LOW-BRANCHING DEXTRAN PRODUCTION BY NEW STRAIN OF LEUCONOSTOC MESENTEROIDES ISOLATED FROM CARROTS IS STIMULATED BY CHANGES IN THE GASEOUS ENVIRONMENT

Carrot (Daucus carota L.) is one of the most important vegetable crops in many countries worldwide, both economically and nutritionally. In Israel, primary inoculum at the field or at the packing house, combined with the volatile environment created during long shipments, creates micro-climate conditions leading to a dramatic change in the microbial populations on the carrots` surface. This microbiome shift allows for the establishment of different phytopathogens causing soft rots of the entire produce. Specifically, this shift, induced by high levels of CO₂, leads to the dominance of the lactic acid bacteria Leuconostoc mesenteroides. It has been found that this new strain of L. mesenteroides, named YL48, produces liquid slime over the carrot surface, termed as oozing. This oozing facilitates the development of other microorganisms, some are phytopathogenic, for example, the mold Mucor fragilis. Characterizing the oozing sugar and protein components leads to the identification of an abundant sugar polymer named dextran, along with several main bacterial glucosyltransferases enzymes involved in EPS (extracellular polymeric substances) production. Dextran is produced by the bacterium while fermenting sucrose, the main sugar in carrots. This dextran shows physiochemical properties favored by the industry, for instance low branching. Low-branching dextran is a valuable compound in a variety of industries, including the biomedical and food ones. Therefore, identifying the optimal environment leading to increased yield of high-quality dextran by L. mesenteroides YL48 has beneficial outcomes, both for the carrot growers and for the industry, looking for new competent bacterial strains and nontoxic efficient growth media.