Immunofluorescent polar tips of Rhizobium japonicum: possible site of attachment or lectin binding

Abstract

Rhizobium japonicum USDA 31 demonstrated marked polarity by binding homologous fluorescent antibody (FA) heavily on one end of the cell. FA prepared against R. japonicum strains 110 and 138, and against R. trifolii TA1 cross-reacted with strain 31 only in the polar tip region. No polar immunofluorescing tips could be seen with FA against two other strains of R. japonicum or with those against several unrelated microorganisms. Common antigens localized only in a polar region were seen in many rhizobia stained with R. japonicum 31 FA: 22 of 23 strains of R. japonicum, 10 of 17 strains of R. trifolii, 3 of 7 strains of R. melitolii, 3 of 6 strains of R. phaseoli, and 3 of 9 strains of R. leguminosarum had some cells with detectable polar tips. The proportion of R. japonicum 31 cells with polar tips was high throughout the growth cycle. Polar tip staining was not affected by drastic cell treatments. A function was proposed for the polar tip region as a site for attachment. R. japonicum 31 cells attached to each other in a tip-to-tip fashion and endwise to fungal hyphae with the polar tip in contact with the hyphal wall. Binding of fluorescein isothiocyanate-labeled soybean lectin to certain strains of R. japonicum gave additional evidence of polarity. Polar binding of both antibody and lectin may provide insights into relationships between rhizobia and roots of host legumes.

Ultrastructure of Rhizobium japonicum in relation to its attachment to root hairs

“…Note the capsular material (c) and its attachment to the root hair surface (RH would be expected from a low lectin-binding strain, where only less than 1% of the population possessed capsule. Polarity of attachment as described in some strains (7,15) was not observed, as the lectin-binding capsule circumscribed the bacteria in this particular strain. Polarized attachment seems to be correlated with a polarized lectin-binding capsule.…”

Bacterial attachment as related to cellular recognition in the rhizobium‐legume symbiosis

“…This alteration in distribution of trifoliin A receptors may possibly explain the distinctive polar attachment of the bacterial cells to the root hair surface toward the end of Phase I attachment. Under certain growth conditions, the receptor sites on R japonicum that bind soybean lectin also accumulate at one cell pole [26,30,31].…”

A comparison of lectin-binding activity in two strains ofRhizobium japonicum

“…The lectin-binding hypothesis was proposed 10 years ago [4] to account for the initiation of specific interaction between host plant and Rhizobium. Although the nature of the soybean lectin receptor on R. japonicum has been controversial, evidence has accumulated in favor of extracellular polysaccharides (EPS) [5][6][7][8][9][10][11][12]. In liquid culture, the latter exist in both capsular and diffusible forms [11,12], both of which may be assayed simultaneously by means of the sensitive hemagglutination inhibition assay (HIA) [11].…”