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Title: Bacterial population dynamics during the ensiling of Medicago sativa (alfalfa) and subsequent exposure to air

Author
item McGarvey, Jeffery - Jeff
item FRANCO, ROBERTA - University Of California
item Palumbo, Jeffrey - Jeff
item Hnasko, Robert
item Stanker, Larry
item MITLOEHNER, FRANK - University Of California

Submitted to: Journal of Applied Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/2/2013
Publication Date: 5/21/2013
Citation: McGarvey, J.A., Franco, R., Palumbo, J.D., Hnasko, R.M., Stanker, L.H., Mitloehner, F. 2013. Bacterial population dynamics during the ensiling of Medicago sativa (alfalfa) and subsequent exposure to air. Journal of Applied Microbiology. 114:1661-1670.

Interpretive Summary: Ensiling is a method to preserve fresh fodder by fermentation, for future use as an animal feed. While this method has been used for over one hundred years little is known about the microbial population dynamics that occur during the ensiling process or during the exposure to air when the material is removed from the silos. We utilized standard chemical, cultural and molecular methods to determine the chemical and bacterial population dynamics that occurred during the ensiling process. We observed significantly different bacterial populations on the alfalfa, silage and silage exposed to air. Before ensiling most of the bacteria belonged to the phylum Proteobaceria and after they shifted to mostly members of the phylum Firmicutes. This is the first report to examine the total bacterial population dynamics during the ensiling of alfalfa and subsequent air exposure using modern molecular techniques.

Technical Abstract: Aims: To describe, at high resolution, the bacterial population dynamics and chemical transformations during the ensiling of alfalfa and subsequent exposure to air. Methods and Results: Samples of alfalfa, ensiled alfalfa, and silage exposed to air were collected and their bacterial population structures compared using 16S rRNA gene libraries containing approximately 1,900 sequences each. Cultural and chemical analyses were also performed to complement the 16S gene sequence data. Sequence analysis revealed significant differences (P<0.05) in the bacterial populations at each time point. The alfalfa derived library contained mostly sequences associated with the Gammaproteobacteria (including the genera: Enterobacter, Erwinia and Pantoea); the ensiled material contained mostly sequences associated with the lactic acid bacteria (LAB) (including the genera: Lactobacillus, Pediococcus, and Lactococcus). Exposure to air, to simulate feed out, resulted in even greater percentages of LAB, especially among the genus Lactobacillus, and a significant drop in bacterial diversity. Conclusions: In depth 16S rRNA gene sequence analysis revealed significant bacterial population structure changes during the ensiling alfalfa and again during the exposure to air. Significance and Impact of the Study: This in depth description of the bacterial population dynamics that occurred during ensiling and simulated feed out expands our knowledge of these processes.