Project description:We describe here a comparative genome analysis of three dairy product isolates of Lactobacillus rhamnosus GG (LGG) and the ATCC 53103 reference strain to the published genome sequence of L. rhamnosus GG. The analysis showed that in two of three isolates, major DNA segments were missing from the genomic islands LGGISL1,2. The deleted DNA segments consist of 34 genes in one isolate and 84 genes in the other and are flanked by identical insertion elements. Among the missing genes are the spaCBA genes, which encode pilin subunits involved in adhesion to mucus and persistence of the strains in the human intestinal tract. Subsequent quantitative PCR analyses of six commercial probiotic products confirmed that two more products contain a heterogeneous population of L. rhamnosus GG variants, including genotypes with or without spaC. These results underline the relevance for quality assurance and control measures targeting genome stability in probiotic strains and justify research assessing the effect of genetic rearrangements in probiotics on the outcome of in vitro and in vivo efficacy studies.
Project description:Carcinogens often generate mutable DNA lesions that contribute to cancer and aging. However, the chemical structure of tumorigenic DNA lesions formed by acetaldehyde remains unknown, although it has long been considered an environmental mutagen in alcohol, tobacco, and food. Here, we identify an aldehyde-induced DNA lesion, forming an intrastrand crosslink between adjacent guanine bases, but not in single guanine bases or in other combinations of nucleotides. The GG intrastrand crosslink exists in equilibrium in the presence of aldehyde, and therefore it has not been detected or analyzed in the previous investigations. The newly identified GG intrastrand crosslinks might explain the toxicity and mutagenicity of acetaldehyde in DNA metabolism.
Project description:Lactobacillus rhamnosus GG has become one of the most widely marketed and studied probiotic strains. Several genes important for probiotic function have been identified, including the spaCBA-srtC1 gene cluster encoding pili, which have been shown to be important for certain of its probiotic properties. The spaCBA-srtC1 gene cluster has been reported to be unstable in L. rhamnosus GG isolated from liquid dairy products and therefore the present study examined the L. rhamnosus GG genome stability throughout an industrial production process from the original deposit to the freeze-dried products including intermediate fermentations and single colony isolates prepared from these samples. The results showed that the original deposit was identical to the reference ATCC and that the genome sequence stayed fully intact throughout the production process. No SNPs or larger genomic changes occurred in any of the samples throughout the production process and the spaCBA-srtC1 gene locus was fully conserved and intact in all 31 samples examined. In addition, phenotypic expression of pili was demonstrated using immune-gold labelling EM. The images showed that pili production was preserved throughout the production process and that the number of pili were consistent in all batches. The present study extends the scope of previous findings to an industrial setting and shows that the region around the spaCBA-srtC1 cluster exhibits high stability in L. rhamnosus GG in an industrial production process.