Chemical Interactions between Mercurial Species and Surface Biomolecules
171
comparison to G+ cells. However, Beveridge (1986) states that proteins associated
to the bilayer can cause aggregates forming transport channels or pores, allowing
molecules to pass through them. He also states the low contribution of the outer
membrane in comparison to the murein sacculus.
7
The Surface of Archaebacterial Cells
The Domain Archaea includes bacterial cells whose basic structures are far
different from those in the Domain Bacteria. Their membranes lack fatty acids,
these being replaced by hydrocarbon moieties bonded to glycerol through ether
linkages. This basic difference makes archean membranes unique in comparison
to other cellular membranes.
Analogously, the cell walls of the organisms in this domain are also markedly
different with several wall types reported. An interesting feature of their cell walls
is the lack of muramic acid and D-amino acids, as observed in the Domain
Bacteria. However, a pseudopeptidoglycan is found in archaean cells, consisting
of amino sugars, N-acetylglucosamine and N-acetyltalosaminuronic acid. Here,
also cross-linked amino acid residues are present, curiously all in their L-form
(Brock et a1. 1994).
The wide variety of archean walls makes it impossible to evaluate their heavy
metal binding capacities, but the overall structure observed for some genera,
allows envisaging interactions with hydroxyl groups from the glucosidic fraction,
as well as with the constituting amino acid residues, exactly as in the Domain
Bacteria.
8
The Surface of Cyanobacterial Cells
As reported in the literature, the external layers of cyanobacteria are similar to
those presented by G- bacterial cells (Drews and Weckesser 1982; Bold and
Wynne 1983). Thus, the heavy metal uptake pattern observed for this division is
expected to be the same as here reported for G- cells.
da Costa and de Fran~a (1996c) studied the uptake of heavy metals by the
cyanobacterium Spirulina maxima using living and oven-dried dead cells, as well
as the effect of cadmium on the growth of these cells. The authors concluded that
living cells have a greater uptake capacity than dead cells. When present in
solution in a concentration of 1.2 mgtl, cadmium affected cellular growth,
diminishing productivity and altering growth rates. The metal was accumulated
in the outer and inner faces of the external membrane, essentially in the lipid
layer. Its presence was not detected in the peptidoglycan fraction or in the
interior of the cells.
171
comparison to G+ cells. However, Beveridge (1986) states that proteins associated
to the bilayer can cause aggregates forming transport channels or pores, allowing
molecules to pass through them. He also states the low contribution of the outer
membrane in comparison to the murein sacculus.
7
The Surface of Archaebacterial Cells
The Domain Archaea includes bacterial cells whose basic structures are far
different from those in the Domain Bacteria. Their membranes lack fatty acids,
these being replaced by hydrocarbon moieties bonded to glycerol through ether
linkages. This basic difference makes archean membranes unique in comparison
to other cellular membranes.
Analogously, the cell walls of the organisms in this domain are also markedly
different with several wall types reported. An interesting feature of their cell walls
is the lack of muramic acid and D-amino acids, as observed in the Domain
Bacteria. However, a pseudopeptidoglycan is found in archaean cells, consisting
of amino sugars, N-acetylglucosamine and N-acetyltalosaminuronic acid. Here,
also cross-linked amino acid residues are present, curiously all in their L-form
(Brock et a1. 1994).
The wide variety of archean walls makes it impossible to evaluate their heavy
metal binding capacities, but the overall structure observed for some genera,
allows envisaging interactions with hydroxyl groups from the glucosidic fraction,
as well as with the constituting amino acid residues, exactly as in the Domain
Bacteria.
8
The Surface of Cyanobacterial Cells
As reported in the literature, the external layers of cyanobacteria are similar to
those presented by G- bacterial cells (Drews and Weckesser 1982; Bold and
Wynne 1983). Thus, the heavy metal uptake pattern observed for this division is
expected to be the same as here reported for G- cells.
da Costa and de Fran~a (1996c) studied the uptake of heavy metals by the
cyanobacterium Spirulina maxima using living and oven-dried dead cells, as well
as the effect of cadmium on the growth of these cells. The authors concluded that
living cells have a greater uptake capacity than dead cells. When present in
solution in a concentration of 1.2 mgtl, cadmium affected cellular growth,
diminishing productivity and altering growth rates. The metal was accumulated
in the outer and inner faces of the external membrane, essentially in the lipid
layer. Its presence was not detected in the peptidoglycan fraction or in the
interior of the cells.