The quest for a histamine free glass of wine
Lactic acid bacteria (LAB) produce energy from the decarboxylation pathway. Decarboxylation is also a way for the bacterium to reduce its acid stress levels by turning amino acids into amines. Unfortunately, the biogenic amines produced by these biochemical pathways, beneficial to the bacterium, can be harmful when inadvertently taken in with food and drink. Researchers based in the wine producing region Bordeaux at the university investigated the complex genetics behind decarboxylation. They found four open reading frames (ORFs) in a strain of Lactobacillus hilgardii, a bacterium they isolated from wine. These were situated on the plasmid, the circular piece of DNA apart from the main chromosome. They code for proteins including the enzyme decarboxylase itself and an enzyme acting as an exchanger for histamine and its precursor histidine. The team then looked at other LABs for similar gene sequences. Fermentation is a common metabolic activity and they sequenced genes from a wide range of bacteria. These were isolated from wine, cheese, sauerkraut, horse digestive tract and squid liver sauce .Similar sequences were found in all the species. However in the case of horse digestive tract and cheese, the genes were on the main chromosome itself. Location of the gene sequences has serious implications for the bacterium and the food producer. Genes on the circular plasmid are transferred to other bacteria during conjugation when bacteria pass on genetic information and may be lost. Genetic location is therefore important from the point of view of genetic stability and inheritance of the pathway genes. The scientists further investigated L. buchineri from the cheese. Closer analysis of one of the genes named hdcC revealed it coded for a membrane protein responsible for histidine/histamine exchange. This was probably a first time discovery for the gene in that particular bacterium. Research of this nature could well lead to the identification of improved strains of LAB. The aim is to produce strains that do not have the genetic capability to produce biogenic amines. The consumer could then enjoy a histamine free glass of wine.
