Trifolitoxin Production and Nodulation Are Necessary for the Expression of Superior Nodulation Competitiveness by Rhizobium leguminosarum bv. trifolii Strain T24 on Clover

Abstract

Many reports document the ability of certain Rhizobium strains to occupy nodules to the exclusion of other strains. The molecular basis of the superior nodulation competitiveness of any strain is not known, although important advances in recent years have been made (7-9, 12, 19, 20 (12,15,16,22,23,25,26).Hodgson et al. (12) have suggested that bacteriocin production by R. leguminosarum bv. trifolii CB782 is involved in its superior nodulation competitiveness. This was shown by co-inoculating CB782 with bacteriocin-sensitive and -resistant strains. However, these sensitive and resistant strains may differ in other respects that affect nodulation competitiveness aside from bacteriocin production. Transposon mutants of CB782 lacking bacteriocin production would demonstrate the role ofbacteriocin production in competitiveness, since Tn5 is a single point mutagen (3). We are studying the basis of the competitiveness expressed by R. leguminosarum bv. trifolii strain T24, which was isolated in Florida from the nodules of Trifolium dubium in 1937 (17, 25).In 1968, Schwinghamer and Belkengren (25) reported that T24 had three important properties: (a) it induces ineffective nodules on clover roots, (b) it produces a very potent antibiotic inhibitory toward strains of Rhizobium, and (c) it prevents nodulatiop by other strains of R. keguminosarum bv. trifolii. Schwinghamer and Belkengren (25) suggested that the basis for the nodulation competitiveness of T24 was its ability to produce an anti-rhizobial compound.The purpose of the experiments described here are to (a) determine using transposon mutagenesis the roles of antibiotic production and nodulation in the expression of nodulation competitiveness by T24, (b) determine the range of anti-rhizobial activity of the T24 antibiotic, and (c) determine whether T24 can induce effective nodules on any available clover species.

A newly discovered gene, tfuA, involved in the production of the ribosomally synthesized peptide antibiotic trifolitoxin

“…Three were found that could no longer produce TFX on minimal medium (BSM-N), i.e., Tn5-1, Tn5-2, and Tn5-3 (34). Tn5-4 is a Tn5 derivative of T24 which is unaffected in TFX production (34). When plasmids harboring the tfxABCDEFG fragment were conjugated into each of the T24::Tn5 derivatives, we noticed that the zone of inhibition produced by the Tn5-2 derivative was smaller than those produced by the Tn5-1 and Tn5-3 derivatives (data not shown).…”

“…In initial studies of the genetics of TFX production, R. leguminosarum bv. trifolii strain T24 was mutagenized with the transposon Tn5 (34). Approximately 5,600 Tn5 mutants were screened.…”

“…A number of features make TFX an interesting antibiotic for study. Its spectrum of activity is quite narrow but includes bacteria that are plant symbionts and plant and animal pathogens (29,34,35). TFX has already been shown to limit nodules formed by TFXsensitive strains (32-34) and so may provide a solution to the Rhizobium competition problem (9, 36).…”

“…Its spectrum of activity is quite narrow but includes bacteria that are plant symbionts and plant and animal pathogens (29,34,35). TFX has already been shown to limit nodules formed by TFXsensitive strains (32)(33)(34) and so may provide a solution to the Rhizobium competition problem (9,36). This problem arises when inoculant strains are not competitive for legume root nodulation against strains indigenous to soil.…”

Evaluation of a Strategy for Identifying Nodulation Competitiveness Genes in Rhizobium Leguminosarum Biovar Phaseoli

“…Such studies have shown that competitiveness is affected by motility and chemotaxis (Ames & Bergman, 1981 ;Caetano-AnollCs et al, 1988;Liu et al, 1989;Mellor et al, 1987;Zdor & Pueppke, 1991), cell surface polysaccharides (Araujo & Handelsman, 1990;Bhagwat & Keister, 1990;Handelsman et al, 1984;Milner et al, 1992;Trinick & Hadobas, 1989;Ugalde et al, 1986;Zdor & Pueppke, 1991;Lagares et al, 1992), bacteriocin production (Triplett & Barta, 1987), succinate-sensitivity (Urban, 1988), and rate of nodule induction (Hahn & Hennecke, 1988). Such studies have also demonstrated that the ability to fix nitrogen (Amarger, 1981;Hahn & Struder, 1986;Sanjuan & Olivares, 1991 b) and to metabolize particular aromatic compounds (Rynne et al, 1988) does not affect competitiveness under the conditions tested.…”