IBBM   21076
INSTITUTO DE BIOTECNOLOGIA Y BIOLOGIA MOLECULAR
Unidad Ejecutora - UE
congresos y reuniones científicas
Título:
Role of two flagella of Bradyrhizobium japonicum in Competition for Nodulation of Soybean
Autor/es:
ALTHABEGOITI, M. JULIA; COVELLI, JULIETA M.; LÓPEZ, M. FLORENCIA; LODEIRO, ANÍBAL R.
Lugar:
San Miguel de Tucumán, Tucumán
Reunión:
Congreso; VII Congreso Argentino de Microbiología General SAMIGE del Bicentenario; 2011
Institución organizadora:
SAMIGE
Resumen:
The
agronomic use of Bradyrhizobium
japonicum in symbiosis with soybean is via inoculation ofseeds
or seed furrow with rhizobia. As a result, the roots of soybean plants develop
nodulesthat once became occupied by B. japonicum can fix
atmospheric N2 to NH4+,
reducing it to an extent that would satisfy all the needs of the plant.
Therefore, the capacity of rhizobia to movefrom the soil or from seeds to the
sites of infection on the roots results determinant for theestablishment of the
symbiosis and consequently motility of B. japonicum is very
interesting tostudy.B. japonicum has two flagellar systems. One
system is composed of a 33 kDa flagellin (thinfilament) and the other consists
of a 65 kDa flagellin (thick filament); it has been proposed thatboth play different
roles (Kanbe et al., 2007). From the parental strains B. japonicum LP
3004(derived from USDA 110, Sm-resistant) and LP 3008 (LP 3004 with an
increased motility)(Althabegoiti et al., 2008), we generated mutants lacking
thin flagellum (LP 6865 and LP 6866),mutants lacking thick flagellum (LP 5843
and LP 5844) and mutants that lack flagella (LP 6543y LP 6644), respectively.
Strains were observed by TEM and mutations and morphology wereconfirmed for
each type of flagellum. After that, liquid cultures of each mutant were
observed ina phase-contrast microscope and only strains that have thick
filament were capable of swimstraightly whereas strains with thin filament
tumbled more frequently. Finally, those that nothave flagella did not swim.With
the purpose of studying contribution of each flagellum in colonization of
soybean rootscompetition experiments were done. Competitiveness was examinated
at field capacity andsoybean was inoculated with mixtures containing each
parental strain together with eachderived mutant. After twenty one days of
growth in greenhouse the occupation of plant noduleswas determinated by their
antibiotic resistance and a statistical analysis was done. As a result,we
observed that mutants lacking thick flagellum and non-motile double mutants
were lesscompetitive that parental strains, but there were not completely
displaced. However, mutantslacking thin flagellum were more competitive for
nodulation. This event suggests that thinfilament is not necessary for B. japonicum movement
to the roots, showing a complex role ofthese flagellins in competitiveness.
They could also have an additional function involved ininteraction with the
plant, opening interesting aspects for further analysis.