Bacteriocin small of fast-growing rhizobia is chloroform soluble and is not required for effective nodulation

Abstract

small bacteriocin is a low-molecular-weight bacteriocin which is common in fast-growing rhizobia. As its activity could not be detected in chloroform-sterilized culture supernatants (P. R. Hirsch, J. Gen. Microbiol. 113:219-228, 1979), the bacteriocin could not be purified in order to study its mechanism of action. We report here that small is soluble in chloroform, an observation which led to effective and simple (partial) purification. Other properties of small are its low molecular weight, which is estimated to be between 700 and 1,500, its resistance to proteolytic enzymes, pectinase, and lysozyme, and its heat stability at pH 5.5 but not at pH 7.0. Its bactericidal action on exponentially growing sensitive cells was not detected until 11 h after its addition. The bactericidal action was preceded by inhibition of cell division. To determine whether smal activity is required for nodulation or nitrogen fixation, a transposon TnS-induced small-negative mutant was isolated. The observation that this strain formed normal, acetylene-reducing root nodules showed that smal production is not a prerequisite for the formation of effective nodules.

Analysis of Quorum-Sensing-Dependent Control of Rhizosphere-Expressed ( rhi ) Genes in Rhizobium leguminosarum bv. viciae

“…C. violaceum CV026 does not detect 3OH,C 14:1 -HSL, and so we measured the effect of mutating rhiI on production of this AHL using A34 as a sensor strain in a bacteriocin-like assay (35). Strain A721 did not induce a zone of growth inhibition, indicating that repression of 3OH,C 14:1 -HSL occurred normally and therefore mutation of rhiI did not affect the ability of pRL1JI to repress production of this AHL (data not shown).…”

“…viciae (15). Indeed the compound previously known as "small bacteriocin" (17,35) had been purified and shown to be 3OH,C 14:1 -HSL (30). It was suggested that this AHL induces stationary phase in R. leguminosarum bv.…”

“…Many strains of the R. leguminosarum biovars viciae, trifolii, and phaseoli (15,17,35,37) make small bacteriocin (and thus probably make 3OH,C 14:1 -HSL) as does Rhizobium etli (26), whereas R. meliloti and the closely related Agrobacterium tumefaciens do not (17,37). In addition, R. etli makes at least six other compounds that are probably AHLs (26).…”

Transposition of Tn1831 to sym plasmids of Rhizobium leguminosarum and Rhizobium trifolii

“…The production of small bacteriocin (Rps) and medium bacteriocin (Mep) was determined using Rhizobium strain 248 and RBL101 as indicator strains [22]. Transduction with RL38JI was performed as described by Buchanan-Wollaston [23].…”

Cloning and Characterization of a Rhizobium leguminosarum Gene Encoding a Bacteriocin with Similarities to RTX Toxins

“…Large bacteriocins have been shown to resemble defective bacteriophages (19,28,41). Small bacteriocins were found to be chloroform soluble and heat labile and to have molecular masses of less than 2,000 daltons (19,50). More recently, small bacteriocins were shown to be acylated homoserine lactone compounds related to quorum-sensing molecules (18,39).…”