Pre-clinical evaluation of the effect of co-medication with antibiotics and oral steroids in Göttingen Minipigs on the biological activity of the probiotic medicinal product TSO (Trichuris suis ova)

The probiotic medicinal product TSO (Trichuris suis ova) is administered to patients with active ulcerative colitis in an ongoing clinical phase IIb trial where the typical co-medications are steroids (prednisolone or budesonide) and antibiotics (e.g., phenoxymethylpenicillin). The present pre-clinical study evaluates the effects of these co-medications on the biological activity of TSO in Göttingen Minipigs. This translationally relevant pre-clinical model allows administration of TSO with and without oral steroids or antibiotics in a manner similar to the administration to patients, followed by quantification of the biological activity of TSO. The biological activity of TSO was not affected by oral steroids but was reduced by oral antibiotics. Fecal calprotectin, the common marker of intestinal inflammation in patients with UC, did not differ between groups.

Global transcriptome analysis of Rhizobium favelukesii LPU83 in response to acid stress

Acidic environments naturally occur worldwide and inappropriate agricultural management may also cause acidification of soils. Low soil pH values are an important barrier in the plant-rhizobia interaction. Acidic conditions disturb the establishment of the efficient rhizobia usually used as biofertilizer. This negative effect on the rhizobia-legume symbiosis is mainly due to the low acid tolerance of the bacteria. Here, we describe the identification of relevant factors in the acid tolerance of Rhizobium favelukesii using transcriptome sequencing. A total of 1924 genes were differentially expressed under acidic conditions, with ∼60% underexpressed. Rhizobium favelukesii acid response mainly includes changes in the energy metabolism and protein turnover, as well as a combination of mechanisms that may contribute to this phenotype, including GABA and histidine metabolism, cell envelope modifications and reverse proton efflux. We confirmed the acid-sensitive phenotype of a mutant in the braD gene, which showed higher expression under acid stress. Remarkably, 60% of the coding sequences encoded in the symbiotic plasmid were underexpressed and we evidenced that a strain cured for this plasmid featured an improved performance under acidic conditions. Hence, this work provides relevant information in the characterization of genes associated with tolerance or adaptation to acidic stress of R. favelukesii.

Multidonor FMT capsules improve symptoms and decrease fecal calprotectin in ulcerative colitis patients while treated - an open-label pilot study

Background: Growing evidence indicates that gut dysbiosis is a factor in the pathogenesis of ulcerative colitis (UC). Fecal microbiota transplantation (FMT) appears to be promising in inducing UC remission, but there are no reports regarding administration using capsules. Methods: Seven patients with active UC, aged 27-50 years, were treated with 25 multidonor FMT capsules daily for 50 days as a supplement to their standard treatment in an open-label pilot study. The primary objective was to follow symptoms through the Simple Clinical Colitis Activity Index (SCCAI). Secondary objectives were to follow changes in fecal calprotectin and microbial diversity through fecal samples and quality of life through the Inflammatory Bowel Disease Questionnaire (IBDQ). Participants were followed through regular visits for six months. Results: From a median of 6 at baseline, the SCCAI of all participants decreased, with median decreases of 5 (p = .001) and 6 (p = .001) after 4 and 8 weeks, respectively. Three of the seven patients had flare-up/relapse of symptoms after the active treatment period. The median F-calprotectin of ≥1800 mg/kg at baseline decreased significantly during the treatment period, but increased again in the follow-up period. The median IBDQ improved at all visits compared to baseline. The fecal microbiota α-diversity did not increase in the study period compared to baseline. All participants completed the treatment and no serious adverse events were reported. Conclusion: Fifty days of daily multidonor FMT capsules temporarily improved symptoms and health-related life quality and decreased F-calprotectin in patients with active UC.

Antisense Oligonucleotides Internally Labeled with Peptides Show Improved Target Recognition and Stability to Enzymatic Degradation

Specific target binding and stability in diverse biological media is of crucial importance for applications of synthetic oligonucleotides as diagnostic and therapeutic tools. So far, these issues have been addressed by chemical modification of oligonucleotides and by conjugation with a peptide, most often at the terminal position of the oligonucleotide. Herein, we for the first time systematically investigate the influence of internally attached short peptides on the properties of antisense oligonucleotides. We report the synthesis and internal double labeling of 21-mer oligonucleotides that target the BRAF V600E oncogene, with a library of rationally designed peptides employing CuAAC "click" chemistry. The peptide sequence has an influence on the specificity and affinity of target DNA/RNA binding. We also investigated the impact of locked nucleic acids (LNAs) on the latter. Lysine residues improve binding of POCs to target DNA and RNA, whereas the distance to lysine correlates exclusively with a decrease in binding of mismatched RNA targets. Glycine and tyrosine residues affect target binding as well. Importantly, the resistance of POCs to enzymatic degradation is dramatically improved by the internal attachment of peptides but not by LNA alone. Independently of the peptide sequence, the conjugates are stable for up to 24 h in 90% human serum and duplexes of POCs with complementary DNA for up to 160 h in 90% human serum. Such excellent stability has not been previously reported for DNA and makes internally labeled POCs an exciting object of study, i.e., showing high target specificity and simultaneous stability in biological media.

The effect of Lactobacillus paracasei subsp. paracasei L. casei W8® on blood levels of triacylglycerol is independent of colonisation

Gut microbiota (GM) dysbiosis has been linked to obesity and its metabolic complications such as cardiovascular disease (CVD). The risk of developing CVD increases with elevated concentration of serum triacylglycerol (TAG). In a blinded, randomised two-arm parallel human intervention study we have previously found that four weeks of supplementation with Lactobacillus paracasei subsp. paracasei L. casei W8® (L. casei W8) compared to placebo reduced the concentration of TAG in 64 young healthy adults, an effect, likely mediated by a decreased stearoyl- CoA desaturase-1 (SCD1) activity. In the present study we analysed faecal samples obtained during the intervention study to investigate whether this effect was related to the ability of L. casei W8 to colonise the human gut after supplementation of L. casei W8 (1010 cfu daily) as determined by qPCR specific for L. paracasei and L. casei (L. casei group); whether L. casei W8 consumption affected GM composition as determined by 16S rRNA gene targeted 454/FLX amplicon sequencing; and whether these changes were associated with changes in TAG concentration and SCD1 activity. Faecal samples were collected at baseline, after four weeks supplementation and two weeks after the supplementation was ended, and fasting blood samples were collected at baseline and after 4 weeks. Four weeks supplementation with L. casei W8 did not affect the overall composition of the GM; however, an increase in the relative abundance of the L. casei group from 8.48×10-6% of the total GM compared to 2.83×10-3% at baseline (P<0.001) was observed. Two weeks after supplementation ended, the relative abundance of the L. casei group was still increased 14 times compared to before the intervention (P<0.01). However, neither the increase in the abundance of the L. casei group nor overall GM composition correlated with changes in blood lipids or SCD1 activity.

Biochemical and Computational Analysis of the Substrate Specificities of Cfr and RlmN Methyltransferases

Cfr and RlmN methyltransferases both modify adenine 2503 in 23S rRNA (Escherichia coli numbering). RlmN methylates position C2 of adenine while Cfr methylates position C8, and to a lesser extent C2, conferring antibiotic resistance to peptidyl transferase inhibitors. Cfr and RlmN show high sequence homology and may be evolutionarily linked to a common ancestor. To explore their individual specificity and similarity we performed two sets of experiments. We created a homology model of Cfr and explored the C2/C8 specificity using docking and binding energy calculations on the Cfr homology model and an X-ray structure of RlmN. We used a trinucleotide as target sequence and assessed its positioning at the active site for methylation. The calculations are in accordance with different poses of the trinucleotide in the two enzymes indicating major evolutionary changes to shift the C2/C8 specificities. To explore interchangeability between Cfr and RlmN we constructed various combinations of their genes. The function of the mixed genes was investigated by RNA primer extension analysis to reveal methylation at 23S rRNA position A2503 and by MIC analysis to reveal antibiotic resistance. The catalytic site is expected to be responsible for the C2/C8 specificity and most of the combinations involve interchanging segments at this site. Almost all replacements showed no function in the primer extension assay, apart from a few that had a weak effect. Thus Cfr and RlmN appear to be much less similar than expected from their sequence similarity and common target.

A novel bacteriophage cocktail reduces and disperses Pseudomonas aeruginosa biofilms under static and flow conditions

Pseudomonas aeruginosa is an opportunistic human pathogen that forms highly stable communities - biofilms, which contribute to the establishment and maintenance of infections. The biofilm state and intrinsic/acquired bacterial resistance mechanisms contribute to resistance/tolerance to antibiotics that is frequently observed in P. aeruginosa isolates. Here we describe the isolation and characterization of six novel lytic bacteriophages: viruses that infect bacteria, which together efficiently infect and kill a wide range of P. aeruginosa clinical isolates. The phages were used to formulate a cocktail with the potential to eliminate P. aeruginosa PAO1 planktonic cultures. Two biofilm models were studied, one static and one dynamic, and the phage cocktail was assessed for its ability to reduce and disperse the biofilm biomass. For the static model, after 4 h of contact with the phage suspension (MOI 10) more than 95% of biofilm biomass was eliminated. In the flow biofilm model, a slower rate of activity by the phage was observed, but 48 h after addition of the phage cocktail the biofilm was dispersed, with most cells eliminated (> 4 logs) comparing with the control. This cocktail has the potential for development as a therapeutic to control P. aeruginosa infections, which are predominantly biofilm centred.

Characterization of the gut microbiota in leptin deficient obese mice - Correlation to inflammatory and diabetic parameters

Gut microbiota have been implicated as a relevant factor in the development of type 2 diabetes mellitus (T2DM), and its diversity might be a cause of variation in animal models of T2DM. In this study, we aimed to characterise the gut microbiota of a T2DM mouse model with a long term vision of being able to target the gut microbiota to reduce the number of animals used in experiments. Male B6.V-Lep(ob)/J mice were characterized according to a number of characteristics related to T2DM, inflammation and gut microbiota. All findings were thereafter correlated to one another in a linear regression model. The total gut microbiota profile correlated to glycated haemoglobin, and high proportions of Prevotellaceae and Lachnospiraceae correlated to impaired or improved glucose intolerance, respectively. In addition, Akkermansia muciniphila disappeared with age as glucose intolerance worsened. A high proportion of regulatory T cells correlated to the gut microbiota and improved glucose tolerance. Furthermore, high levels of IL-10, IL-12 and TNF-α correlated to impaired glucose tolerance, blood glucose or glycated haemoglobin. The findings indicate that gut microbiota may contribute to variation in various disease read-outs in the B6.V-Lep(ob)/J model and considering them in both quality assurance and data evaluation for the B6.V-Lep(ob)/J model may have a reducing impact on the inter-individual variation.

Peptide-LNA oligonucleotide conjugates

Although peptide-oligonucleotide conjugates (POCs) are well-known for nucleic acids delivery and therapy, reports on internal attachment of peptides to oligonucleotides are limited in number. To develop a convenient route for preparation of internally labeled POCs with improved biomedical properties, peptides were introduced into oligonucleotides via a 2'-alkyne-2'-amino-LNA scaffold. Derivatives of methionine- and leucine-enkephalins were chosen as model peptides of mixed amino acid content, which were singly and doubly incorporated into LNA/DNA strands using highly efficient copper(i)-catalyzed azide-alkyne cycloaddition (CuAAC) "click" chemistry. DNA/RNA target binding affinity and selectivity of the resulting POCs were improved in comparison to LNA/DNA mixmers and unmodified DNA controls. This clearly demonstrates that internal attachment of peptides to oligonucleotides can significantly improve biomolecular recognition by synthetic nucleic acid analogues. Circular dichroism (CD) measurements showed no distortion of the duplex structure by the incorporated peptide chains while studies in human serum indicated superior stability of the POCs compared to LNA/DNA mixmers and unmodified DNA references. Molecular modeling suggests strong interactions between positively charged regions of the peptides and the negative oligonucleotide backbones which leads to clamping of the peptides in a fixed orientation along the duplexes.

Specificity and stability of the Acromyrmex-Pseudonocardia symbiosis

The stability of mutualistic interactions is likely to be affected by the genetic diversity of symbionts that compete for the same functional niche. Fungus-growing (attine) ants have multiple complex symbioses and thus provide ample opportunities to address questions of symbiont specificity and diversity. Among the partners are Actinobacteria of the genus Pseudonocardia that are maintained on the ant cuticle to produce antibiotics, primarily against a fungal parasite of the mutualistic gardens. The symbiosis has been assumed to be a hallmark of evolutionary stability, but this notion has been challenged by culturing and sequencing data indicating an unpredictably high diversity. We used 454 pyrosequencing of 16S rRNA to estimate the diversity of the cuticular bacterial community of the leaf-cutting ant Acromyrmex echinatior and other fungus-growing ants from Gamboa, Panama. Both field and laboratory samples of the same colonies were collected, the latter after colonies had been kept under laboratory conditions for up to 10 years. We show that bacterial communities are highly colony-specific and stable over time. The majority of colonies (25/26) had a single dominant Pseudonocardia strain, and only two strains were found in the Gamboa population across 17 years, confirming an earlier study. The microbial community on newly hatched ants consisted almost exclusively of a single strain of Pseudonocardia while other Actinobacteria were identified on older, foraging ants in varying but usually much lower abundances. These findings are consistent with recent theory predicting that mixtures of antibiotic-producing bacteria can remain mutualistic when dominated by a single vertically transmitted and resource-demanding strain.

Early life treatment with vancomycin propagates Akkermansia muciniphila and reduces diabetes incidence in the NOD mouse

AIMS/HYPOTHESIS

Increasing evidence suggests that environmental factors changing the normal colonisation pattern in the gut strongly influence the risk of developing autoimmune diabetes. The aim of this study was to investigate, both during infancy and adulthood, whether treatment with vancomycin, a glycopeptide antibiotic specifically directed against Gram-positive bacteria, could influence immune homeostasis and the development of diabetic symptoms in the NOD mouse model for diabetes.

METHODS

Accordingly, one group of mice received vancomycin from birth until weaning (day 28), while another group received vancomycin from 8 weeks of age until onset of diabetes. Pyrosequencing of the gut microbiota and flow cytometry of intestinal immune cells was used to investigate the effect of vancomycin treatment.

RESULTS

At the end of the study, the cumulative diabetes incidence was found to be significantly lower for the neonatally treated group compared with the untreated group, whereas the insulitis score and blood glucose levels were significantly lower for the mice treated as adults compared with the other groups. Mucosal inflammation was investigated by intracellular cytokine staining of the small intestinal lymphocytes, which displayed an increase in cluster of differentiation (CD)4(+) T cells producing pro-inflammatory cytokines in the neonatally treated mice. Furthermore, bacteriological examination of the gut microbiota composition by pyrosequencing revealed that vancomycin depleted many major genera of Gram-positive and Gram-negative microbes while, interestingly, one single species, Akkermansia muciniphila, became dominant.

CONCLUSIONS/INTERPRETATION

The early postnatal period is a critical time for microbial protection from type 1 diabetes and it is suggested that the mucolytic bacterium A. muciniphila plays a protective role in autoimmune diabetes development, particularly during infancy.

A click chemistry approach to pleuromutilin derivatives, part 2: conjugates with acyclic nucleosides and their ribosomal binding and antibacterial activity

Pleuromutilin is an antibiotic that binds to bacterial ribosomes and thereby inhibit protein synthesis. A new series of semisynthetic pleuromutilin derivatives were synthesized by a click chemistry strategy. Pleuromutilin was conjugated by different linkers to a nucleobase, nucleoside, or phenyl group, as a side-chain extension at the C22 position of pleuromutilin. The linkers were designed on the basis of the best linker from our first series of pleuromutilin derivatives following either conformational restriction or an isosteric methylene to oxygen exchange. The binding of the new compounds to the Escherichia coli ribosome was investigated by molecular modeling and chemical footprinting of nucleotide U2506, and it was found that all the derivatives bind to the specific site and most of them better than pleuromutilin itself. The effect of the side-chain extension was also explored by chemical footprinting of nucleotide U2585, and the results showed that all the compounds interact with this position to varying degrees. Derivatives with a conformational restriction of the linker generally had a higher affinity than derivatives with an isosteric exchange of one of the carbons in the linker with a hydrophilic oxygen. A growth inhibition assay with three different bacterial strains showed significant activity of several of the new compounds.

Identification of 8-methyladenosine as the modification catalyzed by the radical SAM methyltransferase Cfr that confers antibiotic resistance in bacteria

The Cfr methyltransferase confers combined resistance to five different classes of antibiotics that bind to the peptidyl transferase center of bacterial ribosomes. The Cfr-mediated modification has previously been shown to occur on nucleotide A2503 of 23S rRNA and has a mass corresponding to an additional methyl group, but its specific identity and position remained to be elucidated. A novel tandem mass spectrometry approach has been developed to further characterize the Cfr-catalyzed modification. Comparison of nucleoside fragmentation patterns of A2503 from Escherichia coli cfr+ and cfr- strains with those of a chemically synthesized nucleoside standard shows that Cfr catalyzes formation of 8-methyladenosine. In addition, analysis of RNA derived from E. coli strains lacking the m(2)A2503 methyltransferase reveals that Cfr also has the ability to catalyze methylation at position 2 to form 2,8-dimethyladenosine. The mutation of single conserved cysteine residues in the radical SAM motif CxxxCxxC of Cfr abolishes its activity, lending support to the notion that the Cfr modification reaction occurs via a radical-based mechanism. Antibiotic susceptibility data confirm that the antibiotic resistance conferred by Cfr is provided by methylation at the 8 position and is independent of methylation at the 2 position of A2503. This investigation is, to our knowledge, the first instance where the 8-methyladenosine modification has been described in natural RNA molecules.

Genetic labelling and application of the isoproturon-mineralizing Sphingomonas sp. strain SRS2 in soil and rhizosphere

AIMS

To construct a luxAB-labelled Sphingomonas sp. strain SRS2 maintaining the ability to mineralize the herbicide isoproturon and usable for monitoring the survival and distribution of strain SRS2 on plant roots in laboratory systems.

METHODS AND RESULTS

We inserted the mini-Tn5-luxAB marker into strain SRS2 using conjugational mating. In the transconjugant mutants luciferase was produced in varying levels. The mutants showed significant differences in their ability to degrade isoproturon. One luxAB-labelled mutant maintained the ability to mineralize isoproturon and was therefore selected for monitoring colonization of barley roots.

CONCLUSIONS

We successfully constructed a genetically labelled isoproturon-mineralizing-strain SRS2 and demonstrated its ability to survive in soil and its colonization of rhizosphere.

SIGNIFICANCE AND IMPACT OF THE STUDY

The construction of a luxAB-labelled strain SRS2 maintaining the degradative ability, provides a powerful tool for ecological studies serving as the basis for evaluating SRS2 as a bioremediation agent.

Presence of N-acyl homoserine lactones in soil detected by a whole-cell biosensor and flow cytometry

Quorum sensing enables bacteria to regulate expression of certain genes according to population density. N-acyl homoserine lactone (AHL)-based quorum sensing is known to be widespread among gram-negative bacteria. Several bacterial whole-cell biosensors for AHL detection have been developed and some were used in in situ studies of AHL production. From these studies our knowledge of the significance of quorum sensing in various environments has been improved. However, very little is known about production of AHLs in soil environments. In the present study, an approach for detecting AHL production in bulk soil was developed. A whole-cell biosensor based on the regulatory region of the lux-operon from Vibrio fischeri fused to gfp was constructed, resulting in a luxR-PluxI-gfpmut3*-fusion in the high copy plasmid, pAHL-GFP. Escherichia coli MC4100 harboring pAHL-GFP responded to the AHL-compound N-octanoyl homoserine lactone (OHL) by expressing green fluorescence. In situ application of E. coli MC4100/pAHL-GFP was tested by adding OHL in different concentrations to sterile soil microcosms. E. coli MC4100/pAHL-GFP were incubated in the soil microcosms and extracted by an improved Nycodenz-extraction method optimized for flow cytometry. The presence of induced cells was then verified by single-cell analysis by flow cytometry. OHL concentrations between 0.5 and 50 nmol per g soil were detected. When introducing the AHL-producing Serratia liquefaciens to soil microcosms, expression of green fluorescent protein was induced in E. coli MC4100/pAHL-GFP. Thereby, the ability of this strain to detect excretion of AHLs by S. liquefaciens in sterile soil was shown. The use of an improved extraction method and a whole-cell biosensor combined with flow cytometry analysis proved to be promising tools in future studies of AHL production by microbial populations in soil environments.

Recognition of nucleotide G745 in 23 S ribosomal RNA by the rrmA methyltransferase

Methylation of the N1 position of nucleotide G745 in hairpin 35 of Escherichia coli 23 S ribosomal RNA (rRNA) is mediated by the methyltransferase enzyme RrmA. Lack of G745 methylation results in reduced rates of protein synthesis and growth. Addition of recombinant plasmid-encoded rrmA to an rrmA-deficient strain remedies these defects. Recombinant RrmA was purified and shown to retain its activity and specificity for 23 S rRNA in vitro. The recombinant enzyme was used to define the structures in the rRNA that are necessary for the methyltransferase reaction. Progressive truncation of the rRNA substrate shows that structures in stem-loops 33, 34 and 35 are required for methylation by RrmA. Multiple contacts between nucleotides in these stem-loops and RrmA were confirmed in footprinting experiments. No other RrmA contact was evident elsewhere in the rRNA. The RrmA contact sites on the rRNA are inaccessible in ribosomal particles and, consistent with this, 50 S subunits or 70 S ribosomes are not substrates for RrmA methylation. RrmA resembles the homologous methyltransferase TlrB (specific for nucleotide G748) as well as the Erm methyltransferases (nucleotide A2058), in that all these enzymes methylate their target nucleotides only in the free RNA. After assembly of the 50 S subunit, nucleotides G745, G748 and A2058 come to lie in close proximity lining the peptide exit channel at the site where macrolide, lincosamide and streptogramin B antibiotics bind.

Detection of oxytetracycline production by Streptomyces rimosus in soil microcosms by combining whole-cell biosensors and flow cytometry

Combining the high specificity of bacterial biosensors and the resolution power of fluorescence-activated cell sorting (FACS) provided qualitative detection of oxytetracycline production by Streptomyces rimosus in soil microcosms. A plasmid containing a transcriptional fusion between the tetR-regulated P(tet) promoter from Tn10 and a FACS-optimized gfp gene was constructed. When harbored by Escherichia coli, this plasmid produces large amounts of green fluorescent protein (GFP) in the presence of tetracycline. This tetracycline biosensor was used to detect the production of oxytetracycline by S. rimosus introduced into sterile soil. The tetracycline-induced GFP-producing biosensors were detected by FACS analysis, enabling the detection of oxytetracycline encounters by single biosensor cells. This approach can be used to study interactions between antibiotic producers and their target organisms in soil.

Versatile biosensor vectors for detection and quantification of mercury

Three different whole cell biosensor constructs were made by fusing the mercury inducible promoter, P(mer), and its regulatory gene, merR, from transposon Tn21 with reporter genes luxCDABE, lacZYA, or gfp. In Escherichia coli these biosensor constructs responded to low levels of mercury by producing light, beta-galactosidase or green fluorescent protein, respectively. Since the responses were quantitative, the constructs were used to quantify bioavailable mercury in different environments. The constructs were cloned into mini-Tn5 delivery vectors, thus enabling the transfer of the mer-lux, mer-lac or mer-gfp cassettes to a variety of Gram-negative bacteria. The mer-lux cassette was transferred to a Pseudomonas putida strain, which was used to quantify water-extractable mercury in contaminated soil.

Detection and quantification of tetracyclines by whole cell biosensors

Three different mini-Tn5 plasmids, containing a tetracycline-inducible promoter, Ptet and a regulatory gene, tetR, in operon fusions with a reporter gene system (lacZYA, luxCDABE or gfp), were constructed. These biosensor constructs responded to low levels of tetracyclines by producing beta-galactosidase, light or green fluorescent protein. They did so in a quantitative manner, thus enabling the quantification of tetracyclines in the immediate surroundings of the biosensor organism. All three constructs were transferred successfully to different gram-negative bacteria by conjugation. An Escherichia coli strain containing the Ptet-lac construct was used to determine oxytetracycline in milk as a demonstration of the application of these biosensors.

Detection and quantification of tetracyclines by whole cell biosensors

Three different mini-Tn5 plasmids, containing a tetracycline-inducible promoter, Ptet and a regulatory gene, tetR, in operon fusions with a reporter gene system (lacZYA, luxCDABE or gfp), were constructed. These biosensor constructs responded to low levels of tetracyclines by producing beta-galactosidase, light or green fluorescent protein. They did so in a quantitative manner, thus enabling the quantification of tetracyclines in the immediate surroundings of the biosensor organism. All three constructs were transferred successfully to different gram-negative bacteria by conjugation. An Escherichia coli strain containing the Ptet-lac construct was used to determine oxytetracycline in milk as a demonstration of the application of these biosensors.

Macrolide-ketolide inhibition of MLS-resistant ribosomes is improved by alternative drug interaction with domain II of 23S rRNA

The macrolide antibiotic erythromycin and its 6-O-methyl derivative (clarithromycin) bind to bacterial ribosomes primarily through interactions with nucleotides in domains II and V of 23S rRNA. The domain II interaction occurs between nucleotide A752 and the macrolide 3-cladinose moiety. Removal of the cladinose, and substitution of a 3-keto group (forming the ketolide RU 56006), results in loss of the A752 interaction and an approximately 100-fold drop in drug binding affinity. Within domain V, the key determinant of drug binding is nucleotide A2058 and substitution of G at this position is the major cause of drug resistance in some clinical pathogens. The 2058G mutation disrupts the drug-domain V contact and leads to a further > 25 000-fold decrease in the binding of RU 56006. Drug binding to resistant ribosomes can be improved over 3000-fold by forming an alternative and more effective contact to A752 via alkyl-aryl groups linked to a carbamate at the drug 11/12 position (in the ketolide antibiotics HMR 3647 and HMR 3004). The data indicate that simultaneous drug interactions with domains II and V strengthen binding and that the domain II contact is of particular importance to achieve binding to the ribosomes of resistant pathogens in which the domain V interaction is perturbed.

Nickel-induced proliferation of both memory and naive T cells in patch test-negative individuals

Lymphocyte transformation test has often been used as an in vitro test for nickel allergy. We have previously demonstrated the presence of nickel-reactive T cells in individuals with no history of allergic disease and with a negative patch test towards NiSO4. In this study, we show that this proliferative response was mainly confined to T cells within the CD4+ subset. In contrast to conventional recall antigens such as tetanus toxoid, in vitro stimulation using NiSO4 activated both FACS-purified CD4+CD45RA+ 'naive' and CD4+CD45RO+ 'memory' T cells. To determine which cell population reacted with nickel to induce T cell activation, peripheral blood mononuclear cells were separated into macrophages and non-adherent, HLA-DR-depleted T cells. We found that preincubation of monocytes/macrophages but not T cells with NiSO4 resulted in subsequent T cell proliferation. This result demonstrated that nickel did not exhibit any direct effect on the T cell. Furthermore, the NiSO4-induced T cell proliferation could be blocked by antibodies towards MHC class II (HLA-DR) molecules. Our results substantiate the concept that individuals with a negative patch test towards NiSO4 contain in their peripheral blood T cells capable of recognizing nickel or nickel-modified peptides. In contrast to conventional recall antigens, both memory and naive T cells were activated. Thus, when compared with data obtained from nickel-allergic individuals, this study shows a comparable nickel-inducible T cell activation in non-allergic individuals.

Nickel-induced activation of T cells in individuals with negative patch test to nickel sulphate

Contact hypersensitivity to nickel is the most common form of allergic contact dermatitis. To gain insight into the induction of this frequent disease, T cell reactivity towards nickel was investigated in "nonallergic" individuals defined as those with no skin manifestations and a negative patch test towards NiSO4. Surprisingly, we found that nickel induced proliferation of peripheral blood mononuclear cells (PBMC) from 16 of 18 adult individuals tested. This activation was specific, and no stimulation of PBMC was observed using control stimulants at equimolar concentrations. Furthermore, the NiSO4-induced activation required the presence of professional antigen-presenting cells. To describe the functional capacity of the nickel-inducible T cells, cytokine release was investigated in both nickel-allergic and nonallergic individuals. The T cells from both groups released interferon-gamma but no interleukin-4 upon stimulation with nickel, suggesting that the functional capacities of these cell populations were similar in nickel-allergic and nonallergic individuals. Thus, at this level, no qualitative differences could be demonstrated between T cells obtained from nickel-allergic and nonallergic individuals.

The macrolide-ketolide antibiotic binding site is formed by structures in domains II and V of 23S ribosomal RNA

The macrolide antibiotic erythromycin interacts with bacterial 23S ribosomal RNA (rRNA) making contacts that are limited to hairpin 35 in domain II of the rRNA and to the peptidyl transferase loop in domain V. These two regions are probably folded close together in the 23S rRNA tertiary structure and form a binding pocket for macrolides and other drug types. Erythromycin has been derivatized by replacing the L-cladinose moiety at position 3 by a keto group (forming the ketolide antibiotics) and by an alkyl-aryl extension at positions 11/12 of the lactone ring. All the drugs footprint identically within the peptidyl transferase loop, giving protection against chemical modification at A2058, A2059 and G2505, and enhancing the accessibility of A2062. However, the ketolide derivatives bind to ribosomes with widely varying affinities compared with erythromycin. This variation correlates with differences in the hairpin 35 footprints. Erythromycin enhances the modification at position A752. Removal of cladinose lowers drug binding 70-fold, with concomitant loss of the A752 footprint. However, the 11/12 extension strengthens binding 10-fold, and position A752 becomes protected. These findings indicate how drug derivatization can improve the inhibition of bacteria that have macrolide resistance conferred by changes in the peptidyl transferase loop.

Core sequence in the RNA motif recognized by the ErmE methyltransferase revealed by relaxing the fidelity of the enzyme for its target

Under physiological conditions, the ErmE methyltransferase specifically modifies a single adenosine within ribosomal RNA (rRNA), and thereby confers resistance to multiple antibiotics. The adenosine (A2058 in Escherichia coli 23S rRNA) lies within a highly conserved structure, and is methylated efficiently, and with equally high fidelity, in rRNAs from phylogenetically diverse bacteria. However, the fidelity of ErmE is reduced when magnesium is removed, and over twenty new sites of ErmE methylation appear in E. coli 16S and 23S rRNAs. These sites show widely different degrees of reactivity to ErmE. The canonical A2058 site is largely unaffected by magnesium depletion and remains the most reactive site in the rRNA. This suggests that methylation at the new sites results from changes in the RNA substrate rather than the methyltransferase. Chemical probing confirms that the rRNA structure opens upon magnesium depletion, exposing potential new interaction sites to the enzyme. The new ErmE sites show homology with the canonical A2058 site, and have the consensus sequence aNNNcgGAHAg (ErmE methylation occurs exclusively at adenosines (underlined); these are preceded by a guanosine, equivalent to G2057; there is a high preference for the adenosine equivalent to A2060; H is any nucleotide except G; N is any nucleotide; and there are slight preferences for the nucleotides shown in lower case). This consensus is believed to represent the core of the motif that Erm methyltransferases recognize at their canonical A2058 site. The data also reveal constraints on the higher order structure of the motif that affect methyltransferase recognition.

ErmE methyltransferase recognition elements in RNA substrates

Dimethylation by Erm methyltransferases at the N-6 position of adenine 2058 (A2058, Escherichia coli numbering) in domain V of bacterial 23 S rRNA confers resistance to the macrolide-lincosamide-streptogramin B (MLS) group of antibiotics. The ErmE methyltransferase from Saccharopolyspora erythraea methylates a 625 nucleotide transcript of domain V as efficiently as it methylates intact 23 S rRNA. By progressively truncating domain V, the motif required for specific recognition by the enzyme has been localized to a helix and single-stranded region adjacent to A2058. The smallest RNA transcript that shows methyl-accepting activity is a 27-nucleotide stem-loop, corresponding to the 23 S rRNA sequences 2048 to 2063 and 2610 to 2620 (helix 73), with A2058 situated within the hairpin loop. Methylation of A2058 in the truncated RNAs is optimal in the absence of magnesium, and the efficiency of methylation is halved by the presence of 2 to 3 mM magnesium. Magnesium serves to stabilize a conformation in the truncated RNA that prevents efficient methylation. This contrasts to the intact domain V RNA, where 2 mM magnesium ions support a conformation at A2058 that is most readily recognized by ErmE. Methylation of domain V RNA is generally far less susceptible to ionic conditions than the truncated RNAs. The effects of monovalent cations on the methylation of truncated transcripts suggest that RNA structures outside helix 73 support the ErmE interaction. However, interaction with these structures is not essential for specific ErmE recognition of A2058.

[Amebiasis--a differential diagnosis from inflammatory bowel disease]

Entamoeba histolytica is a very uncommon etiology of travelers diarrhoea, but may be an important differential diagnosis to inflammatory bowel disease. A misdiagnosis of amoebic colitis as inflammatory bowel disease followed by inadvertent treatment with corticosteroids may be fatal. Current techniques for the diagnosis of amoebiasis include stool studies, endoscopic biopsy and serology. Demonstration of haematophagous trophozoites in feces or in tissue biopsy is the definitive method for diagnosis. Unfortunately both methods have many drawbacks. If the specimens are negative, serology can support the diagnosis especially in a non-endemic area where a positive test is highly predictive of current disease.

Characterization of the inhibitory effect of growth hormone on primary preadipocyte differentiation

GH exerts adipogenic activity in several preadipocyte cell lines, whereas in primary rat preadipocytes, GH has an antiadipogenic activity. To better understand the molecular mechanism involved in adipocyte differentiation, the expression of adipocyte-specific genes was analyzed in differentiating preadipocytes in response to GH. We found that the expression of both adipocyte determination and differentiation factor 1 (ADD1) and peroxisome proliferator activated receptor gamma(PPARgamma) was induced in preadipocytes during differentiation. In the presence of GH, which markedly inhibited triglyceride accumulation, no reduction in the expression level of ADD1 was observed in response to GH, whereas there was a 50% reduction in the expression of PPARgamma. The DNA binding activity of the PPARgamma/retinoid X receptor-alpha(RXRalpha) to the ARE7 element from the aP2 gene was also reduced by approximately 50% in response to GH. GH inhibited the expression of late markers of adipocyte differentiation, fatty acid synthase, aP2, and hormone-sensitive lipase by 70-80%. The antiadipogenic effect of GH was not affected by the mitogen-activated protein (MAP) kinase/ extracellular-regulated protein (ERK) kinase inhibitor PD 98059, indicating that the mitogen-activated protein kinase pathway was not involved in GH inhibition of preadipocyte differentiation. The expression of preadipocyte factor-1/fetal antigen 1 was decreased during differentiation, and GH treatment prevented this down-regulation of Pref1/FA1. A possible role for Pref-1/FA1 in mediating the antiadipogenic effect of GH was indicated by the observation that FA1 inhibited differentiation as effectively as GH. These data suggest that GH exerts its inhibitory activity in adipocyte differentiation at a step after the induction of ADD1 but before the induction of genes required for terminal differentiation.

The effect of the lacY gene on the induction of IPTG inducible promoters, studied in Escherichia coli and Pseudomonas fluorescens

The role of the Escherichia coli lacY gene product (the lactose permease) in the induction of isopropyl-beta-D-thiogalactopyranoside (IPTG) inducible promoters was studied in E. coli and P. fluorescens. This was done by comparing strains containing a lacIPOZYA chromosomal insert with newly constructed strains containing inserts without the lacY gene (lacIPOZ). The lactose operon inserts were introduced as single-copy chromosomal inserts to eliminate differences in expression caused by differences in copy number. Comparison between the two types of inserts showed that the lactose permease was essential to allow growth on lactose by both bacteria and that the lactose permease plays an important role in transporting the inducer IPTG across the membrane of P. fluorescens. The use of a functional lactose permease allows expression of beta-galactosidase to increase more than fivefold from a wild-type lac promoter in P. fluorescens SS1001. We suggest that an increase in the rate of protein synthesis from lac-type promoters could be enhanced if an active lactose permease is present as well.

Glucagon-mediated Ca2+ signaling in BHK cells expressing cloned human glucagon receptors

From video imaging of fura 2-loaded baby hamster kidney (BHK) cells stably expressing the cloned human glucagon receptor, we found the Ca2+ response to glucagon to be specific, dose dependent, synchronous, sensitive to pertussis toxin, and independent of Ca2+ influx. Forskolin did not elicit a Ca2+ response, but treatment with a protein kinase A inhibitor, the Rp diastereomer of 8-bromoadenosine-3',5'-cyclic monophosphothioate, resulted in a reduced glucagon-mediated Ca2+ response as well as Ca2+ oscillations. The specific phospholipase C inhibitor U-73122 abolished the Ca2+ response to glucagon, and a modest twofold increase in inositol trisphosphate (IP3) production could be observed after stimulation with glucagon. In BHK cells coexpressing glucagon and muscarinic (M1) acetylcholine receptors, carbachol blocked the rise in intracellular free Ca2+ concentrations in response to glucagon, whereas glucagon did not affect the carbachol-induced increase in Ca2+. Furthermore, carbachol, but not glucagon, could block thapsigargin-activated increases in intracellular free Ca2+ concentration. These results indicate that, in BHK cells, glucagon receptors can activate not only adenylate cyclase but also a second independent G protein-coupled pathway that leads to the stimulation of phospholipase C and the release of Ca2+ from IP3-sensitive intracellular Ca2+ stores. Finally, we provide evidence to suggest that cAMP potentiates the IP3-mediated effects on intracellular Ca2+ handling.

Identification of differentially expressed genes in chemically induced skin tumors

Previous studies have demonstrated a role for the fos gene in promoting malignant conversion of mouse skin tumors. In the study reported here, differential display was performed to identify fos- and jun-regulated genes that are differentially expressed during premalignant progression. Total RNA isolated from variants of the papilloma cell line SP-1 transduced with retroviral vectors expressing v-jun and v-fos alone or in tandem was analyzed for the presence of differentially expressed transcripts by using 35 different primer combinations. Differentially expressed clones were rescreened by dot-blot analysis by using cDNA from chemically induced tumors with a high or low risk of malignant conversion. Three differentially displayed fragments were isolated in this analysis. Homology searches indicated that these fragments shared significant homology with the apoptosis inhibitor bcl-2, human alternative splicing factor/splicing factor 2 (ASF/SF2), and a novel gene not present in the GenBank or EMBL databases. In situ hybridization indicated that the expression levels of the bcl-2 homolog increased with malignant potential in chemically derived mouse skin tumors. A similar analysis indicated that expression of the ASF/SF2 homolog was greater in papillomas than in normal skin or in squamous cell carcinomas. Transcripts for this gene were most abundant in the granular layer. The expression pattern of the third differential display fragment was consistent with that of a tumor suppressor gene. This gene was expressed at very high levels in normal skin and benign papillomas but was essentially undetectable in squamous cell carcinomas. Through this approach, we identified known and novel genes that may contribute to malignant progression in epidermal tumors.

The role of GH receptor tyrosine phosphorylation in Stat5 activation

Stimulation of GH receptors leads to rapid activation of Jak2 kinase and subsequent tyrosine phosphorylation of the GH receptor. Three specific tyrosines located in the C-terminal domain of the GH receptor have been identified as being involved in GH-stimulated transcription of the Spi 2.1 promoter. Mutated GH receptors lacking all but one of these three tyrosines are able to mediate a transcriptional response when transiently transfected into CHO cells together with a Spi 2.1 promoter/luciferase construct. Similarly, these GH receptors were found to be able to mediate activation of Stat5 DNA-binding activity, whereas the GH receptor mutant lacking all intracellular tyrosines was not. Synthetic tyrosine phosphorylated peptides corresponding to the GH receptor sequence around the three tyrosines inhibited Stat5 DNA-binding activity while their non-phosphorylated counterparts were ineffective. Tyrosine phosphorylated GST-GH receptor fusion proteins specifically bound to Stat5 in extracts from COS 7 cells transfected with Stat5 cDNA. This binding could be inhibited by tyrosine phosphorylated peptides derived from the GH receptor. This study thus demonstrated that specific GH receptor tyrosine residues, in their phosphorylated state, are involved in transcriptional signaling by directly interacting with Stat5.

Chromosomal insertion of the entire Escherichia coli lactose operon, into two strains of Pseudomonas, using a modified mini-Tn5 delivery system

A 12-kb PstI fragment including the entire E. coli lactose operon (lacIPOZYA) was inserted in one copy into the chromosome of Pseudomonas putida, Pseudomonas fluorescens and an E. coli strain with lac- phenotype. This was made possible by improvements of an already existing mini-Tn5 transposon delivery system (de Lorenzo et al., 1990; Herrero et al., 1990), which integrates cloned DNA fragments at random sites on the chromosome of the recipient bacteria in single copies. This has resulted in: (a) the making of two useful low copy-number cloning vectors both with extensive multi-cloning regions flanked by NotI sites needed in the mini-Tn5 delivery system; (b) the generation of E. coli nonlysogenic strains expressing the pi protein thus being capable of maintaining and delivering R6K-based mini-Tn5 vectors to other E. coli strains; (c) the successful insertion of the E. coli lactose operon into the P. fluorescens chromosome giving P. fluorescens the ability to grow on lactose; (d) evidence from Southern blotting that contradicts the assumption that the mini-Tn5 delivery system always creates one-copy inserts. These improvements allow insertion of large DNA fragments encoding highly expressed proteins into the chromosome of a large variety of Gram-negative bacteria including E. coli.

Nurse-conducted smoking cessation with minimal intervention in a lung clinic: a randomized controlled study

This study aimed to evaluate the effect of a motivational, minimal intervention approach to smoking cessation in an open, randomized design conducted by nurses as routine work in a lung clinic. Subjects who smoked less than 10 cigarettes x day(-1), and subjects who smoked > or = 10 cigarettes x day(-1) and who had refused to participate in a smoking cessation trial with nicotine replacement therapy, were randomly allocated to a motivational approach to smoking cessation or to a control group. The motivational approach consisted of a nurse-conducted 5 min consultation concerning reasons to quit smoking, brochures about smoking cessation and advice about how to quit. After 4-6 weeks, subjects in the motivational group received a letter encouraging them to quit smoking. After 1 year, all subjects were contacted by phone and smoking status reported. Subjects claiming to be abstinent attended the clinic for carbon monoxide verification. A total of 507 subjects were enrolled, 254 in the motivational group and 253 in the control group. The mean age of the motivational group was 51 yrs, 50% were males and they smoked a mean of 13 cigarettes x day(-1). The mean age of the control group was 53 yrs, 61% were males and they smoked a mean of 12 cigarettes x day(-1). At the 1 year follow-up, the success rate for point prevalence (no smoking at 1 year and during the preceding month) was 8, 7% in the motivational group versus 3.6% in the control group (p=0.025). The 12 months sustained success rate (no smoking at all during the year) was 3.1 versus 1.2% (p=0.22). The point prevalence for light smokers (<10 cigarettes x day(-1)) was 13.9% in the motivational group versus 6.3% in control group (p=0.12), and for heavy smokers (10 or more cigarettes x day(-1)) 5.2% versus 1.9% (p=0.20). In conclusion, the effect of this nurse-conducted, minimal intervention, motivational approach seems promising as the quit rate at 1 year follow-up had doubled.

The Gly40Ser mutation in the human glucagon receptor gene associated with NIDDM results in a receptor with reduced sensitivity to glucagon

The pancreatic islet hormone, glucagon, stimulates hepatic glucose production and has also been shown to potentiate glucose-induced insulin secretion. Because glucagon is a key regulator of glucose homeostasis, its receptor, which mediates the actions of glucagon, was considered a candidate gene involved in the pathogenesis of NIDDM. We have previously reported that a single heterozygous missense mutation in exon 2 of the glucagon receptor gene, which changes a glycine to a serine (Gly40Ser), is associated with NIDDM in a French population. In the present study, the signaling properties of this mutant receptor were examined in baby hamster kidney cells and rat insulinoma cells (RIN-5AH) stably transfected with either the wild type or Gly40Ser mutant human glucagon receptor cDNAs. Competition assays using (125)I-labeled glucagon were performed, and in both cell types, the Gly40Ser mutant receptor was found to bind glucagon with an approximately threefold lower affinity compared with the wild type receptor. In both cell types, the production of cAMP in response to glucagon was decreased in cells expressing the mutant receptor compared with those expressing the wild type. Finally, glucagon-stimulated insulin secretion by RIN cells expressing the mutant receptor was decreased such that the dose-response curve was shifted to the right in comparison to that obtained with cells expressing the wild type receptor. These results indicate that this single-point mutation located in the extracellular region of the glucagon receptor decreases the sensitivity of target tissues to glucagon.

Identification of tyrosine residues in the intracellular domain of the growth hormone receptor required for transcriptional signaling and Stat5 activation

The binding of growth hormone (GH) to its receptor results in its dimerization followed by activation of Jak2 kinase and tyrosine phosphorylation of the GH receptor itself, as well as Jak2 and the transcription factors Stat1, -3, and -5. In order to study the role of GH receptor tyrosine phosphorylation in intracellular signaling, we constructed GH receptors in which combinations of tyrosines were mutated to phenylalanines. We identified three tyrosine residues at positions 534, 566, and 627 that were required for activation of GH-stimulated transcription of the serine protease inhibitor (Spi) 2.1 promoter. Any of these three tyrosines is able to independently mediate GH-induced transcription, indicating redundancy in this part of the GH receptor. Tyrosine phosphorylation was not required for GH stimulation of mitogen-activated protein (MAP) kinase activity or for GH-stimulated Ca2+ channel activation since these pathways were normal in cells expressing a GH receptor in which all eight intracellular tyrosines were mutated to phenylalanines. Activation of Stat5 by GH was, however, abolished in cells expressing the GH receptor lacking intracellular tyrosines. This study demonstrates that specific tyrosines in the GH receptor are required for transcriptional signaling possibly by their role in the activation of transcription factor Stat5.

Recognition determinants for proteins and antibiotics within 23S rRNA

Ribosomal RNAs fold into phylogenetically conserved secondary and tertiary structures that determine their function in protein synthesis. We have investigated Escherichia coli 23S rRNA to identify structural elements that interact with antibiotic and protein ligands. Using a combination of molecular genetic and biochemical probing techniques, we have concentrated on regions of the rRNA that are connected with specific functions. These are located in different domains within the 23S rRNA and include the ribosomal GTPase-associated center in domain II, which contains the binding sites for r-proteins L10.(L12)4 and L11 and is inhibited by interaction with the antibiotic thiostrepton. The peptidyltransferase center within domain V is inhibited by macrolide, lincosamide, and streptogramin B antibiotics, which interact with the rRNA around nucleotide A2058. Drug resistance is conferred by mutations here and by modification of A2058 by ErmE methyltransferase. ErmE recognizes a conserved motif displayed in the primary and secondary structure of the peptidyl transferase loop. Within domain VI of rRNA, the alpha-sarcin stem-loop is associated with elongation factor binding and is the target site for ribotoxins including the N-glycosidase ribosome-inactivating proteins ricin and pokeweed antiviral protein (PAP). The orientations of the 23S rRNA domains are constrained by tetiary interactions, including a pseudoknot in domain II and long-range base pairings in the center of the molecule that bring domains II and V closer together. The phenotypic effects of mutations in these regions have been investigated by expressing 23S rRNA from plasmids. Allele-specific priming sites have been introduced close to these structures in the rRNA to enable us to study the molecular events there.

The conformation of 23S rRNA nucleotide A2058 determines its recognition by the ErmE methyltransferase

The ErmE methyltransferase confers resistance to MLS antibiotics by specifically dimethylating adenine 2058 (A2058, Escherichia coli numbering) in bacterial 23S rRNA. To define nucleotides in the rRNA that are part of the motif recognized by ErmE, we investigated both in vivo and in vitro the effects of mutations around position A2058 on methylation. Mutagenizing A2058 (to G or U) completely abolishes methylation of 23S rRNA by ErmE. No methylation occurred at other sites in the rRNA, demonstrating the fidelity of ErmE for A2058. Breaking the neighboring G2057-C2611 Watson-Crick base pair by introducing either an A2057 or a U2611 mutation, greatly reduces the rate of methylation at A2058. Methylation remains impaired after these mutations have been combined to create a new A2057-U2611 Watson-Crick base interaction. The conformation of this region in 23S rRNA was probed with chemical reagents and it was shown that the A2057 and U2611 mutations alone and in combination alter the reactivity of A2058 and adjacent bases. However, mutagenizing position G-->A2032 in an adjacent loop, which has been implicated to interact with A2058, alters neither the ErmE methylation at A2058 nor the accessibility of this region to the chemical reagents. The data indicate that a less-exposed conformation at A2058 leads to reduction in methylation by ErmE. Nucleotide G2057 and its interaction with C2611 maintain the conformation at A2058, and are thus important in forming the structural motif that is recognized by the ErmE methyltransferase.

Pseudoknot in domain II of 23 S rRNA is essential for ribosome function

The structure of domain II in all 23 S (and 23 S-like) rRNAs is constrained by a pseudoknot formed between nucleotides 1005 and 1138, and between 1006 and 1137 (Escherichia coli numbering). These nucleotides are exclusively conserved as 1005C.1138G and 1006C.1137G pairs in all Bacteria, Archaea and chloroplasts, whereas 1005G.1138C and 1006U.1137A pairs occur in Eukarya. We have mutagenized nucleotides 1005C-->G, 1006C-->U, 1137G-->A and 1138G-->C, both individually and in combinations, in a 23 S rRNA gene from the bacterium E. coli. The ability of 23 S rRNA to support cell growth is reduced when either of these base-pairs is disrupted, and it is completely abolished upon disruption of both base-pairs. Each mutant 23 S rRNA is assembled into 50 S subunits, but the mutant subunits do not stably interact with 30 S to engage in protein synthesis. Enzymatic and chemical probing of ribosomal particles reveals increased accessibility in the rRNA structure close to the sites of the mutations. The degree to which the mutations increase rRNA accessibility correlates with the severity of their phenotypic effects. Nucleotide 1131G is extremely reactive to dimethyl sulphate modification in wild-type subunits and ribosomes, but is rendered unreactive when either the pseudoknot is broken or when the r-proteins are removed. The structure of the pseudoknot region is possibly influenced by interaction of an r-protein at or close to the pseudoknot. Re-establishing the pseudoknot Watson-Crick interactions with one "eukaryal" (1005G.1138C or 1006U.1137A) pair and one "bacterial" C.G pair largely restores the structure and function of the rRNA. Bacterial ribosomes containing both these eukaryal pairs also participate in protein synthesis, although at much reduced efficiency, and the structure of their pseudoknot region is partially open and accessible.

Development and testing of improved suicide functions for biological containment of bacteria

We have developed very efficient suicide functions for biological containment based on the lethal Escherichia coli relF gene. The suicide functions are placed in duplicate within a plasmid and arranged to prevent inactivation by deletion, recombination, and insertional inactivation. The efficiency of this concept was tested in a plasmid containment system that prevents transfer of plasmids to wild-type bacteria. Protection against plasmid transfer was assayed in test tubes and in rat intestine. Protection was efficient and refractory to inactivation by mutation and transposons. The efficiency of the suicide system was also tested in soil and seawater. We show that unprecedented suicide efficiency can be achieved in soil and seawater after suicide induction by IPTG (isopropyl-beta-D-thiogalactopyranoside). More than 7 orders of magnitude reduction in suicide bacteria was achieved.

Glucagon receptor mRNA distribution in rat tissues

In addition to glucagon's role in regulating glucose production from the liver, a number of extrahepatic effects of glucagon have been reported. We have therefore examined various rat tissues for glucagon receptor mRNA expression. In liver, kidney, heart, adipose tissue, spleen, pancreatic islets, ovary, and thymus, glucagon receptor mRNA expression was found to be relatively abundant whereas lower levels were detected in stomach, small intestine, adrenal gland, thyroid, and skeletal muscle. The presence of glucagon receptor mRNA in tissues known to be responsive to glucagon suggests that these effects are mediated by specific glucagon receptors. Furthermore, the finding of glucagon receptor mRNA in the spleen, thymus, thyroid, adrenal gland, ovary, and skeletal muscle, where glucagon is not generally considered to act, indicates that there may be novel actions of glucagon that have yet to be determined.

[Incidence of MMA after prostaglandin-induced parturition (author's transl)]

In a sowherd suffering from high incidence of MMA which demanded an intensive postparturient treatment to reduce baby pig mortality the effect on postparturient diseases of induction of parturition with Prostaglandin was examined. After treatment of 19 sows on day 112 of gestation with 12.5 mg Prostaglandin, parturition in 15 sows took place on an average of 25 hours after injection; the gestation period was 113.1 +/- 0.5 days. Three sows that did not respond to the treatment farrowed 3-6 days after treatment and one sow farrowed few hours after treatment. In a non-treated identical group of animals the gestation period averaged 113.4 +/- 1.5 days. No difference was found between the two groups concerning number of stillborn pgis, baby pig mortality within first eight days of life, incidence of MMA or intensity of postparturient medical treatment.