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Research Project: Improved Processes for the Preservation and Utilization of Vegetables, Including Cucumber, Sweetpotato, Cabbage, and Peppers to Produce Safe, High Quality Products with Reduced Energy Use and Waste

Location: Food Science Research

Title: Phenotypic and genotypic diversity of Lactobacillus buchneri strains isolated from spoiled, fermented cucumber

Author
item Daughtry, Katheryne - North Carolina State University
item Johanningsmeier, Suzanne
item Sanozky-dawes, Rosemary - North Carolina State University
item Klaenhammer, Todd - North Carolina State University
item Barrangou, Rodolphe - North Carolina State University

Submitted to: International Journal of Food Microbiology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/28/2018
Publication Date: 5/25/2018
Citation: Daughtry, K., Johanningsmeier, S.D., Sanozky-Dawes, R., Klaenhammer, T.R., Barrangou, R. 2018. Phenotypic and genotypic diversity of Lactobacillus buchneri strains isolated from spoiled, fermented cucumber. International Journal of Food Microbiology. 280:46-56. https://doi.org/10.1016/j.ijfoodmicro.2018.04.044.
DOI: https://doi.org/10.1016/j.ijfoodmicro.2018.04.044

Interpretive Summary: Characterization of spoilage organisms is a key step in the development of stabilization procedures for low salt vegetable fermentations. Lactobacillus buchneri, a common non-pathogenic bacteria, can degrade lactic acid and cause spoilage of fermented cucumbers, especially in fermentations with reduced salt concentrations. To better understand the ability of this organism to cause spoilage, cultures isolated from spoiled, fermented cucumber were compared for their differences in genetic make-up and ability to degrade lactic acid in laboratory media and fermented cucumbers. Several unique strains of L. buchneri were identified and characterized, representing the diversity of this organism from a single environmental niche.

Technical Abstract: Lactobacillus buchneri is a Gram-positive, obligate heterofermentative, facultative anaerobe commonly affiliated with spoilage of food products. Notably, L. buchneri is able to metabolize lactic acid into acetic acid and 1,2-propanediol. Although beneficial to the silage industry, this metabolic capability is detrimental to preservation of cucumbers by fermentation. The objective of this study was to characterize isolates of L. buchneri purified from both industrial and experimental fermented cucumber after the onset of secondary fermentation. Genotypic and phenotypic characterization included 16S rRNA sequencing, DiversiLab® rep-PCR, colony morphology, API 50 CH carbohydrate analysis, and ability to degrade lactic acid in modified MRS and fermented cucumber media. Distinct groups of isolates were identified with differing colony morphologies that varied in color (translucent white to opaque yellow), diameter (1mm–11 mm), and shape (umbonate, flat, circular or irregular). Growth rates in MRS revealed strain differences, and a wide spectrum of carbon source utilization was observed. Some strains were able to ferment as many as 21 of 49 tested carbon sources, including inulin, fucose, gentiobiose, lactose, mannitol, potassium ketogluconate, saccharose, raffinose, galactose, and xylose, while others metabolized as few as eight carbohydrates as the sole source of carbon. All isolates degraded lactic acid in both fermented cucumber medium and modified MRS, but exhibited differences in the rate and extent of lactate degradation. Isolates clustered into eight distinct groups based on rep-PCR fingerprints with 20 of 36 of the isolates exhibiting >97% similarity. Although isolated from similar environmental niches, significant phenotypic and genotypic diversity was found among the L. buchneri cultures. A collection of unique L. buchneri strains was identified and characterized, providing the basis for further analysis of metabolic and genomic capabilities of this species to enable control of lactic acid degradation in fermented plant materials.