DNA cloning in Lactobacillus helveticus by the exconjugation of recombinant mob-containing plasmid constructs from strains of transformable lactic acid bacteria

Genome sequence and analysis of Lactobacillus helveticus

The microbiological characterization of lactobacilli is historically well developed, but the genomic analysis is recent. Because of the widespread use of Lactobacillus helveticus in cheese technology, information concerning the heterogeneity in this species is accumulating rapidly. Recently, the genome of five L. helveticus strains was sequenced to completion and compared with other genomically characterized lactobacilli. The genomic analysis of the first sequenced strain, L. helveticus DPC 4571, isolated from cheese and selected for its characteristics of rapid lysis and high proteolytic activity, has revealed a plethora of genes with industrial potential including those responsible for key metabolic functions such as proteolysis, lipolysis, and cell lysis. These genes and their derived enzymes can facilitate the production of cheese and cheese derivatives with potential for use as ingredients in consumer foods. In addition, L. helveticus has the potential to produce peptides with a biological function, such as angiotensin converting enzyme (ACE) inhibitory activity, in fermented dairy products, demonstrating the therapeutic value of this species. A most intriguing feature of the genome of L. helveticus is the remarkable similarity in gene content with many intestinal lactobacilli. Comparative genomics has allowed the identification of key gene sets that facilitate a variety of lifestyles including adaptation to food matrices or the gastrointestinal tract. As genome sequence and functional genomic information continues to explode, key features of the genomes of L. helveticus strains continue to be discovered, answering many questions but also raising many new ones.

Green fluorescent protein is a reliable reporter for screening signal peptides functional in Lactobacillus reuteri

A signal peptide (SP)-probe vector pNICE-gfpSP, which employed a green fluorescent protein (Gfp) as the SP-selection marker, was constructed for use in Lactobacillus reuteri. This chimerical plasmid allowed cloning and screening DNA fragments with the SP function by direct visualization of the expressed fluorescence activity around cells. Assay of fluorescent intensity in their culture supernatant with spectrofluorometry further enabled quantifying the secretion efficiency of the identified SP fragment.

Worst-case scenarios for horizontal gene transfer from Lactococcus lactis carrying heterologous genes to Enterococcus faecalis in the digestive tract of gnotobiotic mice

Since genetically modified (GM) lactic acid bacteria (LAB) might be released in open environments for future nutritional and medical applications, the purpose of this study was to determine an upper limit for the horizontal gene transfer (HGT) in the digestive tract (DT) from Lactococcus lactis carrying heterologous genes (lux genes encoding a bacterial luciferase) to Enterococcus faecalis. Two enterococcal wide host-range conjugative model systems were used: (i) a system composed of a mobilizable plasmid containing the heterologous lux genes and a native conjugative helper plasmid; and (ii) a Tn916-lux transposon. Both systems were tested under the most transfer-prone conditions, i.e. germfree mice mono-associated with the recipient E. faecalis. No transfer was observed with the transposon system. Transfers of the mobilizable plasmid carrying heterologous genes were below 10(2) transconjugants per g of faeces for a single donor dose and reached between 10(3) and 10(4) transconjugants per g of faeces when continuous inoculation of the donor strain was used. Once established in mice, transconjugants persisted at low levels in the mouse DT.

Completed sequence of plasmid pIP501 and origin of spontaneous deletion derivatives

The sequence of plasmid pIP501 (30,603 bp) was completed using previously published and newly acquired data. The sites at which two spontaneous deletions had occurred were identified. One was between tracts of repeated heptamers and the other between regions of secondary structure associated with plasmid replication. A high level of identity ( >95%) between plasmid pIP501 and part of plasmid pRE25, which had been isolated from Enterococcus faecalis associated with a food source, was confirmed.