Genomic Stability and Phenotypic Characteristics of Industrially Produced Lacticaseibacillus rhamnosus GG in a Yogurt Matrix.

Lacticaseibacillus rhamnosus GG is a widely marketed probiotic with well-documented probiotic properties. Previously, deletion of the mucus-adhesive spaCBA-srtC1 genes in dairy isolates was reported. In this study, we examined the genome preservation of industrially produced L. rhamnosus GG (DSM 33156) cofermented in yogurts. In total, DNA of 66 samples, including 60 isolates, was sequenced. Population samples and 59 isolates exhibited an intact genome. One isolate exhibited loss of spaCBA-srtC1. In addition, we examined phenotypes related to the probiotic properties of L. rhamnosus GG either from frozen pellets or cofermented in yogurt. L. rhamnosus GG from frozen pellets induced a response in intestinal barrier function in vitro, in contrast to frozen pellets of the starter culture. Yogurt matrix, containing only the starter culture, induced a response, but cofermentation with L. rhamnosus GG induced a higher response. Conversely, only the starter culture stimulated cytokine secretion in dendritic cells, and it was observed that the addition of L. rhamnosus GG to the starter culture reduced the response. We conclude that the L. rhamnosus GG genome is preserved in yogurt and that common in vitro probiotic effects of L. rhamnosus GG are observed when examined in the yogurt matrix. IMPORTANCELacticaseibacillus rhamnosus GG is a well-documented probiotic strain recognized for its high acid and bile tolerance and properties of adhesion to enterocytes and mucus. The strain exhibits SpaCBA pili, which have been demonstrated to play an important role in adhesion and therefore are relevant for persistence in the gastrointestinal tract. Recently we demonstrated that the genome and phenotypes of L. rhamnosus GG are preserved throughout an industrial production pipeline. However, as gene deletions in L. rhamnosus GG were previously reported for isolates from dairy products, a key question on the genomic stability of L. rhamnosus GG in a yogurt matrix remained. The aim of this study was to analyze genome stability and phenotypic characteristics of L. rhamnosus GG in yogurt. We found that the genome of L. rhamnosus GG is well conserved when the organism is cofermented in yogurt. Some phenotypic characteristics are consistent in all product matrixes, while other characteristics are modulated.

Lactobacillus rhamnosus GG Genomic and Phenotypic Stability in an Industrial Production Process.

Lactobacillus rhamnosus GG is one of the most widely marketed and studied probiotic strains. In L. rhamnosus GG, the spaCBA-srtC1 gene cluster encodes pili, which are important for some of the probiotic properties of the strain. A previous study showed that the DNA sequence of the spaCBA-srtC1 gene cluster was not present in some L. rhamnosus GG variants isolated from liquid dairy products. To examine the stability of the L. rhamnosus GG genome in an industrial production process, we sequenced the genome of samples of L. rhamnosus GG (DSM 33156) collected at specific steps of the industrial production process, including the culture collection stock, intermediate fermentations, and final freeze-dried products. We found that the L. rhamnosus GG genome sequence was unchanged throughout the production process. Consequently, the spaCBA-srtC1 gene locus was intact and fully conserved in all 31 samples examined. In addition, different production batches of L. rhamnosus GG exhibited consistent phenotypes, including the presence of pili in final freeze-dried products, and consistent characteristics in in vitro assays of probiotic properties. Our data show that L. rhamnosus GG is highly stable in this industrial production process.IMPORTANCELactobacillus rhamnosus GG is one of the best-studied probiotic strains. One of the well-characterized features of the strain is the pili encoded by the spaCBA-srtC1 gene cluster. These pili are involved in persistence in the gastrointestinal tract and are important for the probiotic properties of L. rhamnosus GG. Previous studies demonstrated that the L. rhamnosus GG genome can be unstable under certain conditions and can lose the spaCBA-srtC1 gene cluster. Since in vitro studies have shown that the loss of the spaCBA-srtC1 gene cluster decreases certain L. rhamnosus GG probiotic properties, we assessed both the genomic stability and phenotypic properties of L. rhamnosus GG throughout an industrial production process. We found that neither genomic nor phenotypic changes occurred in the samples. Therefore, we demonstrate that L. rhamnosus GG retains the spaCBA-srtC1 cluster and exhibits excellent genomic and phenotypic stability in the specific industrial process examined here.

E2F1 and E2F2 have opposite effects on radiation-induced p53-independent apoptosis in Drosophila.

The ability of ionizing radiation (IR) to induce apoptosis independent of p53 is crucial for successful therapy of cancers bearing p53 mutations. p53-independent apoptosis, however, remains poorly understood relative to p53-dependent apoptosis. IR induces both p53-dependent and p53-independent apoptoses in Drosophila melanogaster, making studies of both modes of cell death possible in a genetically tractable model. Previous studies have found that Drosophila E2F proteins are generally pro-death or neutral with regard to p53-dependent apoptosis. We report here that dE2F1 promotes IR-induced p53-independent apoptosis in larval imaginal discs. Using transcriptional reporters, we provide evidence that, when p53 is mutated, dE2F1 becomes necessary for the transcriptional induction of the pro-apoptotic gene hid after irradiation. In contrast, the second E2F homolog, dE2F2, as well as the net E2F activity, which can be depleted by mutating the common cofactor, dDp, is inhibitory for p53-independent apoptosis. We conclude that p53-dependent and p53-independent apoptoses show differential reliance on E2F activity in Drosophila.

Modulation of ionizing radiation-induced apoptosis by bantam microRNA in Drosophila.

In Drosophila, heterozygosity in the pro-apoptotic gene hid significantly reduces apoptosis that is induced by ionizing radiation (IR). Therefore, mechanisms that regulate Hid levels can potentially contribute to life-or-death decision of an irradiated cell. 3'UTR of hid mRNA contains 5 potential binding sites for bantam microRNA. Ectopic expression of ban attenuated apoptosis that results from ectopic expression of hid but the significance of this regulation under physiological conditions remained to be investigated. We report here that ban is needed to limit IR-induced apoptosis in larval imaginal discs. Using tubulin-EGFP ban sensors with ban consensus sequences in the 3'UTR, we find that EGFP decreases following IR, indicating that IR activates ban. Likewise, a tubulin-EGFP reporter with hid-3'UTR is repressed in irradiated discs and this repression requires ban consensus sites in the hid 3'UTR. ban mutant larvae show increased sensitivity to killing by IR, which is suppressed by a mutation in hid. These results can fit into a model in which IR activates ban and ban represses hid to limit IR-induced apoptosis. miRNAs have been shown previously to be induced by radiation but this is the first report that a miRNA is functionally important for radiation responses.

Insulin-like peptide 5 is a microbially regulated peptide that promotes hepatic glucose production.

OBJECTIVE: Insulin-like peptide 5 (INSL5) is a recently identified gut hormone that is produced predominantly by L-cells in the colon, but its function is unclear. We have previously shown that colonic expression of the gene for the L-cell hormone GLP-1 is high in mice that lack a microbiota and thus have energy-deprived colonocytes. Our aim was to investigate if energy deficiency also affected colonic Insl5 expression and to identify a potential role of INSL5. METHODS: We analyzed colonic Insl5 expression in germ-free (GF), conventionally raised (CONV-R), conventionalized (CONV-D) and antibiotic-treated mice, and also assessed the effect of dietary changes on colonic Insl5 expression. In addition, we characterized the metabolic phenotype of Insl5-/- mice. RESULTS: We showed that colonic Insl5 expression was higher in GF and antibiotic-treated mice than in CONV-R mice, whereas Insl5 expression in the brain was higher in CONV-R versus GF mice. We also observed that colonic Insl5 expression was suppressed by increasing the energy supply in GF mice by colonization or high-fat feeding. We did not observe any differences in food intake, gut transit or oral glucose tolerance between Insl5-/- and wild-type mice. However, we showed impaired intraperitoneal glucose tolerance in Insl5-/- mice. We also observed improved insulin tolerance and reduced hepatic glucose production in Insl5-/- mice. CONCLUSIONS: We have shown that colonic Insl5 expression is regulated by the gut microbiota and energy availability. We propose that INSL5 is a hormone that could play a role in promoting hepatic glucose production during periods of energy deprivation.

Microbial modulation of energy availability in the colon regulates intestinal transit.

Gut microbiota contribute to host metabolic efficiency by increasing energy availability through the fermentation of dietary fiber and production of short-chain fatty acids (SCFAs) in the colon. SCFAs are proposed to stimulate secretion of the proglucagon (Gcg)-derived incretin hormone GLP-1, which stimulates insulin secretion (incretin response) and inhibits gastric emptying. We find that germ-free (GF) and antibiotic-treated mice, which have severely reduced SCFA levels, have increased basal GLP-1 levels in the plasma and increased Gcg expression in the colon. Increasing energy supply, either through colonization with polysaccharide-fermenting bacteria or through diet, suppressed colonic Gcg expression in GF mice. Increased GLP-1 levels in GF mice did not improve the incretin response but instead slowed intestinal transit. Thus, microbiota regulate the basal levels of GLP-1, and increasing these levels may be an adaptive response to insufficient energy availability in the colon that slows intestinal transit and allows for greater nutrient absorption.

Ionizing radiation induces caspase-dependent but Chk2- and p53-independent cell death in Drosophila melanogaster.

Ionizing radiation (IR) can induce apoptosis via p53, which is the most commonly mutated gene in human cancers. Loss of p53, however, can render cancer cells refractory to therapeutic effects of IR. Alternate p53-independent pathways exist but are not as well understood as p53-dependent apoptosis. Studies of how IR induces p53-independent cell death could benefit from the existence of a genetically tractable model. In Drosophila melanogaster, IR induces apoptosis in the imaginal discs of larvae, typically assayed at 4-6 hr after exposure to a LD(50) dose. In mutants of Drosophila Chk2 or p53 homologs, apoptosis is severely diminished in these assays, leading to the widely held belief that IR-induced apoptosis depends on these genes in Drosophila. In this article, we show that IR-induced apoptosis still occurs in the imaginal discs of chk2 and p53 mutant larvae, albeit with a delay. We demonstrate that this phenomenon is a true apoptotic response because it requires caspase activity and the chromosomal locus that encodes the pro-apoptotic genes reaper, hid, and grim. We also show that Chk2- and p53-independent apoptosis is IR dose-dependent and is therefore probably triggered by a DNA damage signal. We conclude that Drosophila has Chk2- and p53-independent pathways to activate caspases and induce apoptosis in response to IR. This work establishes Drosophila as a model for p53-independent apoptosis, which is of potential therapeutic importance for inducing cell death in p53-deficient cancer cells.

Genotoxic methylating agents modulate extracellular signal regulated kinase activity through MEK-dependent, glutathione-, and DNA methylation-independent mechanisms in lung epithelial cells.

Mitogen-activated protein kinases (MAPKs) play a central role in transmitting stress-induced signals stimulated by genotoxic agents. The present study is the first to investigate the mechanisms by which genotoxic alkylating agents modulate MAPKs by directly measuring the effects of methylating agents on MAPK activity, DNA methylation, and intracellular glutathione levels. The effects of acetoxymethylmethylnitrosamine (AMMN), N-nitroso-N-methylurethane (NMUR), and N-methyl-N-nitrosourea (MNU) on these parameters were compared in a fetal rat lung cell line model (MP48). These compounds were chosen because they methylate DNA via a methanediazonium intermediate and, therefore, should induce similar cellular methylation patterns, although they produce different side products upon decomposition. All three compounds stimulated the activation of the stress-activated MAPKs, c-Jun N-terminal kinase, and p38. In contrast to what has been reported for other methylating agents, these compounds also stimulated the activation of extracellular signal regulated kinase (ERK), a MAPK typically activated by mitogenic agents. O6-methylguanine (O6-mG) is widely considered to be the critical toxic lesion induced by methylating agents, including AMMN, NMUR, and MNU, which form DNA adducts through SN1 reactions. O6-mG does not appear to be a key regulator of MAPK activity by these compounds, however. There is no direct relationship between the levels of O6-mG and the levels of MAPK activation, and formation of O6-mG does not appear to be sufficient to stimulate MAPK activation. The present studies also indicate that depletion of glutathione is not required or sufficient to stimulate MAPK activation by the methylating agents investigated here. The use of a pharmacological inhibitor indicates that these methylating agents activate ERK through a signaling pathway that requires the ERK kinase MEK. Altogether, these data indicate that genotoxic methylating agents activate MAPKs through mechanisms that are likely to involve the alkylation of cellular targets other than DNA.