Roberta Congestri

Optical properties of diatom nanostructured biosilica in Arachnoidiscus sp: micro-optics from mother nature.

Some natural structures show three-dimensional morphologies on the micro- and nano- scale, characterized by levels of symmetry and complexity well far beyond those fabricated by best technologies available. This is the case of diatoms, unicellular microalgae, whose protoplasm is enclosed in a nanoporous microshell, made of hydrogenated amorphous silica, called frustule. We have studied the optical properties of Arachnoidiscus sp. single valves both in visible and ultraviolet range. We found photonic effects due to diffraction by ordered pattern of pores and slits, accordingly to an elaborated theoretical model. For the first time, we experimentally revealed spatial separation of focused light in different spots, which could be the basis of a micro-bio-spectrometer. Characterization of such intricate structures can be of great inspiration for photonic devices of next generation.

Capsular polysaccharides of cultured phototrophic biofilms.

Phototrophic biofilm samples from an Italian wastewater treatment plant were studied in microcosm experiments under varying irradiances, temperatures and flow regimes to assess the effects of environmental variables and phototrophic biomass on capsular exopolysaccharides (CPS). The results, obtained from circular dichroism spectroscopy and High Performance Liquid Chromatography, suggest that CPS have a stable spatial conformation and a complex monosaccharide composition. The total amount present was positively correlated with the biomass of cyanobacteria and diatoms, and negatively with the biovolume of green algae. The proportion of uronic acids showed the same correlation with these taxon groups, indicating a potential role of cyanobacteria and diatoms in the removal of residual nutrients and noxious cations in wastewater treatment. While overall biofilm growth was limited by low irradiance, high temperature (30°C) and low flow velocity (25 l h−1) yielded the highest phototrophic biomass, the largest amount of CPS produced, and the highest proportion of carboxylic acids present.

Shedding light on diatom photonics by means of digital holography

Diatoms are among the dominant phytoplankters in the worlds oceans, and their external silica investments, resembling artificial photonic crystals, are expected to play an active role in light manipulation. Digital holography allowed studying the interaction with light of Coscinodiscus wailesii cell wall reconstructing the light confinement inside the cell cytoplasm, condition that is hardly accessible via standard microscopy. The full characterization of the propagated beam, in terms of quantitative phase and intensity, removed a long-standing ambiguity about the origin of the light confinement. The data were discussed in the light of living cell behavior in response to their environment.

Dynamics of Dinophysis sensu lato species (Dinophyceae) in a coastal Mediterranean environment (Adriatic Sea)

Species of Dinophysis Ehrenberg sensu lato were collected opportunistically along the southern Adriatic coasts (Apulia, Italy) during a survey of phytoplankton community structure and dynamics carried out from 1995 to 1997. Most previous reports of Dinophysis spp. in the Adriatic Sea concentrated on northern populations, with few data available on phytoplankton inhabiting the southern coastal areas. Thus, the present study is the first on Dinophysis sensu lato species composition and spatio-temporal distribution in these essentially oligotrophic waters. Twelve Dinophysis species were identified; some of which can be assigned to the genus Phalacroma. Dinophysis sacculus, D. fortii, D. caudata, Phalacroma rotundatum and P. mitra are potentially producers of diarrhetic shellfish poisoning. Seasonal changes in Dinophysis and Phalacroma populations are presented, as well as their relationships with hydrographic and biotic factors. These dinoflagellates were associated with mixing conditions, low water temperatures and high nutrient inputs. Furthermore, the statistical analysis evidenced significant correlations of Dinophysis species to chlorophyll a and phytoplankton. Ecological implications arising from the data are discussed

Electronic tongue for microcystin screening in waters.

The potentiometric E-tongue system was employed for water toxicity estimation in terms of cyanobacterial microcystin toxins (MCs) detection. The data obtained from E-tongue were correlated to the MCs content detected by the standard chromatographic technique UHPLC-DAD (Ultra High Performance Liquid Chromatography with Diode Array Detector), as far as by the colorimetric enzymatic approach. The prediction of MCs released by toxic Microcystis aeruginosa strains was possible with Root Mean Squared Error of Validation (RMSEV) lower or very close to 1µg/L, the provisional guideline value of WHO for MCs content in potable waters. The application of E-tongue system opens up a new perspective offset for fast and inexpensive analysis in the field of environmental monitoring, offering also the possibility to distinguish toxin producing and non-toxic M. aeruginosa strains present in potable water.

Phosphorus removal coupled to bioenergy production by three cyanobacterial isolates in a biofilm dynamic growth system

ABSTRACT In the present study a closed incubator, designed for biofilm growth on artificial substrata, was used to grow three isolates of biofilm-forming heterocytous cyanobacteria using an artificial wastewater secondary effluent as the culture medium. We evaluated biofilm efficiency in removing phosphorus, by simulating biofilm-based tertiary wastewater treatment and coupled this process with biodiesel production from the developed biomass. The three strains were able to grow in the synthetic medium and remove phosphorus in percentages, between 6 and 43%, which varied between strains and also among each strain according to the biofilm growth phase. Calothrix sp. biofilm turned out to be a good candidate for tertiary treatment, showing phosphorus reducing capacity (during the exponential biofilm growth) at the regulatory level for the treated effluent water being discharged into natural water systems. Besides phosphorus removal, the three cyanobacterial biofilms produced high quality lipids, whose profile showed promising chemical stability and combustion behavior. Further integration of the proposed processes could include the integration of oil extracted from these cyanobacterial biofilms with microalgal oil known for high monounsaturated fatty acids content, in order to enhance biodiesel cold flow characteristics.

DIATOMS (BACILLARIOPHYTA) IN PHOTOTROPHIC BIOFILMS COLONISING AN ITALIAN WASTEWATER TREATMENT PLANT

The diatom assemblages within phototrophic biofilms in secondary treatment tanks of the Fiumicino Airport (Rome, Italy) wastewater treatment plant were investigated. Qualitative and quantitative comparisons were made between assemblages in sedimentation and chlorination tanks, on the tank walls and artificial substrata, on four sampling occasions. The assemblages were characterised by a rather stable species composition, low species diversity and dominance of raphid taxa. Correspondence analysis of diatom relative abundance data with regard to seasonal, site and substratum variation revealed both temporal and spatial differences in species assemblages. Rather than species composition changing over time between different sampling sites and surfaces, the proportional contributions of individual species to the assemblages varied with season. Biovolume data indicated that this outdoor system supported extensive diatom growth (high diatom biomass productivity). The potential use of autochthonous, diatom biofilms in tertiary wastewater treatment (removal of residual nutrients and pollutants) as opposed to conventional physico-chemical technologies is discussed with respect to the protection of receiving water bodies and the development of sustainable waste treatment.

Light-induced changes in photosynthesis and structure of cyanobacterial cultured biofilms from an Italian wastewater treatment plant

The photosynthetic and light acclimation capability of phototrophic biofilms collected seasonally from the wastewater treatment plant (WWTP) of Fiumicino Airport (Rome, Italy) was tested in culture at different irradiance conditions. Photosynthesis versus Irradiance (P/I) curves were recorded on 15, 30 and 45 day aged communities and chlorophylls, carotenoids and phycobiliproteins quantified. Light microscopy observations were performed to evaluate inoculum species composition and taxonomic shifts over time in cultured biofilms. Phototrophs acclimated to different irradiances by varying the photosynthetic efficiency, maximum photosynthetic rate and pigment content. Community age and biomass variation also affected photosynthesis-light response. Marked shifts towards the prevalence of cyanobacteria were observed in summer and autumn biofilms kept at the highest experimental irradiances. Data indicated high productivity and acclimation potential of cultured phototrophic biofilms in view of their application for bioremediation technologies.

Polymer composite random lasers based on diatom frustules as scatterers

In this work the possibility to exploit the ability of multiple scattering and localization of light shown by diatom silica shells (frustules) for photoluminescence amplification in a random laser was investigated. To this aim polymethylmethacrylate matrix composite random lasers based on rhodamine B and frustules as gain medium and scatterers, respectively, were prepared by solvent casting. Two different kinds of frustules were used, the first represented by diatomite, a fossil material composed of a mixture of frustules from different diatom species, without specific shape, size and porosity; the second were living diatom frustules from freshwater biofilm, a more homogeneous biosilica, dominated by one frustule type. Chemical properties, morphology and photoluminescence of both biosilica fillers were investigated. Random laser experiments were carried out on polymer composites. The diatomite material was characterised by rectangular and circular pores, ranging from 25 nm to 1 μm in size and showed weak photoluminescence upon excitation at 405 nm. Biofilm frustules were more homogeneous in size and microstructure, with average length of about 20 μm and pore diameters between 20 and 100 nm. The frustule photoluminescence, observed after irradiation at 488, 515, 543 and 635 nm was higher than in diatomite. In addition, the two biosilica materials differed with respect to the presence of superficial silanol groups, that were not detected in diatomite. Random laser experiments showed an incoherent random lasing effect in all polymer composites. The laser threshold diminished at increasing frustule content, with a lowest value recorded using biofilm frustules (308 kW cm−2). This is probably due to the frustule size exhibited in this almost monospecific biosilica, that was in the range of most typical morphology-dependent resonators.

Cytomorphology and distribution of periphytic cyanobacteria in one Italian waste water treatment plant

Cyanobacterial species composition of periphytic community living in Fiumicino (Rome, Italy) Airport waste water treatment plant (WWTP) was followed over a two year period in the sedimentation and chlorination tanks. A total of 5 Chroococcalean and 12 Oscillatorialean species was identified. Spatio-temporal distribution of taxa was rather constant during the year, and only two filamentous species seemed to be affected by chlorine treatment. Chl a/Chl b and Chl a/Chl c ratios showed homogeneous distribution of cyanobacteria, diatoms and green algae within the biofilm. Nucleic acid arrangement inside the cells was evaluated using the fluorochrome DAPI. Calcofluor White and AO labelling also provided EPS localisation in epifluorescence. TEM techniques were used to observe ultrastructural features of taxa.