172
A.C.A. da Costa
Vymazal (1987), studying the toxicity and accumulation of cadmium in
cyanobacteria, discussed, mainly, the mode of action of cadmium on the cells as
well as toxicity and factors affecting tolerance to the heavy metal. Some other
papers on the interaction of heavy metal ions with cyanobacterial strains such as
Synechococcus sp. (Olafson et al. 1988) and Synechocystis (Garnham et al. 1993a,
b) are also available from the literature.
9
The Surface of Algal Cells
The interaction between algal cells and metallic species is also directly linked to
their polysaccharide content and surface components, as primary receptors of
the metal. However, the different algal divisions encompass distinct polysaccharides types, and it is not in the scope of the present chapter to describe, in details
all their chemical structure. For a detailed review on their chemical composition,
one can consult the literature (Percival 1979; Brawley and Wetherbee 1981).
Several papers describe a wide variety of algal species and their behaviour
when present in metal-contaminated solutions. Overnell (1975), working with the
marine algae Dunaliella tertiolecta and Phaeodactylum tricornutum, observed a
marked cell potassium loss in the presence of heavy metal elements. Specifically
for mercury, the authors observed that this metal is transported through the
outer membrane of the cells in the direction of the chloroplasts. In this way, the
photosynthetic activity is interrupted, no damage being caused to the cell
membrane as reflected in potassium leakage, however. If mercury was present as
methylmercury, the reflection of its action on potassium loss indicates a selective
action on the membrane, and it is directly associated to a complete inhibition of
oxygen evolution.
Accordingly, in other works the green algae Chlorella are reported as
bioaccumulators of toxic metals (Sakaguchi et al. 1979; da Costa and Leite 1993;
da Costa et al. 1994), as well as precious elements (Cordery et al. 1994; Ting et al.
1995); in this last case a direct enzymatic action on gold compounds is observed
at the membrane level.
Wang and Wood (1984) observed an adsorptive phenomenon during the
bioaccumulation of nickel by algae, for a series of algal and cyanobacterial
strains, emphasizing a surface phenomenon when the interaction took place.
Crist et al. (1981), going into deeper details on the behaviour of Vaucheria sp.
during the accumulation of heavy metals, highlighted the amino acid contents of
proteins in the cell wall as the primary agents responsible for the accumulation.
Xue (1989) also indicated these interactions showing an interesting schematic
representation, both at the surface as well as at intracellular levels.
However, a different and important feature is related to the bioaccumulation of
mercury, as described by Wilkinson et al. (1989). The authors, studying the
behaviour of Chlorella cells in the presence of labelled and unlabelled HgCI2 ,
proved the marked volatilization of mercury, indicating the possibility of its
A.C.A. da Costa
Vymazal (1987), studying the toxicity and accumulation of cadmium in
cyanobacteria, discussed, mainly, the mode of action of cadmium on the cells as
well as toxicity and factors affecting tolerance to the heavy metal. Some other
papers on the interaction of heavy metal ions with cyanobacterial strains such as
Synechococcus sp. (Olafson et al. 1988) and Synechocystis (Garnham et al. 1993a,
b) are also available from the literature.
9
The Surface of Algal Cells
The interaction between algal cells and metallic species is also directly linked to
their polysaccharide content and surface components, as primary receptors of
the metal. However, the different algal divisions encompass distinct polysaccharides types, and it is not in the scope of the present chapter to describe, in details
all their chemical structure. For a detailed review on their chemical composition,
one can consult the literature (Percival 1979; Brawley and Wetherbee 1981).
Several papers describe a wide variety of algal species and their behaviour
when present in metal-contaminated solutions. Overnell (1975), working with the
marine algae Dunaliella tertiolecta and Phaeodactylum tricornutum, observed a
marked cell potassium loss in the presence of heavy metal elements. Specifically
for mercury, the authors observed that this metal is transported through the
outer membrane of the cells in the direction of the chloroplasts. In this way, the
photosynthetic activity is interrupted, no damage being caused to the cell
membrane as reflected in potassium leakage, however. If mercury was present as
methylmercury, the reflection of its action on potassium loss indicates a selective
action on the membrane, and it is directly associated to a complete inhibition of
oxygen evolution.
Accordingly, in other works the green algae Chlorella are reported as
bioaccumulators of toxic metals (Sakaguchi et al. 1979; da Costa and Leite 1993;
da Costa et al. 1994), as well as precious elements (Cordery et al. 1994; Ting et al.
1995); in this last case a direct enzymatic action on gold compounds is observed
at the membrane level.
Wang and Wood (1984) observed an adsorptive phenomenon during the
bioaccumulation of nickel by algae, for a series of algal and cyanobacterial
strains, emphasizing a surface phenomenon when the interaction took place.
Crist et al. (1981), going into deeper details on the behaviour of Vaucheria sp.
during the accumulation of heavy metals, highlighted the amino acid contents of
proteins in the cell wall as the primary agents responsible for the accumulation.
Xue (1989) also indicated these interactions showing an interesting schematic
representation, both at the surface as well as at intracellular levels.
However, a different and important feature is related to the bioaccumulation of
mercury, as described by Wilkinson et al. (1989). The authors, studying the
behaviour of Chlorella cells in the presence of labelled and unlabelled HgCI2 ,
proved the marked volatilization of mercury, indicating the possibility of its