Genetics of nitrogen compounds metabolism by lactic acid bacteria

CRISTINA REGUANT, MARÍA C. MANCA DE NADRA AND ALBERT BORDONS

Nitrogen Compounds Metabolism by Lactic Acid Bacteria, 2008

Transworld Research Network

Año: 2008; p. 127 - 154

Contributing to the increasing importance of lactic acid bacteria (LAB) in fermentation, agriculture, food, and more recently, medicine, recent efforts have been done to determine the genome sequences of LAB strains. Since 2001, the genomes of 43 strains of different species of order Lactobacillales have been completed and 41 more genomes are being almost completed. This explosion of available genome sequences will accelerate their knowledge and their exploitation. In relation to the nitrogen metabolism, one of the more relevant aspects is proteolysis. For instance, Lactococcus lactis has an elaborate proteolytic system consisting of extracellular proteinases, intracellular peptidases and membrane-located peptide uptake systems. Genes involved in proteolysis had already been cloned, sequenced and analyzed before whole genome sequencing took off. Genes coding amino acid transporters are also very relevant in LAB. Although most LAB lack the genes for amino acid biosynthesis, Lc. lactis possesses all the genes required, and transcriptional regulation of trp, leu-ilvald, arg, his and metC-cysK operons has been characterized in it. The arcABC gene cluster, responsible for arginine catabolism, is well characterized in different LAB species of wine, such as Oenococcus oeni or Lactobacillus hilgardii. Since the arginine catabolism pathway can produce ethyl carbamate precursors, the presence of these genes and their regulation has been studied. Another important aspect of amino acid catabolism is the knowledge of genes related with their decarboxylation and production of biogenic amines, mainly histamine, cause of the safety concerns in fermented foods, such as cheese and wine. Genes hdc and tdc for histidine and tyrosine decarboxylase respectively, have been characterized in different LAB and specific methods to detect them have been designed. almost completed. This explosion of available genome sequences will accelerate their knowledge and their exploitation. In relation to the nitrogen metabolism, one of the more relevant aspects is proteolysis. For instance, Lactococcus lactis has an elaborate proteolytic system consisting of extracellular proteinases, intracellular peptidases and membrane-located peptide uptake systems. Genes involved in proteolysis had already been cloned, sequenced and analyzed before whole genome sequencing took off. Genes coding amino acid transporters are also very relevant in LAB. Although most LAB lack the genes for amino acid biosynthesis, Lc. lactis possesses all the genes required, and transcriptional regulation of trp, leu-ilvald, arg, his and metC-cysK operons has been characterized in it. The arcABC gene cluster, responsible for arginine catabolism, is well characterized in different LAB species of wine, such as Oenococcus oeni or Lactobacillus hilgardii. Since the arginine catabolism pathway can produce ethyl carbamate precursors, the presence of these genes and their regulation has been studied. Another important aspect of amino acid catabolism is the knowledge of genes related with their decarboxylation and production of biogenic amines, mainly histamine, cause of the safety concerns in fermented foods, such as cheese and wine. Genes hdc and tdc for histidine and tyrosine decarboxylase respectively, have been characterized in different LAB and specific methods to detect them have been designed.