Effects of Engineered Nanoparticles on the Assembly of Exopolymeric Substances from Phytoplankton

The unique properties of engineered nanoparticles (ENs) that make their industrial applications so attractive simultaneously raise questions regarding their environmental safety. ENs exhibit behaviors different from bulk materials with identical chemical compositions. Though the nanotoxicity of ENs has been studied intensively, their unintended environmental impacts remain largely unknown. Herein we report experimental results of EN interactions with exopolymeric substances (EPS) from three marine phytoplankton species: Amphora sp., Ankistrodesmus angustus and Phaeodactylum tricornutum. EPS are polysaccharide-rich anionic colloid polymers released by various microorganisms that can assemble into microgels, possibly by means of hydrophobic and ionic mechanisms. Polystyrene nanoparticles (23 nm) were used in our study as model ENs. The effects of ENs on EPS assembly were monitored with dynamic laser scattering (DLS). We found that ENs can induce significant acceleration in Amphora sp. EPS assembly; after 72 hours EN-EPS aggregation reached equilibrium, forming microscopic gels of ∼4–6 µm in size. In contrast, ENs only cause moderate assembly kinetic acceleration for A. angustus and P. tricornutum EPS samples. Our results indicate that the effects of ENs on EPS assembly kinetics mainly depend on the hydrophobic interactions of ENs with EPS polymers. The cycling mechanism of EPS is complex. Nonetheless, the change of EPS assembly kinetics induced by ENs can be considered as one potential disturbance to the marine carbon cycle

The influence of surface chemistry on the control of cellular behavior:studies with a marine diatom and a wettability gradient

The marine diatom Amphora coffeaeformis is involved in biofilm formation on most illuminated marine surfaces, including ships and sediment particles. In sediments, cells of Amphora attach to sand particles and cause them to bind together. Although studies of the adhesion of diatoms to substrata as a function of differential surface chemistries have been published, none of these have used substrata where the differential surface properties are generated by the spatial packing of a single chemical of moiety. In this study, gradients of wettability on glass surfaces are generated by the relative proximity of covalently-bound methyl groups. Amphora is not motile on surfaces where the water contact was greater than 40 degrees, although cells do attach to these surfaces. Also, it appears that diatoms can increase the wettability of a surface during the course of an experiment. Furthermore, evidence is presented that Amphora produces a factor that causes dispersal of cells over a surface. Measurement of the speed of diatoms on a surface gives a good indication of the ability of the cell motility polymer to interact with that surface. (C) 1999 Elsevier Science B.V. All rights reserved

Time of FLight-Secondary Ion Mass Spectrometry on isolated extracellular fractions and intact biofilms of three species of benthic diatoms

Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS) was used to study compositional characteristics of Extracellular Polymeric Substances (EPS) and compared these to characteristics of the EPS-matrix of intact diatom biofilms. Three benthic diatoms species were investigated, Cylindrotheca closterium, Navicula mutica and Nitzschia cf. brevissima. Comparison of the ToF-SIMS spectra of sequentially extracted EPS-fractions by cluster analysis and multidimensional scaling analysis (MDS) indicated that soluble and bound EPS were not distinguishable based on their ion spectra. On the contrary the water insoluble bicarbonate soluble (WIBS)-EPS-fraction formed a distinct cluster showing that this material was compositionally different from the other EPS-fractions. Ion spectra of the EPS-fractions were dissimilar to results obtained from intact biofilms. This suggested that during the extraction procedure, the structure of the EPS irreversibly changed, which alters the fragmentation patterns of the extracellular surface layer. Furthermore, from the examination of the positive ion spectra it was shown that the overall composition of EPS in the intact biofilms was different between diatom species. In spite of these differences, several common peak patterns were shared between different species. This suggests the presence of common structural components in the EPS of these diatoms that may play a role in building the surface EPS-layer. [KEYWORDS: ToF-SIMS ; Benthic diatoms ; Extracellular polymeric substances ; EPS ; Biofilm

Time of FLight-Secondary Ion Mass Spectrometry on isolated extracellular fractions and intact biofilms of three species of benthic diatoms

Time of Flight-Secondary Ion Mass Spectrometry (ToF-SIMS) was used to study compositional characteristics of Extracellular Polymeric Substances (EPS) and compared these to characteristics of the EPS-matrix of intact diatom biofilms. Three benthic diatoms species were investigated, Cylindrotheca closterium, Navicula mutica and Nitzschia cf. brevissima. Comparison of the ToF-SIMS spectra of sequentially extracted EPS-fractions by cluster analysis and multidimensional scaling analysis (MDS) indicated that soluble and bound EPS were not distinguishable based on their ion spectra. On the contrary the water insoluble bicarbonate soluble (WIBS)-EPS-fraction formed a distinct cluster showing that this material was compositionally different from the other EPS-fractions. Ion spectra of the EPS-fractions were dissimilar to results obtained from intact biofilms. This suggested that during the extraction procedure, the structure of the EPS irreversibly changed, which alters the fragmentation patterns of the extracellular surface layer. Furthermore, from the examination of the positive ion spectra it was shown that the overall composition of EPS in the intact biofilms was different between diatom species. In spite of these differences, several common peak patterns were shared between different species. This suggests the presence of common structural components in the EPS of these diatoms that may play a role in building the surface EPS-layer. [KEYWORDS: ToF-SIMS ; Benthic diatoms ; Extracellular polymeric substances ; EPS ; Biofilm]

Algal Species and Light Microenvironment in a Low-pH, Geothermal Microbial Mat Community

Unicellular algae are the predominant microbial mat-forming phototrophs in the extreme environments of acidic geothermal springs. The ecology of these algae is not well known because concepts of species composition are inferred from cultivated isolates and microscopic observations, methods known to provide incomplete and inaccurate assessments of species in situ. We used sequence analysis of 18S rRNA genes PCR amplified from mat samples from different seasons and different temperatures along a thermal gradient to identify algae in an often-studied acidic (pH 2.7) geothermal creek in Yellowstone National Park. Fiber-optic microprobes were used to show that light for algal photosynthesis is attenuated to <1% over the 1-mm surface interval of the mat. Three algal sequences were detected, and each was present year-round. A Cyanidioschyzon merolae sequence was predominant at temperatures of ≥49°C. A Chlorella protothecoides var. acidicola sequence and a Paradoxia multisita-like sequence were predominant at temperatures of ≤39°C

Intracellular versus extracellular iron accumulation in freshwater periphytic mats across a mine water treatment lagoon

Despite the importance of periphyton–metal interactions in bioremediation schemes and in phosphorus (P) cycling, the processes controlling metal accumulation in periphytic mats are still poorly understood. Iron (Fe) accumulation in periphytic mats was examined across a Fe settlement lagoon receiving mine drainage in Scotland, UK, between March and June 2008. Quantification and mapping of intracellular and extracellular Fe concentrations in periphyton samples using scanning electron microscopy–energy dispersive spectroscopy suggested that Fe accumulation was dominated by the association of Fe-rich precipitates with the extracellular polymeric substances matrix, rather than biotic uptake. Intracellular Fe concentrations were significantly higher in periphyton samples exposed to the highest dissolved Fe concentrations. Neither intracellular nor extracellular Fe concentrations were significantly affected by light availability or cell density. While diatoms dominated the periphyton communities there was no significant association of diatom functional groups with Fe accumulation, indicating that community composition may not affect the function of periphytic mats with respect to Fe removal. Scale-up calculations based on the mean measured Fe accumulation rate by periphyton substrates of 0.021 g m−2 day−1 showed that exposure of large surface areas of periphyton substrate in the settlement lagoon would only increase the Fe removal efficiency of the lagoon by c.1%