Archives of Microbiology

, Volume 186, Issue 2, pp 119–128

Effects of N-starvation and C-source on Bradyrhizobium japonicum exopolysaccharide production and composition, and bacterial infectivity to soybean roots

  • Juan Ignacio Quelas
  • Silvina L. López-García
  • Adriana Casabuono
  • M. Julia Althabegoiti
  • Elías J. Mongiardini
  • Julieta Pérez-Giménez
  • Alicia Couto
  • Aníbal R. Lodeiro
Original Paper

DOI: 10.1007/s00203-006-0127-3

Cite this article as:
Quelas, J.I., López-García, S.L., Casabuono, A. et al. Arch Microbiol (2006) 186: 119. doi:10.1007/s00203-006-0127-3

Abstract

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 ΔP22. 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 ΔP22 the EPS had no galactose but had galacturonic acid, thus indicating that it was not produced from oxidation of UDP-galactose. Infectivity was lower in ΔP22 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 ΔP22 infectivity under N-starvation.

Keywords

Bradyrhizobium japonicumEPSNitrogenInfectivitySymbiosisSoybean

Abbreviations

CPS

Capsular polysaccharide

DAI

Days after inoculation

EPS

Exopolysaccharide

Gal

Galactose

GalA

Galacturonic acid

Glc

Glucose

GlcA

Glucuronic acid

Mal

Malate

Man

Mannose

Mtl

Mannitol

PHB

Polyhydroxybutyrate

OD500

Optical density at 500 nm

RDU

Relative distance unit

RT

Root tip

SBL

Soybean lectin

SERH

Smallest emergent root hairs

Copyright information

© Springer-Verlag 2006

Authors and Affiliations

  • Juan Ignacio Quelas
    • 1
  • Silvina L. López-García
    • 1
  • Adriana Casabuono
    • 2
  • M. Julia Althabegoiti
    • 1
  • Elías J. Mongiardini
    • 1
  • Julieta Pérez-Giménez
    • 1
  • Alicia Couto
    • 2
  • Aníbal R. Lodeiro
    • 1
  1. 1.Instituto de Bioquímica y Biología Molecular (IBBM), Departamento de Ciencias Biológicas, Facultad de Ciencias ExactasUniversidad Nacional de La PlataLa PlataArgentina
  2. 2.Centro de Investigaciones en Hidratos de Carbono (CIHIDECAR), Departamento de Química Orgánica, Facultad de Ciencias Exactas y NaturalesUniversidad de Buenos AiresBuenos AiresArgentina