Gill G. Geesey

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.

The influence of welding procedures on bacterial colonization of stainless steel weldments

The US food processing industry requires that food contact stainless steel surfaces have a No. 4 surface finish, with welds having a surface finish equivalent to the parent plate. To meet this standard, most welds must be ground and polished, which significantly increases the cost of fabrication. Two laboratories have independently compared colonization of seven plasma arc welds, not subjected to grinding and polishing by either the human pathogen Listeria monocytogenes, or a 3-member bacterial consortium containing Flavobacterium spp. that were isolated from weldments in a seafood processing plant. Bacteria did not appear to preferentially colonize the surface of welds over that of adjacent parent 304L stainless steel with a 2B finish (equivalent to No. 4). The results suggest that the current practice of grinding and polishing welds to achieve a No. 4 surface finish that meets current food industry roughness standards may have no significant influence on short-term bacterial accumulation.

Development of an artificial biofilm to study the effects of a single microcolony on mass transport

Alginate harvested from a mucoid strain of Pseudomonas aeruginosa, grown on YTG agar plates, was used to develop an artificial biofilm. The alginate was sterilized and fixed to a glass slide where it served as the biofilm matrix. High densities of P. aeruginosa were injected into specific locations within the alginate matrix to represent microcolonies similar to those found in natural biofilms. Dissolved oxygen microelectrodes, with tip diameters of 10 μm, were constructed and used to measure oxygen profiles through the artificial biofilm. Using mathematical models the kinetic parameters for microbial respiration were extracted from the profiles. The activity of immobilized microorganisms was monitored and the dynamics of dissolved oxygen transport to a single microcolony was evaluated.

Polysaccharide-specific probes inhibit adhesion of Hyphomonas rosenbergii strain VP-6 to hydrophilic surfaces

Biofilm formation commences with the adhesion of microorganisms to surfaces. Information regarding the initial bond between a bacterium and a solid surface is essential for devising methods to inhibit the onset of biofilm formation. Three different types of polysaccharide-specific probes, cationic metals, dyes, and lectins, were used to bind the exopolysaccharide of Hyphomonas rosenbergii, a budding, prosthecate marine bacterium. Probes, which specifically bind complex carbohydrates, inhibit the adhesion of H. rosenbergii to hydrophilic surfaces. These results suggest that the polysaccharide portion of H. rosenbergii capsular, extracellular polymeric-substance is involved in the primary adhesion process. Journal of Industrial Microbiology & Biotechnology (2000) 25, 81–85.

Influence of protein conditioning films on binding of a bacterial polysaccharide adhesin from Hyphomonas MHS-3.

A putative polysaccharide adhesin which mediates non-specific attachment of Hyphomonas MHS-3 (MHS-3) to hydrophilic substrata has been isolated and partially characterized. A polysaccharide-enriched portion of the extracellular polymeric substance (EPS(P)) from MHS-3 was separated into four fractions using high performance size exclusion chromatography (HPSEC). Comparison of chromatograms of EPS(P) from MHS-3 and a reduced adhesion strain (MHS-3 rad) suggested that one EPS(P) fraction, which consisted of carbohydrate, served as an adhesin. Adsorption of this fraction to germanium (Ge) was investigated using attenuated total reflection Fourier transform infrared (ATR/FT-IR) spectrometry. Binding curves indicated that the isolated fraction had a relatively high affinity for Ge when ranked against an adhesive protein from Mytilis edulis, mussel adhesive protein (MAP) and an acidic polysaccharide (alginate from Macrocystis pyrifera). Spectral features were used to identify the fraction as a polysaccharide previously reported to adsorb preferentially out of the EPS(P) mixture. Conditioning the Ge substratum with either bovine serum albumin (BSA) or MAP decreased the adsorption of the adhesive polysaccharide significantly. Conditioning Ge with these proteins also decreased adhesion of whole cells.

Adhesive extracellular polymers of hyphomonas MHS‐3: Interaction of polysaccharides and proteins

The adsorption behavior of extracellular polymeric substances (EPS) from the marine bacterium Hyphomonas MHS‐3 was investigated using attenuated total reflection Fourier transform infrared (ATR/FT‐IR) spectrometry. The protein fraction of the crude EPS (EPSC) (propanol precipitated/extracted with EDTA) dominated the adsorption onto the germanium substratum. Removal of the Protease K accessible portion of the EPSC protein, and treatment with RNase and DNase, yielded a hygroscopic substance (EPSP) which contained at least one adhesive polysaccharide component. Conditioning the substratum with EPSC diminished adsorption of the polysaccharide fractions in EPSP; pre‐adsorbed EPSC protein was not displaced. The rate of EPSC adsorption on substrata conditioned with EPSP was slower than to clean germanium; however, the projected surface coverage of protein after long times, based on an empirical datafit, was the same as that for a clean substratum; the EPSC proteins did not displace the pre‐adsorbed adhesive poly...

Adhesion of biofilms to inert surfaces: A molecular level approach directed at the marine environment

Protein/ligand interactions involved in mediating adhesion between microorganisms and biological surfaces have been well-characterized in some cases (e.g. pathogen/host interactions). The strategies microorganisms employ for attachment to inert surfaces have not been so clearly elucidated. An experimental approach is presented which addresses the issues from the point of view of molecular interactions occurring at the interface.

FINAL REPORT - Biogeochemistry of Uranium Under Reducing and Re-oxidizing Conditions:An Integrated Laboratory and Field Study and Acceptable Endpoints for Metals and Radionuclides: Quantifying the Stability of Uranium and Lead Immobilized Under Sulfate Reducing Conditions

Our understanding of subsurface microbiology is hindered by the inaccessibility of this environment, particularly when the hydrogeologic medium is contaminated with toxic substances. Research in our labs indicated that the composition of the growth medium (e.g., bicarbonate complexation of U(VI)) and the underlying mineral phase (e.g., hematite) significantly affects the rate and extent of U(VI) reduction and immobilization through a variety of effects. Our research was aimed at elucidating those effects to a much greater extent, while exploring the potential for U(IV) reoxidation and subsequent re-mobilization, which also appears to depend on the mineral phases present in the system. In situ coupons with a variety of mineral phases were placed in monitoring wells at the NABIR FRC. These coupons showed that the mineral phase composition significantly affected the resulting attached phase microbial community. Our comparative use of both batch and open flow reactors (more representative of field conditions) indicates that hydrodynamics and continual influx of substrate and contaminants can also yield significantly different results than those obtained with closed serum bottles. To this end, the following overall experimental hypothesis tested was the following: On a mineral surface under anaerobic conditions, accumulations of secondary inorganic precipitates are controlled by a) themorexa0» bacteria associated with the mineral surface, b) the electron acceptors available for anaerobic bacterial respiration, and c) local hydrodynamics and pH buffers govern micro- and meso-scale interaction of U in the presence of electron donors and acceptors, and nutrients.«xa0less

MICROBIALLY PROMOTED SOLUBILIZATION OF STEEL CORROSION PRODUCTS AND FATE OF ASSOCIATED ACTINIDES

Microorganisms have the capacity to modify iron oxides during anaerobic respiration. When the dissimilatory sulfate-reducing bacterium Desulfovibrio desulfuricans G20 respires soluble sulfate during colonization of the solid-phase iron oxide hematite, the sulfide product reacts with the iron to produce the insoluble iron sulfide, pyrrhotite. When soluble uranium is present as uranyl ion, these microorganisms reduce the U(VI) to U(IV) as insoluble uraninite on the hematite surface. There is also evidence that a stable form of U is produced under these conditions that displays an oxidation state between U(VI) and U(iv). The dissimilatory iron reducing bacterium, Shewanella oneidensis MR1 can utilize insoluble hematite as the sole electron acceptor for anaerobic respiration during growth and biofilm development on the mineral. The growth rate, maximum cell density and detachment rate for this bacterium are significantly greater on hematite than on magnetite (111) and (100). The difference could not be attributed to iron site density in the iron oxide. A gene (ferA) encoding a c-tyoe cytochrome involved in dissimulatory iron reduction in the bacterium Geobacter sulfurreducens was completed sequenced and characterized. The sequence information was used to develop an in-situ reverse transcriptase polymerase chain reaction assay that could detect expression of the gene during growth and biofilm development on ferrihydrite at the single cell and microcolony level. X-ray photoelectron spectroscopic analysis revealed that the ferrihydrite was reduced during expression of this gene. The assay was extended to detect expression of genes involved in sulfate reduction and hydrogen reduction in sulfate-reducing bacteria. This assay will be useful to assess mechanisms of biotransformation of minerals including corrosion products on buried metal containers containing radionuclide waste. In summary, the research has shown that dissimilatory sulfate and iron reducing bacteria can modify the iron oxide surfaces that they colonize and promote the reduction and precipitation of actinides such as uranium at these sites