Keywords
Genetically engineered microorganism · Heavy metals · Bioremediation ·
Biosorption · Siderophores · Microbial remediation
12.1 Introduction
Microorganisms and metals are present together with a long period of time in
history. This is represented through the presence of a vast variety of divalent and
transition metals in the active centres of different enzymes. Various chemical
properties of the metal are utilized for maintenance of the structure of protein as
well as catalysis of key reactions in the metabolic pathways. Metals are needed in
minuscule quantities for performing usual cell metabolism, while their intake is
dependent on complex homeostatic mechanisms that guarantee enough but not
excess increase. Various other metals have no biologically important function and
cause damage, mostly because of their desire for the sulfhydryl groups in proteins,
which they obstruct and make inactive. Therefore, physiologically, metals are of
three main types: (i) those which are necessary and are not harmful like Ca and Mg,
(ii) necessary but damaging at an elevated level (usually, Fe, Mn, Zn, Cu, Co, Ni and
Mo) and (iii) harmful like Hg or Cd. The chemical identity of the specific element is
responsible for interactions with metals. The need of living systems to both gain and
discard metals has selected a variety of mechanisms of interaction which make
microorganisms adapted to an altering and often unfriendly environment. The
appearance of metal tolerance determinants is a very early event in evolution (Silver
1998). In recent times, mobilization from metal ores by man has formed new, metalrich places with higher selective pressure for metal tolerance. Various prokaryotes
have particular resistance determinants which can withstand different concentration
of various elements through a number of mechanisms. Different types of bacteria
have the capability to withstand toxic concentrations of metals which pollute the
environment. This information formed the basis for new approaches to remediate
heavy metal pollution which creates more damage than all other types of pollution in
combination (Nriagu and Pacyna 1988). Microorganisms are successfully used in the
treatment of heavy metal pollution in a number of approaches. Various upcoming
technologies are dependent on increase in the biosorption of metals into biomass or
the precipitation of ions by using some metal-related aspect of bacterial metabolism.
Due to their specific physico-chemical characters, mercury and metalloids (As) can
occasionally be taken away from contaminate sites through microbes that change
them into volatile species, which is an alternative to the immobilization/precipitation
strategy (Valls and de Lorenzo 2002).
316
N. Srivastava
Genetically engineered microorganism · Heavy metals · Bioremediation ·
Biosorption · Siderophores · Microbial remediation
12.1 Introduction
Microorganisms and metals are present together with a long period of time in
history. This is represented through the presence of a vast variety of divalent and
transition metals in the active centres of different enzymes. Various chemical
properties of the metal are utilized for maintenance of the structure of protein as
well as catalysis of key reactions in the metabolic pathways. Metals are needed in
minuscule quantities for performing usual cell metabolism, while their intake is
dependent on complex homeostatic mechanisms that guarantee enough but not
excess increase. Various other metals have no biologically important function and
cause damage, mostly because of their desire for the sulfhydryl groups in proteins,
which they obstruct and make inactive. Therefore, physiologically, metals are of
three main types: (i) those which are necessary and are not harmful like Ca and Mg,
(ii) necessary but damaging at an elevated level (usually, Fe, Mn, Zn, Cu, Co, Ni and
Mo) and (iii) harmful like Hg or Cd. The chemical identity of the specific element is
responsible for interactions with metals. The need of living systems to both gain and
discard metals has selected a variety of mechanisms of interaction which make
microorganisms adapted to an altering and often unfriendly environment. The
appearance of metal tolerance determinants is a very early event in evolution (Silver
1998). In recent times, mobilization from metal ores by man has formed new, metalrich places with higher selective pressure for metal tolerance. Various prokaryotes
have particular resistance determinants which can withstand different concentration
of various elements through a number of mechanisms. Different types of bacteria
have the capability to withstand toxic concentrations of metals which pollute the
environment. This information formed the basis for new approaches to remediate
heavy metal pollution which creates more damage than all other types of pollution in
combination (Nriagu and Pacyna 1988). Microorganisms are successfully used in the
treatment of heavy metal pollution in a number of approaches. Various upcoming
technologies are dependent on increase in the biosorption of metals into biomass or
the precipitation of ions by using some metal-related aspect of bacterial metabolism.
Due to their specific physico-chemical characters, mercury and metalloids (As) can
occasionally be taken away from contaminate sites through microbes that change
them into volatile species, which is an alternative to the immobilization/precipitation
strategy (Valls and de Lorenzo 2002).
316
N. Srivastava