Drying of cells leads to damage resulting from crowding of cytoplasmic components, condensation of the nucleoid, increases in the Tm of membrane phase transitions, and imposition of stress upon cell walls. Prolonged desiccation leads to oxidation of proteins, DNA and membrane components through metal-dependent Fenton reactions, while Maillard reactions generate cross-linked products between the carbonyl groups of reducing sugars and the primary amines of nucleic acids and proteins. Although such damage restricts many organisms to aqueous environments, some, including many cyanobacteria, can tolerate the air-dried state for prolonged periods. Cyanobacteria in the Tintenstrich communities of exposed rock faces, Microcoleus and Lyngbya spp. in intertidal mats, chasmoendolithic Chroococcidiopsis spp. in the rocks of hot and cold deserts, and terrestrial epilithic crusts of Tolypothrix and Nostoc are examples that show a marked capacity to withstand the removal of their cellular water. For Nostoc commune, the mechanisms of desiccation tolerance reflect both simple and complex interactions at the structural, physiological and molecular levels.

If the depletion of the stratospheric ozone shield continues, the influx of solar UV-B radiation (280–320 nm) will increase in the near future. In photosynthetic organisms there are several targets for the deleterious UV-B radiation, such as proteins, DNA and membranes. Cyanobacteria use three different types of strategies to counteract UV damage: (i) stress avoidance by gliding mechanisms, (ii) stress defence by synthesis of UV-absorbing compounds, antioxidants and extracellular polysaccharides, and (iii) repair mechanisms including DNA repair and resynthesis of UV-sensitive proteins. In the past, most studies concentrated on the physiological aspects of UV tolerance whereas the molecular basis of UV tolerance in cyanobacteria is poorly understood. We will summarize the effects of and responses to UV-B at the physiological and molecular levels and present data on the influence of UV-B irradiation on the proteome of the terrestrial cyanobacterium Nostoc commune. SDS-PAGE and high-resolution two-dimensional gel electrophoresis were used to analyse the influence of UV-B on the proteome of N. commune. The resolution of SDS-PAGE turned out to be far too low to monitor the UV acclimation process. In contrast to the latter technique, two-dimensional electrophoresis showed that the UV-B response is extremely complex, involving the induction and the repression of a large number of proteins.

The cyanobacterial fossil record is among the oldest for any group of organisms, possibly reaching back to 3500 Ma ago. The molecular phylogeny of cyanobacteria is complementary to the fossil findings, confirming the antiquity of the group, the role of cyanobacteria in the evolution of planetary primary production, and the symbiotic origins of plastids in algae and plants from cyanobacterial ancestors. The study of fossil cyanobacteria followed the discovery of Precambrian microbial fossils by S.A Tyler and E.S. Barghoorn in 1954, and is still developing. Most fossil cyanobacteria are preserved in permineralized conditions in cherts and phosphorites or as organic compressions in shales. The interpretation of fossil cyanobacteria is aided by the study of modern counterparts, preferably within their natural habitats. These comparisons include the post mortem degradation of cellular remains. The fortuitous preservation and fossilization of ancient cyanobacterial communities in growth position, i.e. in the synsedimentary context, allows one to draw conclusions about their palaeoenvironment, including interactions between cyanobacteria and ancient sediments. These relations are based on cyanobacterial ecological requirements, and they compare well with behavioural responses of modern cyanobacteria in microbial mats and modern stromatolites. The general trend in the evolution of cyanobacteria is one of gradually increasing complexity and diversity, but the group shows a conservative maintenance of morphological adaptations to successful ecological niches. Accordingly, a large proportion of ancient morphological types is still represented among modern cyanobacteria. Fossil to Recent counterparts are identified for several coccoid and filamentous cyanobacteria. Evidence for heterocystous cyanobacteria is indirect, through identification of fossil akinetes.

Nostoc caeruleum, N. commune, N. microscopicum, N. parmelioides, N. pruniforme, N. verrucosum and N. zetterstedtii are all cyanobacteria forming macroscopically visible colonies. They were selected for a nature conservation case study. Their specific identity is easily determined, and reliable historical records are available. Life conditions for these species in Europe in the ‘virgin’ postglacial biosphere, historical reports and the present-day situation are surveyed. Data concerning type materials, supplements to the protologues, and morphology are presented. The classic descriptions and diagnoses based only on herbarium material are supplemented by ontogenetic details. Global/regional changes in the biosphere (climate, regulation of lake levels and river flows, import of plant nutrients, water pollution, acidification, etc.) and their consequences for aquatic biocoenoses are reviewed. The analysis of man-made impacts on the environment enables us to evaluate the present state of habitats where these algae occur today or where they are now extinct. Documented changes in environmental conditions in the past serve as a basis for assessing the likely future developments of the biotopes and of the whole landscape where these cyanobacteria form part of the biocoenoses. However, there are few recent detailed ecological studies on benthic and terrestrial cyanobacteria. It is not yet clear which of the different components covered by the comprehensive term ‘eutrophication’ is the decisive factor for the changes in aquatic biocoenoses and the decline of cyanobacterial biodiversity.

The diversity and abundance of terrestrial, lithophytic cyanobacteria in tropical biomes and the variety of rock habitats which they occupy are discussed. The following results are presented in detail. Exposed rock surfaces on different continents and under different climatic conditions are occupied by a cosmopolitan, well-adapted, low-diversity microbial community dominated by cyanobacteria and cyanobacterial lichens. For inselbergs (isolated rock outcrops) in dry savanna, the ratio of rock covered by lichens to that covered by free cyanobacteria is approximately 5:3. In humid savannas this ratio is approximately 1:26, and in rainforests there are hardly any lichens on rocks. The primary production of epilithic communities, expressed as CO2 fixed calculated from chlorophyll a, can reach an annual 27 g m−2. When calculated for a hypothetical inselberg, production values for very dry thorn bush savanna, dry savanna and humid savanna are 1:3·2:4·2 on the basis of the entire inselberg, and 1:3·2:1·4 when calculated on a square metre basis (due to a larger area covered but lower productivity in the humid savanna). Biofilm communities are important in biogenic weathering and they enrich the soils surrounding the rocks with nitrogen.

Tropical marine ecosystems are characterized by a specific cyanobacterial flora, temperature most probably being the major factor limiting the geographic distribution of the species. When compared with the open ocean, the highest biodiversity of cyanobacteria is observed in the littoral zones where they form intertidal and infralittoral mats, live as endoliths in carbonate substrates or form symbiotic associations, especially with sponges and ascidians. Their diversity, which especially in the less accessible infralittoral is still largely unknown, is also a source of diverse bioactive compounds, some of which are important as herbivore deterrents. As photosynthetic organisms, cyanobacteria sensu lato (including Prochlorophyta) are important contributors to benthic and open ocean primary production, but their main role in the tropical marine ecosystems appears to be as nitrogen fixers. Of primary importance in the often oligotrophic tropical oceans is the non-heterocystous, planktonic bloom-forming Trichodesmium, which probably represents a major nitrogen source for the marine and global nitrogen cycle.

For activity and survival in extreme terrestrial Antarctic habitats, lithobiontic cyanobacteria depend on key biomolecules for protection against environmental stress and for optimization of growth conditions. Their ability to synthesize such molecules is central to their pioneering characteristics and major role as primary producers in Antarctic desert habitats. Pigmentation is especially important in protecting them against enhanced UVB damage during stratospheric ozone depletion (the Ozone Hole) during the Antarctic spring and subsequent photoinhibition in the intense insolation of the summer. To be effective, especially for the screening of highly shade-adapted photosystems of cyanobacteria, protective pigments need to be located strategically. Antarctic lithic cyanobacterial communities are therefore stratified, as in soil biofilms of Alexander Island, the benthic stromatolitic mats of ice-covered hypersaline lakes in the McMurdo Dry Valleys, and the endolithic communities within translucent Beacon sandstone outcrops of Victoria Land. The protective pigments include scytonemin, carotenoids, anthroquinones and mycosporine-like amino acids. To detect and locate photoprotective pigments in situ in free-living cyanobacteria and cyanolichens from hot and cold desert habitats, we have used Fourier-transform Raman micro-spectroscopy. With appropriate power inputs for labile molecules, this high-precision, non-intrusive laser-based technique can not only identify biomolecules in their natural state but also locate them spatially within the habitat relative to the components of the community, which require protection. In conjunction with direct and epifluorescence microscopy it provides a spatial and functional description of the protective strategy of a community. We present the unique Raman spectrum of scytonemin and use its primary and corroborative peaks to identify it within the plethora of other biochemical constituents of several natural cyanobacterial communities, including an Antarctic endolith. The remote-sensing aspect of this technique makes it suitable not only for spatial biochemical analysis of present and palaeontological Antarctic communities but also for analogous putative habitats on Mars.

Geomicrobiological analysis of calcifying biofilms of three alkaline salt lakes characterized by moderate to high carbonate alkalinity indicates that microbial carbonate rock formation is not directly linked to cyanobacterial carbon fixation. The present review summarizes results from two published case studies that have been carried out at Pyramid Lake, USA, and Lake Nuoertu, PR China. New observations and data are presented for a current project on Satonda Crater Lake, Indonesia, that revise previous conclusions concerning the relationship between cyanobacteria and biofilm calcification. Extracellular polymeric substances (EPS) in the investigated lakes are mostly produced by cyanobacteria; their properties are discussed as key factors in biofilm calcification. In particular, EPS are capable of binding divalent cations (e.g. Ca2+) from the liquid phase by their carboxylate and sulphate groups. Therefore, despite a high supersaturation of the lake water with respect to calcium carbonate minerals, precipitation does not take place immediately. A delayed onset of precipitation can be achieved by a continuous Ca2+ supply that exceeds the Ca2+-binding capacity of the EPS, and/or an exoenzymatic degradation (decarboxylation, cleavage) of mucous substances that reduces the binding capacity and causes secondary Ca2+ release. The resulting microcrystalline precipitates are randomly distributed within the EPS, usually away from any of the living cyanobacteria. This suggests that the effect of photosynthetic CO2 fixation in increasing supersaturation is of secondary importance at high alkalinities. In contrast to biofilm-covered surfaces, calcium carbonate minerals nucleate and grow rapidly at surfaces poor in EPS when the critical supersaturation level for non-enzymatically controlled carbonate precipitation is reached. Examples of such surfaces poor in EPS are dead, lysed green algal cells and thin, discontinuous biofilms in voids of microbial reef rocks. Calcium carbonate crystals directly linked to cyanobacterial cells or filaments have been observed only exceptionally, e.g. on Calothrix.

The production of potent toxins by bloom-, scum- and mat-forming cyanobacteria, in fresh-, brackish and marine waters, appears to be a global phenomenon. Cyanobacterial toxins can also be produced by cyanobacteria from terrestrial sources. The range and number of known cyanobacterial toxins are increasing apace as associated poisoning incidents are investigated, and increasingly powerful analytical methods are applied to complement toxicity-based studies on both natural samples and laboratory isolates of cyanobacteria. Water quality management to reduce toxic cyanobacterial mass developments, and schemes to mitigate the potential effects of cyanobacterial toxins, require an understanding of the occurrence and properties of the toxins and of the exposure routes via which the toxins present risks to health. Here, we review advances in the recognition of cyanobacterial toxins and their toxicity, and of the exposure routes with reference to human health, namely via skin contact, inhalation, haemodialysis and ingestion (the oral route).

The global carbonate cycle has been controlled and maintained by life processes for at least 3.5 billion years. Within the exogenic carbonate cycle and in very different environments cyanobacteria appear in ‘key positions’ in that they actively and passively influence carbonate cycling. In the carbonate cycle, cyanobacteria play an important and sometimes decisive role. Cycling of carbon and carbonate is linked to biological processes. Some build up specific carbonate structures, some destroy carbonate substrates and others do both simultaneously. All these processes take place from the high mountains down to the sea in various terrestrial and freshwater as well as marine environments. The photosynthetic activity of cyanobacteria, their extracellular polymeric substances and possibly also their adherent heterotrophic bacteria are responsible for the construction of various carbonate structures and the ability to penetrate carbonate material. Boring activity of euendoliths results in biological corrosion and disintegration of carbonate surfaces. Grazing organisms on carbonate surfaces colonized by epi- and endolithic cyanobacteria produce specific biokarst forms and specific grains which can contribute to nearshore sedimentation. Biological corrosion and abrasion together constitute bioerosion. The results of all these processes are calcareous crusts, typical traces and biokarst forms which in many cases have a high fossilization potential, and therefore can be powerful ecological, palaeoecological and facies indicators in recent as well as in fossil environments.