Rhizobia from Lanzarote, the Canary Islands, That Nodulate Phaseolus vulgaris Have Characteristics in Common with Sinorhizobium meliloti Isolates from Mainland Spain

Abstract

The stable, low-molecular-weight (LMW) RNA fractions of several rhizobial isolates of Phaseolus vulgaris grown in the soil of Lanzarote, an island of the Canary Islands, were identical to a less-common pattern found within Sinorhizobium meliloti (assigned to group II) obtained from nodules of alfalfa and alfalfa-related legumes grown in northern Spain. The P. vulgaris isolates and the group II LMW RNA S. meliloti isolates also were distinguishable in that both had two conserved inserts of 20 and 46 bp in the 16S-23S internal transcribed spacer region that were not present in other strains of S. meliloti. The isolates from P. vulgaris nodulated bean but not Medicago sativa, while those recovered from Medicago, Melilotus, and Trigonella spp. nodulated both host legumes. The bean isolates also were distinguished from those of Medicago, Melilotus, and Trigonella spp. by nodC sequence analysis. The nodC sequences of the bean isolates were most similar to those reported for S. meliloti bv. mediterranense and Sinorhizobium fredii bv. mediterranense (GenBank accession numbers DQ333891 and AF217267, respectively). None of the evidence placed the bean isolates from Lanzarote in the genus Rhizobium, which perhaps is inconsistent with seed-borne transmission of Rhizobium etli from the Americas to the Canaries as an explanation for the presence of bean-nodulating rhizobia in soils of Lanzarote.

Bacterial Associations with Legumes

“…C. arietinum can be nodulated by strains of several species of Mesorhizobium, but all of them carry nearly identical nodC genes and belong to the symbiovar ciceri Laranjo et al, 2008). In contrast, P. vulgaris is very promiscuous, and can be nodulated by different symbiovars that carry very divergent symbiotic genes (Michiels et al, 1998;Zurdo-Piñeiro et al, 2009). The study of the promiscuity degree of legumes deserves more investigations to fill the the lack of knowledge about all the endosymbionts able to nodulate each legume.…”

“…The nod genes of the operon nodABC are determinants of the host range (Winsor 1989;Györgypal et al, 1991;Relic et al, 1994;Roche et al, 1996;Perret et al, 2000). Within these genes, the nodC has been widely analyzed in Downloaded by [Istanbul Universitesi Kutuphane ve Dok] at 14:48 05 November 2014 rhizobial strains and found to be related not only with the host range of rhizobia but also with the promiscuity degree of the hosts (Roche et al, 1996;Perret et al, 2000;Laguerre et al, 2001;Rivas et al, 2007;Iglesias et al, 2007;Zurdo-Piñeiro et al, 2009, Ruíz-Díez et al, 2012a. The analysis of this gene allowed confirmation that P. vulgaris is a very promiscuous host as it can be nodulated by several divergent nodC symbiovars such as phaseoli, gallicum, giardinii and mediterranense, and that C. arietinum is a very resctrictive host as it can be nodulated only by the symbiovar ciceri (Table 3).…”

“…It has been known for many years that legumes have different promiscuity degrees. Whereas some of them can be nodulated by several species of rhizobia such as Macroptilium or Phaseolus Michiels et al, 1998;Zurdo-Piñeiro et al, 2009;García-Fraile et al, 2010), others are restrictive hosts for nodulation such as Cicer, Trifolium or Vicia (Broughton and Perret 1999). In the same way, rhizobial strains can have a broad or a narrow host range.…”

“…For example, Vicia and Trifolium are restrictive hosts and there are no cross-nodulation abilities between biovars viciae and trifolii; however, strains of these two biovars can nodulate the legume host of the biovar phaseoli because Phaseolus is a promiscuous legume. For this reason the suitability of the definition of biovars affecting this type of legumes has been discussed (Zurdo-Piñeiro et al, 2009). This point can be solved by using a phylogenetic criterion based on the nodC gene analysis which makes it possible to clearly distinguish the biovars viciae, trifolii and phaseoli (García-Fraile et al, 2010).…”

“…Thus, in the biovar medicaginis of E. meliloti, nodC gene sequence analysis supported the existence of this biovar defined on the basis of nodA gene analysis (Bailly et al, 2007). The nodC gene was used, for instance, to define the biovar mediterranense that include strains of E. fredii and E. meliloti able to nodulate Phaseolus, but not Medicago (Mnasri et al, 2007), or the new biovar lancerottense that was recently described within E. meliloti to include the strains able to nodulate Lotus endemic of Canary Islands (León-Barrios et al, 2009). These strains harbour a nodC gene phylogenetically unrelated to those carried by other E. meliloti biovars and by M. loti.…”