Lactobacillus hilgardii ISE5211 was isolated from an Italian red wine spontaneously undergoing malo-lactic fermentation. Besides performing malate decarboxylation, this strain is also able to produce histamine (4 g/L) and it has been proved that the genetic determinants for histidine decarboxylase (HDC) are plasmid-encoded . Since in lactic acid bacteria (LAB) malate and histidine decarboxylation contribute both to counteract acidic stress and to energy supply, the present study was intended to detect possible competitions between the two routes. The bacterial strain was grown in microaerophylic conditions, in uncontrolled pH, in a MRS medium with and without excess of histidine and/or malate. In control conditions (no histidine and no malate) no histamine is produced, but this metabolite became important when histidine is present in the culture broth. When malate is added to the histidine fortified medium, no significant reduction or delay in histamine accumulation occurs, suggesting that the two pathways proceed in parallel without any interference. At the same time, also the presence of histidine has no effects on the malo-lactic fermentation : malo-lactic enzyme kinetic parameters are similar for malate grown-cells and malate plus histidine grown cells, while no malo-lactic activity is detected in cells grown in histidine medium without malate. On the basis that also the arginine deiminase (ADI) pathway can play the same role in acidity control (one of its end-metabolites is ammonia) and energy supply (ATP production) we set up a second series of experiments for finding possible interferences between histidine decarboxylation and the ADI route. In this case a slight but significant delay in histamine accumulation takes place when histidine and arginine are simultaneously present, as compared to the medium where histidine is alone and, moreover, a biosynthetic control exerted by arginine over the histidine decarboxylase enzyme ( HDC) can be proved by means of both SDS-PAGE and 2DE maps. The biosynthesis of some ADI pathway enzymes is also attenuated in histidine plus arginine medium as respect to the condition of having arginine alone. So these two pathways seem to display some competition. The results obtained from the present investigation confirm the role of histidine decarboxylation in pH homeostasis and energy metabolism, suggesting that some mechanisms exists in Lactobacillus hilgardii ISE5211 to control the parallel, ATP and ammonia producing, ADI route. None of similar, on the contrary, has been observed for controlling malo-lactic fermentation in this strain.
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