Nodulation factors from Rhizobium tropici are sulfated or nonsulfated chitopentasaccharides containing an N-methyl-N-acylglucosaminyl terminus

Abstract

Phaseolus vulgaris (common bean) can be nodulated by several Rhizobium species. Among them, Rhizobium tropici has a relatively broad host range, as it is able to infect beans, Leucaena trees, and several other legumes. This work describes the isolation and the characterization of extracellular factors (Nod factors) whose production from R. tropici was triggered by the transcriptional activation of its nod genes. These factors consist of a chitopentaose backbone in which the N-acetyl group of the nonreducing end glucosaminyl residue is replaced by an N-methyl-N-vaccenoyl one. Some of these molecules are sulfated on position 6 of the terminal reducing glucosamine.

Rhizobium tropici nodulation factor sulfation is limited by the quantity of activated form of sulfate

“…For Nod factor production, all the R. tropioci derivatives used in this study were grown in liquid minimal medium, in the same conditions as previously described [15]. Induction of R. tropici nodulation genes was achieved using 1.5 mM naringenin (4',5,7-trihydroxyflavanone; Sigma).…”

“…This crude extract was purified by HPLC on a semi-preparative Cls reversed-phase column (250 x 7.5 ram; Spherisorb ODS2, 5 mm; ColoChrom), using a water/acetonitrile gradient [15]. Each of the Nod factor containing fractions were further purified by HPLC on an analytical C18 reversed-phase column (250 x 4.6 mm, Spherisorb ODS1, 5 am, ColoChrom), as described for NodRt-V (Me,S) factors [15].…”

“…Each of the Nod factor containing fractions were further purified by HPLC on an analytical C18 reversed-phase column (250 x 4.6 mm, Spherisorb ODS1, 5 am, ColoChrom), as described for NodRt-V (Me,S) factors [15]. Detection was done by UV absorbance at 220 nm.…”

“…Previously, we have shown that the broad host range tropical bacterium R. tropici [14] (strain CFN299) produces partially sulfated nodulation factors [15]. This ability to produce a mixture of sulfated and non-sulfated Nod factors is believed to play a role in the broad host-range of this species.…”

Especificidade hospedeira de variantes Bradyrhizobium spp em soja (cvs peking e clark), caupi e guandu

“…Por exemplo: Rhizobium etli e R. loti têm o mesmo fator Nod, mas nodulam com espécies distintas de feijoeiro (Cardenas et al, 1995), o mesmo sendo observado com dois biovares de R. leguminosarum que embora tenham o mesmo fator Nod, também nodulam com espécies diferentes (Orgambide et al, 1995). Outro exemplo interessante que pode ser citado é a nodulação de feijoeiro com R. tropici e R. etlli, porém nesse caso existem diferentes tipos de fator Nod (Poupot et al, 1993). Contudo, cada vez mais se acredita que tal especificidade esteja relacionada com um conjunto de fatores e não com um único fator (Vargas & Hungria, 1997).…”