Putrescine producing Lactococcus lactis : Sequencing and 1 transcriptional analysis of the biosynthesis gene cluster

25 Lactococcus lactis is a prokaryotic microorganism with great importance as a starter 26 culture and has become the model species among the lactic acid bacteria. The long and 27 safe history of use of L. lactis in dairy fermentations has resulted in the classification of 28 this species as GRAS (General Regarded As Safe) or QPS (Qualified Presumption of 29 Safety). However, our group has identified several strains of L. lactis subsp. lactis and 30 L. lactis subsp. cremoris which are able to produce putrescine from agmatine via the 31 agmatine deiminase (AGDI) pathway. Putrescine is a biogenic amine that confers 32 undesirable flavor characteristics and may even have toxic effects. The AGDI cluster of L. 33 lactis is composed of a putative regulatory gene, aguR, followed by the genes encoding 34 the catabolic enzymesaguB, aguD, aguA and aguC. These genes are transcribed as an 35 operon, which is induced in the presence of agmatine. In some strains, an IS element 36 interrupts the transcription of the cluster, which results in a non-putrescine producing 37 phenotype. Based on this knowledge, a PCR-based test was developed in order to 38 differentiate non-producing L. lactis strains from those with a functional AGDI cluster. 39 The analysis of the AGDI cluster and their flanking regions revealed that the capacity to 40 produce putrescine via the AGDI pathway could be a specific characteristic that has 41 been lost during the adaptation to the milk environment by a process of reductive 42 genome evolution. 43