High Levels of CO Induce Spoilage by Leuconostoc mesenteroides by Upregulating Dextran Synthesis Genes.

During nonventilated storage of carrots, CO gradually accumulates to high levels and causes modifications in the carrot's microbiome toward dominance of and The lactic acid bacterium secretes a slimy exudate over the surface of the carrots. The objective of this study was to characterize the slime components and the potential cause for its secretion under high CO levels. A proteomic analysis of the exudate revealed bacterial glucosyltransferases as the main proteins, specifically, dextransucrase. A chemical analysis of the exudate revealed high levels of dextran and several simple sugars. The exudate volume and dextran amount were significantly higher when was incubated under high CO levels than when incubated in an aerated environment. The treatment of carrot medium plates with commercial dextransucrase or exudate protein extract resulted in similar sugar profiles and dextran production. Transcriptome analysis demonstrated that dextran production is related to the upregulation of the dextransucrase-encoding genes and during the first 4 to 8 h of exposure to high CO levels compared to aerated conditions. A phylogenetic analysis of YL48 revealed a high similarity to other genes harbored by different species. The ecological benefit of dextran production under elevated CO requires further investigation. However, this study implies an overlooked role of CO in the physiology and fitness of in stored carrots, and perhaps in other food items, during storage under nonventilated conditions. The bacterium is known to cause spoilage of different types of foods by secreting a slimy fluid that damages the quality and appearance of the produce. Here, we identified a potential mechanism by which high levels of CO affect the spoilage caused by this bacterium by upregulating dextran synthesis genes. These results have broader implications for the study of the physiology, degradation ability, and potential biotechnological applications of .