René Peter Schneider

Chemical defenses of seaweeds against microbial colonization

Any living or non-living surface immersed in seawaterrapidly acquires a bacterial biofilm. For living marineorganisms, biofilm formation can result in the death ofthe host, and thus there is strong evolutionary pressure formarine eukaryotes to evolve mechanisms which inhibit orcontrol the development of biofilms on their surfaces.Some marine eukaryotes are indeed successful incontrolling biofilms on their surfaces, and in manyinstances this control is achieved by the production ofinhibitory chemicals which act at or near the surface ofthe organism. In some cases these natural inhibitors aresimply toxic to bacteria. However, increasingly it appearsthat at least some of these compounds act by interferingspecifically with bacterial characteristics which effect theability of bacteria to colonize their hosts, such asattachment, surface spreading, or the production ofextracellular macromolecules. As an example, theAustralian seaweed Delisea pulchra appears tocontrol bacterial colonization by interfering with abacterial regulatory system (the acylated homoserinelactone system) that regulates several colonizationrelevant bacterial traits. Understanding how marineorganisms control specific bacterial colonization traitsshould provide us with insights into new technologies forthe control of biofilms on artificial surfaces.

Retention of the Gramnegative marine bacterium SW8 on surfaces — effects of microbial physiology, substratum nature and conditioning films

Abstract The effect of films of organic compounds, the conditioning films (CF), adsorbed to the inanimate substrata stainless steel, germanium, polypropylene and perspex on retention of either the carbon (acetate)- or nitrogen (ammonia)-limited nonmotile Gram-negative marine bacterium SW8 was investigated. CF were deposited from marine or freshwater aquatic samples and from solutions containing bovine serum albumin, myoglobin, lactoglobulin or humic acids. SW8 was exposed to both “clean” and CF-coated test substrata in laminar fluid flow chambers for 10 min. CF modified attachment of SW8 relative to clean substrata in 70% of the cases. The following categories of CF were observed: (i) CF that appeared to control retention of SW8 irrespective of the type of substratum; (ii) CF that either increased or decreased the retention of SW8 on all substrata without altering the relative order of retention on the substrata and (iii) CF that affected retention of SW8 in an apparently substratum-specific manner. When retention of the two phenotypes differed, carbon-limited SW8 attached in higher numbers than nitrogen-limited SW8. No correlation was found between water contact angles on either “clean” or CF-coated substrata and retention of cells. In some experiments, SW8 was retained in aggregates. Such aggregation predominated on hydrophobic substrata, with nitrogen-limited organisms and on materials coated with CF from environmental waters. No difference in hydrophobicity or surface charge was found between the two physiologically different states of the organism. The ecological implications of these results and possible mechanisms of interactions of organisms with CF-coated substrata are discussed.

Bacterial adhesion to solid substrata coated with conditioning films derived from chemical fractions of natural waters

Dissolved organic carbon from seawater and freshwater was separated into hydrophilic-base, hydrophilic-neutral, hydrophilic-acid as well as hydrophobic-base, hydrophobic-neutral, and hydrophobic-acid fractions which were used to form conditioning films on hydrophilic stainless steel and aluminium as well as on hydrophobic polypropylene and perspex. Water contact angles indicated that every conditioning film modified the wettability of clean substrata; the wettability of hydrophobic surfaces was generally increased and that of hydrophilic surfaces decreased. Adhesion results with carbon- and nitrogen-limited phenotypes of the Gram-negative bacterium SW8 suggested that adhesive or abhesive components of conditioning films were not associated with particular chemical fractions. The proportion of conditioning films derived from water fractions which modified the attachment of carbon-limited SW8 on hydrophobic and hydrophilic substrata was 29 and 71 %, respectively. These films generally reduced the number of ...

The relevance of X-ray photoelectron spectroscopy for analysis ofmicrobial cell surfaces: a critical view

Abstract X-ray photoelectron spectroscopy (XPS) has been employed by a number of investigators to study the surface chemistry of a variety of microorganisms. The purpose of this presentation is to examine the basis of the technique in terms of its applicability to living microorganisms. Because XPS must be carried out under conditions of high vacuum, it is necessary to remove free water from the specimens prior to analysis. This is achieved by freeze drying the specimens suspended in distilled water before insertion in the instrument. What does this do to the surface integrity of the microorganisms? A number of steps in the process of preparing microorganisms for XPS examination may lead to the introduction of artefacts in the estimation of surface properties. These include the choice of organism, the growth conditions employed, the centrifugation of the cell suspension, the resuspension of the cells in distilled water, the freezing and drying processes, the ultrahigh vacuum conditions employed in XPS and the possibility of X-ray damage to surface structures on the cells. Some of these processes may result in the leakage of internal cellular components or even to complete lysis of the cells prior to XPS examination, with major problems resulting from the adsorption to intact cell surfaces of released macromolecules. Reports of good correlations between XPS characterisation of surfaces and other measured physical parameters need to be regarded with caution, because most of these surface analytical techniques only provide a net value, but no indication of localisation, for the cell surface property in question. Such potential errors may be vital in considerations of the interactions between the organisms and solid substrata.

The effect of growth conditions on survival and recovery of Klebsiella oxytoca after exposure to chlorine

A strain of Klebsiella oxytoca isolated from within Sydneys water distribution system was grown under a range of physiological conditions including batch cultures and continuous culture under both carbon and nitrogen limitation. Cells were then exposed to varying concentrations of total chlorine. The initial growth conditions affected the ability of cells to survive. Cells grown under batch conditions in a medium containing mineral salts and yeast extract were the most resistant. The resistance to chlorine was not related to the presence of polysaccharide or differences in protein levels but to the formation of aggregates. The initial growth conditions also influenced the recovery of cells after the removal of chlorine stress.

Comparative analysis of thermodynamic approaches and diagnostic liquids for determination of contact angle-derived physicochemical parameters of solids coated with conditioning films: A practitioner's perspective

The equation of state (ES), the Lifshitz-van der Waals acid-base approach (LWAB), and the geometric mean equation (GME) were evaluated for calculation of physicochemical parameters from contact angles of the four diagnostic liquids: water (w), formamide (f), α-bromonaphthalene (α-br), and diiodomethane (di) measured on clean and conditioning film-coated substrata (stainless steel, germanium, polypropylene, perspex). Surface free energy and its components (dispersive and polar components in GME, as well as Lifshitz-van der Waals, electron-donor and electron-acceptor components in LWAB) were assessed in all approaches with all liquid combinations possible. The Gram-negative bacterium SW8 grown under carbon-limited conditions was used to calculate the solid-bacterium interfacial free energy and the free energy of adhesion of SW8 to solid substrata. These two parameters and the solid-liquid interfacial free energy were calculated only for combinations of diagnostic liquids that included water contact angles. ...

Modification of substratum physicochemistry by material adsorbed from groundwater—analysis by contact angles and relevance to microbial adhesion

Stainless steel, polypropylene, shale, and andesite were coated with films derived from shallow (5–13 m) and deep (35–65 m) groundwaters representing a cross section through a fractured bedrock aquifer. Contact angles of water, formamide, and di‐iodomethane measured on clean and conditioned interfaces were used to calculate physicochemical surface properties by the Lifshitz‐van der Waals acid‐base approach. Interfacial parameters were also determined for the interaction of carbon‐limited cells of the Gram‐negative bacterium SW8 with these surfaces. The alteration of surface free energy attributable to conditioning films was generally moderate, as was their impact on the Lifshitz‐van der Waals component of surface free energy. Most coatings did, however, significantly modify the acid‐base components of surface free energy of both hydrophilic and hydrophobic substrata, and the substratum‐water and the bacterium‐water interfacial tensions, as well as the free energy of adhesion of bacteria to substrata. The ...

Use of Fluorescent Lectin Probes for Analysis of Footprints from Pseudomonas aeruginosa MDC on Hydrophilic and Hydrophobic Glass Substrata

ABSTRACT Microbial footprints of Pseudomonas aeruginosa MDC attached for 1 h to clean or silanized glass were analyzed with fluorescently labeled lectin probes. Footprint composition varied, depending on cell physiology and substratum surface chemistry. This suggests that substratum physicochemistry affected the structure of cell surfaces of adsorbed organisms.

Evidence for the contribution of humic substances to conditioning films from natural waters.

The presence of humic substances in conditioning films deposited on solid surfaces from natural waters was investigated using electron impact (EI), chemical ionization (CI) and secondary ion time‐of‐flight mass spectrometry (TOFSIMS). EI and CI spectra of a freshwater sample from a pond in Centennial Park, Sydney, Australia, showed a high degree of similarity with spectra of humic acids purchased from Fluka and Sigma as well as with reference humic acid and fulvic acid from the International Humic Substances Society, suggesting that most of the organic matter in the pond water was of humic origin. All the complex electron impact mass spectra feature series of high‐intensity ions separated by 14 Da or 18 Da, which can be attributed to CH2 and OH2 respectively. Thermal desorption profiles of all samples generated by EI and CI were qualitatively similar. The secondary desorption peaks were less well‐defined in CI compared to EI. Positive ion thermal desorption profiles displayed a two‐step ionisation, with a sharp and well‐defined initial desorption peak at t∼50s, followed by a broader desorption peak with a maximum intensity at t ∼ 100 s post‐heating. The Centennial Park natural organic matter (NOM) differed from the other humic fractions in having two additional broad desorption peaks between the two described previously, and a less‐defined initial peak. Infrared spectroscopy showed that proteinaceous matter in the lake water was insignificant in comparison with functional groups indicative of humic substances. TOFSIMS characterization showed almost identical spectra for Aldrich humic acid and Centennial Park NOM in the high mass region of 2000 Da to 3000 Da. Each spectrum contains approximately 25 groups of ion peaks, separated by 74 Da from group to group. Each group is composed of 6 or 7 individual peaks. The spectral features are consistent with a macromolecular structure of humic acid where aromatic rings are joined to the macrostructure via aliphatic spacer molecules.