Abstract Detail

Don Kaplan - his legacy: Influencing teaching and research

Fujishige, N.A. [1], Kapadia, N.N. [1], Hirsch, Ann M. [1].

A feeling for the microorganism: Structure on a small scale. Biofilms and root colonization..

Biofilms are structured communities of bacterial cells enclosed in a self-produced polymeric matrix and adherent to an inert or living surface; they have clinical, industrial and environmental impacts. We are interested in studying the role of biofilm formation in the early stages of the Rhizobium-legume symbiosis, in which Gram-negative rhizobia provide fixed nitrogen to a host-legume, and in return, the legume provides carbon-containing molecules. The details of how the symbionts recognize each other are well known: plant flavonoids induce rhizobial nodulation (nod) genes, which act together to synthesize Nod factor. Differentially substituted Nod factors serve as species-specific morphogens to elicit development changes in the plant root. Because root colonization is an important early step in the establishment of the symbiosis, we looked at rhizobial attachment in greater detail. We developed conditions for analyzing biofilms of Rhizobium leguminosarum bv. viciae and Sinorhizobium meliloti using the plate assay described by O’Toole et al. (1999. Methods Enzymol. 310:91-109). This assay allows us to screen a large number of mutants and thus serves as an excellent model system for studying root colonization. Our goal is to characterize the genes involved in aggregation and attachment because these appear to be shared in both biofilm formation and rhizobial entry of legume root cells. By screening S. meliloti symbiotic mutants, we found a number that are impaired in biofilm formation on both the host legume roots and on inert surfaces. When plasmids containing the genes represented by these mutations were transferred to wild-type S. meliloti or to Agrobacterium tumefaciens, the transconjugants exhibited enhanced biofilm formation over the wild-type strains.

1 - UCLA, Dept. of MCD Biology and Mol Biol Institute, 405 Hilgard Avenue, Los Angeles, California, 90095-1606, USA

Keywords:
biofilm
symbiosis
Leguminosae
Rhizobium.

Presentation Type: Symposium
Session: 33-1
Location: Ballroom 2 (Cliff Lodge)
Date: Tuesday, August 3rd, 2004
Time: 1:30 PM
Abstract ID:83