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Conditional-replication, integration, excision, and retrieval plasmid-host systems for gene structure-function studies of bacteria.

ABSTRACT: We have developed a series of powerful and versatile conditional-replication, integration, and modular (CRIM) plasmids. CRIM plasmids can be replicated at medium or high copy numbers in different hosts for making gene (or mutant) libraries. They can be integrated in single copies into the chromosomes of Escherichia coli and related bacteria to study gene function under normal physiological conditions. They can be excised from the chromosome, e.g., to verify that phenotypes are caused by their presence. Furthermore, they can be retrieved singly or en masse for subsequent molecular analyses. CRIM plasmids are integrated into the chromosome by site-specific recombination at one of five different phage attachment sites. Integrants are selected as antibiotic-resistant transformations. Since CRIM plasmids encode different forms of resistance, several can be used together in the same cell for stable expression of complex metabolic or regulatory pathways from diverse sources. Following integration, integrants are stably maintained in the absence of antibiotic selection. Each CRIM plasmid has a polylinker or one of several promoters for ectopic expression of the inserted DNA. Their modular design allows easy construction of new variants with different combinations of features. We also report a series of easily curable, low-copy-number helper plasmids encoding all the requisite Int proteins alone or with the respective Xis protein. These helper plasmids facilitate integration, excision ("curing"), or retrieval of the CRIM plasmids.

SUBMITTER: Haldimann A

PROVIDER: S-EPMC100134 | biostudies-literature | 2001 Nov

REPOSITORIES: biostudies-literature

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Conditional-replication, integration, excision, and retrieval plasmid-host systems for gene structure-function studies of bacteria.

Haldimann A A Wanner B L BL

Journal of bacteriology 20011101 21

We have developed a series of powerful and versatile conditional-replication, integration, and modular (CRIM) plasmids. CRIM plasmids can be replicated at medium or high copy numbers in different hosts for making gene (or mutant) libraries. They can be integrated in single copies into the chromosomes of Escherichia coli and related bacteria to study gene function under normal physiological conditions. They can be excised from the chromosome, e.g., to verify that phenotypes are caused by their pr ...[more]

PMID: 11591683

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Project description:Impacts of plasmid carriage on its host cell were comprehensively analyzed using conjugative plasmid pCAR1 in the three different kinds of hosts, Pseudomonas putida KT2440, P. aeruginosa PAO1, and P. fluorescens Pf0-1. Various analyses of the host phenotype showed that pCAR1 carriage reduced host fitness, swimming motility, and resistances to osmotic- or pH-stress, and brought about the alterations of primary metabolic capacities in the TCA cycle or those several steps away from the TCA cycle in the host cells. Growth phase-dependent transcriptome analyses were performed with the classification of the annotated genes based on their identities among the three hosts and their putative functions. pCAR1 carriage affected host transcriptome more greatly at the transition and stationary phases in each host. The transcriptome responses were more similar between KT2440 and PAO1 than between other host combinations, and many genes, such as for ribosomal proteins, F-type ATPase, and RNAP core, in both strains were commonly not suppressed in their stationary phases. These responses may have resulted in the reduction of host fitness, motility, and stress resistances. Host-specific responses to plasmid carriage were transcriptional changes of genes on putative prophage or foreign DNA regions. The extent of the impacts in host phenotypes and transcriptomes was similarly the largest in KT2440 and the lowest in Pf0-1. The host alterations controlled by pCAR1 carriage are important for understanding the fate of the plasmid and its host, plasmid maintenance, expression of plasmid genes, the host cell physiology, and host survivability in the environment. The growth-dependent change of chromosomal RNA maps from exponential to early stationary phases of pCAR1-harboring KT2440 and non-pCAR1 harboring KT2440 were compared. The growth-dependent change of chromosomal RNA maps from exponential to early stationary phases of pCAR1-harboring PAO1 and non-pCAR1 harboring PAO1 were compared. The growth-dependent change of chromosomal RNA maps from exponential to early stationary phases of pCAR1-harboring Pf0-1 and non-pCAR1 harboring Pf0-1 were compared. The growth-dependent change of RNA maps from exponential to early stationary phases of plasmid pCAR1possessed by 3 kinds of hosts were compared.

Project description:UnlabelledResistance to methicillin and other β-lactam antibiotics in staphylococci is due to mecA, which is carried on a genomic island, staphylococcal cassette chromosome mec (SCCmec). The chromosomal excision and integration of SCCmec are mediated by the site-specific recombinase CcrAB or CcrC, encoded within this element. A plasmid-borne system was constructed to assess the activities of CcrA and CcrB in the excision and integration of SCCmec in Escherichia coli and Staphylococcus aureus. The excision frequency in E. coli mediated by CcrAB from methicillin-resistant S. aureus (MRSA) strain N315 was only 9.2%, while the integration frequency was 31.4%. In S. aureus the excision and integration frequencies were 11.0% and 18.7%, respectively. Truncated mutants identified the N-terminal domain of either CcrB or CcrA to be necessary for both integration and excision, while the C-terminal domain was important for recombination efficiency. Site-directed mutagenesis of the N-terminal domain identified S11 and R79 of CcrA and S16, R89, T149, and R151 of CcrB to be residues essential for catalytic activities, and the critical location of these residues was consistent with a model of the tertiary structure of the N terminus of CcrA and CcrB. Furthermore, CcrAB and CcrC, cloned from a panel of 6 methicillin-resistant S. aureus strains and 2 methicillin-resistant Staphylococcus epidermidis strains carrying SCCmec types II, IV, and V, also catalyzed integration at rates 1.3 to 10 times higher than the rates at which they catalyzed excision, similar to the results from N315. The tendency of SCCmec integration to be favored over excision may explain the low spontaneous excision frequency seen among MRSA strains.ImportanceSpontaneous excision of the genomic island (SCCmec) that encodes resistance to beta-lactam antibiotics (methicillin resistance) in staphylococci would convert a methicillin-resistant strain to a methicillin-susceptible strain, improving therapy of difficult-to-treat infections. This study characterizes a model system by which the relative frequencies of excision and integration can be compared. Using a plasmid-based model for excision and integration mediated by the recombinases CcrA and CcrB, integration occurred at a higher frequency than excision, consistent with the low baseline excision frequency seen in most strains. This model system can now be used to study conditions and drugs that may raise the SCCmec excision frequency and generate strains that are beta-lactam susceptible.

Dataset Information

Conditional-replication, integration, excision, and retrieval plasmid-host systems for gene structure-function studies of bacteria.

Publications

Conditional-replication, integration, excision, and retrieval plasmid-host systems for gene structure-function studies of bacteria.

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