Early Graft, Limb and Mortality Outcomes from the Omniflow II Bio-Synthetic Graft.

BACKGROUND: Omniflow II biosynthetic grafts are a commonly used alternative to autologous grafts in vascular bypass procedures. They are chosen for their purported resilience to infection, often in instances of existing graft failure or infection. We examined the short term, 1-3 year outcomes of Omniflow grafts in terms of patency, limb survival and mortality in a sample of 24 individuals. METHODS: This is a single centred retrospective study of Omniflow II grafts implanted between September 23, 2015 and April 05, 2018 in our department. It includes grafts in all anatomical locations. Primary outcome measures were overall patient survival and time to this, primary graft patency (patency with no intervention) and then limb survival at 1 and 3 years. Kaplan-Meier survival analysis was plotted for the 3 primary outcome measures. RESULTS: A total of 24 grafts from 24 individuals were included with mean age 71.4 ± 11.7. We included 5 female and 19 male patients. The commonest indication was rest pain/claudication (N = 8) followed by graft occlusion (N = 6). Femoro-popliteal bypass (N = 13) and Femoro-distal bypass (N = 5) were the commonest procedures. Kaplan-Meier survival analysis demonstrated that 1 and 3-year primary patency rates were 54.2% and 37.5% respectively with Limb survival probability of 75% at 1 year and 70.8% at 3 years. These rates were all considerably lower than those found in previous comparative studies. Mortality however, compared favourably with 1 and 3-year survival probability 91.7% and 87.5% on average 296 days (range 95-451 days) after graft implantation. CONCLUSIONS: We found that rates of primary patency and limb salvage for this graft type were markedly lower than in comparable studies. Further work in the form of a RCT is indicated.

Surgery for deep venous insufficiency.

BACKGROUND: Chronic deep venous insufficiency is caused by incompetent vein valves, blockage of large-calibre leg veins, or both; and causes a range of symptoms including recurrent ulcers, pain and swelling. Most surgeons accept that well-fitted graduated compression stockings (GCS) and local care of wounds serve as adequate treatment for most people, but sometimes symptoms are not controlled and ulcers recur frequently, or they do not heal despite compliance with conservative measures. In these situations, in the presence of severe venous dysfunction, surgery has been advocated by some vascular surgeons. This is an update of the review first published in 2000. OBJECTIVES: To assess the effects of surgical management of deep venous insufficiency on ulcer healing and recurrence, complications of surgery, clinical outcomes, quality of life (QoL) and pain. SEARCH METHODS: The Cochrane Vascular Information Specialist searched the Cochrane Vascular Specialised Register, CENTRAL, MEDLINE, Embase and CINAHL databases, and the WHO ICTRP and ClinicalTrials.gov trials registries to 23 June 2020. SELECTION CRITERIA: We considered randomised controlled trials (RCTs) of surgical treatment versus another surgical procedure, usual care or no treatment, for people with deep venous insufficiency. DATA COLLECTION AND ANALYSIS: Two review authors independently assessed trials for inclusion, extracted data and assessed the risk of bias with the Cochrane risk of bias tool. We evaluated the certainty of the evidence using GRADE. We were unable to pool data due to differences in outcomes reported and how these were measured. Outcomes of interest were ulcer healing and recurrence, complications of surgery, clinical changes, QoL and pain. MAIN RESULTS: We included four RCTs (273 participants) comparing valvuloplasty plus surgery of the superficial venous system with surgery of the superficial venous system for primary valvular incompetence. Follow-up was two to 10 years. All included studies investigated primary valve incompetence. No studies investigated other surgical procedures for the treatment of people with deep venous insufficiency or surgery for secondary valvular incompetence or venous obstruction. The certainty of the evidence was downgraded for risk of bias concerns and imprecision due to small numbers of included trials, participants and events. None of the studies reported ulcer healing or ulcer recurrence. One study included 27 participants with active venous ulceration at the time of surgery; the other three studies did not include people with ulcers. There were no major complications of surgery, no incidence of deep vein thrombosis and no deaths reported (very low-certainty evidence). All four studies reported clinical changes but the data could not be pooled due to different outcome measures and reporting of the data. Two studies assessed clinical changes using subjective and objective measurements, as specified in the clinical, aetiological, anatomical and pathophysiological (CEAP) classification score (low-certainty evidence). One study reported mean CEAP severity scores and one study reported change in clinical class using CEAP. At baseline, the mean CEAP severity score was 18.1 (standard deviation (SD) 4.4) for limbs undergoing external valvuloplasty with surgery to the superficial venous system and 17.8 (SD 3.4) for limbs undergoing surgery to the superficial venous system only. At three years post-surgery, the mean CEAP severity score was 5.2 (SD 1.6) for limbs that had undergone external valvuloplasty with surgery to the superficial venous system and 9.2 (SD 2.6) for limbs that had undergone surgery to the superficial venous system only (low-certainty evidence). In another study, participants with progressive clinical dynamics over the five years preceding surgery had higher rates of improvement in clinical condition in the treatment group (valvuloplasty plus ligation) compared with the control group (ligation only) (80% versus 51%) after seven years of follow-up. Participants with stable preoperative clinical dynamics demonstrated similar rates of improvement in both groups (95% with valvuloplasty plus ligation versus 90% with ligation only) (low-certainty evidence). One study reported disease-specific QoL using cumulative scores from a 10-item visual analogue scale (VAS) and reported that in the limited anterior plication (LAP) plus superficial venous surgery group the score decreased from 49 to 11 at 10 years, compared to a decrease from 48 to 36 in participants treated with superficial venous surgery only (very low-certainty evidence). Two studies reported pain. Within the QoL VAS scale, one item was 'pain/discomfort' and scores decreased from 4 to 1 at 10 years for participants in the LAP plus superficial venous surgery group and increased from 2 to 3 at 10 years in participants treated with superficial venous surgery only. A second study reported that 'leg heaviness and pain' was resolved completely in 36/40 limbs treated with femoral vein external valvuloplasty plus high ligation and stripping of the great saphenous vein (GSV) and percutaneous continuous circumsuture and 22/40 limbs treated with high ligation and stripping of GSV and percutaneous continuous circumsuture alone, at three years' follow-up (very low-certainty evidence). AUTHORS' CONCLUSIONS: We only identified evidence from four RCTs for valvuloplasty plus surgery of the superficial venous system for primary valvular incompetence. We found no studies investigating other surgical procedures for the treatment of people with deep venous insufficiency, or that included participants with secondary valvular incompetence or venous obstruction. None of the studies reported ulcer healing or recurrence, and few studies reported complications of surgery, clinical outcomes, QoL and pain (very low- to low-certainty evidence). Conclusions on the effectiveness of valvuloplasty for deep venous insufficiency cannot be made.

Developing an experimental necrotic enteritis model in turkeys - the impact of Clostridium perfringens, Eimeria meleagrimitis and host age on frequency of severe intestinal lesions.

BACKGROUND: Necrotic enteritis is a significant problem to the poultry industry globally and, in Norway up to 30% of Norwegian turkey grow-outs can be affected. However, despite an awareness that differences exist between necrotic enteritis in chickens and turkeys, little information exists concerning the pathogenesis, immunity, microbiota or experimental reproduction of necrotic enteritis in turkeys. In particular, it is important to determine the appearance of the gross lesions, the age dependency of the disease and the role of netB toxin of Clostridium perfringens. To this end, we report our findings in developing an in vivo experimental model of necrotic enteritis in turkeys. RESULTS: A four tier (0-3) scoring system with clearly defined degrees of severity of macroscopic intestinal lesions was developed, based on 2312 photographic images of opened intestines from 810 B.U.T. 10 or B.U.T. Premium turkeys examined in nine experiments. Loss of macroscopically recognizable villi in the anterior small intestine was established as the defining lesion qualifying for a score 3 (severe intestinal lesions). The developed scoring system was used to identify important factors in promoting high frequencies of turkeys with severe lesions: a combined Eimeria meleagrimitis and Clostridium perfringens challenge, challenge at five rather than 3 weeks of age, the use of an Eimeria meleagrimitis dose level of at least 5000 oocysts per bird and finally, examination of the intestines of 5-week-old turkeys at 125 to 145 h after Eimeria meleagrimitis inoculation. Numbers of oocysts excreted were not influenced by Clostridium perfringens inoculation or turkey age. Among three different lesion score outcomes tested, frequency of severe lesions proved superior in discriminating between impact of four combinations of Clostridium perfringens inoculation and turkey age at challenge. CONCLUSIONS: This study provides details for the successful establishment of an in vivo model of necrotic enteritis in turkeys.

Rh(DPEPhos)-Catalyzed Alkyne Hydroacylation Using ß-Carbonyl-Substituted Aldehydes: Mechanistic Insight Leads to Low Catalyst Loadings that Enables Selective Catalysis on Gram-Scale.

The detailed mechanism of the hydroacylation of ß-amido-aldehyde, 2,2-dimethyl-3-morpholino-3-oxopropanal, with 1-octyne using [Rh( cis-κ2-P,P-DPEPhos)(acetone)2][BArF4]-based catalysts, is described [ArF = (CF3)2C6H3]. A rich mechanistic landscape of competing and interconnected hydroacylation and cyclotrimerization processes is revealed. An acyl-hydride complex, arising from oxidative addition of aldehyde, is the persistent resting state during hydroacylation, and quaternary substitution at the ß-amido-aldehyde strongly disfavors decarbonylation. Initial rate, KIE, and labeling studies suggest that the migratory insertion is turnover-limiting as well as selectivity determining for linear/branched products. When the concentration of free aldehyde approaches zero at the later stages of catalysis alkyne cyclotrimerization becomes competitive, to form trisubstituted hexylarenes. At this point, the remaining acyl-hydride turns over in hydroacylation and the free alkyne is now effectively in excess, and the resting state moves to a metallacyclopentadiene and eventually to a dormant α-pyran-bound catalyst complex. Cyclotrimerization thus only becomes competitive when there is no aldehyde present in solution, and as aldehyde binds so strongly to form acyl-hydride when this happens will directly correlate to catalyst loading: with low loadings allowing for free aldehyde to be present for longer, and thus higher selectivites to be obtained. Reducing the catalyst loading from 20 mol % to 0.5 mol % thus leads to a selectivity increase from 96% to ∼100%. An optimized hydroacylation reaction is described that delivers gram scale of product, at essentially quantitative levels, using no excess of either reagent, at very low catalyst loadings, using minimal solvent, with virtually no workup.

Synthetic approaches to the C11-C27 fragments of bryostatins.

The modified Julia reaction and acyl carbanion chemistry, especially reactions of 2-lithiated dithianes, have been investigated for the synthesis of intermediates that are the synthetic equivalents of the C11-C27 fragments of bryostatins. The modified Julia reaction using 2-benzothiazolylsulfones was found to be more useful for the formation of the C16-C17 double-bond than the classical Julia reaction using phenylsulfones, and bulky sulfones gave very good (E)-stereoselectivity. The alkylation of a dithiane monoxide that corresponded to a C19-acyl carbanion using (E)-1-bromobut-2-ene was efficient but the use of a more complex allylic bromide corresponding to the C20-C27 fragment of the bryostatins was unsuccessful, possibly due to competing elimination reactions. This meant that the use of C19 dithianes for the synthesis of 20-deoxybryostatins would have to involve the stepwise assembly of the C20-C27 fragment from simpler precursors. However, lithiated C19 dithianes gave good yields of adducts with aldehydes and conditions were developed for the stereoselective conversion of the major adducts into methoxyacetals that corresponded to the C17-C27 fragment of 20-oxygenated bryostatins. A convergent synthesis of the C11-C27 fragment of a 20-deoxybryostatin was subsequently achieved using a 2-benzothiazolylsulfone corresponding to the intact C17-C27 fragment.

Total synthesis of 7-des-O-pivaloyl-7-O-benzylbryostatin 10.

The first total synthesis of a derivative of a 20-deoxybryostatin, namely 7-des-O-pivaloyl-7-O-benzylbryostatin 10 is described. Preliminary studies demonstrated that the modified Julia reactions of 2-benzothiazolylsulfones corresponding to the C17-C27 fragment with aldehydes corresponding to the C1-C16 fragment, provided an efficient and stereoselective assembly of advanced intermediates with the (E)-16,17-double-bond. The synthesis of the C1-C16 fragment was then modified so that the C1 acid was present as its allyl ester before the Julia coupling. A more efficient synthesis of the C17-C27 sulfone was developed in which a key step was the bismuth mediated coupling of an allylic bromide with an aldehyde in the presence of an acrylate moiety in the allylic bromide. A scalable synthesis of an advanced macrolide was completed using the modified Julia reaction followed by selective deprotection and macrolactonisation. The final stages of the synthesis required selective hydroxyl deprotection and the introduction of the sensitive C19-C21 unsaturated keto-ester functionality. Unexpected selectivities were observed during studies of the hydroxyl group deprotections. In particular, cleavage of tri-isopropylsilyl ethers of the exocyclic primary allylic alcohols was observed in the presence of the triethylsilyl ether of the secondary alcohol at C19. Model studies helped in the design of the methods used to introduce the C19-C21 keto-ester functionality and led to the completion of a total synthesis of a close analogue of bryostatin 10 in which a benzyloxy group rather than the pivaloyloxy group was present at C7.

Stoichiometry of SecYEG in the active translocase of Escherichia coli varies with precursor species.

We have established a reconstitution system for the translocon SecYEG in proteoliposomes in which 55% of the accessible translocons are active. This level corresponds to the fraction of translocons that are active in vitro when assessed in their native environment of cytoplasmic membrane vesicles. Assays using these robust reconstituted proteoliposomes and cytoplasmic membrane vesicles have revealed that the number of SecYEG units involved in an active translocase depends on the precursor undergoing transfer. The active translocase for the precursor of periplasmic galactose-binding protein contains twice the number of heterotrimeric units of SecYEG as does that for the precursor of outer membrane protein A.

Surgery for deep venous incompetence.

BACKGROUND: Chronic deep venous incompetence (DVI) is caused by incompetent vein valves and/or blockage of large-calibre leg veins and causes a range of symptoms including recurrent ulcers, pain and swelling. Most surgeons accept that well-fitted graduated compression stockings (GCS) and local care of wounds serve as adequate treatment for most patients, but sometimes symptoms are not controlled and ulcers recur frequently, or they do not heal despite compliance with conservative measures. In these situations, in the presence of severe venous dysfunction, surgery has been advocated by some vascular surgeons. This is an update of the review first published in 2000. OBJECTIVES: To assess the effects of surgical management of deep venous incompetence in terms of ulcer healing, ulcer recurrence and alleviation of symptoms. SEARCH METHODS: For this update, the Cochrane Peripheral Vascular Diseases Group Trials Search Co-ordinator searched the Specialised Register (last searched October 2014) and the Cochrane Central Register of Controlled Trials (CENTRAL) (2014, Issue 9). SELECTION CRITERIA: Randomised controlled trials of surgical treatment for patients with DVI. DATA COLLECTION AND ANALYSIS: For this update, two review authors (RRG and SCH) extracted data independently. All included studies required full risk of bias assessment in line with current procedures of The Cochrane Collaboration. Two review authors (RRG and SCH) independently assessed risk of bias and consulted with a third review author (AA) when necessary. MAIN RESULTS: Four studies with 273 participants were included. All included studies reported clinical outcomes following valvuloplasty. We found no studies investigating other surgical procedures for the treatment of patients with DVI. All included studies investigated primary valve incompetence. We found no trials that investigated the results of surgery for secondary valvular incompetence or the obstructive form of DVI. Because different outcome measures were used, it was not possible to pool the results of included studies. The methodological quality of the included studies was low, mainly because information regarding randomisation and blinding was missing, or because data were incomplete or were presented poorly. Ulcer healing and ulcer recurrence were not reported in one study, and the remaining three studies did not include participants with ulcers or with active ulceration. Three studies reported no significant complications of surgery and no incidence of DVT during follow-up. One study did not report on the occurrence of complications. Clinical changes were assessed by subjective and objective measurements, as specified in the clinical, aetiological, anatomical, and pathophysiological (CEAP) classification score. This requires vascular laboratory measurements of lower limb haemodynamics before and after surgery. Tests include an overall evaluation of venous function with venous refilling time (VRT) or ambulatory venous pressure (AVP). Two small trials comparing external valvuloplasty using limited anterior plication in combination with ligation of incompetent superficial veins against ligation alone (L) showed that ligation plus limited anterior plication produced significant improvement in AVP: The mean difference was -15 mm Hg (95% confidence interval (CI) -20.9 to -9.0) at one year and -15 mm Hg (95% CI -21 to -8.9) at two years. Sustainable statistically significant improvement in AVP and VRT was achieved by ligation and limited anterior plication at 10 years in one study. However, AVP values after surgery remained relatively high, causing its benefit to be questioned. Similarly, another study including participants who were deteriorating preoperatively showed sustained mild clinical improvement for seven years in those subjected to valvuloplasty compared with participants undergoing superficial venous surgery alone. However, this benefit was lost when the condition of participants was stable preoperatively. One small study (n = 40) with grade 3 reflux and no participants with ulcers reported that external valvuloplasty of the femoral vein combined with surgical repair of the superficial venous system improved the haemodynamic status of the lower limbs, restored valvular function more effectively and achieved better outcomes than surgical repair of the superficial venous system alone. AUTHORS' CONCLUSIONS: No evidence was found for benefit or harm of valvuloplasty in the treatment of patients with DVI secondary to primary valvular incompetence. The individual trials included in this review were small; they used different methods of assessment and overall were of poor quality. They did not include participants with severe DVI. Trials investigating the effects of other surgical procedures on deep veins are needed. Until the findings of such trials become available, the benefit of valvuloplasty remains uncertain.

Multicomponent, Mannich-type assembly process for generating novel, biologically-active 2-arylpiperidines and derivatives.

A multicomponent, Mannich-type assembly process commencing with commercially available bromobenzaldehydes was sequenced with [3+2] dipolar cycloaddition reactions involving nitrones and azomethine ylides to generate collections of fused, bicyclic scaffolds based on the 2-arylpiperidine subunit. Use of the 4-pentenoyl group, which served both as an activator in the Mannich-type reaction and a readily-cleaved amine protecting group, allowed sub-libraries to be prepared through piperidine N-functionalization and cross-coupling of the aryl bromide. A number of these derivatives displayed biological activities that had not previously been associated with this substructure. Methods were also developed that allowed rapid conversion of these scaffolds to novel, polycyclic dihydroquinazolin-2-ones, 2-imino-1,3-benzothiazinanes, dihydroisoquinolin-3-ones and bridged tetrahydroquinolines.

Distinct forms of structural plasticity of adult-born interneuron spines in the mouse olfactory bulb induced by different odor learning paradigms.

The morpho-functional properties of neural networks constantly adapt in response to environmental stimuli. The olfactory bulb is particularly prone to constant reshaping of neural networks because of ongoing neurogenesis. It remains unclear whether the complexity of distinct odor-induced learning paradigms and sensory stimulation induces different forms of structural plasticity. In the present study, we automatically reconstructed spines in 3D from confocal images and performed unsupervised clustering based on morphometric features. We show that while sensory deprivation decreased the spine density of adult-born neurons without affecting the morphometric properties of these spines, simple and complex odor learning paradigms triggered distinct forms of structural plasticity. A simple odor learning task affected the morphometric properties of the spines, whereas a complex odor learning task induced changes in spine density. Our work reveals distinct forms of structural plasticity in the olfactory bulb tailored to the complexity of odor-learning paradigms and sensory inputs.

Multivariate evaluation of the effectiveness of treatment efficacy of cypermethrin against sea lice (Lepeophtheirus salmonis) in Atlantic salmon (Salmo salar).

BACKGROUND: The sea louse Lepeophtheirus salmonis is the most important ectoparasite of farmed Atlantic salmon (Salmo salar) in Norwegian aquaculture. Control of sea lice is primarily dependent on the use of delousing chemotherapeutants, which are both expensive, and toxic to other wildlife. The method most commonly used for monitoring treatment effectiveness relies on measuring the percentage reduction in the mobile stages of Lepeophtheirus salmonis only. However, this does not account for changes in the other sea lice stages and may result in misleading or incomplete interpretation regarding the effectiveness of treatment. With the aim of improving the evaluation of delousing treatments, we explored multivariate analyses of bath treatments using the topical pyrethroid, cypermethrin, in salmon pens at five Norwegian production sites. RESULTS: Conventional univariate analysis indicated reductions of over 90% in mobile stages at all sites. In contrast, multivariate analyses indicated differing treatment effectiveness between sites (p-value < 0.01) based on changes in the proportion and abundance of the chalimus and PAAM (pre-adult and adult males) stages. Low water temperatures and shortened intervals between sampling after treatment may account for the differences in the composition of chalimus and PAAM stage groups following treatment. Using multivariate analysis, such factors could be separated from those which were attributable to inadequate treatment or chemotherapeutant failure. CONCLUSIONS: Multivariate analyses for evaluation of treatment effectiveness against multiple life cycle stages of L. salmonis yield additional information beyond that derivable from univariate methods. This can aid in the identification of causes of apparent treatment failure in salmon aquaculture.

Relative entropy differences in bacterial chromosomes, plasmids, phages and genomic islands.

BACKGROUND: We sought to assess whether the concept of relative entropy (information capacity), could aid our understanding of the process of horizontal gene transfer in microbes. We analyzed the differences in information capacity between prokaryotic chromosomes, genomic islands (GI), phages, and plasmids. Relative entropy was estimated using the Kullback-Leibler measure. RESULTS: Relative entropy was highest in bacterial chromosomes and had the sequence chromosomes > GI > phage > plasmid. There was an association between relative entropy and AT content in chromosomes, phages, plasmids and GIs with the strongest association being in phages. Relative entropy was also found to be lower in the obligate intracellular Mycobacterium leprae than in the related M. tuberculosis when measured on a shared set of highly conserved genes. CONCLUSIONS: We argue that relative entropy differences reflect how plasmids, phages and GIs interact with microbial host chromosomes and that all these biological entities are, or have been, subjected to different selective pressures. The rate at which amelioration of horizontally acquired DNA occurs within the chromosome is likely to account for the small differences between chromosomes and stably incorporated GIs compared to the transient or independent replicons such as phages and plasmids.

Infected endovascular aneurysm repair graft complicated by vertebral osteomyelitis.

Endovascular aneurysm repair (EVAR) is now an established method of treating abdominal aortic aneurysms. Endovascular stent graft infection is a rare complication of EVAR. Diagnosis can be difficult and subsequent management challenging as a significant number of patients are unfit for further surgery and, untreated, graft infection is almost inevitably fatal. We present a case of an infected EVAR graft complicated by vertebral osteomyelitis that was treated conservatively. We discuss the diagnostic and therapeutic difficulties encountered and review the current literature on this evolving subject.

APPLICATIONS OF MULTICOMPONENT ASSEMBLY PROCESSES TO THE FACILE SYNTHESES OF DIVERSELY FUNCTIONALIZED NITROGEN HETEROCYCLES.

Several multicomponent assembly processes have been developed for the synthesis of intermediates that may be elaborated by a variety of cyclizations to generate a diverse array of highly functionalized heterocycles from readily-available starting materials. The overall approach enables the efficient preparation of libraries of small molecules derived from fused, privileged scaffolds.

Deciphering heterogeneous populations of migrating cells based on the computational assessment of their dynamic properties.

Neuronal migration is a highly dynamic process, and multiple cell movement metrics can be extracted from time-lapse imaging datasets. However, these parameters alone are often insufficient to evaluate the heterogeneity of neuroblast populations. We developed an analytical pipeline based on reducing the dimensions of the dataset by principal component analysis (PCA) and determining sub-populations using k-means, supported by the elbow criterion method and validated by a decision tree algorithm. We showed that neuroblasts derived from the same adult neural stem cell (NSC) lineage as well as across different lineages are heterogeneous and can be sub-divided into different clusters based on their dynamic properties. Interestingly, we also observed overlapping clusters for neuroblasts derived from different NSC lineages. We further showed that genetic perturbations or environmental stimuli affect the migratory properties of neuroblasts in a sub-cluster-specific manner. Our data thus provide a framework for assessing the heterogeneity of migrating neuroblasts.

Orientation of SecA and SecB in complex, derived from disulfide cross-linking.

SecA is the ATPase that acts as the motor for protein export in the general secretory, or Sec, system of Escherichia coli. The tetrameric cytoplasmic chaperone SecB binds to precursors of exported proteins before they can become stably folded and delivers them to SecA. During this delivery step, SecB binds to SecA. The complex between SecA and SecB that is maximally active in translocation contains two protomers of SecA bound to a tetramer of SecB. The aminoacyl residues on each protein that are involved in binding the other have previously been identified by site-directed spin labeling and electron paramagnetic resonance (EPR) spectroscopy; however, that study provided no information concerning the relative orientation of the proteins within the complex. Here we used our extensive collection of single-cysteine variants of the two proteins and subjected pairwise combinations of SecA and SecB to brief oxidation to identify residues in close proximity. These data were used to generate a model for the orientation of the two proteins within the complex.

Cytotoxicity of the Bacillus cereus Nhe enterotoxin requires specific binding order of its three exoprotein components.

This study focuses on the interaction of the three components of the Bacillus cereus Nhe enterotoxin with particular emphasis on the functional roles of NheB and NheC. The results demonstrated that both NheB and NheC were able to bind to Vero cells directly while NheA lacked this ability. It was also shown that Nhe-induced cytotoxicity required a specific binding order of the individual components whereby the presence of NheC in the priming step as well as the presence of NheA in the final incubation step was mandatory. Priming of cells with NheB alone and addition of NheA plus NheC in the second step failed to induce toxic effects. Furthermore, in solution, excess NheC inhibited binding of NheB to Vero cells, whereas priming of cells with excess NheC resulted in full toxicity if unbound NheC was removed before addition of NheB. By using mutated NheC proteins where the two cysteine residues in the predicted beta-tongue were replaced with glycine (NheCcys-) or where the entire hydrophobic stretch was deleted (NheChr-), the predicted hydrophobic beta-tongue of NheC was found essential for binding to cell membranes but not for interaction with NheB in solution. All data presented here are compatible with the following model. The first step in the mode of action of Nhe is associated with binding of NheC and NheB to the cell surface and probably accompanied by conformational changes. These events allow subsequent binding of NheA, leading to cell lysis.

Analysis of intra-genomic GC content homogeneity within prokaryotes.

BACKGROUND: Bacterial genomes possess varying GC content (total guanines (Gs) and cytosines (Cs) per total of the four bases within the genome) but within a given genome, GC content can vary locally along the chromosome, with some regions significantly more or less GC rich than on average. We have examined how the GC content varies within microbial genomes to assess whether this property can be associated with certain biological functions related to the organism's environment and phylogeny. We utilize a new quantity GCVAR, the intra-genomic GC content variability with respect to the average GC content of the total genome. A low GCVAR indicates intra-genomic GC homogeneity and high GCVAR heterogeneity. RESULTS: The regression analyses indicated that GCVAR was significantly associated with domain (i.e. archaea or bacteria), phylum, and oxygen requirement. GCVAR was significantly higher among anaerobes than both aerobic and facultative microbes. Although an association has previously been found between mean genomic GC content and oxygen requirement, our analysis suggests that no such association exits when phylogenetic bias is accounted for. A significant association between GCVAR and mean GC content was also found but appears to be non-linear and varies greatly among phyla. CONCLUSIONS: Our findings show that GCVAR is linked with oxygen requirement, while mean genomic GC content is not. We therefore suggest that GCVAR should be used as a complement to mean GC content.

Formation of very large conductance channels by Bacillus cereus Nhe in Vero and GH(4) cells identifies NheA + B as the inherent pore-forming structure.

The nonhemolytic enterotoxin (Nhe) produced by Bacillus cereus is a pore-forming toxin consisting of three components, NheA, -B and -C. We have studied effects of Nhe on primate epithelial cells (Vero) and rodent pituitary cells (GH(4)) by measuring release of lactate dehydrogenase (LDH), K(+) efflux and the cytosolic Ca(2+) concentration ([Ca(2+)](i)). Plasma membrane channel events were monitored by patch-clamp recordings. Using strains of B. cereus lacking either NheA or -C, we examined the functional role of the various components. In both cell types, NheA + B + C induced release of LDH and K(+) as well as Ca(2+) influx. A specific monoclonal antibody against NheB abolished LDH release and elevation of [Ca(2+)](i). Exposure to NheA + B caused a similar K(+) efflux and elevation of [Ca(2+)](i) as NheA + B + C in GH(4) cells, whereas in Vero cells the rate of K(+) efflux was reduced by 50% and [Ca(2+)](i) was unaffected. NheB + C had no effect on either cell type. Exposure to NheA + B + C induced large-conductance steps in both cell types, and similar channel insertions were observed in GH(4) cells exposed to NheA + B. In Vero cells, NheA + B induced channels of much smaller conductance. NheB + C failed to insert membrane channels. The conductance of the large channels in GH(4) cells was about 10 nS. This is the largest channel conductance reported in cell membranes under quasi-physiological conditions. In conclusion, NheA and NheB are necessary and sufficient for formation of large-conductance channels in GH(4) cells, whereas in Vero cells such large-conductance channels are in addition dependent on NheC.

Genome-Scale Metabolic Reconstruction and in Silico Perturbation Analysis of the Polar Diatom Fragilariopsis cylindrus Predicts High Metabolic Robustness.

Diatoms are major primary producers in polar environments where they can actively grow under extremely variable conditions. Integrative modeling using a genome-scale model (GSM) is a powerful approach to decipher the complex interactions between components of diatom metabolism and can provide insights into metabolic mechanisms underlying their evolutionary success in polar ecosystems. We developed the first GSM for a polar diatom, Fragilariopsis cylindrus, which enabled us to study its metabolic robustness using sensitivity analysis. We find that the predicted growth rate was robust to changes in all model parameters (i.e., cell biochemical composition) except the carbon uptake rate. Constraints on total cellular carbon buffer the effect of changes in the input parameters on reaction fluxes and growth rate. We also show that single reaction deletion of 20% to 32% of active (nonzero flux) reactions and single gene deletion of 44% to 55% of genes associated with active reactions affected the growth rate, as well as the production fluxes of total protein, lipid, carbohydrate, DNA, RNA, and pigments by less than 1%, which was due to the activation of compensatory reactions (e.g., analogous enzymes and alternative pathways) with more highly connected metabolites involved in the reactions that were robust to deletion. Interestingly, including highly divergent alleles unique for F. cylindrus increased its metabolic robustness to cellular perturbations even more. Overall, our results underscore the high robustness of metabolism in F. cylindrus, a feature that likely helps to maintain cell homeostasis under polar conditions.