Carbohydrate binding activities of Bradyrhizobium japonicum: unipolar localization of the lectin BJ38 on the bacterial cell surface.

Abstract

A polyclonal antiserum generated against the Bradyrhizobiumjaponicum lectin BJ38 was characterized to be specifically directed against the protein. Treatment of B. japonicum cells with this antiserum and subsequent visualization with transmission electron microscopy and both conventional and confocal fluorescence microscopy revealed BJ38 at only one pole of the bacterium. BJ38 appeared to be organized in a tuft-like mass, separated from the bacterial outer membrane. BJ38 localization was coincident with the attachment site for (i) homotypic agglutination to other B. japoncum cells, (it) adhesion to the cultured soybean cell line SB-1, and (iu) adsorption to Sepharose beads covalently derivatized with lactose. In contrast, the plant lectin soybean agglutinin labeled the bacteria at the pole distant from the bacterial attachment site. These results indicate that the topological distribution of BJ38 is consistent with a suggested role for this bacterial lectin in the polar binding ofB.japonium to other ceUs and surfaces.Bradyrhizobiumjaponicum normally infects roots of soybean plants leading to symbiotic nitrogen fixation (1-3). We have documented (4) that this bacterial strain exhibits four saccharide-specific binding activities: (i) adsorption to Sepharose beads derivatized with lactose (Lac-Sepharose), (ii) homotypic autoagglutination, (iii) heterotypic binding to cultured soybean (SB-1) cells, and (iv) heterotypic adhesion to soybean roots. In all four of these assays, galactose inhibited the binding but a C-2 derivative of the monosaccharide N-acetyl-D-galactosamine failed to yield the same effect. Mutants ofB. japonicum, designated as N4 and N6, that were isolated on the basis of a defect in one binding activity (SB-1 cell binding) showed a concomitant loss in the other three binding capacities (4). These observations suggested that all four of the carbohydrate-specific binding processes may be mediated by the same component(s) and mechanism(s). Consistent with this proposal, we have purified a carbohydrate binding protein, designated BJ38 (Mr 38,000), which has an affinity for galactose and lactose "13-and 240-fold higher, respectively, than its affinity for N-acetyl-D-galactosamine (5). This carbohydrate binding specificity correlates well with that of the B. japonicum binding activities. It was proposed, therefore, that BJ38 may mediate the carbohydrate binding activities of B. japonicum.In all four carbohydrate-specific binding activities tested, B. japonicum bound in a polar fashion (4). Thus, any hypothesis implicating a role of BJ38 in these binding assays would require that the lectin be exposed at the surface of the bacterium where attachment occurs. In the present communication, we report the characterization of a specific anti-BJ38 antibody that has allowed us to identify the topological distribution of BJ38 on the bacterial cell surface. MATERIALS AND METHODSCeUl Cultures. B. japonicum (RilOd) was originally obtained from Barry Chelm of Michigan State University. This bacterial strain was ...

In Vitro Culture and Phylogenetic Analysis of "Candidatus Arsenophonus triatominarum," an Intracellular Bacterium from the Triatomine Bug, Triatoma infestans

“…4), bacteria exhibited clustering and unipolar agglutination. This phenomenon has been observed with cultures of the plant symbiont Bradyrhizobium japonicum, and agglutination between bacterial cells and soybean cells is known to be mediated by a lactose-specific lectin (24). Specific processes of host cell adhesion and invasion are characteristic of many intracellular microorganisms.…”

A unipolarly located, cell-surface-associated agglutinin, RapA, belongs to a family of Rhizobium-adhering proteins (Rap) in Rhizobium leguminosarum bv. trifolii The GenBank accession numbers for the sequences reported in this paper are AF265222, AF265223, AF315809 and AF315810.

“…Polarity is a well-characterized feature also in the attachment behaviour of B. japonicum, where the BJ38 lectin and the receptors for the soybean lectin are situated at opposite poles. The BJ38 pole has been shown to make the contact with the soybean root (Loh et al, 1993). At present we do not know if the RapA pole corresponds to the trifoliin A pole (Dazzo et al, 1982 ;Sherwood et al, 1984) or the opposite one.…”

“…In Bradyrhizobium japonicum, a bacterial lactose-sensitive lectin located at one pole of the bacteria has been reported to determine the specific binding of the bacteria to soybean roots (Loh et al, 1993 ;Ho et al, 1994). An -fucose-sensitive lectin produced by Bradyrhizobium sp.…”

A Rhizobiales-Specific Unipolar Polysaccharide Adhesin Contributes to Rhodopseudomonas palustris Biofilm Formation across Diverse Photoheterotrophic Conditions

“…Beyond C. crescentus and A. tumefaciens, polar polysaccharide adhesins are also a common morphological trait across ecologically diverse Alphaprotebacteria (1,14,18), especially among Rhizobiales species (19)(20)(21)(22)(23)(24)(25). However, the genetic and biochemical diversity of the adhesins across this clade is unclear.…”