Two novel conjugative plasmids from a single strain of Sulfolobus

Abstract

Two conjugative plasmids (CPs) were isolated and characterized from the same 'Sulfolobus islandicus' strain, SOG2/4. The plasmids were separated from each other and transferred into Sulfolobus solfataricus. One has a high copy number and is not stable (pSOG1) whereas the other has a low copy number and is stably maintained (pSOG2). Plasmid pSOG2 is the first Sulfolobus CP found to have these characteristics. The genomes of both pSOG plasmids have been sequenced and were compared to each other and the available Sulfolobus CPs. Interestingly, apart from a very well-conserved core, 70 % of the pSOG1 and pSOG2 genomes is largely different and composed of a mixture of genes that often resemble counterparts in previously described Sulfolobus CPs. However, about 20 % of the predicted genes do not have known homologues, not even in other CPs. Unlike pSOG1, pSOG2 does not contain a gene for the highly conserved PlrA protein nor for obvious homologues of partitioning proteins. Unlike pNOB8 and pKEF9, both pSOG plasmids lack the so-called clustered regularly interspaced short palindrome repeats (CRISPRs). The sites of recombination between the two genomes can be explained by the presence of recombination motifs previously identified in other Sulfolobus CPs. Like other Sulfolobus CPs, the pSOG plasmids possess a gene encoding an integrase of the tyrosine recombinase family. This integrase probably mediates plasmid site-specific integration into the host chromosome at the highly conserved tRNA Glu loci.

Biological Diversity of Prokaryotic Type IV Secretion Systems

“…Only a few archaeal conjugation systems have been described, so far only for crenarchaeal species (91,174,217,243,250). An early study reported that Haloferax volcanii bidirectionally translocates chromosomal DNA transfer during conjugation, and large structures (2 mm long and 0.1 mm wide) bridging cells were postulated to mediate transfer (228).…”

Archaeal Extrachromosomal Genetic Elements

“…In the original host, pSOG1 exists at a very low copy number (153). After introduction into S. solfataricus through conjugation, pSOG1 was recovered as a high-copy-number plasmid.…”

“…This protein was first identified in a few cryptic plasmids through genome comparisons and was designated plasmid regulatory protein A (PlrA) (150). Genes encoding homologs of PlrA are also present in some archaeal conjugative plasmids (152,153) and in all known genomes of members of the Sulfolobaceae, including 10 Sulfolobus strains, Metallosphaera sedula, and Acidianus hospitalis. Since this ORF is absent from all other archaeal genomes and genetic elements, the genomic copies of plrA in the Sulfolobaceae are speculated to be derived from cryptic and conjugative plasmids via HGT.…”

“…As a second example, pSOG1 and pSOG2, two CPs from S. islandicus SOG2/4, share ϳ1/3 sequence homology (153). In the original host, pSOG1 exists at a very low copy number (153).…”

“…Interestingly, this plasmid was stably maintained in both S. islandicus and S. solfataricus, suggesting that it did not activate the defense action of the host CRISPR systems. Since both CPs were derived from the same host, it was postulated that these CPs or their ancestors might have undergone genetic variation during conjugation (153).…”