical Abstract: Aims: To describe the bacterial populations and their dynamics during the development of almond drupes. Methods and Results: We examined 16S rRNA gene libraries derived from the bacterial populations on almond drupes at three stages of development: 1) when the drupes were full sized, but before embryo development, 2) when the drupe hulls first began to split and 3) when the drupes were fully mature, but before harvesting. Our data revealed that the immature drupes were colonized by relatively few OTU, belonging mostly to common phyllosphere associated bacteria within the genera Pseudomonas, Pantoea, Methylobacterium, and Sphingomonas. However, after the hulls first began to split the level of bacterial diversity increased and continued to do so until the drupes were fully mature. At the last sampling period, we observed several sequences belonging to bacteria that are not usually associated with the phyllosphere, including some identical to Salmonella enterica. Conclusions: The bacterial populations on almond drupes before hull split were composed of relatively few OTU, most of which were commonly associated with the phyllosphere. However, after hull split the level of microbial diversity increased, which was mostly due to increased levels bacteria that are not normally associated with the phyllosphere, including Salmonella enterica. Significance and Impact of Study: This is the first report of the bacterial populations associated with almond drupes and their dynamics during development. Of specific significance is the observation that Salmonella enterica was present on the drupes just prior to harvesting, which may represent a critical control point.