Analysis of the Role of
            <i>recA</i>
            in Phenotypic Switching of
            <i>Pseudomonas tolaasii</i>

Sinha, Himanshu; Pain, Arnab; Johnstone, Keith

doi:10.1128/jb.182.22.6532-6535.2000

Cited by 30 publications

(25 citation statements)

References 20 publications

Supporting

Mentioning

Contrasting

Order By: Relevance

“…Although this result cannot exclude the possibility that recombinational processes are involved in this phase variation, it shows that RecA and RecB are not essential for the repair of mutations in gacS and gacA of PCL1171. A similar observation was made for P. tolaasii (37), where RecA was not needed for the removal of the duplication in pheN (37).…”

Section: Vol 187 2005 Gacs and Pseudomonas Colony Phase Variation 597mentioning

confidence: 65%

Molecular Nature of Spontaneous Modifications ingacSWhich Cause Colony Phase Variation inPseudomonassp. Strain PCL1171

et al. 2005

View full text Add to dashboard Cite

is caused by spontaneous mutations in gacA or/and gacS. Mutation of gac reduced both the length of the lag phase and the generation time. Isolation and sequencing of the gacS genes from the phase II bacteria revealed one insertion as well as several random point mutations, deletions, and DNA rearrangements. Most phase II colonies reverted with a high frequency, resulting in wild-type gacA and gacS genes and a phase I phenotype. Some phase II bacteria retained the phase II phenotype but changed genotypically as a result of (re)introduction of mutations in either gacA or gacS. The reversion of gacA or gacS to the wild type was not affected by mutation of recA and recB. We conclude that in Pseudomonas sp. strain PCL1171, mutations in gacA and gacS are the basis for phase variation from phase I to phase II colonies and that, since these mutations are efficiently removed, mutations in gac result in dynamic switches between the "wild-type" population and the subpopulations harboring spontaneous mutations in gacA and or gacS, thereby enabling both populations to be maintained.Phase variation is a process of reversible, high-frequency phenotypic switching that is mediated by mutation, reorganization, or modification of DNA. This process is used by several bacterial species to generate population diversity that increases bacterial fitness and is important in niche adaptation (33). Phase variation can sometimes be observed by the appearance of morphologically distinct colonies or sectors within a colony (8,12). In contrast to spontaneous mutations, which occur at a frequency of approximately 10 Ϫ7 mutations per cell per generation, phase variation occurs at frequencies higher than 10 Ϫ5 switches per cell per generation (12). Four mechanisms of phase variation are known (12): (i) slipped-strand mispairing, dependent on variations in the length of a repeat tract, switching a gene on or off as a result of frameshifts, or regulating the level of expression by altering promoter spacing; (ii) genomic rearrangements, based on invertible elements or recombination events resulting in gene conversions; (iii) differential methylation, based on the presence of methylation sites within a promoter, which can regulate the binding of regulatory proteins; and (iv) random unprogrammed variation, which can switch traits on and off via random reversible mutations (3).Phase variation has been reported to regulate the production of pili (22), outer membrane proteins (22), flagella (13), fimbriae (1), surface lipoproteins and other surface-exposed structures (8,12,29), secondary metabolites (5, 38), and secreted enzymes such as proteases, lipases, and chitinases (5, 38). In a previous paper (38), we reported that out of 46 Pseudomonas strains antagonistic against the wheat-pathogenic fungus Geaumannomyces graminis pv. tritici R3-11A (27), 43 displayed colony phase variation. One of these strains, PCL1171, was selected for study of the molecular basis of phase variation. In this strain, antagonistic activity, morphology, and expression of second...

show abstract

Section: Vol 187 2005 Gacs and Pseudomonas Colony Phase Variation 597mentioning

confidence: 65%

Molecular Nature of Spontaneous Modifications ingacSWhich Cause Colony Phase Variation inPseudomonassp. Strain PCL1171

et al. 2005

View full text Add to dashboard Cite

show abstract

“…However, the introduction of gacA gene into the F variant did not complement morphology. Although the appearance of gacA/gacS-related phenotypes among phase variants in different species of fluorescent pseudomonads (12,15,24,54) and the alteration in pyoverdin production in a P. aeruginosa sss mutant suggest that the gacA gene might be subjected to phase variation, phenotype selection is also possible. Our results, the sequencing of gacA allele in variant F showing point mutations, and the appearance of gacA mutants from plants inoculated with F113-sss2 demonstrated that during rhizosphere colonization, this gene is not subjected to phase variation, but a selection of the phenotype is occurring.…”

Section: Discussionmentioning

confidence: 99%

Phenotypic Selection and Phase Variation Occur during Alfalfa Root Colonization by Pseudomonas fluorescens F113

et al. 2002

View full text Add to dashboard Cite

During colonization of the alfalfa rhizosphere, Pseudomonas fluorescens F113 undergoes phenotypic variation, resulting in the appearance of colonies with different morphology. Among phenotypic variants, three isolates, C, F, and S were selected, with the C variant showing colony morphology identical to that of the inoculated wild-type strain and F and S having a translucent and diffuse morphology. Phenotypic variants F and S were shown to preferentially colonize distal parts of the roots and showed alterations in motility, swimming faster than the C variant and swarming under conditions that did not allow swarming of the C variant. The motility behavior correlated with overproduction of the fliC-encoded protein flagellin but not with hyperflagellation. Flagella of the F and S variants were several times longer than those of the C variant, and overproduction of flagellin was regulated at the transcriptional level. Variant F showed alterations in traits that have been shown to be important for rhizosphere colonization, such as siderophore, cyanide, and exoprotease production, and these phenotypes were complemented by a cloned gacA. Sequence analysis of the gacA alelle in variant F suggested selection of the phenotype in the rhizosphere. Variant F was also affected in other phenotypes, such as lipopolysaccharide structure and flocculation in unshaken liquid medium, which were not complemented by the gacA or gacS gene. Mutation of the F113 sss gene, encoding a site-specific recombinase, showed that most of the phenotypic variation was due to the activity of this recombinase, indicating that phase variation occurs during rhizosphere colonization.Bacterial phase variation consists of the diversification of a population into subpopulations which present genotypic and phenotypic differences. It has been described for a variety of species, mostly within gram-negative bacteria (reviewed in reference 26). Phase variation is typical of bacteria that occupy heterogeneous ecological niches and has been related to adaptation to different environmental situations and to sudden changes in the ecosystem (49). Under these conditions, phase variation would generate a mixed population able to colonize different parts of the ecosystem, and in the case of rapid environmental changes, part of the initial population would survive (17).Phase variation predominantly affects surface components of cells, such as membrane antigens, flagella, and fimbriae, causing morphological alterations in colonies that allow easy detection (26). Typical examples are fimbrial variation in Escherichia coli, flagellar variation in Salmonella spp., and variation in surface antigens in several species of the genus Neisseria. From a genetic point of view, phase variation often results from genomic rearrangements that can be caused by several molecular mechanisms. The best-studied mechanisms are the action of a site-specific recombinase that can produce inversions or deletions of specific sites of the genome (1), mutations in homopolymeric tracts that produce fr...

show abstract

“…Instead, they may have arisen through a topoisomerase I-mediated process (6). In vitro biofilm-associated acapsular phase variants with tandem sequence duplications in cps3D have also been described in the literature (33) and may arise through either recA-independent or recAdependent mechanisms, or through both types of mechanisms (27,31,32).…”

Section: Discussionmentioning

confidence: 99%

Characterization of In Vitro Biofilm-Associated Pneumococcal Phase Variants of a Clinically Relevant Serotype 3 Clone

2007

View full text Add to dashboard Cite

An increasing proportion of children with acute otitis media due to Streptococcus pneumoniae have serotype 3 infections since licensure of the seven-valent pneumococcal conjugate vaccine. These serotype 3 strains are genetically related by molecular subtyping. During otitis media with effusion and recurrent otitis media, biofilms commonly develop. Pneumococcal in vitro biofilms are comprised of phase variants that differ in colony morphology. By using a representative strain of the mucoid serotype 3 clone, rough phase variants with a diverse array of mutations were detected in biofilms formed in vitro. Most phase variants had mutations in the cps3D gene, the first gene of the capsular operon. Eleven had single nucleotide polymorphisms (SNPs) in the cps3D gene, one had an SNP in the ؊10 promoter, and three had large deletions in the cps3D gene. Reversion to the mucoid phenotype was associated with reversion of the mutation in the cps3D gene. Unlike the phase variants detected in the nasopharynx, which have at least 20% of the parental amount of capsule, the in vitro biofilm-associated phase variants had <12% of the parental amount of capsule, as determined by capsule enzyme-linked immunosorbent assays. Using real-time reverse transcription-PCR, we determined that capsule expression in the phase variants was likely regulated at multiple levels. These in vitro phase variation data, which underscore the plasticity of the pneumococcus, need to be confirmed with in vivo analyses of the middle ear mucosa during otitis media.

show abstract

Analysis of the Role of recA in Phenotypic Switching of Pseudomonas tolaasii

Cited by 30 publications

References 20 publications

Molecular Nature of Spontaneous Modifications ingacSWhich Cause Colony Phase Variation inPseudomonassp. Strain PCL1171

Molecular Nature of Spontaneous Modifications ingacSWhich Cause Colony Phase Variation inPseudomonassp. Strain PCL1171

Phenotypic Selection and Phase Variation Occur during Alfalfa Root Colonization by Pseudomonas fluorescens F113

Characterization of In Vitro Biofilm-Associated Pneumococcal Phase Variants of a Clinically Relevant Serotype 3 Clone

Contact Info

Product

Resources

About