Bariloche protein symposium argentine society for biochemistry and molecular biology

36
BIOCELL, 27 (Suppl. I), 2003
S17.
MOLECULAR EVIDENCES FOR THE ACQUISITION OF
ENDOSIMBIONTS BY THE Euglenozoa
Opperdoes, Fred R.
Universite Catholique de Louvain, Brussels, Belgium.
S18.
THE  Salmonella enterica MAGNESIUM STIMULON
Soncini, Fernando C.; Castelli, M. Eugenia; Lejona, Sergio;
Spinelli, Silvana; Aguirre, Andrés; Cabeza, M. Laura, and García
Véscovi, Eleonora.
Instituto de Biología Molecular y Celular de Rosario (IBR-
CONICET), and Facultad de Cs. Bioquímicas y Farmacéuticas
(UNR), Rosario, Argentina. E-mail: [e-mail]
In the pathogenic bacterium Salmonella enterica, magnesium plays
a fundamental role during the infection process. Salmonella utilizes
the level of environmental Mg
2+
 as a signal to control the expression
of several essential virulence determinants. We have identified
that this sensing process is mediated by a specific signal-
transduction system known as PhoP/PhoQ. Extracellular Mg
2+
controls a specific response-regulator (PhoP) phosphatase activity
in the membrane-associated sensor protein PhoQ, inactivating the
transcriptional regulator. Phosphorylation of the response regulator
promotes its self-association, allowing the protein to recognize
and interact with a direct-repeat sequence located in the promoter
region of a set of PhoP-activated genes (pags). On the other hand,
pags that do not harbor the PhoP-box at their promoter regions
are indirectly controlled by this system. We are currently
investigating putative intermediaries in their Mg
2+
-controlled
regulation. Interestingly, most of these indirectly-regulated genes
are Salmonella-specific and were probably acquired by horizontal
transfer. Recently, we have uncovered a novel Mg
2+
 regulatory
system that coordinates with PhoP/PhoQ the cellular distribution
and homeostasis of Mg
2+
. The analysis of this system is also
relevant to understand how intracellular Mg
2+
 is kept within a
precise range to guarantee the proper function of vital intracellular
mechanisms.
S19.
REGULATION OF Xanthomonas campestris VIRULENCE
FACTORS AND THEIR ROLE IN THE INTERACTION
WITH PLANTS
Adrián A. Vojnov.
Fundación Instituto Leloir, Argentina. E-mail: [e-mail]
The phytopathogenic bacterium Xanthomonas campestris pv.
campestris  (Xcc) is the causal agent of black rot disease of
cruciferous plant. Xcc produces a range of extracellular enzymes
and extracellular polysaccharide (EPS) which are collectively
essential for pathogenesis. The production of these factors is
regulated by a cluster of genes called rpf (for regulation of
pathogenicity  factors). Two of the genes, rpfF and rpfB, have
previously been implicated in the synthesis of a diffusible
regulatory molecule, DSF. The gum gene cluster of Xcc comprises
12 genes whose products are involved in the biosynthesis of the
polysaccharide xanthan. These genes are expressed as an operon
from a promoter upstream of the first gene, gumB. A reporter
plasmid was constructed in which the promoter region of the gum
operon was fused to gusA. The expression of the gumgusA fusion
in bacteria recovered from inoculated turnip leaves was maximal
at the later phases of growth and was subjected to regulation by
rpfF. In addition, Xcc produces a neutral cyclic glucan containing
16 glucose residues. Mutations in both rpfF  and  rpfC  lead to
reductions in levels of cyclic glucan. â-1,2-glucan were infiltrated
as a pre-treatment on Nicotiana benthamiana leaves 24h previously
to Xanthomonas infection, restoring the necrosis production in all
mutants. By northern blot experiment, glucans turn out to be a
suppressor of PR1, a defense gene marker, and hence of the vegetal
immunity system.
S20.
PHYTOREMEDIATION EMPLOYING IN VITRO
CULTURES
Agostini, Elizabeth.
Dpto. de Biología Molecular, FCEFQyN, Univ. Nacional de Río
Cuarto. Argentina. E-mail: [e-mail]
Phytoremediation consists in the use of plants to remove, destroy
or sequester hazardous substances from the environment and offers
many potential advantages over traditional remediation
technologies, particularly its public acceptance and considerably
lower cost.
Recently, the number of results obtained with the help of in vitro
cultures, such as hairy roots, is rapidly increasing. These cultures
could be used for screening plants suitable for the removal of
organic and inorganic pollutants and they allow to study the
enzymatic catalysis involved in the bioconversion of pollutants to
non-toxic metabolites without the interference of other plant organs
or the microbiota. We have investigated the use of hairy root
cultures as inexpensive enzyme-containing tissues that are easy
to apply in the removal of phenolic compounds from aqueous
solutions. The optimum conditions (H
2
O
2
 concentration, pH, time
of exposure) to obtain high efficiencies in the process were
established. Appropriate controls were included. Peroxidase and
laccase activities and the remaining amount of phenols, were
determined. The polymerization catalyzed by peroxidases would
be the main mechanism involved in the removal process. We also
determined the possibility of re-using the roots for various
consecutive cycles, with high removal efficiency. These features
make this system an interesting alternative for use in continuos
detoxification programs.

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