INVESTIGADORES
LOPEZ GARCIA Silvina Laura
artículos
Título:
Effects of N-starvation and C-source on Bradyrhizobium japonicum exopolysaccharide production and composition, and bacterial infectivity to soybean roots.
Autor/es:
JUAN IGNACIO QUELAS, SILVINA L. LÓPEZ-GARCÍA, ADRIANA CASABUONO, M. JULIA ALTHABEGOITI, ELÍAS J. MONGIARDINI, JULIETA PÉREZ-GIMÉNEZ, ALICIA COUTO, ANÍBAL R. LODEIRO
Revista:
ARCHIVES OF MICROBIOLOGY
Editorial:
Springer
Referencias:
Lugar: Berlin, Alemania; Año: 2006 vol. 186 p. 119 - 128
ISSN:
0302-8933
Resumen:
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The exopolysaccharide (EPS) is an
extracellular molecule that in Bradyrhizobium japonicum affects bacterial efficiency to nodulate soybean. Culture conditions
such as N availability, type of C-source,
or culture age can modify
the amount and composition of EPS. To better understand the relationship among these
conditions for EPS production, we analyzed their influence on EPS in B. japonicum USDA 110 and its derived
mutant DP22. This mutant has a
deletion including the 3¢ region of exoP, exoT, and the 5¢ region of exoB, and produces a shorter EPS devoid of
galactose. The studies were carried out in
minimal media with the N-source at starving or sufficient levels, and mannitol
or malate as the only C-source. Under N-starvation there was a net EPS
accumulation, the levels being similar in the wild type and the mutant with
malate as the C-source. By contrast, the amount of EPS diminished in
N-sufficient conditions, being poyhydroxybutyrate accumulated with culture age.
Hexoses composition was the same in both N-situations, either with mannitol or
malate as the only C-source, in contrast to previous observations made with different strains. This result suggests
that the change in EPS composition in response to the environment is not
general in B.
japonicum.
The wild type EPS composition was 1 glucose:0.5 galactose:0.5 galacturonic
acid:0.17 mannose. In DP22
the EPS had no galactose but had galacturonic acid, thus indicating that it was
not produced from oxidation of UDPgalactose. Infectivity was lower in DP22 than in USDA 110. When the mutant
infectivity was compared between N-starved or N-sufficient cultures, the
N-starved were not less infective, despite the fact that the amounts of altered
EPS produced by this mutant under N-starvation were higher than in
N-sufficiency. Since this altered EPS does not bind soybean lectin, the interaction
of EPS with this protein was not involved in increasing DP22 infectivity under N-starvation.