ADI pathway and histidine decarboxylation are reciprocally regulated in Lactobacillus hilgardii ISE 5211: proteomic evidence

Amine production by amino acid decarboxylation is a common feature that is used by lactic acid bacteria (LAB) to complement lactic fermentation, since it is coupled with a proton-extruding antiport system which leads to both metabolic energy production and the attenuation of intracellular acidity. Analogous roles are played in LAB by both malolactic fermentation (MLF) and the arginine deiminase (ADI) pathway. The present investigation was aimed at establishing reciprocal interactions between amino acid decarboxylation and the two above mentioned routes. The analyses were carried out on a Lactobacillus hilgardii strain (ISE 5211) that is able to decarboxylate histidine to histamine, which had previously been isolated from wine and whose complete genome is still unknown. The 2DE proteomic approach, followed by MALDI TOF-TOF and De Novo Sequencing, was used to study the protein expression levels. The experimental evidence has indicated that malate does not influence histidine decarboxylase (HDC) biosynthesis and that histidine does not affect the malolactic enzyme level. However, the expression of the ADI route enzymes, arginine deiminase and ornithine transcarbamylase, is down-regulated by histidine: this biosynthetic repression is more important (4-fold) in cultures that are not supplemented with arginine, but is also significant (2-fold) in an arginine supplemented medium that normally induces the ADI pathway. On the other hand, arginine partially represses HDC expression, but only when histidine and arginine are both present in the culture medium. This proteomic study has also pointed out a down-regulation exerted by histidine over sugar metabolism enzymes and a GroEL stress protein. These data, together with the reciprocal antagonism between arginine deimination and histidine decarboxylation, offer clue keys to the understanding of the accumulation of lactate, amine, ammonia and ethylcarbamate in wine, with consequent implications on different health risk controls.