**1. Introduction**

58 Novel Approaches and Their Applications in Risk Assessment

UNCED (United Nations Conference on Environment and Development) (1993).

UN (United Nations Department of Economic and Social Affairs) (2008). *The Millenium Development Goals Report 2008*, ISBN 978-92-1-101173-9, New York, USA Zschiesche, Michael & Pham Ngoc Han (2008). *Studie zum Umweltrecht in Vietnam,* 

Action from Rio, Rio de Janeiro, Brazil, June 03-14, 1992

Germany

Proceedings of Earth Summit Agenda 21 - The United Nations Programme of

*Unabhängiges Institut für Umweltfragen (UfU)*, Unpublished manuscript, Berlin,

Cyanobacteria are a diverse well adapted group of organisms that presents amazing morphological diversity. Cyanobacteria can be unicellular or colonial (filamentous, spherical or amorphous) (Fig. 1). Since cyanobacteria have cells larger than normal bacterial cells and behavior more similar to algae, they were classified under the microalgae for a long time and acquire the name of blue-green algae or Cyanophyta (Whitton & Potts 2000). Cyanobacteria is a phylum of bacteria that obtain their energy through photosynthesis. The name "cyanobacteria" comes from their coloration (cyano = blue). The vegetative cell wall is of Gram-negative type and in some species the peptidoglycan layer is considerably thicker than in other bacteria. Many unicellular and filamentous cyanobacteria possess an "envelope" outside the lipopolysaccharide (LPS) "outer membrane", which is called: sheath, glycocalyx, or capsule, and depending on the consistency, gel, mucilage or slime. The sheaths of cyanobacteria are predominantly polysaccharide, but a part of its weight may be polypeptides, and depending on the species, some types of sugar residues may be involved (Castenholz, 2001).

Fig. 1. Optical microscopy photographs of cyanobacteria presenting different morphologies. The arrow indicates the heterocyst cell in *Anabena circinalis*.

Risk Assessment of Cyanobacteria and Cyanotoxins,

**2. Why the surveillance on cyanobacteria?** 

human and animal health (McPhail & Jarema, 2005).

oxygenic photosynthetic prokaryotes.

the Particularities and Challenges of *Planktothrix* spp. Monitoring 61

Cyanobacteria can be found in the most diverse environments like hot springs, salt marshes, soils, fresh, brackish, and marine waters (Sze, 1986). In sum, cyanobacteria are ubiquitous

Cyanobacteria are common constituents of the phytoplankton in aquatic environments. In optimal conditions these phytoplanktons can develop massively and form blooms, becoming the dominant organism in the water column and creating serious problems in water quality (Cood, 2000; Vasconcelos, 2006). The water quality deterioration produced by cyanobacterial blooms includes foul odours and tastes, deoxygenation of bottom waters (hypoxia and anoxia), fish kills, food web alterations and toxicity. Other threatening characteristic of these organisms is their ability to produce toxins that affects other living organisms and humans (Carmichael, 2001). The capacity of mass development together with the ability to produce potent toxins enlightens the importance of implementing regular monitoring programs for cyanobacteria and cyanotoxins in freshwater environments, in order to minimize potential health risks to animal and human populations that results from exposure through drinking and recreational activities. The implementation of surveillance programs on cyanobacteria involves understanding the ecophysiology of cyanobacteria, bloom dynamics, conditions that promote blooms, production of toxins and their impact in

Cyanobacteria possess some ecostrategies that allows them to overcome other organism and become dominant. In general there are four constraints on cyanobacteria growth as prerequisites for bloom enhancement: light, nutrients, temperature and stability of the water column. Cyanobacteria requires low light intensities for growth, compared with algae, which provides competitive advantages in lakes which are turbid due to growth of other phytoplankton. They also have a higher affinity for uptake phosphorous and nitrogen than many other photosynthetic organisms and they have a substantial storage capacity for phosphorous (Mur et al., 1999). Some genera like *Anabaena, Aphanizomenon*, *Cylindrospermopsis*, *Nodularia* and *Nostoc* have specialized cells (heterocysts) (Fig. 1) for nitrogen fixation and blooms of these genera can often be related with periodic nitrogen limitation. This means that they can compete other phytoplankton under conditions of

The success of some cyanobacteria is also due to the presence of gas vacuoles that provide buoyancy regulation. During water stratification conditions cyanobacteria can migrate in the water column, accessing light in the surface layers and nutrients near the sediment. During photosynthesis, carbohydrates are accumulated which makes them heavy and sinking away from light and when the carbohydrates are respired, buoyancy is restored. As large colonies sink faster than small ones or single cells, genera like *Microcystis*, *Anabaena*, *Aphanizomenon* and *Nodularia* have scum-forming strategies (Vance, 1965; Mur et al., 1999). Cyanobacteria also produce active substances that inhibits the growth of competing algae and grazers that feed upon them, which can also promote cyanobacteria proliferation (Briand et al., 2003; Granéli & Hansen, 2006; Sunda et al., 2006; van Apeldoorn et al., 2007; Figueredo et al. 2007). As a consequence of the characteristics mentioned above the cyanobacterial cells numbers in water bodies vary seasonally. In temperate regions, seasonal successions of organisms belonging to different phytoplankton taxa are often observed. Whereas at the beginning of

phosphorous and nitrogen limitation (Briand et al., 2003; Sunda et al., 2006).

Cyanobacteria are autotrophs and possess all the photosynthetic pigment (chlorophyll *a*, carotenoids, allophycocyanin, phycobilins, phycoerythrins) except chlorophyll *b* (Castenholz, 2001). Prochlorophytes are also cyanobacteria that contain chlorophyll *a* and *b*, but, opposing to other cyanobacteria, lack phycobiliproteins (Castenholz, 2001). Cyanobacteria have the ability to use low light intensities effectively, since they are able to produce the accessory pigments needed to adsorb light most efficiently in the habitat in which they are present, providing them a great advantage for the colonization of a wide range of ecological niches (van den Hoek et al., 1995; WHO, 1999). Phycobiliprotein synthesis is particularly susceptible to environmental influences, especially light quality. The chromatic adaptation is largely attributable to a change in the ratio between phycocyanin and phycoerythrin in the phycobilisomes. The photosynthetic pigments are located in thylakoids that are free in the cytoplasm near the cell periphery (Fig. 2). Cell colours vary from blue-green to violet-red due to the chlorophyll *a* masking by the carotenoids and accessory pigments. The pigments are involved in phycobilisomes, which are found in rows on the outer surface of the thylakoids (Fig. 2) (WHO, 1999). Cyanobacteria are also able of storing essential nutrients and metabolites within their cytoplasm. Prominent cytoplasmic inclusions such as glycogen and cyanophycin granules (polymers of the amino acids arginine and asparagine), polyphosphate bodies, carboxysomes (containing the primary enzyme for photosynthetic CO2 fixation, ribulose 1,5-bisphosphate carboxylase-oxygenase: RuBisCO) and gas vacuoles (Fig. 2) can be observed by electron microscopy. The occurrence of fimbriae (pili) is abundant in many cyanobacteria with varying patterns. Some filamentous forms are also able of gliding (sliding) (van den Hoek et al., 1995; WHO, 1999; Castenholz, 2001).

Fig. 2. Cyanobacteria cell structure. (A)Transmission electron micrographs showing the ultrastructure of an *Anabena circinalis* vegetative cell; (B) Schematic diagram of a cyanobacterial vegetative cell. S: external 4-layered cell wall; OM: outer membrane; PL: peptidoglycan layer; CM: cytoplasmic membrane; CW: cell wall; E: cell envelope; TH: thylakoid; PB: phycobilisome; CY: cytoplasm; GV: gas vesicle; GG: glycogen granules; N: nucleoplasmic region; C: carboxysome; PP: polyphosphate granule; CP: cyanophycin granule; LP: lipid droplets (adapted from van den Hoek et al., 1995; Castenholz, 2001).

Cyanobacteria can be found in the most diverse environments like hot springs, salt marshes, soils, fresh, brackish, and marine waters (Sze, 1986). In sum, cyanobacteria are ubiquitous oxygenic photosynthetic prokaryotes.
