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Biomedical subjects

M E Callow

Publications and source records attributed to M E Callow.

16 recordsLinked to original sources
PubMed2006

Mussel (Mytilus edulis) byssus deposition in response to variations in surface wettability.

Mussels (Mytilus edulis) are economically important in their role as an aquaculture species and also with regard to marine biofouling. They attach tenaciously to a wide variety of submerged surfaces by virtue of collagenous attachment threads termed 'byssi'. The aim of this study was to characterize the spreading of the byssal attachment plaque, which mediates attachment to the surface, on a range of surfaces in response to changes in wettability. To achieve this, well characterized self-assembled monolayers of omega-terminated alkanethiolates on gold were used, allowing correlation of byssal plaque spreading with a single surface characteristic--wettability. The present results were inconsistent with those from previous studies, in that there was a positive correlation between plaque size and surface wettability; a trend which is not explained by conventional wetting theory for a three-phase system. A recent extension to wetting theory with regard to hydrophilic proteins is discussed and the results of settlement assays are used to attempt reconciliation of these results with those of similar previous studies and, also, with recent data presented for the spreading of Ulva linza spore adhesive.

Adhesiveness↗
PubMed2006

Biofilms.

Biofilms of bacteria, frequently in association with algae, protozoa and fungi, are found on all submerged structures in the marine environment. Although it is likely that for the majority of organisms a biofilmed surface is not a pre-requisite for settlement, in practice, colonization by spores and larvae of fouling organisms almost always takes place via a biofilmed surface. Therefore, the properties of the latter may be expected to influence colonization, positively or negatively. Biofilms are responsible for a range of surface-associated and diffusible signals, which may moderate the settling behaviour of cells, spores and larvae. However, there is no consensus view regarding either cause and effect or the mechanism(s) by which biofilms moderate settlement. Studies with mixed biofilms, especially field experiments, are difficult to interpret because of the conflicting signals produced by different members of the biofilm community as well as their spatial organisation. Molecular techniques highlight the deficiencies of culture methods in identifying biofilm bacteria; hence, the strains with the most impact on settlement of spores and larvae may not yet have been isolated and cultured. Furthermore, secondary products isolated from cultured organisms may not reflect the situation that pertains in nature. The evidence that bacterial quorum sensing signal molecules stimulate settlement of spores of the green macroalga, Ulva, is discussed in some detail. New molecular and analytical tools should provide the opportunity to improve our fundamental understanding of the interactions between fouling organisms and biofilms, which in turn may inform novel strategies to control biofouling.

4-Butyrolactone↗
PubMed2005

The influence of surface energy on the wetting behaviour of the spore adhesive of the marine alga Ulva linza (synonym Enteromorpha linza).

The environmental scanning electron microscope has been used to image the adhesive pads secreted by zoospores of the marine alga Ulva linza as they settle on a range of self-assembled and grafted monolayers of different wettability, under natural, hydrated conditions. Results reveal that the diameter of the adhesive pad is strongly influenced by surface wettability, the adhesive spreading more (i.e. wetting the surface better) on the more hydrophilic surfaces. This is in direct contrast to previous observations on the spreading of marine bioadhesives and is in apparent contradiction to the predictions of the Young-Dupre equation for three-phase systems. In this paper, we attempt an explanation based upon thermodynamic analysis of the wetting properties of hydrophilic proteins.

Adhesiveness↗
PubMed2004

Activity of commercial enzymes on settlement and adhesion of cypris larvae of the barnacle Balanus amphitrite, spores of the green alga Ulva linza, and the diatom Navicula perminuta.

Fouling species produce adhesive polymers during the settlement, adhesion and colonization of new surfaces in the marine environment. The present paper tests the hypothesis that enzymes of the appropriate specificity may prevent biofouling by hydrolysing these adhesive polymers. Seventeen commercially available enzyme preparations designed originally for bulk use in a range of end-use applications were tested for their effects on the settlement and/or adhesion of three major fouling species, viz. the green alga Ulva linza, the diatom Navicula perminuta and the barnacle Balanus amphitrite. The serine-proteases were found to have the broadest antifouling potential reducing the adhesion strength of spores and sporelings of U. linza, cells of N. perminuta and inhibiting settlement of cypris larvae of B. amphitrite. Mode-of-action studies on the serine-protease, Alcalase, indicated that this enzyme reduced adhesion of U. linza in a concentration-dependent manner, that spores of the species could recover their adhesive strength if the enzyme was removed and that the adhesive of U. linza and juvenile cement of B. amphitrite became progressively less sensitive to hydrolysis as they cured.

Adhesives↗
PubMed2004

Roughness-dependent removal of settled spores of the green alga Ulva (syn. Enteromorpha) exposed to hydrodynamic forces from a water jet.

Topographic features change the hydrodynamic regime over surfaces subjected to flow. Hydrodynamic microenvironments around topographic structures may have consequences for recruitment and removal of propagules of marine benthic organisms. The settlement and adhesion of zoospores from the green alga Ulva linza (syn. Enteromorpha linza) to defined topographies was investigated. A range of topographic size scales (Rz: 25-100 microm) was manufactured from plankton nets, creating patterns with ridges and depressions. The topographic scales span a roughness similar to that of natural substrata and antifouling coatings. Spores were removed from the surfaces by a calibrated water jet. Fewer spores were removed from the smallest topographic structure tested (Rz: 25 microm) compared to both the smooth (Rz: 1) and the roughest (Rz: 100 microm) structures. Zoospores that settled in depressions were less likely to be removed compared to spores on the ridges. The results in terms of the interaction between surface topography and hydrodynamic forces have implications for both natural substrata exposed to wave action and antifouling surfaces on ships' hulls. The possible effects of topography on increasing zoospore adhesion and offering a refuge from hydrodynamic forces are discussed.

Adhesiveness↗
PubMed2003

Three models to relate detachment of low form fouling at laboratory and ship scale.

Since fouling-release coating systems do not prevent settlement, various methods to quantify the tenacity of adhesion of fouling organisms on these systems have been offered. One such method is the turbulent channel flow apparatus. The question remains how the results from laboratory scale tests relate to the self-cleaning of a ship coated with a fouling-release surface. This paper relates the detachment strength of low form fouling determined in the laboratory using a turbulent channel flow to the conditions necessary for detachment of these organisms in a turbulent boundary layer at ship scale. A power-law formula, the ITTC-57 formula, and a computational fluid dynamics (CFD) model are used to predict the skin-friction at ship scale. The results from all three methods show good agreement and are illustrated using turbulent channel flow data for sporelings of the green macrofouling alga Enteromorpha growing on a fouling-release coating.

Adhesiveness↗
PubMed2001

Brefeldin A affects adhesion of zoospores of the green alga Enteromorpha.

Primary adhesion of zoospores of the green macroalga Enteromorpha to substrata involves a massive release of adhesive glycoproteins from Golgi-derived, membrane-bounded vesicles in the anterior region of the spore, followed by rapid curing. This process is sensitive to low concentrations (5-10 microg x ml(-1)) of the secretion-inhibiting antibiotic, brefeldin A (BFA). The proportion of cells that settled in BFA was reduced by approximately 50%, but the effect was fully reversed by washing in seawater to remove the BFA. Ultrastructural observations showed that BFA caused the breakdown of Golgi stacks in the majority of cells examined. When settled cells were subjected to shear stress, a greater proportion of those settled in the presence of BFA were detached, compared with controls, indicating reduced adhesion strength in the presence of the antibiotic. The most likely reason for this is that strong adhesion to substrata either requires the synthesis of extra adhesive materials beyond those present in the swimming spore, or the secretion of an additional component required for adhesive curing. The novel use of atomic force microscopy in force modulation mode demonstrated that the adhesive secreted by most spores in the presence of BFA did not undergo the rapid curing process typical of control spores. However, some variation between zoospores was observed, with some cells showing no ultrastructural changes and normal adhesive curing. These results are discussed in relation to variations observed in the propensity and competence of spores to settle, which may be reflected in differential requirements for de novo synthesis and secretion of materials needed for full adhesion.

Antifungal Agents↗
PubMed2000

Use of self-assembled monolayers of different wettabilities to study surface selection and primary adhesion processes of green algal (Enteromorpha) zoospores.

We investigated surface selection and adhesion of motile zoospores of a green, macrofouling alga (Enteromorpha) to self-assembled monolayers (SAMs) having a range of wettabilities. The SAMs were formed from alkyl thiols terminated with methyl (CH(3)) or hydroxyl (OH) groups or mixtures of CH(3)- and OH-terminated alkyl thiols and were characterized by measuring the advancing contact angles and by X-ray photoelectron spectroscopy. There was a positive correlation between the number of spores that attached to the SAMs and increasing contact angle (hydrophobicity). Moreover, the sizes of the spore groups (adjacent spores touching) were larger on the hydrophobic SAMs. Video microscopy of a patterned arrangement of SAMs showed that more zoospores were engaged in swimming and "searching" above the hydrophobic sectors than above the hydrophilic sectors, suggesting that the cells were able to "sense" that the hydrophobic surfaces were more favorable for settlement. The results are discussed in relation to the attachment of microorganisms to substrata having different wettabilities.

Cell Adhesion↗
PubMed1999

Phosphate release and heavy metal accumulation by biofilm-immobilized and chemically-coupled cells of a Citrobacter sp. pre-grown in continuous culture.

A heavy metal-accumulating Citrobacter sp. was grown in carbon-limiting continuous culture in an air-lift fermentor containing raschig rings as support for biofilm development. Planktonic cells from the culture outflow were immobilized in parallel on raschig rings by chemical coupling (silanization), for quantitative comparison of phosphatase activity and uranyl uptake by both types of immobilized cell. The flow rate giving 50% conversion of substrate to product (phosphate) in flow-through reactors was higher, by 35-40%, for the biofilm-immobilized cells, possibly exploiting a pH-buffering effect of inorganic phosphate species within the extracellular polymeric material. Upon incorporation of uranyl ions (0.2 mM UO22+), both types of cell removed more than 90% of the input UO22+ at slow flow rates, but the chemically-coupled cells performed better at higher flow rates. The deposited material (HUO2PO4) subsequently removed Ni2+ from a second flow via intercalative ion exchange of Ni2+ into the crystalline HUO2PO4.4H2O lattice. This occurred irrespective of the method of coupling of the biomass to the support and suggested that uranyl phosphate accumulated by both types of cell has potential as a bio-inorganic ion exchanger-a potential use for the uranium recoved from primary waste treatment processes.

Animals↗
PubMed1998

Fungal volatilization of arsenic and antimony and the sudden infant death syndrome.

Fungal volatilization of antimony and other group Vb elements has been proposed to have a causal role in the sudden infant death syndrome (SIDS; cot death). The ability of fungi to produce volatile arsenic and antimony compounds in pure culture was examined using Scopulariopsis brevicaulis, reported as an inhabitant of PVC cot mattress covers, and Phaeolus schweinitzii, a wood decay fungus known to be a good volatilizer of arsenic. Volatile arsenic compounds were detected from all cultures grown on arsenic-supplemented media, but antimony volatilization was not reliably detected. Although antimony levels above the baseline sensitivity of the analytical technique were detected in four (out of 24) of the samples analyzed, the concentrations recorded were too low to be reliably interpreted as evidence for volatilization. Our results are discussed in relation to hypotheses regarding the causes of SIDS.

Antimony↗
PubMed1983

Fertilization in brown algae. V. Further investigations of lectins as surface probes.

The binding of FITC- (fluorescein isothiocyanate), Au- and 125I-labelled lectins (conA, RCA120 (Ricinus communis agglutinin, MW 120 000) and FBP (fucose-binding protein from Lotus tetragonobolus)) to gametes of Fucus serratus and their physiological effects on fertilization have been studied. Results indicate that eggs strongly bind FITC- and Au-labelled conA and RCA120, whilst FITC-FBP binds strongly to sperm. All three iodinated lectins bound to eggs but this was apparently non-specific and similar in magnitude to the binding of iodinated bovine serum albumin. The results suggested the possibility of two distinct types of lectin receptor on egg surfaces: non-specific, highly abundant receptors and less abundant, specific receptors, possibly locally aggregated. All three lectins inhibit fertilization, FBP being the most effective.

Eukaryota↗
PubMed1983

Fertilization in brown algae. IV. Appearance of sperm-specific antigens on fertilized eggs.

Flagella antigens from sperm of Fucus serratus have been used to raise antibodies in rabbits. The immunoglobulin G fraction inhibits fertilization with some degree of species specificity. The antigens detected on sperm are not present on unfertilized egg membranes, but appear after fertilization. The common antigens on the fertilized egg can be distinguished from the cell wall material that is also released on fertilization.

Epitopes↗
PubMed1979

Fertilization in brown algae. II. Evidence for lectin-sensitive complementary receptors involved in gamete recognition in Fucus serratus.

Fertilization in Fucus serratus is directly proportional to the number of sperm added, saturating at approximately 250 sperm per egg with an apparent Km of 120 sperm per egg. The effect of a range of lectins on fertilization has been tested. Preincubation of gametes with Con A and fucose-binding protein (FBP) inhibited fertilization. At low concentrations this was by specifically binding to eggs; at high concentrations pretreatment of either gametes inhibited fertilization probably due to cytotoxicity. Fertilization was not inhibited by simple sugar haptens, but polysaccharides containing fucosyl or mannosyl residues (yeast mannan, fucoidan, ascophyllan) inhibited fertilization by binding to sperm. Pretreatment of eggs with alpha-fucosidase or alpha-mannosidase was effective in inhibiting fertilization. All the results indirectly demonstrate that fertilization in Fucus serratus is based on an association between fucosyl- and mannosyl-containing ligands on the egg surface and specific carbohydrate-binding receptors on the sperm surface.

Carbohydrates↗
PubMed1978

The role of Golgi bodies in polysaccharide sulphation in Fucuszygotes.

The cell wall of 24-h zygotes of Fucus serratus is composed of 3 layers--an inner fibrillar layer (sulphated fucan), an outer fibrillar layer (alginic aicd/cellulose) and an exterior amorphous layer (sulphated fucan, alginic acid). The 2 layers containing sulphated fucan are preferentially thickened at the rhizoid pole. Light- and electron-microscope autoradiographic pulse-chase experiments on 22-h zygotes using 35SO2-(4) show the Golgi bodies to be the sites of fucan sulphation. The isolation and characterization of isolated Golgi-rich fractions from 22-h zygotes shows that the first detectable labelled macromolecule is associated with these fractions 2 min after addition of 35SO2-(4). The sulphate acceptor molecule has been partially characterized. 35S-APS and 35S-paps are detectable in the soluble fraction 0.5 min after addition of 35SO2-(4). The results are discussed in relation to other published work on the differentiation of Fucus embryos and on polysaccharide sulphation.

Autoradiography↗
PubMed1978

Fertilization in brown algae. I. SEM and other observations on Fucus serratus.

The cell wall secreted immediately following sperm entry into an egg can be visualized by the fluorescent dye Calcofluor white. Cell wall secretion precedes nuclear fusion by 10-20 min. SEM observations of the surface of unfertilized and fertilized eggs and sperm attachment to eggs are described. These results are discussed in relation to fertilization in sea urchins and the biochemical phenomena associated with egg-sperm recognition in Fucus.

Cell Wall↗