Poster: Plant Pathogen/Symbiont Interactions

Abs # 755: Biofilm formation by rhizobia on roots and inert surfaces

Presenter:	Fujishige, Nancy A., nfujishi@ucla.edu
Authors	Fujishige, Nancy A. (A)   Jankaew, Katherine  (A)   Butcher, Chris  (A)   Kapadia, Neel  (A)   Hirsch, Ann M. (A) (B)
Affiliations:	(A): University of California, Los Angeles Department of Molecular, Cell and Developmental Biology (B): University of California, Los Angeles Molecular Biology Institute

In the Rhizobium-legume symbiosis, Gram-negative rhizobia provide fixed-nitrogen to a host-legume. In return, the legume provides carbohydrates and houses the rhizobia in root nodules. Symbionts recognize each other by exchanging species-specific molecular signals. For instance, lectins are carbohydrate-binding proteins, which immunolocalize to root hair tips. They are thought to mediate attachment to compatible rhizobia by binding to the characteristic surface polysaccharide(s) of the bacteria. In a previous study of transgenic alfalfa plants carrying either the soybean or pea lectin gene, we found that strains that normally do not nodulate alfalfa would do so, but only if the nod genes of the compatible Sinorhizobium meliloti were transferred to the heterologous strain. Furthermore, we observed greater attachment of the transconjugent Bradyrhizobium japonicum or Rhizobium leguminosarum bv. viciae to the appropriate transgenic root¹. We analyzed these strains for the ability to form biofilms. Biofilms are structured communities of microbes enclosed in a self-produced polymeric matrix and adherent to an inert or living surface. Biofilms constitute the majority of bacterial biomass in natural environments, and may improve survival under adverse environmental conditions. We hypothesize that rhizobia express genes for biofilm formation under conditions where their hosts do not develop nitrogen-fixing nodules or when faced with other environmental stresses. To test this hypothesis, we developed assay conditions for biofilm formation of R. leguminosarum bv. viciae and S. meliloti. Furthermore, we will discuss mutants that are impaired in biofilm formation on both plant roots as well as on inert surfaces. ¹van Rhijn et al., 2001. Plant Physiol. 125: 133-144.