In Vitro Fermentation Evaluation of Engineered Sense and Respond Probiotics in Polymicrobial Communities

Synthetic biology provides a means of engineering tailored functions into probiotic bacteria. Of particular interest is introducing microbial sense and response functions; however, techniques for testing in physiologically relevant environments, such as those for the intended use, are still lacking. Typically, engineered probiotics are developed and tested in monoculture or in simplified cocultures still within ideal environments. In vitro fermentation models using simplified microbial communities now allow us to simulate engineered organism behavior, specifically organism persistence and intended functionality, within more physiologically relevant, tailored microbial communities. Here, probiotic bacteria Escherichia coli Nissle and Lactobacillus plantarum engineered with sense and response functionalities were evaluated for the ability to persist and function without adverse impact on commensal bacteria within simplified polymicrobial communities with increasing metabolic competition that simulate gut microbe community dynamics. Probiotic abundance and plasmid stability, measured by viability qPCR, decreased for engineered E. coli Nissle relative to monocultures as metabolic competition increased; functional output was not affected. For engineered L. plantarum, abundance and plasmid stability were not adversely impacted; however, functional output was decreased universally as metabolic competition was introduced. For both organisms, adverse effects on select commensals were not evident. Testing engineered probiotics in more physiologically relevant in vitro test beds can provide critical knowledge for circuit design feedback and functional validation prior to the transition to more costly and time-consuming higher-fidelity testing in animal or human studies.

In vitro fermentation test bed for evaluation of engineered probiotics in polymicrobial communities

In vitro fermentation systems offer significant opportunity for deconvoluting complex metabolic dynamics within polymicrobial communities, particularly those associated with the human gut microbiome. In vitro gut models have broad experimental capacity allowing rapid evaluation of multiple parameters, generating knowledge to inform design of subsequent in vivo studies. Here, our method describes an in vitro fermentation test bed to provide a physiologically-relevant assessment of engineered probiotics circuit design functions. Typically, engineered probiotics are evaluated under pristine, mono- or co-culture conditions and transitioned directly into animal or human studies, commonly resulting in a loss of desired function when introduced to complex gut communities. Our method encompasses a systematic workflow entailing fermentation, molecular and functional characterization, and statistical analyses to validate an engineered probiotic’s persistence, plasmid stability and reporter response. To demonstrate the workflow, simplified polymicrobial communities of human gut microbial commensals were utilized to investigate the probiotic Escherichia coli Nissle 1917 engineered to produce a fluorescent reporter protein. Commensals were assembled with increasing complexity to produce a mock community based on nutrient utilization. The method assesses engineered probiotic persistence in a competitive growth environment, reporter production and function, effect of engineering on organism growth and influence on commensal composition. The in vitro test bed represents a new element within the Design-Build-Test-Learn paradigm, providing physiologically-relevant feedback for circuit re-design and experimental validation for transition of engineered probiotics to higher fidelity animal or human studies.

Method for Modeling the Small Intestine and Resident Microbiome Through in Vitro Fermentation (P20-001-19)

Objectives

The human small intestine is a complex and dynamic organ tasked with enzymatic digestion and absorption of nutrients. Design of a small intestine model can provide detailed systematic knowledge of these processes; model design challenges include differential pH and oxygen availability along the length of the small intestine, food-dependent host secretion of digestive compounds, complex nutrient absorption processes, and microbiome interactions with both food and host. Numerous in vitro models have been developed to simulate the small intestine, but physiological relevance is limited. Here, we present an in vitro fermentation model of the small intestine to include microbiota and enhance physiological relevance.

Methods

A stepwise biofidelic model design approach was implemented with initial stages consisting of simulating ileum conditions, including pH and residence time, utilizing an automated bioreactor system for real-time monitoring and control of fermentation parameters, with incorporation of digestive enzymes and bile acids for breakdown of food inputs. Nutrient absorption, simulated using hollow-fiber columns to emulate passive diffusion, was initially optimized using small molecules to mimic dietary digestion byproducts; validation with food components, such as starch or whey powder, is planned. A mock microbial community, with organisms selected to represent major phyla and functions of the small intestine microbiota, was designed, implemented, and characterized in fermentations representing “fed-state” ileum conditions.

Results

Design and validation of the model with mock food components will be presented, along with steps taken to integrate in situ nutrient absorption and mock microbial community. Initial characterization of the microbial community indicates synergistic growth dynamics and nutrient utilization under “fed-state” conditions.

Conclusions

These efforts will be the foundation for our long-term goal of simulating the small intestine to complement our large intestine fermentation model, jA2COB, creating a complete in vitro fermentation model of the lower GI tract. Insight gleaned from this model, alone or in concert with in vivo studies, can inform nutritional strategies to restore and maintain host gut homeostasis.

Funding Sources

Funded by U.S. Army NSRDEC core applied research funds.

In Vitro Exploration of Healthy and Stressed Gut Microbiota Metabolism (P20-002-19)

Objectives

From a military perspective, the gut microbiome serves as an ideal tool to enhance Soldier gut and immune health and to improve survivability and performance. Our work employs in vitro tools as a means to elucidate systematic processes of colonic bacterial metabolism of dietary inputs under native and stressed conditions. This talk will focus on the use of in vitro fermentation to investigate both the prebiotic potential of cranberry proanthocyanidins (PAC) within a healthy microbiome and stress-induced alterations in microbial inter-species competition for fermentable fiber.

Methods

Fermentations were performed in triplicate, utilizing fecal inocula derived from at least three individuals, in a nutrient-rich anaerobic medium with sampling at 0 and 24 hrs. Within PAC supplementation studies, samples were analyzed for bacterial identification (16 s rRNA sequencing) and metabolite content (GC-FID and GC/MS). Stressed metabolism studies, which utilized fecal samples before and after a 21-day change in diet challenge (habitual vs. Meal Ready-to-Eat), employed media supplemented with resistant starch under ascending colon domain-specific conditions; samples taken were analyzed for bacterial identification (16 s rRNA) and enumeration of select organisms (qPCR).

Results

Bacterial population dynamics within PAC supplementation studies indicated a dose-dependent increase in several beneficial taxa, including Ruminococcus spp (P < 0.05). Phenolic metabolite generation as a function of PAC dosage identified several compounds associated with anti-inflammatory activity, including 3-(4-OH-phenyl) propionic acid (P < 0.001). Within stressed metabolism studies, Lactobacillus spp. growth was attenuated as a function of sudden change in diet (P ≤ 0.001), whereas growth of R. bromii was enhanced (P ≤ 0.05), indicating potential for an acute stressor to impact gut bacteria functional metabolism.

Conclusions

In vitro fermentation elucidated both a potential prebiotic effect of cranberry PAC on gut microbiota and the impact of sudden change in diet on inter-species competition for nutritional substrates. Understanding of gut microbiota metabolism dynamics could direct future dietary supplementation strategies to build resiliency against military-relevant stressors and offset negative impacts of dysbiosis.

Funding Sources

Defense Health Program.

Acute stressor alters inter-species microbial competition for resistant starch-supplemented medium

Gut microbiome community dynamics are maintained by complex microbe-microbe and microbe-host interactions, which can be disturbed by stress. In vivo studies on the dynamics and manipulation of those interactions are costly and slow, but can be accelerated using in vitro fermentation. Herein, in vitro fermentation was used to determine how an acute stressor, a sudden change in diet, impacts inter-bacterial species competition for resistant starch-supplemented medium (RSM). Fermentation vessels were seeded with fecal samples collected from 10 individuals consuming a habitual diet or U.S. military rations for 21 days. Lactobacillus spp. growth in response to RSM was attenuated following ration consumption, whereas growth of Ruminococcus bromii was enhanced. These differences were not evident in the pre-fermentation samples. Findings demonstrate how incorporating in vitro fermentation into clinical studies can increase understanding of stress-induced changes in nutrient-microbiome dynamics, and suggest that sudden changes in diet may impact inter-species competition for substrates.

The current state and future direction of DoD gut microbiome research: a summary of the first DoD gut microbiome informational meeting

The gut microbiome is increasingly recognized as integral to human health, and is emerging as a mediator of human physical and cognitive performance. This has led to the recognition that US Department of Defense (DoD) research supporting a healthy and resilient gut microbiome will be critical to optimizing the health and performance of future Warfighters. To facilitate knowledge dissemination and collaboration, identify resource capabilities and gaps, and maximize the positive impact of gut microbiome research on the Warfighter, DoD partners in microbiome research participated in a 2-day informational meeting co-hosted by the Natick Soldier Research, Engineering and Development Center (NSRDEC) and the US Army Research Institute of Environmental Medicine (USARIEM) on 16–17 November 2015. Attendee presentations and discussions demonstrated that multiple DoD organizations are actively advancing gut microbiome research. Common areas of research included the influence of military-relevant stressors on interactions between the microbiome and Warfighter biology, manipulation of the microbiome to influence Warfighter health, and use of the microbiome as a biomarker of Warfighter health status. Although resources and capabilities are available, they vary across laboratories and it was determined that centralizing certain DoD capabilities could accelerate progress. More significantly, the meeting created a foundation for a coordinated gut microbiome and nutrition research program aligning key DoD partners in the area of microbiome research. This report details the presentations and discussions presented during the 1st DoD Gut Microbiome Informational Meeting.

Alcohol and drug treatment outcome studies: new methodological review (2005-2010) and comparison with past reviews

OBJECTIVE

Several methodological reviews of alcohol treatment outcome studies and one review of drug studies have been published over the past 40 years. Although past reviews demonstrated methodological improvements in alcohol studies, they also found continued deficiencies. The current review allows for an updated evaluation of the methodological rigor of alcohol and drug studies and, by utilizing inclusion criteria similar to previous reviews, it allows for a comparative review over time. In addition, this is the first review that compares the methodology of alcohol and drug treatment outcome studies published during the same time period.

METHOD

The methodology for 25 alcohol and 11 drug treatment outcome studies published from 2005 through 2010 that met the review's inclusion criteria was evaluated. The majority of variables evaluated were used in prior reviews.

RESULTS

The current review found that more alcohol and drug treatment outcome studies are now using continuous substance use measures and assessing problem severity. Although there have been methodological improvements over time, the current reviews differed little from their most recent past counterpart. Despite this finding, some areas, particularly the continued low reporting of demographic data, needs strengthening.

CONCLUSIONS

Improvement in the methodological rigor of alcohol and drug treatment outcome studies has occurred over time. The current review found few differences between alcohol and drug study methodologies as well as few differences between the current review and the most recent past alcohol and drug reviews.

Effects of feeding fiber-fermenting bacteria to pigs on nutrient digestion, fecal output, and plasma energy metabolites

Inclusion of feedstuffs with higher plant cell wall (fiber) content in swine diets has increased in recent years due to greater availability and lower cost, especially coproduct feeds, such as corn distillers dried grains with soluble (DDGS). Limitations of feeding higher fiber diets include increased fecal output, which can exceed manure storage volumes, and decreased energy density, which can decrease growth performance; dietary treatments that ameliorate these limitations would benefit pork producers. Grower pigs (n = 48; 61.1 kg initial BW) were used to establish the effects of supplementation of fiber-fermenting bacteria in a 2 × 4 factorial, consisting of 2 diets (standard and high fiber) and 4 bacterial treatments (A, no bacteria; and B, C, and D bacterial supplements). Increased fiber came from inclusion of soybean hulls (10%) and corn DDGS (20%) in the diet. The 3 bacterial supplements (all Bacteroides strains) were isolated from fecal enrichment cultures and selected for their fiber-fermenting capacity. The high fiber diet increased fecal output, blood cholesterol, and triglyceride concentrations, and digestibility of NDF, ADF, and S; CP digestibility decreased (P ≤ 0.10). The improved fiber digestibility and altered energy status of pigs fed the high fiber diet was primarily due to fermentation of soybean hulls, resulting in increased short-chain fatty acid production and absorption, and decreased dietary starch content. Overall, pigs fed the bacterial treatments had only increased blood cholesterol concentrations (P = 0.10). When individual bacterial treatments were compared, pigs fed Bacteria B had decreased fecal output (P ≤ 0.10) and both blood glucose and cholesterol concentrations were increased (P ≤ 0.10) compared with the other 3 treatments, indicating an improved energy status. Pigs fed Bacteria B increased both CP and ADF (P ≤ 0.10), and tended (P = 0.16) to have increased NDF digestibilities compared with pigs fed no bacteria (Treatment A), whereas pigs fed the other 2 bacterial treatments did not differ from pigs fed Bacteria B for nutrient digestibility. Both had similar fecal outputs to pigs fed no bacteria. This is the first report of reduction in fecal output and increased fiber digestibility with pigs fed live bacteria. Successful application of this bacterial treatment could result in improved pig performance and decreased manure volumes, both of which would improve profitability of producers.

Aqueous-based spinning of fibers from self-assembling structural proteins

There has been long-standing interest in generating fibers from structural proteins and a great deal of work has been done in attempting to mimic dragline spider silk. Dragline silk balances stiffness, strength, extensibility, and high energy to break. Mimicking these properties through aqueous-based spinning of recombinant silk protein is a significant challenge; however, an approach has been developed that facilitates the formation of fibers approaching the mechanical properties seen with natural dragline silk. Due to the multitude of solution, spinning and post-spinning variables one has to consider, the method entails a multivariate approach to protein solution processing and fiber spinning. Optimization to maximize mechanical integrity of the fibers is performed by correlating the solution and spinning variables to mechanical properties and using this information for subsequent fiber spinning studies. Here, the method is described in detail and emphasizes the lessons learned during the iterative variable analysis process, which can be used as a basis for aqueous-based fiber spinning of other structural proteins.

Membrane permeability and antimicrobial kinetics of cecropin P1 against Escherichia coli

The interaction of cecropin P1 (CP1) with Escherichiacoli was investigated to gain insight into the time-dependent antimicrobial action. Biophysical characterizations of CP1 with whole bacterial cells were performed using both fluorescent and colorimetric assays to investigate the role of membrane permeability and lipopolysaccharide (LPS) binding in lytic behavior. The kinetics of CP1 growth inhibition assays indicated a minimal inhibitory concentration (MIC) of 3 microM. Bactericidal kinetics at the MIC indicated rapid killing of E.coli (<30 min). Membrane permeability studies illustrated permeation as a time-dependent event. Maximum permeability at the MIC occurred within 30 min, which correlates to the bactericidal action. Further investigation showed that the immediate permeabilizing action of CP1 is concentration-dependent, which correlates to the concentration-dependent nature of the inhibition assays. At the MIC and above, the immediate permeability was significant enough that the cells could not recover and exhibit growth. Below the MIC, immediate permeability was evident, but the level was insufficient to inhibit growth. Dansyl polymyxin B displacement studies showed LPS binding is essentially the same at all concentrations investigated. However, it does appear that only the immediate interaction is important, because binding continued to increase over time beyond cell viability. Our studies correlated CP1 bactericidal kinetics to membrane permeability suggesting CP1 concentration-dependent killing is driven by the extent of the immediate permeabilizing action of the peptide.

Lattice Boltzmann simulation of catalytic reactions

A lattice Boltzmann model is developed to simulate finite-rate catalytic surface chemistry. Diffusive wall boundary conditions are established to account for catalytic reactions in multicomponent mixtures. Implementation of wall boundary conditions with chemical reactions is based on a general second-order accurate interpolation scheme. Results of lattice Boltzmann simulations for a four-component mixture with a global catalytic methane oxidation reaction in a straight channel are in excellent agreement with a finite volume Navier-Stokes solver in terms of both the flow field and species concentrations.

Lattice Boltzmann model for the simulation of multicomponent mixtures

A lattice Boltzmann (LB) model for the simulation of realistic multicomponent mixtures is constructed. In the hydrodynamic limit, the LB model recovers the equations of continuum mechanics within the mixture-averaged diffusion approximation. The present implementation can be used to simulate realistic mixtures with arbitrary Schmidt numbers and molecular masses of the species. The model is applied to the mixing of two opposed jets of different concentrations and the results are in excellent agreement with a continuum model. An application to the simulation of mixtures in microflows is also presented. Results compare well with existing kinetic theory predictions of the slip coefficient for mixtures in a Couette flow.

Hydrodynamics beyond Navier-Stokes: exact solution to the lattice Boltzmann hierarchy

The exact solution to the hierarchy of nonlinear lattice Boltzmann (LB) kinetic equations in the stationary planar Couette flow is found at nonvanishing Knudsen numbers. A new method of solving LB kinetic equations which combines the method of moments with boundary conditions for populations enables us to derive closed-form solutions for all higher-order moments. A convergence of results suggests that the LB hierarchy with larger velocity sets is the novel way to approximate kinetic theory.

Simulation of binary mixtures with the lattice Boltzman method

A lattice Boltzman model for the simulation of binary mixtures is presented. Contrary to previous models, the present formulation is able to simulate mixtures with different Schmidt numbers and arbitrary molecular mass ratio of the components. In the hydrodynamic limit, the Navier-Stokes and the Stefan-Maxwell binary diffusion equations are recovered. The model is used for the simulation of binary diffusion and mixing layers. The results are found to be in good agreement with a derived similarity solution and with the predictions of a transient spectral element code.

Recombinant expression of indolicidin concatamers in Escherichia coli

Antimicrobial peptides are part of the innate immune system of vertebrates and invertebrates. They are active against gram-negative and gram-positive bacteria, fungi, and protozoa. Currently, most antimicrobial peptides are extracted from host organisms or produced by solid-phase peptide synthesis. Recombinant protein expression in Escherichia coli is a tool for greater production yields at a decreased cost and reduces the use of hazardous materials. We have constructed a concatamer of indolicidin and successfully expressed a fusion product with thioredoxin in E. coli BL21DE3. Codons for methionine residues flanking individual indolicidin genes were incorporated for cyanogen bromide cleavage of the fusion protein and liberation of active monomeric indolicidin. Peptide yields of 150 microg/l monomeric indolicidin were achieved in this first report of recombinant production of indolicidin with demonstrated antimicrobial activity.

Phase change of a confined subcooled simple liquid in a nanoscale cavity

The phase transition of a simple liquid bounded between two parallel walls a few nanometers apart is investigated with molecular dynamics simulations. Vapor nucleation in a liquid confined in a microchannel of only a few nanometers in size cannot be achieved by increasing the temperature at the wall. Already small changes in temperature cause a large rise in pressure, in terms of orders of magnitude. On the other hand, using the fact that some fluids thermally contract on cooling, e.g., the argon liquid investigated here, reducing the temperature places the fluid in the liquid-vapor coexistence regime. If the bottom wall temperature is further reduced, the fluid will crystallize starting from the bottom surface, creating a "frozen" bubble in the crystallized state. It was found that the confining walls and not the quenching rate primarily affect the crystallization process. However, the fastest cooling rate investigated herein led to a decrease of the boiling initiation temperature. At a lower cooling rate, the vapor nucleation temperature was the same as the equilibrium boiling temperature for the confined liquid. Small temperatures in the confined system result in dominating attraction forces at the fluid-wall interface exposing the fluid to tensile stress. The increased influence of the walls results in a significant decrease of the boiling as well as freezing temperatures.

Solidification of gold nanoparticles in carbon nanotubes

The structure and the solidification of gold nanoparticles in a carbon nanotube are investigated using molecular dynamics simulations. The simulations indicate that the predicted solidification temperature of the enclosed particle is lower than its bulk counterpart, but higher than that observed for clusters placed in vacuum. A comparison with a phenomenological model indicates that, in the considered range of tube radii (R(CNT)) of 0.5 < R(CNT) < 1.6 nm, the solidification temperature depends mainly on the length of the particle with a minor dependence on R(CNT).

Acid Extraction and Purification of Recombinant Spider Silk Proteins

A procedure has been developed for the isolation of recombinant spider silk proteins based upon their unique stability and solubilization characteristics. Three recombinant silk proteins, (SpI)7, NcDS, and [(SpI)4/(SpII)1]4, were purified by extraction with organic acids followed by affinity or ion exchange chromatography resulting in 90-95% pure silk solutions. The protein yield of NcDS (15 mg/L culture) and (SpI)7 (35 mg/L) increased 4- and 5-fold, respectively, from previously reported values presumably due to a more complete solubilization of the expressed recombinant protein. [(SpI)4/(SpII)1]4, a hybrid protein based on the repeat sequences of spidroin I and spidroin II, had a yield of 12.4 mg/L. This method is an effective, reproducible technique that has broad applicability for a variety of silk proteins as well as other acid stable biopolymers.

Oscillatory behavior of nanodroplets

Molecular dynamics (MD) simulations were performed in order to investigate the phenomenon of free oscillations of nanodroplets and the extent to which the continuum theory for such oscillations holds at nanoscales. The effect of temperature on these oscillations is also studied. The surface tension, a key property for the phenomenon of interest, was evaluated and compared with the experimental values of argon, showing that with an appropriate choice of the cutoff distance in the MD simulations, it is possible to predict the surface tension with good approximation. Nanoscale capillary waves on the free surface of the droplet were observed and compared to continuum theoretical predictions of the same. The nanodroplet interface thickness calculated based on continuum theory for these waves agreed well with the molecular dynamics calculation of the interface thickness. The frequencies of the oscillation of the droplet were calculated for all the studied temperatures and compared with the classical continuum theory. Although the simulated system cannot be considered strictly as a continuum, a good overall agreement was found.

A rapid selective extraction procedure for the outer membrane protein (OmpF) from Escherichia coli

Porins are essential pore-forming proteins found in the outer membrane of several gram-negative bacteria. Investigating the relationships between molecular structure and function involves an extremely time-consuming and labor-intensive purification procedure. We report a method for rapid extraction of the outer membrane protein, OmpF, from freeze-dried Escherichia coli cells using valeric acid, alleviating the effort and time in sample preparation. Extraction results in a highly enriched fraction containing OmpF as 76% of the total protein content. The apparent molecular mass determined by SDS-PAGE mobility was 38,900, similar to that of the monomeric form of OmpF. N-terminal sequencing yielded 23 amino acids with 100% identity to the published OmpF sequence. The trimeric form of OmpF was observed in unheated samples run on SDS-PAGE and analysis of these samples by periodic acid/silver staining revealed the presence of unbound lipopolysaccharides. Furthermore, this method should prove useful for isolating other outer membrane proteins.

Spider silk fibers spun from soluble recombinant silk produced in mammalian cells

Spider silks are protein-based "biopolymer" filaments or threads secreted by specialized epithelial cells as concentrated soluble precursors of highly repetitive primary sequences. Spider dragline silk is a flexible, lightweight fiber of extraordinary strength and toughness comparable to that of synthetic high-performance fibers. We sought to "biomimic" the process of spider silk production by expressing in mammalian cells the dragline silk genes (ADF-3/MaSpII and MaSpI) of two spider species. We produced soluble recombinant (rc)-dragline silk proteins with molecular masses of 60 to 140 kilodaltons. We demonstrated the wet spinning of silk monofilaments spun from a concentrated aqueous solution of soluble rc-spider silk protein (ADF-3; 60 kilodaltons) under modest shear and coagulation conditions. The spun fibers were water insoluble with a fine diameter (10 to 40 micrometers) and exhibited toughness and modulus values comparable to those of native dragline silks but with lower tenacity. Dope solutions with rc-silk protein concentrations >20% and postspinning draw were necessary to achieve improved mechanical properties of the spun fibers. Fiber properties correlated with finer fiber diameter and increased birefringence.

[Smoking cessation course organized by the Italian League for the fight against tumors in Milan and Rome: determinants of cessation after the course and after a year]

The Italian League against Cancer organizes a group behaviour therapy program for smoking cessation in Milan and Rome. Groups meet for 8-9 sessions; sessions are managed by a therapist. In the analized courses participants are 43-44 years on the average, with a middle/high level of education. They are heavy smokers with a high level of nicotine dependence and they greatly trust in the program. At the end of the program 67% of participants in Milan and 76% in Rome declare they no longer smoke. One year later, phone interviews show that 22% of participants in Milan and 25% in Rome are still non smokers. At the end of the program quitting-smoking predictors are: attendance at at least 6-7 sessions, smoking less than 30 cigarettes a day before the course and male gender; one year later attendance at at least 6-7 sessions, and scarce nicotine dependence (smoking less than 30 cigarettes a day before the program or a low score at the Fagerström Tolerance Questionnaire).

[Dynamic obstruction to left ventricular outflow during dobutamine stress echocardiography: the probable mechanisms and clinical implications]

We observed the development of left ventricular outflow tract dynamic obstruction in some patients during dobutamine stress echocardiography. The purpose of this study was to identify the possible mechanisms and to consider the clinical implications. From 11/04/94 to 01/09/97 we studied 547 patients; 42 patients developed dynamic obstruction, defined as a late peak Doppler velocity profile that exceeded baseline outflow velocity by at least 1 m/s. The encountered mechanisms were: increased myocardial contractility; systolic anterior motion of the mitral valve; decreased venous return to the left ventricle, and peculiar characteristics of the left ventricular geometry. The results of this study show that the dynamic obstruction is mainly due to the first mechanism and secondarily to some characteristics of the left ventricular geometry. The hypotension observed in a few cases is not related to the dynamic obstruction but to beta 2 receptor hypersensibility to dobutamine. The symptoms, like dyspnea and chest pain, experienced by these patients are related to the dynamic obstruction rather than to the presence of coronary artery disease. In conclusion, we think that patients who develop dynamic obstruction, without wall motion abnormalities, during dobutamine stress echocardiography, may behave pathophysiologically as patients with obstructive hypertrophic cardiomyopathy, in whom diastolic dysfunction and outflow tract obstruction are responsible for symptoms. Therefore, these patients require a pharmacological treatment with beta blockers and/or non-dihydropyridine calcium channel blockers.

Evolution of repetitive proteins: spider silks from Nephila clavipes (Tetragnathidae) and Araneus bicentenarius (Araneidae)

Spider silks are highly repetitive proteins, characterized by regions of polyalanine and glycine-rich repeating units. We have obtained two variants of the Spidroin 1 (NCF-1) silk gene sequence from Nephila clavipes. One sequence (1726 bp) was from a cloned cDNA, and the other (1951 bp) was from PCR of genomic DNA. When these sequences are compared with each other and the previously published Spidroin 1 sequence, there are differences due to sequence rearrangements, as well as single base substitutions. These variations are similar to those that have been reported from other highly repetitive genes, and probably represent the results of unequal cross-overs. We have also obtained 708 bp of sequence from pCR of genomic DNA from Araneus biocentenarius. This sequence shows considerable similarity to a dragline sequence (ADF-3) from A. diadematus, as well as Spidroin 2 (NCF-2) from N. clavipes. Minor but consistent differences in the repeating unit sequence between A. bicentenarius and A. diadematus suggest that concerted evolution or gene conversion processes are acting to maintain similarity among repeat units within a single gene.

Purification and characterization of recombinant spider silk expressed in Escherichia coli

A partial cDNA clone, from the 3' end of the dragline silk gene was isolated from Nephila clavipes major ampullate glands. This clone contains a 1.7-kb insert, consisting of a repetitive coding region of 1.4-kb and a 0.3-kb nonrepetitive coding region; 1.5-kb of the 1.7-kb fragment was cloned into Escherichia coli and a 43-kDa recombinant silk protein was expressed. Characterization of the purified protein by Western blot, amino acid composition analysis, and matrix-assisted laser desorption ionization/time-of-flight mass spectrometry confirms it to be spider dragline silk.

[Vein patency in patients with pacemaker implanted via subclavian vein: digital phlebography assessment]

Venous thrombosis is a well-known complication of permanent cardiac pacemaker implantation, particularly, chronic occlusion of the subclavian vein is reported to occur in 20-33% of the cases where the percutaneous approach is performed. We examined 135 asymptomatic patients with digital venography to asses the frequency of venous thromboses causing stenosis and occlusion of the subclavian or anonymous arteries in pacemaker carriers. We considered both one- (44) and two-chamber (91) pacemakers and investigated a possible statistically significant difference between them: we found 21 venous thromboses (15%), seven of them in one-chamber pacemakers (15.9%) and 14 two-chambers pacemakers (15.3%). None of our 94 male and 41 female patients was on anticoagulants or had any evidence of coagulation disorders. Venography was performed 39.3 months (mean) after pacemaker implantation (range: 3-120 months). We conclude that digital venography is a simple and relatively noninvasive method permitting better depiction of subclavian, anonymous and caval veins than Doppler US and also showing some vascular abnormalities which may complicate pacemaker implantation.

Sequence conservation in the C-terminal region of spider silk proteins (Spidroin) from Nephila clavipes (Tetragnathidae) and Araneus bicentenarius (Araneidae)

The polymerase chain reaction (PCR) has been used to amplify the portion of the Spidroin 1 gene that codes for the C-terminal part of the silk protein of the spider Nephila clavipes. Along with some substitution mutations of minor consequence, the PCR-derived sequence reveals an additional base missing from the previously published Nephila Spidroin 1 sequence. Comparison of the PCR-derived sequence with the equivalent region of Spidroin 2 indicates that the insertion of this single base results in greatly increased similarity in the resulting amino acid sequences of Spidroin 1 and Spidroin 2 (75% over 97 amino acids). The same PCR primers also amplified a fragment of the same length from Araneus bicentenarius. This sequence is also very similar to Spidroin 1 of Nephila (71% over 238 bases excluding the PCR primers, which translates into 76% over 79 amino acids).