INVESTIGADORES
MONGIARDINI Elias Javier
artículos
Título:
Analysis of two polyhydroxyalkanoate synthases in Bradyrhizobium japonicum USDA 110.
Autor/es:
QUELAS, JUAN IGNACIO; MONGIARDINI, ELIAS JAVIER; PEREZ-GIMENEZ, JULIETA; PARISI, GUSTAVO; LODEIRO, ANIBAL
Revista:
JOURNAL OF BACTERIOLOGY
Editorial:
AMER SOC MICROBIOLOGY
Referencias:
Lugar: Washington; Año: 2013 p. 3145 - 3155
ISSN:
0021-9193
Resumen:
Bradyrhizobium japonicum USDA 110 has five polyhydroxyalkanoate (PHA)
synthases (PhaC) annotated in its genome: bll4360 (phaC1), bll6073
(phaC2), blr3732 (phaC3), blr2885 (phaC4), and bll4548 (phaC5). All
these proteins possess the catalytic triad and conserved amino acid
residues of polyester synthases and are distributed into four different
PhaC classes. We obtained mutants in each of these paralogs and analyzed
phaC gene expression and PHA production in liquid cultures. Despite the
genetic redundancy, only phaC1 and phaC2 were expressed at significant
rates, while PHA accumulation in stationary-phase cultures was impaired
only in the ΔphaC1 mutant. Meanwhile, the ΔphaC2 mutant produced more
PHA than the wild type under this condition, and surprisingly, the phaC3
transcript increased in the ΔphaC2 background. A double mutant, the
ΔphaC2 ΔphaC3 mutant, consistently accumulated less PHA than the ΔphaC2
mutant. PHA accumulation in nodule bacteroids followed a pattern similar
to that seen in liquid cultures, being prevented in the ΔphaC1 mutant
and increased in the ΔphaC2 mutant in relation to the level in the wild
type. Therefore, we used these mutants, together with a ΔphaC1 ΔphaC2
double mutant, to study the B. japonicum PHA requirements for survival,
competition for nodulation, and plant growth promotion. All mutants, as
well as the wild type, survived for 60 days in a carbon-free medium,
regardless of their initial PHA contents. When competing for nodulation
against the wild type in a 1:1 proportion, the ΔphaC1 and ΔphaC1 ΔphaC2
mutants occupied only 13 to 15% of the nodules, while the ΔphaC2 mutant
occupied 81%, suggesting that the PHA polymer is required for successful
competitiveness. However, the bacteroid content of PHA did not affect
the shoot dry weight accumulation.