Barbara Wigglesworth-Cooksey

Influence of calcium and other cations on surface adhesion of bacteria and diatoms : A review

Association with a surface is an important aspect of survival for microorganisms in natural and manmade environments/Both bacteria and diatoms are involved in such associations. In many cases, this leads to surface fouling, which often results in surface deterioration and mechanical failure in industrial systems. We now know that microorganisms exploit many strategies to establish associations with surfaces. As in the case of other cellular processes, calcium ions seem to play an important role in adhesion of cells to surfaces. Calcium is involved in non‐specific interactions such as neutralization of the electrical double layer between cell and substratum surface as well as specific adhesive interactions that cannot be replaced by other cations. The unique properties of calcium ions promote both specific and non‐specific interactions with protein and polysaccha‐ride adhesin molecules at the cell surface. As important, but less well understood, calcium ions also influence the way microbial cells interact with different substrata.

Use of Fluorophore-Conjugated Lectins To Study Cell-Cell Interactions in Model Marine Biofilms

ABSTRACT Biofilms dominated by pennate diatoms are important in fields as diverse as ship biofouling and marine littoral sediment stabilization. The architecture of a biofilm depends on the fact that much of its mass consists of extracellular polymers. Although most illuminated biofilms in nature are dominated by phototrophs, they also contain heterotrophic bacteria. Given the close spatial association of the two types of organisms, cell-cell interaction is likely. Fluorophore-conjugated lectins were used to demonstrate the sites of the various extracellular polymers in three species of diatoms. Based on their lectin staining properties, the polymers in different species appeared to be similar, but their involvement in the process of attachment to a surface differed. In a coculture Pseudoalteromonas sp. strain 4 or its sterilized spent medium reduced the ability of Amphora coffeaeformis and Navicula sp. strains 1 and D to adhere, inhibited motility, and caused agglutination and eventually diatom cell lysis. Diatoms could be protected from the negative effects of the bacterial spent medium if d-galactose or mannan was included in the incubation medium. The active principle of the spent medium is probably a lectin/agglutinin that is able to bind to the extracellular polymers of the diatoms that are involved in adhesion and motility. Awareness of interactions of this type is important in the study of natural biofilms.

Can diatoms sense surfaces?: State of our knowledge

When pennate diatoms adhere they do so by the secretion of an adhesive polymer. By the use of chemosensing leading to directed motility as an analogous system, potential sources of extracellular signals for this secretion have been examined. Evidence has accumulated that sensing of simple sugars (D‐glucose, D‐mannose) involves specific receptors and a Ca2+ flux. The evidence is discussed in terms of a receptor‐controlled secretion model for diatom adhesion. Means by which surfaces may be sensed by diatoms are proposed. It may be possible to design antifoulant molecules that interfere with surface‐sensing by binding to chemosensory receptors.

Cell–cell and cell–surface interactions in an illuminated biofilm: Implications for marine sediment stabilization†

Most wetted surfaces that are illuminated support a population of phototrophs. The marine sediment is no exception and there the major component of the microphytobenthic population is diatoms. These organisms are credited with stabilizing the sediment against physical disturbance by virtue of the extracellular carbohydrate polymers that they elaborate. However, diatoms synthesize and secrete several carbohydrate polymers and it is not certain which of them is involved in the stabilization process. In order to investigate this, we have constructed small glass bead-filled flow through bioreactors to mimic marine sediments. The flow rate through the bioreactors was found to reflect the physical stability of the bead bed. Thus flow rate was measured as a function of diatom growth and the production of three operationally-defined polymers, i.e., those soluble in the medium, those soluble in 0.5 M NaHCO3 at 90 °C and those not soluble in either solvent (matrix polymer). Growth of the diatoms did not change the hydraulic conductivity of the bioreactors. For Amphora coffeaeformis, neither did the production of medium-soluble nor NaHCO3-soluble polymers. However, matrix polymer accumulation was directly correlated with a reduction in flow (regression coefficient R2 = 0.96) and stabilization against physical disturbance. Results with species of Navicula were not as clear. Both NaHCO3-soluble and matrix polymers were involved in producing the flow reduction. In the same manner we also measured the effect of Pseudoalteromonas haloplanktis growth on bead bed hydraulic conductivity and bead bed stability. Growing alone, no effect was found, but in co-culture with a single diatom species, the bacteria reduced the diatom effect on flow through the bioreactors seen earlier, however did not reduce the extent of their growth. Confocal scanning laser microscopy of beads colonized with diatoms alone, or diatoms in co-culture with bacteria, revealed that P. haloplanktis was able to inhibit diatom adhesion to the beads. When the bacteria were present there was less matrix polymer evident. We speculate that this interference with diatom metabolic activity was either the result of less matrix polymer synthesis, or its hydrolysis by the bacteria. The results are applicable to mixed species biofilms of this type on surfaces other than sediments.

Microelastic properties of minimally adhesive surfaces: A comparative study of RTV11™ and Intersleek elastomers™

A comparative study of two commercially available elastomers, RTV11™ and Intersleek™, has been conducted employing atomic force microscopy (AFM) and surface and bulk analysis techniques. The results confirmed the presence of CaCO3 (rhombohedral calcite) filler particles in RTV11 and revealed TiO2 (tetragonal rutile) and Fe3O4 (cubic magnetite) as filler particles in Intersleek formulation. Time-of-flight secondary ion mass spectroscopy (TOF-SIMS) depth profiling revealed average threshold depths of ∼100 nm for the onset of filler particles. Indentation curves obtained from AFM force-volume imaging demonstrated that the presence of these particles significantly alters the local elastic properties of the coating. While the particle-free, high-compliance regions followed Hertzian behavior to a reasonable approximation, the low-compliance domains, where the subsurface filler particles reside, showed a significant deviation from this model. The Hertzian model, applied to the particle-free regions, gave values ...

A Computer‐based image analysis system for biocide screening

A computer-based image analysis system that measures the behavioral response of the marine diatom Amphora coffeaeformis to potentially toxic challenges is described. At any one time the system is capable of measuring in a population of about 80 cells, changes in the number motile, their speed, direction, and if they are turning, their angular velocity and acceleration. Chemical compounds that interfere with the generation of energy, protein or glycoprotein synthesis, calcium homeostasis and cytoskeletal activity, change the motile behavior of the cell. A pre-requisite of motility is that the cells be attached to a substratum. It is proposed that the system, which requires only a 1-2 minute data collection period per replicate, could be used to screen for potential antifouling activity in chemical agents, and it is speculated that it could be used also for measuring the physicochemical interaction between attached motile organisms and their substratum, as well as in environment toxicology measurements.