The genetic organization and evolution of the broad host range mercury resistance plasmid pSB102 isolated from a microbial population residing in the rhizosphere of alfalfa

Abstract

Employing the biparental exogenous plasmid isolation method, conjugative plasmids conferring mercury resistance were isolated from the microbial community of the rhizosphere of field grown alfalfa plants. Five different plasmids were identified, designated pSB101-pSB105. One of the plasmids, pSB102, displayed broad host range (bhr) properties for plasmid replication and transfer unrelated to the known incompatibility (Inc) groups of bhr plasmids IncP-1, IncW, IncN and IncA/C. Nucleotide sequence analysis of plasmid pSB102 revealed a size of 55 578 bp. The transfer region of pSB102 was predicted on the basis of sequence similarity to those of other plasmids and included a putative mating pair formation apparatus most closely related to the type IV secretion system encoded on the chromosome of the mammalian pathogen Brucella sp. The region encoding replication and maintenance functions comprised genes exhibiting different degrees of similarity to RepA, KorA, IncC and KorB of bhr plasmids pSa (IncW), pM3 (IncP-9), R751 (IncP-1beta) and RK2 (IncP-1alpha), respectively. The mercury resistance determinants were located on a transposable element of the Tn5053 family designated Tn5718. No putative functions could be assigned to a quarter of the coding capacity of pSB102 on the basis of comparisons with database entries. The genetic organization of the pSB102 transfer region revealed striking similarities to plasmid pXF51 of the plant pathogen Xylella fastidiosa.

High diversity of bacterial mercuric reductase genes from surface and sub-surface floodplain soil (Oak Ridge, USA)

“…The sequences obtained with the forward primer were identical. The Dyella-like isolates had merA genes that differed somewhat from the closest match, pSB102, a full-sequenced plasmid from Alfalfa rhizosphere (Schneiker et al, 2001).…”

Antibiotic Resistance Pattern Among Gram Negative Mercury Resistant Bacteria Isolated From Contaminated Environments

“…In mercury contaminated areas, bacteria can exchange plasmids and transposons carrying mercury resistance genes. This event increases the number of resistant bacteria in such environments (28).…”

Horizontal gene transfer between bacteria

“…Replicon typing and sequencing of the complete plasmid (Tauch et al, 2002) revealed that this cryptic plasmid of a size of approx. 45 kbp was not related to any of the known BHR plasmids except to plasmid pSB102 (Schneiker et al, 2001). Sequencing of plant-associated bacteria revealed that many phytopathogenic and symbiotic bacteria carry plasmids (Vivian et al, 2001;Zhao et al, 2005), pathogenicity islands (Arnold et al, 2003) or integrons (Gillings et al, 2005).…”

“…Recipients functioning as a genetic sink, and introduced under laboratory or in situ conditions, have acquired MGEs conferring selectable traits such as mercury or antibiotic resistance from the bacterial fraction of bulk or rhizosphere soil (Drønen et al, 1998;Heuer and Smalla, 2007;Heuer et al, 2002;van Overbeek et al, 2002). Mercury resistance was used as an effective selective marker to exogenously isolate self-transferable plasmids from the phytosphere of different crops in Gram-negative recipients (Lilley and Bailey, 1997;Lilley et al 1994;Schneiker et al, 2001;Smit et al, 1998) or from mercury-polluted soils (Drønen et al, 1998). Capturing degradative genes resident on MGEs has also been successfully demonstrated from soils treated with 2,4-D, but not from untreated controls (Top et al, 1995;.…”