162
A.C.A. da Costa
physical or chemical process. On the other hand, if this interaction is not restricted
to a simple reaction due to the chemical structure of the biological material, this
means that, if the interaction is driven by metabolic activities of the cells, then the
process is usually termed metals bioaccumulation. It is important to mention that
metals bioaccumulation also involves a certain degree of metal recovery through
chemical constituents of the external layers in cells.
The proteins and structural polysaccharides of the cells contain a series of
available metal binding sites; these binding groups include carboxyl, thiol,
phosphate, sulphydril and amine groups. These usually occur as components of
the cell wall and cytoplasmic membrane and also external layers, with the
different layers of the cellular envelopes lodging distinct chemical groups of
varying potential for metal interaction.
4
A Brief Overview of the Classification of Living Organisms
In order to understand the chemical interactions between biosurface structures
and metals, it may be interesting to consider a brief overview of the living world
phylogeny. It is not in the scope of the present chapter to consider the surface
structures of all living organisms, due to their wide variability and also due to the
lack of available information on cell biology for all the groups classified.
Proposed in 1969 by R. H. Whittaker, the five-kingdom classification of living
organisms considered distinct levels of cellular organization (Pelczar et al. 1993).
From Whittaker's five-kingdom concept of classification, from ancestral forms,
five different kingdoms arose, according to their level of cellular organization:
Kingdom Monera, including prokaryotes (bacteria); Kingdom Protista, including
eukaryotes (microbial cells, mainly algae and protozoa); and, at the same level of
cellular organization, Kingdom Plantae (photosynthetic green plants and higher
algae), Kingdom Fungi (organisms containing cell walls but lacking chlorophyll)
and Kingdom Animalia, including food-ingesting animals.
From Whittaker's classification, prokaryotic cells, eukaryotic cells, as well as
yeasts and moulds, are classified in the Kingdom Monera, Protista and Fungi,
thus encompassing all microbial cells. Later, at the end of the 1970s, it was stated
that prokaryotes and eukaryotes probably evolved to different directions from
the so-called universal ancestor of all cells. The previously used five-kingdom
classification did not consider evolutionary lines among living organims, but
only structural similarities between them. Further studies described only three
evolutionary lines in the phylogenetic tree, based on the analysis of ribosomal
RNA sequencing (Brock et al. 1994). These evolutionary lines were based on the
data obtained by Carl R. W oese, and were called Domains of Life, whereby this
level of classification supplanted the "kingdom" in terms of biological taxons.
These domains, as determined by W oese, are of a much broader significance in
terms of biological classification, but they still revealed a very wide range of
biological organisms, now grouped into only domains: (1) Domain Bacteria:
A.C.A. da Costa
physical or chemical process. On the other hand, if this interaction is not restricted
to a simple reaction due to the chemical structure of the biological material, this
means that, if the interaction is driven by metabolic activities of the cells, then the
process is usually termed metals bioaccumulation. It is important to mention that
metals bioaccumulation also involves a certain degree of metal recovery through
chemical constituents of the external layers in cells.
The proteins and structural polysaccharides of the cells contain a series of
available metal binding sites; these binding groups include carboxyl, thiol,
phosphate, sulphydril and amine groups. These usually occur as components of
the cell wall and cytoplasmic membrane and also external layers, with the
different layers of the cellular envelopes lodging distinct chemical groups of
varying potential for metal interaction.
4
A Brief Overview of the Classification of Living Organisms
In order to understand the chemical interactions between biosurface structures
and metals, it may be interesting to consider a brief overview of the living world
phylogeny. It is not in the scope of the present chapter to consider the surface
structures of all living organisms, due to their wide variability and also due to the
lack of available information on cell biology for all the groups classified.
Proposed in 1969 by R. H. Whittaker, the five-kingdom classification of living
organisms considered distinct levels of cellular organization (Pelczar et al. 1993).
From Whittaker's five-kingdom concept of classification, from ancestral forms,
five different kingdoms arose, according to their level of cellular organization:
Kingdom Monera, including prokaryotes (bacteria); Kingdom Protista, including
eukaryotes (microbial cells, mainly algae and protozoa); and, at the same level of
cellular organization, Kingdom Plantae (photosynthetic green plants and higher
algae), Kingdom Fungi (organisms containing cell walls but lacking chlorophyll)
and Kingdom Animalia, including food-ingesting animals.
From Whittaker's classification, prokaryotic cells, eukaryotic cells, as well as
yeasts and moulds, are classified in the Kingdom Monera, Protista and Fungi,
thus encompassing all microbial cells. Later, at the end of the 1970s, it was stated
that prokaryotes and eukaryotes probably evolved to different directions from
the so-called universal ancestor of all cells. The previously used five-kingdom
classification did not consider evolutionary lines among living organims, but
only structural similarities between them. Further studies described only three
evolutionary lines in the phylogenetic tree, based on the analysis of ribosomal
RNA sequencing (Brock et al. 1994). These evolutionary lines were based on the
data obtained by Carl R. W oese, and were called Domains of Life, whereby this
level of classification supplanted the "kingdom" in terms of biological taxons.
These domains, as determined by W oese, are of a much broader significance in
terms of biological classification, but they still revealed a very wide range of
biological organisms, now grouped into only domains: (1) Domain Bacteria: