CYANOBACTERIA:
Their roles in the evolution, ecology, water quality and environmental health of aquatic ecosystems
Cyanobacteria (blue-green algae) are the Earth's oldest known (>2.5 billion years) oxygen-producing, photosynthetic microorganisms, yet today they still exhibit remarkable adaptations and diversification in response to evolutionary change. The early evolution of Earth's oxygen-rich atmosphere is most likely due to cyanobacterial photosynthesis. There is fossil evidence, in ancient laminated carbonaceous rocks, called stromatolites (which were produced by the cyanobacteria), for their importance as primary producers in the early stages biological evolution. Cyanobacteria are morphologically and physiologically diverse. Morphological groups include coccoid, filamentous non-heterocystous and heterocystous genera. These groups and widely distributed in terrestrial and aquatic habitats. All heterocystous and some coccoid/filamentous genera use atmospheric nitrogen (N2) for growth through nitrogen fixation. This self-fertilizing capability allows cyanobacteria to inhabit and at times dominate N-deplete aquatic and terrestrial ecosystems ranging from desert soils to vast regions of the open ocean. Cyanobacterial nitrogen fixation can contribute a significant fraction of the biologically-available nitrogen to these ecosystems.
These “pioneer” microbes have survived and adapted to the range of geochemical changes marking the evolution of the Earth's biosphere. They tolerate desiccation, hypersalinity, hyperthermal conditions and high ultraviolet radiation, often for extensive periods (many decades or even centuries). Over their long evolutionary history, they have formed numerous endosymbiotic and mutualistic associations with microorganisms, higher plant and animals. Examples include; lichens (fungi), ferns, cycads, diatoms, seagrasses, sponges and even polar bears. Cyanobacteria can move by gliding, using mucilaginous excretions as propellant, or in the case of planktonic genera, by altering buoyancy through gas vesicle formation and collapse. Recently, cyanobacteria have exploited human alterations of aquatic environments, most notably nutrient-enhanced primary production, or eutrophication. Worldwide, cyanobacterial blooms are visible, well-documented, widespread indicators of freshwater, brackish and marine eutrophication. Toxic blooms pose serious water quality, fisheries resource, animal and human health problems, including foul odors and tastes, hypoxia, fish, bird, mammalian and even human sickness and death. Nutrient cycling and food web dynamics may be altered, and blooms can contribute large amounts of “new” carbon as fuel for hypoxia and anoxia.
Harmful cyanobacterial blooms (CyanoHABs) have been present for centuries in nutrient-enriched inland, estuarine and coastal waters. Proliferation into more recently eutrophying waters is also underway. Examples include expansion of planktonic nitrogen fixing and non-fixing genera (Table 1) in freshwater, estuarine and marine habitats worldwide. Freshwater and marine aquaculture operations are also susceptible to cyanoHAB invasions. Molecular analyses indicate that the diversity of cyanoHABs at genera, species and strain levels is much greater than can be observed microscopically. Using highly specific and sensitive 16S rRNA and nitrogen fixing gene ( nifH ) sequence analysis techniques, we can detect and characterize (at species and strain-levels) invasive, toxic nitrogen fixing cyanobacteria that are proliferating in eutrophying lakes, rivers, estuaries and coastal waters. Particularly aggressive species include heterocystous Cylindrospermopsis raciborskii , Anabaeana flos aquae , Nodularia spumigena , but there many additional species capable of taking advantage of nutrient-enriched and hydrologically-altered (impounded) waters. Non-N 2 fixing analog species which thrive in N and phosphorus (P)-enriched waters include the coccoid colonial bloom-former Microcystis spp. and filamentous Oscillatoria spp. and Planktonthix spp. Collaborative research efforts with colleague from US, Finnish, and Danish laboratories are underway to streamline molecular approaches for early detection and routine CyanoHAB monitoring, using microarray and quantitative PCR techniques.