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Identification of a new insertion element, similar to gram-negative IS26, on the lactose plasmid of Streptococcus
1Central Institute for Microbiological Research, Tokyo, Japan.
Abstract:
In Streptococcus lactis ML3, the lactose plasmid (pSK08) forms cointegrates with a conjugal plasmid (pRS01). It has been proposed that cointegration is mediated by insertion sequences (IS) present on pSK08 (D. G. Anderson and L.L. McKay, J. Bacteriol. 158:954-962, 1984). We examined the junction regions of the cointegrate pPW2 and the corresponding regions of pSK08 (donor) and pRS01 (target) and identified a new IS element on pSK08 (ISS1S) which was involved in and duplicated during formation of pPW2. ISS1S was 808 base pairs (bp) in size, had 18-bp inverted repeats (GGTTCTGTTGCAAAGTTT) at its ends, contained a single long open reading frame encoding a putative protein of 226 amino acids, and generated 8-bp direct repeats of target DNA during cointegrate formation. An iso-IS element, ISS1T, which is duplicated in some other cointegrate plasmids, was also found on pSK08. ISS1T was also 808 bp in size and was identical to ISS1S in sequence except for 4 bp, none of which altered the inverted repeats or amino acid sequence of the open reading frame. Comparison of ISS1 with gram-negative IS26 revealed strong homologies in size (820 bp), sequence of inverted repeats (GGCACTGTTGCAAA), size of direct repeats generated after cointegration (8 bp), and number, size, and amino acid sequence (44.5% identical) of the open reading of frame.
Insights
A new insertion sequence, ISS1S, was identified on the lactose plasmid pSK08 in Streptococcus lactis ML3. This element, along with its variant ISS1T, mediates cointegrate formation with conjugal plasmids, showing homology to gram-negative IS elements.
Area of Science:
- Microbiology
- Molecular Biology
- Genetics
Background:
- Plasmids play crucial roles in bacterial adaptation and gene transfer.
- Cointegrate formation between plasmids is a significant mechanism for genetic exchange.
- Insertion sequences (IS) are mobile genetic elements implicated in plasmid recombination.
Purpose of the Study:
- To investigate the role of insertion sequences (IS) in the cointegration of lactose plasmid (pSK08) and conjugal plasmid (pRS01) in Streptococcus lactis ML3.
- To characterize a novel IS element identified on pSK08 involved in cointegrate formation.
Main Methods:
- Analysis of junction regions in cointegrate plasmid pPW2 and its parental plasmids pSK08 and pRS01.
- DNA sequencing to identify and characterize insertion sequence elements.
- Comparative sequence analysis of identified IS elements with known IS elements.
Main Results:
- Identification of a new IS element, ISS1S (808 bp), on pSK08, characterized by 18-bp inverted repeats and generating 8-bp direct repeats of target DNA.
- ISS1S was found to be involved in and duplicated during the formation of the cointegrate plasmid pPW2.
- An iso-IS element, ISS1T, was also identified on pSK08, showing high sequence identity to ISS1S.
- Significant homologies were observed between ISS1 and the gram-negative IS26 element, including size, inverted repeat sequences, and direct repeat generation.
Conclusions:
- The novel insertion sequence ISS1S is actively involved in mediating cointegrate formation between lactose and conjugal plasmids in Streptococcus lactis.
- ISS1S and its variant ISS1T represent a new family of IS elements with potential implications for horizontal gene transfer.
- The homology to IS26 suggests a conserved mechanism of cointegration across different bacterial domains.