Genetic transfer in bioleaching microorganisms
Laboratoire de Chimie Bactérienne, Institut de Biologie Moléculaire et de Microbiologie,
C.N.R.S., 13402, Marseille Cedex 20, France
Genetic transfer techniques allow the
introduction of ge
netic material into cells.
The three classical approaches are
the transfer of genetic
information via a bacteriophage
(virus) particle (Figure 1)
the transfer of
conjugative or mobilizable plasmids
from one bacterium to anoth
cell contact (Figure 2)
electrotransformation, by exposing
the cells in the presence of free DNA
to a pulsed electric field which
destabilizes transiently the bacterial
membrane and permits the entry of
the DNA into the cell (Figure 3).
tic transfer from one
can be used to express heterologous genes in
the recipient bacteria or to bring back genes
that have been modified in more accurate
hosts by genetic engineering. The later
approach allows the construction of mutants
precisely defined at the molecular level,
which can help elucidating the physiology of
s or improve some of their
specific metabolic properties.
Genetic transfer in bioleaching
s is a
real challenge because their life conditions
extreme and quite different from the
Genetic engineering is usually performed in
this eubacterium which is consequently often
used as donor cells. While the former are
strict or moderate acidophiles and obligatory
facultative chemoautolithotrophs, the later
is neutrophilic and heterotrophic. The main
problem is therefore to find the conditions in
which both donor and recipient cells have
enough energy to survive. Furthermore,
s grow slowly with v
low cell yields making them difficult to
Nevertheless, genetic transfer was made
possible in some bioleaching
(Table 1). This has allowed the expression
the phosphofructokinase gene (
interestingly the transposon Tn5 was shown
to be able to transpose into the chromosome
, opening the way to
random transposon insertion mutagenesis
(9). Finally, conjugation by marker exchange
mutagenesis has allowed the construction of
only "constructed" mutant described so far
1; 2; 10; 11
6; 7; 8; 9
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Figure 1. Transduction
DNA packaging in phage capsid
transducing phage infection to a new microbial cell
Recomibination between the microbe chromosome and the DNA
transduced by the
Figure 2. Conjugation
A conjugation tube forms between the donor cell
and the recipient cell. A single strand from the
plasmid DNA is transferred throught the tube
from the donor to the recipient cells.
stranded DNA is for
med from the single
strand in both the donor and the recipient cells
Figure 3: Electrotransformation
When the electric fiel is applied, the ions
move according to their charge
Pathways are formed across the
membrane allowing th
e entrance of DNA
When the electric field is stopped, the