Comparison of minisatellite polymorphisms in the Bacillus cereus complex: a simple assay for large-scale screening and identification of strains most closely related to Bacillus anthracis

Polymorphism of five tandem repeats that are monomorphic in Bacillus anthracis was investigated in 230 isolates of the B. cereus group and in 5 sequenced B. cereus genomes in search for markers allowing identification of B. cereus and B. thuringiensis strains most closely related to B. anthracis. Using this multiple-locus variable number of tandem repeat analysis (MLVA), a cluster of 30 strains was selected for further characterization. Eventually, six of these were characterized by multilocus sequence type analysis. One of the strains is only six point mutations (of almost 3,000 bp) away from B. anthracis and was also proposed to be closest to B. anthracis by MLVA analysis. However, this strain remains separated from B. anthracis by a number of significant genetic events observed in B. anthracis, including the loss of the hemolysin activity, the presence of four prophages, and the presence of the two virulence plasmids, pXO1 and pXO2. One particular minisatellite marker provides an efficient assay to identify the subset of B. cereus and B. thuringiensis strains closely related to B. anthracis. Based on these results, a very simple assay is proposed that allows the screening of hundreds of strains from the B. cereus complex, with modest equipment and at a low cost, to eventually fill the gap with B. anthracis and better understand the origin and making of this dangerous pathogen.     

Autotrophic and mixotrophic hydrogen photoproduction in sulfur-deprived chlamydomonas cells

In Chlamydomonas reinhardtii cells, H2 photoproduction can be induced in conditions of sulfur deprivation in the presence of acetate. The decrease in photosystem II (PSII) activity induced by sulfur deprivation leads to anoxia, respiration becoming higher than photosynthesis, thereby allowing H2 production. Two different electron transfer pathways, one PSII dependent and the other PSII independent, have been proposed to account for H2 photoproduction. In this study, we investigated the contribution of both pathways as well as the acetate requirement for H2 production in conditions of sulfur deficiency. By using 3-(3,4-dichlorophenyl)-1,1-dimethylurea (DCMU), a PSII inhibitor, which was added at different times after the beginning of sulfur deprivation, we show that PSII-independent H2 photoproduction depends on previously accumulated starch resulting from previous photosynthetic activity. Starch accumulation was observed in response to sulfur deprivation in mixotrophic conditions (presence of acetate) but also in photoautotrophic conditions. However, no H2 production was measured in photoautotrophy if PSII was not inhibited by DCMU, due to the fact that anoxia was not reached. When DCMU was added at optimal starch accumulation, significant H2 production was measured. H2 production was enhanced in autotrophic conditions by removing O2 using N2 bubbling, thereby showing that substantial H2 production can be achieved in the absence of acetate by using the PSII-independent pathway. Based on these data, we discuss the possibilities of designing autotrophic protocols for algal H2 photoproduction.     

The in vitro skin irritation of chemicals: optimisation of the EPISKIN prediction model within the framework of the ECVAM validation process

In view of the increasing need to identify non-animal tests able to predict acute skin irritation of chemicals, the European Centre for the Validation of Alternative Methods (ECVAM) focused on the evaluation of appropriate in vitro models. In vitro tests should be capable of discriminating between irritant (I) chemicals (EU risk: R38) and non-irritant (NI) chemicals (EU risk: "no classification"). Since major in vivo skin irritation assays rely on visual scoring, it is still a challenge to correlate in vivo clinical signs with in vitro biochemical measurements. Being particularly suited to test raw materials or chemicals with a wide variety of physical properties, in vitro skin models resembling in vivo human skin were involved in prevalidation processes. Among many other factors, cytotoxicity is known to trigger irritation processes, and can therefore be a first common event for irritants. A refined protocol (protocol 15min-18hours) for the EPISKIN model had been proposed for inclusion in the ECVAM formal validation study. A further improvement on this protocol, mainly based on a post-treatment incubation period of 42 hours (protocol 15min-42hours), the optimised protocol, was applied to a set of 48 chemicals. The sensitivity, specificity and accuracy with the MTT assay-based prediction model (PM) were 85%, 78.6% and 81.3% respectively, with a low rate of false negatives (12%). The improved performance of this optimised protocol was confirmed by a higher robustness (homogeneity of individual responses) and a better discrimination between the I and NI classes. To improve the MTT viability-based PM, the release of a membrane damage marker, adenylate kinase (AK), and of cytokines IL-1alpha and IL-8 were also investigated. Combining these endpoints, a simple two-tiered strategy (TTS) was developed, with the MTT assay as the first, sort-out, stage. This resulted in a clear increase in sensitivity to 95%, and a fall in the false-positive rate (to 4.3%), thus demonstrating its usefulness as a "decision-making" tool. The optimised protocol proved, both by its higher performances and by its robustness, to be a good candidate for the validation process, as well as a potential alternative method for assessing acute skin irritation.     

Geranylgeranylated, but not farnesylated, RhoB suppresses Ras transformation of NIH-3T3 cells

RhoB is a low molecular weight GTPase that is both farnesylated (RhoB-F) and geranylgeranylated (RhoB-GG) in cells. Based on data from rodent cell models, it has been suggested that RhoB displays differential effects on cell transformation, according to the nature of its prenylation. To test directly this hypothesis, we generated GTPase-deficient RhoB mutants that are exclusively either farnesylated or geranylgeranylated. We show that in Ras-transformed murine NIH-3T3 cells, RhoB-F enhances, whereas RhoB-GG and RhoB (F/GG) suppresses anchorage-dependent and -independent cell growth as well as tumor growth in nude mice. We then demonstrate that Ras constitutive activation of the tumor survival pathways Akt and NF-kappa B are blocked by RhoB-GG, but not by RhoB-F, providing further support for the opposing role of RhoB-F and RhoB-GG in Ras malignant transformation in NIH-3T3 cells. In addition, both RhoB (F/GG) and RhoB-GG induce apoptosis in Ras-transformed NIH-3T3 cells whereas RhoB-F has no effect. Our data demonstrate that RhoB-F and RhoB-GG which differ only by a 5-carbon isoprene behave differently in rodent cells highlighting the important role of prenyl groups in protein function and emphasize the potency of RhoB to regulate negatively the oncogenic signal.     

Parallel solid-phase synthesis and characterization of new sulfonamide and carboxamide proline derivatives as potential CNS agents

A solid-phase synthesis of the 64-member library of novel sulfonamide and carboxamide proline derivatives, focused on the 5-HT7 receptor antagonist SB-258741, was described. The final compounds were obtained in good yields and high purity upon cleavage from SynPhase Lanterns, functionalized by a BAL linker. The library representatives were screened for 5-HT7, 5-HT1A and D2 receptors to explore the impact of a tertiary amine moiety, the length of an alkylene spacer and the aryl fragment on the receptor affinity. The preliminary biological results provided data for further investigation aimed at a search for 5-HT7 receptor agents, and permitted the identification of several compounds with significant 5-HT1A receptor affinity.     

Respiration metabolism of Group B Streptococcus is activated by environmental haem and quinone and contributes to virulence

Group B Streptococcus (GBS) is a common constituent of the vaginal microflora, but its transmission to newborns can cause life-threatening sepsis, pneumonia and meningitis. Energy metabolism of this opportunist pathogen has been deduced to be strictly fermentative. We discovered that GBS undergoes respiration metabolism if its environment supplies two essential respiratory components: quinone and haem. Respiration metabolism led to significant changes in growth characteristics, including a doubling of biomass and an altered metabolite profile under the tested conditions. The GBS respiratory chain is inactivated by: (i) withdrawing haem and/or quinone, (ii) treating cultures with a respiration inhibitor or (iii) inactivating the cydA gene product, a subunit of cytochrome bd quinol oxidase, in all cases resulting in exclusively fermentative growth. cydA inactivation reduced GBS growth in human blood and strongly attenuated virulence in a neonatal rat sepsis model, suggesting that the animal host may supply the components that activate GBS respiration. These results suggest a role of respiration metabolism in GBS dissemination. Our findings show that environmental factors can increase the flexibility of GBS metabolism by activating a newly identified respiration chain. The need for two environmental factors may explain why GBS respiration metabolism was not found in previous studies.     

Gap, a mycobacterial specific integral membrane protein, is required for glycolipid transport to the cell surface

The cell envelope of mycobacteria is a complex multilaminar structure that protects the cell from stresses encountered in the environment, and plays an important role against the bactericidal activity of immune system cells. The outermost layer of the mycobacterial envelope typically contains species-specific glycolipids. Depending on the mycobacterial species, the major glycolipid localized at the surface can be either a phenolglycolipid or a peptidoglycolipid (GPL). Currently, the mechanism of how these glycolipids are addressed to the cell surface is not understood. In this study, by using a transposon library of Mycobacterium smegmatis and a simple dye assay, six genes involved in GPLs synthesis have been characterized. All of these genes are clustered in a single genomic region of approximately 60 kb. We show by biochemical analyses that two non-ribosomal peptide synthetases, a polyketide synthase, a methyltransferase and a member of the MmpL family are required for the biosynthesis of the GPLs backbone. Furthermore, we demonstrate that a small integral membrane protein of 272 amino acids named Gap (gap: GPL addressing protein) is specifically required for the transport of the GPLs to the cell surface. This protein is predicted to contain six transmembrane segments and possesses homologues across the mycobacterial genus, thus delineating a new protein family. This Gap family represents a new paradigm for the transport of small molecules across the mycobacterial envelope, a critical determinant of mycobacterial virulence.     

Novel cyclized Pifithrin-alpha p53 inactivators: synthesis and biological studies

Starting from various cyclic or bicyclic ketones, we have synthesized novel Pifithrin-alpha analogues bearing different methyl substituted phenyl ketone groups at the N3-position of the 2-iminothiazole heterocycle. From stability studies in a biological medium as well as under specific chemical conditions, we have shown by NMR techniques that through a dehydration process, some derivatives can generate their corresponding cyclized analogues. All of the new analogues, Pifithrin-like and polycyclic dehydrated derivatives were assessed for their p53 inactivation potency by measuring survival of cortical neurons, whose death was induced by the DNA-damaging agent etoposide. Pifithrin-alpha like 2f as well as the cyclic dehydrated 6b analogue were found to be one log more potent p53 inactivators than reference compound Pft-alpha, with EC50 values ranging around 30 nM. These results support the finding that p53 inactivation by Pft-alpha analogues could be also due to the presence of the cyclic dehydrated Pft-alpha forms, generated in situ in the biological assay incubation medium.