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Mycoplasma genitalium: an efficient strategy to generate genetic variation from a minimal genome.

Ma L, Jensen JS, Myers L, Burnett J, Welch M, Jia Q, Martin DH - Mol. Microbiol. (2007)

Bottom Line: In order to establish the origin of the MG192 variants, we examined nine genomic loci containing partial copies of the MgPa operon, known as MgPar sequences.Our analysis suggests that the MG192 sequence variation is achieved by recombination between the MG192 expression site and MgPar sequences via gene cross-over and, possibly, also by gene conversion.It appears plausible that M. genitalium has the ability to generate unlimited variants from its minimized genome, which presumably allows the organism to adapt to diverse environments and/or to evade host defences by antigenic variation.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, Louisiana State University Health Sciences Center, New Orleans, LA 70112, USA. lma1@lsuhsc.edu

ABSTRACT
Mycoplasma genitalium, a human pathogen associated with sexually transmitted diseases, is unique in that it has smallest genome of any known free-living organism. The goal of this study was to investigate if and how M. genitalium uses a minimal genome to generate genetic variations. We analysed the sequence variability of the third gene (MG192 or mgpC) of the M. genitalium MgPa adhesion operon, demonstrated that the MG192 gene is highly variable among and within M. genitalium strains in vitro and in vivo, and identified MG192 sequence shifts in the course of in vitro passage of the G37 type strain and in sequential specimens from an M. genitalium-infected patient. In order to establish the origin of the MG192 variants, we examined nine genomic loci containing partial copies of the MgPa operon, known as MgPar sequences. Our analysis suggests that the MG192 sequence variation is achieved by recombination between the MG192 expression site and MgPar sequences via gene cross-over and, possibly, also by gene conversion. It appears plausible that M. genitalium has the ability to generate unlimited variants from its minimized genome, which presumably allows the organism to adapt to diverse environments and/or to evade host defences by antigenic variation.

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Homologous recombination between MG192 and MgPar 8 in the M. genitalium type strain G37 during in vitro passage. A. Alignment of a portion of the MG192 variable region and MgPar 8 in G37-P1 and G37-P35 showing the sequence exchange in the recombination site. Identical sequences are highlighted in the same colour. The number of plasmid clones analysed for each locus is listed in Table 3. All clones analysed for each locus showed homogenous sequence except for the AGT short tandem repeat number variation, with only the most common repeat number shown in this alignment. The sequences of the MG192 and MgPar 8 identified in G37-P35 have been submitted to GenBank under Accession No. EF117280 and EF7289 respectively. B. A model of homologous recombination between MG192 and MgPar 8 in the G37 type strain. Nucleotide positions shown are relative to the full-length MG192 or MgPar 8 of G37-P1, both of which are identical to those of G37T. Regions containing the longest stretch of identical sequences are indicated by the same shading and colour. The regions between dotted vertical lines (corresponding to the sequences shown in A) indicate where sequence exchanges took place, with reciprocal exchange (gene cross-over) shown by two curved arrows and non-reciprocal exchange (gene conversion) shown by one straight arrow.
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fig03: Homologous recombination between MG192 and MgPar 8 in the M. genitalium type strain G37 during in vitro passage. A. Alignment of a portion of the MG192 variable region and MgPar 8 in G37-P1 and G37-P35 showing the sequence exchange in the recombination site. Identical sequences are highlighted in the same colour. The number of plasmid clones analysed for each locus is listed in Table 3. All clones analysed for each locus showed homogenous sequence except for the AGT short tandem repeat number variation, with only the most common repeat number shown in this alignment. The sequences of the MG192 and MgPar 8 identified in G37-P35 have been submitted to GenBank under Accession No. EF117280 and EF7289 respectively. B. A model of homologous recombination between MG192 and MgPar 8 in the G37 type strain. Nucleotide positions shown are relative to the full-length MG192 or MgPar 8 of G37-P1, both of which are identical to those of G37T. Regions containing the longest stretch of identical sequences are indicated by the same shading and colour. The regions between dotted vertical lines (corresponding to the sequences shown in A) indicate where sequence exchanges took place, with reciprocal exchange (gene cross-over) shown by two curved arrows and non-reciprocal exchange (gene conversion) shown by one straight arrow.

Mentions: We passed the G37 ATCC strain serially 35 times in vitro and examined the entire MG192 variable region at three passage levels (designated here as G37-P1, G37-P17 and G37-P35) as well as in the genomic DNA of G37 directly obtained from ATCC (designated here as G37-D). In each passage, sequencing of individual plasmid clones of the PCR products identified a mixture of three to five MG192 sequences that differed from each other only in the number of the AGT tandem repeats (Table 2). Aside from the AGT repeat number variation, the MG192 sequence in G37-D and G37-P1 was identical to that of the published G37T genome sequence, whereas the MG192 sequence in G37-P17 and G37-P35 was identical between them but different from that of G37T (Fig. 2). Compared with the G37T MG192 sequence, G37-P17 and G37-P35 exhibited sequence variation resulting from 16 nucleotide substitutions and one triplet insertion in the regions flanking the AGT repeat motif (Fig. 3A). None of these nucleotide substitutions or insertions introduced frameshifts or stop codons in the predicted ORFs while the deduced amino acid sequence of these variants differed from that of G37T MG192.


Mycoplasma genitalium: an efficient strategy to generate genetic variation from a minimal genome.

Ma L, Jensen JS, Myers L, Burnett J, Welch M, Jia Q, Martin DH - Mol. Microbiol. (2007)

Homologous recombination between MG192 and MgPar 8 in the M. genitalium type strain G37 during in vitro passage. A. Alignment of a portion of the MG192 variable region and MgPar 8 in G37-P1 and G37-P35 showing the sequence exchange in the recombination site. Identical sequences are highlighted in the same colour. The number of plasmid clones analysed for each locus is listed in Table 3. All clones analysed for each locus showed homogenous sequence except for the AGT short tandem repeat number variation, with only the most common repeat number shown in this alignment. The sequences of the MG192 and MgPar 8 identified in G37-P35 have been submitted to GenBank under Accession No. EF117280 and EF7289 respectively. B. A model of homologous recombination between MG192 and MgPar 8 in the G37 type strain. Nucleotide positions shown are relative to the full-length MG192 or MgPar 8 of G37-P1, both of which are identical to those of G37T. Regions containing the longest stretch of identical sequences are indicated by the same shading and colour. The regions between dotted vertical lines (corresponding to the sequences shown in A) indicate where sequence exchanges took place, with reciprocal exchange (gene cross-over) shown by two curved arrows and non-reciprocal exchange (gene conversion) shown by one straight arrow.
© Copyright Policy
Related In: Results  -  Collection

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fig03: Homologous recombination between MG192 and MgPar 8 in the M. genitalium type strain G37 during in vitro passage. A. Alignment of a portion of the MG192 variable region and MgPar 8 in G37-P1 and G37-P35 showing the sequence exchange in the recombination site. Identical sequences are highlighted in the same colour. The number of plasmid clones analysed for each locus is listed in Table 3. All clones analysed for each locus showed homogenous sequence except for the AGT short tandem repeat number variation, with only the most common repeat number shown in this alignment. The sequences of the MG192 and MgPar 8 identified in G37-P35 have been submitted to GenBank under Accession No. EF117280 and EF7289 respectively. B. A model of homologous recombination between MG192 and MgPar 8 in the G37 type strain. Nucleotide positions shown are relative to the full-length MG192 or MgPar 8 of G37-P1, both of which are identical to those of G37T. Regions containing the longest stretch of identical sequences are indicated by the same shading and colour. The regions between dotted vertical lines (corresponding to the sequences shown in A) indicate where sequence exchanges took place, with reciprocal exchange (gene cross-over) shown by two curved arrows and non-reciprocal exchange (gene conversion) shown by one straight arrow.
Mentions: We passed the G37 ATCC strain serially 35 times in vitro and examined the entire MG192 variable region at three passage levels (designated here as G37-P1, G37-P17 and G37-P35) as well as in the genomic DNA of G37 directly obtained from ATCC (designated here as G37-D). In each passage, sequencing of individual plasmid clones of the PCR products identified a mixture of three to five MG192 sequences that differed from each other only in the number of the AGT tandem repeats (Table 2). Aside from the AGT repeat number variation, the MG192 sequence in G37-D and G37-P1 was identical to that of the published G37T genome sequence, whereas the MG192 sequence in G37-P17 and G37-P35 was identical between them but different from that of G37T (Fig. 2). Compared with the G37T MG192 sequence, G37-P17 and G37-P35 exhibited sequence variation resulting from 16 nucleotide substitutions and one triplet insertion in the regions flanking the AGT repeat motif (Fig. 3A). None of these nucleotide substitutions or insertions introduced frameshifts or stop codons in the predicted ORFs while the deduced amino acid sequence of these variants differed from that of G37T MG192.

Bottom Line: In order to establish the origin of the MG192 variants, we examined nine genomic loci containing partial copies of the MgPa operon, known as MgPar sequences.Our analysis suggests that the MG192 sequence variation is achieved by recombination between the MG192 expression site and MgPar sequences via gene cross-over and, possibly, also by gene conversion.It appears plausible that M. genitalium has the ability to generate unlimited variants from its minimized genome, which presumably allows the organism to adapt to diverse environments and/or to evade host defences by antigenic variation.

View Article: PubMed Central - PubMed

Affiliation: Department of Medicine, Louisiana State University Health Sciences Center, New Orleans, LA 70112, USA. lma1@lsuhsc.edu

ABSTRACT
Mycoplasma genitalium, a human pathogen associated with sexually transmitted diseases, is unique in that it has smallest genome of any known free-living organism. The goal of this study was to investigate if and how M. genitalium uses a minimal genome to generate genetic variations. We analysed the sequence variability of the third gene (MG192 or mgpC) of the M. genitalium MgPa adhesion operon, demonstrated that the MG192 gene is highly variable among and within M. genitalium strains in vitro and in vivo, and identified MG192 sequence shifts in the course of in vitro passage of the G37 type strain and in sequential specimens from an M. genitalium-infected patient. In order to establish the origin of the MG192 variants, we examined nine genomic loci containing partial copies of the MgPa operon, known as MgPar sequences. Our analysis suggests that the MG192 sequence variation is achieved by recombination between the MG192 expression site and MgPar sequences via gene cross-over and, possibly, also by gene conversion. It appears plausible that M. genitalium has the ability to generate unlimited variants from its minimized genome, which presumably allows the organism to adapt to diverse environments and/or to evade host defences by antigenic variation.

Show MeSH
Related in: MedlinePlus