213 research outputs found
Influence of electrical properties on the evaluation of the surface hydrophobicity of Bacillus subtilis
The surface hydrophobicity of nine Bacillus subtilis strains in different states (spores, vegetative cells, and dead cells) was assessed by water contact angle measurements, hydrophobic interaction chromatography (HIC) and bacterial adhesion to hydrocarbon (BATH). Electrokinetic properties of B, subtilis strains were characterized by zeta potential measurements and found to differ appreciably according to the strain, Correlations between HIC data, BATH data and zeta potential showed that HIC and RATH are influenced by electrostatic interactions. Water contact angle measurements thus provide a better estimate of cell surface hydrophobicity. The water contact angle of B. subtilis varied according to the strain and the state, the spores tending to be more hydrophobic than vegetative cells. (C) 2001 Elsevier Science B.V. All rights reserved
Delta activity independent of its activity as a ligand of Notch
BACKGROUND: Delta, Notch, and Scabrous often function together to make different cell types and refine tissue patterns during Drosophila development. Delta is known as the ligand that triggers Notch receptor activity. Scabrous is known to bind Notch and promote Notch activity in response to Delta. It is not known if Scabrous binds Delta or Delta has activity other than its activity as a ligand of Notch. It is very difficult to clearly determine this binding or activity in vivo as all Notch, Delta, and Scabrous activities are required simultaneously or successively in an inter-dependent manner. RESULTS: Using Drosophila cultured cells we show that the full length Delta promotes accumulation of Daughterless protein, fringe RNA, and pangolin RNA in the absence of Scabrous or Notch. Scabrous binds Delta and suppresses this activity even though it increases the level of the Delta intracellular domain. We also show that Scabrous can promote Notch receptor activity, in the absence of Delta. CONCLUSION: Delta has activity that is independent of its activity as a ligand of Notch. Scabrous suppresses this Delta activity. Scabrous also promotes Notch activity that is dependent on Delta's ligand activity. Thus, Notch, Delta, and Scabrous might function in complex combinatorial or mutually exclusive interactions during development. The data reported here will be of significant help in understanding these interactions in vivo
Antimicrobial and antiadhesive properties of a biosurfactant isolated from Lactobacillus paracasei ssp. paracasei A20
Aims: The aim of this study was to determine the antimicrobial and antiadhesive properties of a biosurfactant isolated from Lactobacillus paracasei ssp. paracasei A20 against several micro-organisms, including Gram-positive and Gram-negative bacteria, yeasts and filamentous fungi.
Methods and Results: Antimicrobial and antiadhesive activities were determined using the microdilution method in 96-well culture plates. The biosurfactant showed antimicrobial activity against all the micro-organisms assayed, and for twelve of the eighteen micro-organisms (including the pathogenic Candida albicans, Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis and Streptococcus agalactiae), the minimum inhibitory concentration (MIC) and the minimum bactericidal concentration (MBC) were achieved for biosurfactant concentrations between 25 and 50 mg ml−1. Furthermore, the biosurfactant showed antiadhesive activity against most of the micro-organisms evaluated.
Conclusions: As far as we know, this is the first compilation of data on antimicrobial and antiadhesive activities of biosurfactants obtained from lactobacilli against such a broad group of micro-organisms. Although the antiadhesive activity of biosurfactants isolated from lactic acid bacteria has been widely reported, their antimicrobial activity is quite unusual and has been described only in a few strains.
Significance and Impact of the Study: The results obtained in this study regarding the antimicrobial and antiadhesive properties of this biosurfactant opens future prospects for its use against micro-organisms responsible for diseases and infections in the urinary, vaginal and gastrointestinal tracts, as well as in the skin, making it a suitable alternative to conventional antibiotics.This work was supported by FCT (Portugal) under the scope of the Project BIOSURFA: Biosurfactants: potential applications for microbial adhesion inhibition in medical devices (PTDC/SAU-BEB/73498/2006)
Boundary friction characterisation of a used cylinder liner subject to fired engine conditions and surface deposition
In cylinder friction contributes as a primary source of parasitic dissipations in IC engines. For future engines to become more efficient, with enhanced fuel economy and increased power output, accurate prediction of new designs is required over the full lifetime of an engine. The work carried out presents use of a local pressure coefficient of boundary shear strength of asperities value, taking into account the localised effects of surface texture, coating and surface deposition. XPS spectra analysis was also carried out to identify the surface depositions as a result of combustion, not previously taken into account during piston ring pack simulation. Friction was shown by simulation to drop by up to 30% between the compression and combustion stroke as a result of using a carriable coefficient of boundary shear strength of asperities. It was found that piston varnish on the liner corresponded to higher values of the pressure coefficient of boundary shear strength of asperities, therefore showing the importance of using real system components run under representative operating conditions or numerical analyses
Low metabolic activity of biofilm formed by Enterococcus faecalis isolated from healthy humans and wild mallards (Anas platyrhynchos)
It is widely known that Enterococcus faecalis virulence is related to its biofilm formation. Although Enterococci are common commensal organisms of the gastrointestinal tract, the difference between commensal and pathogen strains remain unclear. In this study, we compare the biochemical profile of the biofilms formed by two groups of medical and two groups of commensal strains. The medical strains were isolated as pathogens from infections of urinary tract and other infections (wounds, pus and bedsores), and the commensal strains were taken from faeces of healthy volunteers and faeces of wild mallards (Anas platyrhynchos) living in an urban environment. The properties of biofilms formed by medical and commensal strains differed significantly. Commensal strains showed lower metabolic activity and glucose uptake and higher biofilm biomass than the medical ones. Consistent with glucose uptake experiments, we found that the glucose dehydrogenase gene was more expressed in medical strains. These results indicate that higher metabolic activity and lower protein concentration of E. faecalis cells within biofilms are formed during infections.This work was supported by the Medical University of Gdansk research grant (GUMed W-65) and was financed partly by University of Gdansk research grant (BW 1440-5-0099-7). We are grateful to Katarzyna Zolkos for her help in catching mallards and Magdalena Remisiewicz for correcting the English. Catarina Seabra helped in preparing assays
Characterisation of spin coated engineered <i>Escherichia coli</i> biofilms using atomic force microscopy
The ability of biofilms to withstand chemical and physical extremes gives them the potential to be developed as robust biocatalysts. Critical to this issue is their capacity to withstand the physical environment within a bioreactor; in order to assess this capability knowledge of their surface properties and adhesive strength is required. Novel atomic force microscopy experiments conducted under growth conditions (30° C) were used to characterise Escherichia coli biofilms, which were generated by a recently developed spin-coating method onto a poly-L-lysine coated glass substrate. High-resolution topographical images were obtained throughout the course of biofilm development, quantifying the tip-cell interaction force during the 10 day maturation process. Strikingly, the adhesion force between the Si AFM tip and the biofilm surface increased from 0.8 nN to 40 nN within 3 days. This was most likely due to the production of extracellular polymer substance (EPS), over the maturation period, which was also observed by electron microscopy. At later stages of maturation, multiple retraction events were also identified corresponding to biofilm surface features thought to be EPS components. The spin coated biofilms were shown to have stronger surface adhesion than an equivalent conventionally grown biofilm on the same glass substrate
Antifungal activity of lipopeptides from bacillus XT1 CECT 8661 against Botrytis cinerea
This work aims to explore the capacity of a Bacillus methylotrophicus (later heterotypic
synonym of Bacillus velezensis) strain named XT1 CECT 8661 against the necrotrophic
plant pathogen Botrytis cinerea and to identify the compounds responsible for its
activity. Q_TOF electrospray mass spectrometry analysis allows us to detect several
lipopeptides – surfactin, bacillomycin, and fengycin – in XT1 cultures. In vitro antibiosis
studies demonstrated the efficiency of the lipopeptide fraction for the inhibition of
fungal growth. In fact, microscopy studies (SEM/TEM) revealed, an alteration of the
morphology of the phytopathogen in interaction with lipopeptides, with resistance
structures appearing in the early stages of growth of the fungus. Our studies, carried out
with tomatoes, grapes, and strawberries have demonstrated the efficiency of Bacillus
XT1 CECT 8661 lipopeptides against B. cinerea infection and it capability to trigger
the antioxidant activity in fruit. Overall, the results of this study highlight the potential of
lipopeptides of this strain as an effective biological control agent against the colonisation
of B. cinerea.This study was supported by the European Project for Industrial
Doctorates “H2020” (UGR-Ref. 4726), by the Ramón y Cajal
Project (RYC-2014-15532) from MINECO and the Project Retos-
Colaboración from MINECO (2015, RTC-2015-4121-2)
Asperity level tribological investigation of automotive bore material and coatings
Choosing in-cylinder surfaces is complex. A well-chosen surface has low friction and wear. Conversely, poor oversight often leads to premature failure through wear and scuffing. Typically cylinder bore surfaces are selected experientially. This paper demonstrates the use of Atomic Force Microscopy in LFM mode, characterising typical cylinder bore materials and coatings. The approach uses integrated LFM with continuum contact mechanics. It evaluates the real contact area and effective elastic modulus of the surface, including the effect of any reactive surface film. Surface energy and shear strength, as well as the coefficient of friction in nanoscale interactions are also determined. These properties are measured for 6 cylinder bore materials, including for composite Nickel-Silicon Carbide and DLC, used for high performance engines
Thorium speciation in seawater
Author Posting. © The Authors, 2006. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Marine Chemistry 100 (2006): 250-268, doi:10.1016/j.marchem.2005.10.024.Since the 1960’s, thorium isotopes occupy a special place in the oceanographer’s toolbox as
tracers for determining rates and mechanisms of oceanic scavenging, particle dynamics, and
carbon fluxes. Due to their unique and constant production rates from soluble parent nuclides of
uranium and radium, their disequilibrium can be used to calculate rates and time scales of
sinking particles. In addition, by ratio-ing particulate 234Th (as well, in principle, other Thnuclides)
to carbon (and other elements), and linking this ratio to the parent-daughter
disequilibrium in the water column, it is possible to calculate fluxes of carbon and other
elements. Most of these applications are possible with little knowledge of the dissolved chemical
properties of thorium, other than its oxidation state (IV) and tendency to strongly sorb to
surfaces, i.e., its “particle- or surface-activity”. However, the use of any tracer is hindered by a
lack of knowledge of its chemical properties. Recent observations in the variability of carbon to
234Th ratios in different particle types, as well as of associations of Th(IV) with various marine
organic biomolecules has led to the need for a review of current knowledge and what future
endeavors should be taken to understand the marine chemistry of thorium.The writing of this paper was supported, in parts by NSF (OCE-0351559; OCE-0350758, and
OCE 0354757)
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