Extracellular polysaccharides and polysaccharide-containing biopolymers from Azospirillum species: properties and the possible role in interaction with plant roots

Abstract

This paper reviews the results obtained in studies of the extracellular polysaccharides, lipopolysaccharide-protein complexes, polysaccharide-lipid complexes, lipopolysaccharides, and O-specific polysaccharides from bacteria of the genus Azospirillum. On the basis of present knowledge, the possible roles of the extracellular polysaccharides and polysaccharide-containing complexes of azospirilla in interaction with the roots of plants are discussed. Some pieces of evidence are considered in light of the lectin hypothesis originally proposed for the legume-Rhizobium symbiosis. In the context of these views of Azospirillumcereal associative pairs, a key process at the early stages of the interaction is the specific reaction of cereal root lectins with the extracellular polysaccharide components, containing N-acetyl-D-glucosamine as part of their structure. z

Halomonas maura is a physiologically versatile bacterium of both ecological and biotechnological interest

“…Although the exact mechanism of how it interacts with plant roots is not yet fully understood we can affirm that its anchoring capacity depends, among other factors, upon the production of extracellular polysaccharide, as it does with other diazotrophic and symbiotic microorganisms such as Azospirillum (Skvortsov and Ignatov 1998) and Sinorhizobium meliloti (Gonza´lez et al 1996).…”

“…Plasmids have also been described in other diazotrophs; all Azospirillum species, for example, possess plasmids of sizes ranging from 160 to over 592 Kb. Megaplasmids in other soil bacteria are known to carry essential information for plant interaction (Skvortsov and Ignatov 1998). The Agrobacterium virulence (vir) genes as well as the Rhizobium nodulation (nod) and host-specific nodulation (hsn) genes are encoded in megaplasmids.…”

The moderately halophilic bacteriumHalomonas maurais a free-living diazotroph

“…1) where the oxygen pressure was suitable both for its growth and for the activation of the genes responsible for nitrogenase synthesis, in the same way that Azospirillum, another free-living, aerobic, diazotrophic bacterium does [23]. Thus we first satisfied ourselves that strain S-31 T of H. maura was capable of growing in such a medium in a zone close to the substrate surface (Fig.…”

Co-inoculation of Legumes with Azospirillum and Symbiotic Rhizobia

“…The nature of this fi brillar material has not been determined yet. Extracellular polysaccharide production also has been related to the process of fl occulation of Azospirillum cells and might be similar to the fi brillar material produced during root association (Burdman et al 1998 ;Skvortsov and Ignatov 1998 ). The major outer membrane protein of A. brasilense appears to be involved in cell aggregation and the fi rst step of attachment.…”