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

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 (1 mm-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.