Prevalence of pSmeSM11a-like plasmids in indigenous Sinorhizobium meliloti strains isolated in the course of a field release experiment with genetically modified S. meliloti strains

Abstract

Plasmid pSmeSM11a, residing in the indigenous Sinorhizobium meliloti strain SM11 originating from a field in Strassmoos (Bavaria, Germany), was analysed previously at the genomic level. Thirty-seven indigenous S. meliloti strains, originating from two different locations in Germany, were screened for genes identified previously on pSmeSM11a. Seven of these strains harbour accessory plasmids that are very similar to pSmeSM11a. The identified pSmeSM11a-like plasmids are c. 130-150 kb in size and possess nearly identical restriction profiles. Up to 30 genes identified previously on pSmeSM11a could be detected on these plasmids by hybridisation experiments, e.g., the nodulation genes nodP and nodQ, the ethylene level modulation gene acdS and the taurine metabolism gene tauD. A few pSmeSM11a genes were also detected on other plasmids. The reference plasmid pSmeSM11a contains a region that is similar to a segment of S. meliloti strain Rm1021 pSymA. Regions with similarity to pSymA were also detected on the aforementioned seven pSmeSM11a-like plasmids. The specifications of these regions are nearly identical to the one on pSmeSM11a and differ from Rm1021 pSymA as determined by nucleotide sequence analysis. Two further plasmids similar to pSmeSM11a completely lack the pSymA-region. Those strains carrying accessory plasmids that contain the acdS gene encoding 1-aminocyclopropane-1-carboxylate deaminase are able to grow on 1-aminocyclopropane-1-carboxylate as the sole source of nitrogen, demonstrating functionality of the acdS gene product. About 36% of the analysed plasmids, including three pSmeSM11a-like plasmids, could be transferred to another S. meliloti recipient strain, allowing for their dissemination in S. meliloti populations.

Population genomics of Sinorhizobium medicae based on low-coverage sequencing of sympatric isolates

“…This involves the acdS gene, which encodes an enzyme that increases nodulation by metabolising a precursor of ethylene (Ma et al, 2004), and has been described from the plasmid pSmeSM11a. This gene was present in 89% of S. meliloti isolates sampled in Germany (Kuhn et al, 2008). Surprisingly, not one of the S. medicae strains that we sampled had this gene.…”

“…The genome of S. medicae WSM 419 also includes a 219-kb plasmid called pSMED03. Although S. meliloti 1021 does not have any comparable plasmid, additional plasmids have also been observed in some other strains of this species Olivares, 1993, 1994;Stiens et al, 2006Stiens et al, , 2007Kuhn et al, 2008). Based on sequencing of several loci, S. medicae is less diverse than S. meliloti, especially at chromosomal loci (Bailly et al, 2006;van Berkum et al, 2006).…”

“…Novel genomic sequences have been described both from the cryptic plasmids of the strain SM11 (Stiens et al, 2006(Stiens et al, , 2007 and also from a representational difference analysis based on the strain ATCC 9930 (Guo et al, 2005). These new sequences occur with a wide range of frequencies in natural populations of S. meliloti (Guo et al, 2005;Kuhn et al, 2008). Some of this genetic material might have an important role in the adaptation of Medicago symbionts.…”

Fate and Ecological Interactions of Firefly Luc Gene-Tagged Sinorhizobium Meliloti 2011-Bacteria in Soil Inhabited by High Levels of Indigenous Alfalfa Nodulating Populations

“…Moreover, the acdS gene encoding ACC deaminase was identified, which was proposed to be involved in reducing the phytohormone ethylene and thereby influencing nodulation events (Stiens et al 2006). A recent study which addressed the distribution of pSmeSM11a specific sequences in strains belonging to dominant ERIC fingerprint groups of the FAL study (Selbitschka et al 2006) and of this work demonstrated the widespread occurrence of such plasmid types (Kuhn et al 2008). In conclusion, these studies provided some clue about the possible cause why the indigenous population had readily outcompeted strains L1 and L33 for alfalfa nodulation at both release sites.…”

Rhizobial plasmids — replication, structure and biological role

“…In recent years, the multipartite genomes have been sequenced in several symbiotic rhizobial species including: S. meliloti 1021 [50][51][52] [62]. pSymA is absolutely necessary for symbiosis, bearing the nodule formation (nod) and most nitrogen fixation, as well as some catabolic genes and transporters, but no essential genes [50][51][52].…”