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Phototrophic microbial communities present in the Roman Catacombs were characterized and different species of terrestrial epilithic cyanobacteria were found to occur as dominant organisms. Eucapsis, Leptolyngbya, Scytonema, and Fischerella were the most frequently encountered cyanobacterial taxa, while a few species of green algae and the diatom Diadesmis gallica occurred in minor amounts. Streptomyces strains, a few genera of eubacteria, and to a lesser extent fungi were always present in the same microhabitats and contributed to the deterioration of stone surfaces. The combined use of light and electron microscopy evidenced the structural relationships among rodshaped or filamentous bacteria and cyanobacterial cells, as well as the presence of polysaccharide capsules and sheaths, and of mineral precipitates on S. julianum filaments. The significance of the intimate association among the microorganisms was discussed in relation to the damage caused by the growth of biological patinas on stone surfaces.

The ecophysiological, cytomorphological, biochemical and molecular data presently available for the acidophilic red algal species Cyanidium caldarium, Cyanidioschyzon merolae and Galdieria sulphuraria are summarised. The taxonomic position of the three genera is discussed and emendements to the generic diagnosis are presented.[PUBLICATION ABSTRACT]

The biological colonization of rocks in the Cave of Bats (Cueva de Los Murciélagos, Zuheros, Spain) was studied in order to reveal the diversity of microorganisms involved in the biofilm formation. The culturable, metabolically active fraction of biodeteriogens present on surfaces was investigated focusing on morphological, ultrastructural, and genetic features, and their presence related to the peculiar environmental conditions of the underground site. PCR-ITS analysis and 16S rDNA sequences were used to clusterize and characterize the isolated strains. The presence of bacterial taxa associated to the photosynthetic microflora and fungi within the biofilm contributed to clarify the relationships inside the microbial community and to explain the alteration observed at the different sites. These results will contribute to the application of more successful strategies for the preventive conservation of subterranean archaeological sites.

Although N2‐fixing cyanobacteria contribute significantly to oceanic sequestration of atmospheric CO2, little is known about how N2 fixation and carbon fixation (primary production) interact in natural populations of marine cyanobacteria. In a developing cyanobacterial bloom in the Baltic Sea, rates of N2 fixation (acetylene reduction) showed both diurnal and longer‐term fluctuations. The latter reflected fluctuations in the nitrogen status of the cyanobacterial population and could be correlated with variations in the ratio of acetylene reduced to 15N2 assimilated. The value of this ratio may provide useful information about the release of newly fixed nitrogen by a cyanobacterial population. However, although the diurnal fluctuations in N2 fixation broadly paralleled diurnal fluctuations in carbon fixation, the longer‐term fluctuations in these two processes were out of phase.

Cyanobacterial biofilms present on stone surfaces in Roman hypogea were studied with the aim of assessing their deteriogenic activity on the colonised substrata. In order to achieve this, non-destructive methods were developed and applied to measure pH variation induced via photosynthesis and respiration in representative cyanobacteria from Roman catacombs. Amperometric and potentiometric microsensors were also used on Scytonema biofilms in culture in order to measure photosynthesis and assess pH decreases and increases during dark-light periods. Measurements of pH showed that, starting with values slightly below neutral, the pH in Scytonema biofilms increased by 0.24-0.77 units in the transition from dark to 1000 mu mol photon m super(-2) s super(-1) irradiance. Comparison of photosynthesis and pH curves recorded simultaneously on the same artificial biofilm showed a maximum increase in pH value at irradiances higher than those saturating photosynthesis. Alkalinisation of the substrate during illumination occurred to a sufficient extent to induce precipitation of mineral compounds, especially on calcareous substrates such as those present in Roman hypogea.

Although N 2 ‐fixing cyanobacteria contribute significantly to oceanic sequestration of atmospheric CO 2 , little is known about how N 2 fixation and carbon fixation (primary production) interact in natural populations of marine cyanobacteria. In a developing cyanobacterial bloom in the Baltic Sea, rates of N 2 fixation (acetylene reduction) showed both diurnal and longer‐term fluctuations. The latter reflected fluctuations in the nitrogen status of the cyanobacterial population and could be correlated with variations in the ratio of acetylene reduced to 15 N 2 assimilated. The value of this ratio may provide useful information about the release of newly fixed nitrogen by a cyanobacterial population. However, although the diurnal fluctuations in N 2 fixation broadly paralleled diurnal fluctuations in carbon fixation, the longer‐term fluctuations in these two processes were out of phase.

The abundance and cellular location of Fe-containing superoxide dismutase (Fe-SOD) in trichomes of Nodularia, Aphanizomenon and Anabaena collected from various depths in the Baltic Sea, and in trichomes of a cultured Nodularia strain, BC Nod-9427, isolated from the Baltic Sea, was examined by immunogold labelling. For trichomes collected from natural populations the areal concentration of Fe-SOD labelling decreased with depth: trichomes collected from surface accumulations had between 8 and 11 gold particles μm−2 whereas trichomes collected from a depth of 18 m were unlabelled. When trichomes collected from a depth of 10 m (mean areal labelling density 0·5 gold particles μm−2) were exposed to the higher irradiances present at 1 m, the areal concentration of Fe-SOD increased to 3·5–4 gold particles μm−2 within 4 h. When cultures of Nodularia strain BC Nod-9427, adapted to low light (10 μmol m−2 s−1), were transferred to an incident irradiance of 1350 μmol m−2 s−1, a doubling of the areal concentration of Fe-SOD gold label was observed within 1 h. Addition of 3-(3,4-dichlorophenyl)-1,1′-dimethylurea (DCMU) to cultures immediately before their transfer to increased illumination resulted in a decrease in areal Fe-SOD concentrations whereas addition of CdCl2 caused an increase over and above that induced by the elevated irradiance. These results suggest that Baltic Sea cyanobacteria are able to modulate their Fe-SOD content but that this might be in response to oxidative stress rather than to light per se.

The crater lake Lake Albano is an increasingly diminishing water resource in terms of volume, the lake level has dropped more than four meters since the 1960s, and water quality resulting from elevated levels of nitrogen and phosphorus. The area of the lake, and the volcano as a whole, is also considered to be geologically hazardous due to continual shallow seismic activity, gaseous emissions and hydrothermal activity. Therefore, most research has been focussed on the geological aspects of the Albano lake system, whilst long-term limnological studies have been lacking. A meromictic classification was given to the lake, but this was based on one year studies of the surface water only. Presented and discussed are the results of a water chemistry and biological study of the full depth profile of Lake Albano from 2004 to 2008. During winter 2005-2006 the lake underwent a complete overturn, resulting in an influx of nutrient rich hypolimnetic water into the upper productive layers and oxygenated epilimnetic water into the deepest water layers. The effect of full overturn on the phytoplankton community is described and compared with those of meromictic years. The interplay between natural and anthropological processes on water quality and water usages is also discussed.