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Results for “Megaplasmids”

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PubMed1994

Primary sequence and evidence for a physiological function of the flavohemoprotein of Alcaligenes eutrophus.

The flavohemoprotein (FHP) encoding gene of the strictly respiratory Gram-negative bacterium Alcaligenes eutrophus was isolated from a megaplasmid library by using FHP-specific antibodies and oligonucleotide probes based on the amino-terminal polypeptide sequence of FHP, determined previously (Zhu, H., and Riggs, A. F. (1992) Proc. Natl. Acad. Sci. U.S.A. 89, 5015-5019). The fhp gene codes for a monomeric polypeptide of 403 amino acids (M(r) 44,796) whose structure is highly homologous to the proteins of the two-domain flavohemoglobin family, comprising the hemoproteins from Escherichia coli and Saccharomyces cerevisiae. FHP consists of an amino-terminal-located O2-binding hemoglobin domain and a carboxyl-terminal-located redoxactive domain with potential binding sites for NAD(P)H and FAD. Two potential binding motifs for NARL and FNR upstream of fhp suggest a role of FHP in the anaerobic metabolism of A. eutrophus. Isogenic Fhp-negative mutants showed no significant delay in aerobic or anaerobic growth. Compared with the wild type, however, the mutant did not accumulate nitrous oxide during denitrification with nitrite as electron acceptor. This property was restored by complementation. The result suggests that FHP interacts directly or indirectly with the gas metabolism during denitrification in A. eutrophus.

Alcaligenes↗

PubMedDate not supplied

[Transposon Tn5 and its derivatives used in genetic analysis of bacteria].

The review deals with the derivatives of transposon Tn5 carrying new genes of antibiotic resistance. The derivatives were constructed for mobilization of genetically labeled replicons, for direct selection of mutants having lost the marked plasmids, for obtaining the genes with the strong constitutive or regulated expression, for isolation of conditional mutations, for faster physical mapping of megaplasmids.

Bacteria↗

PubMed1998

[Formation of deletional derivatives of the Ti-plasmid pGV3850 in a conjugative transfer from Agrobacterium tumefaciens to Escherichia coli].

The process of the transfer of the Ti-plasmid vector pGV3850 with the plasmid pBR322 inserted into the T-DNA region from Agrobacterium tumefaciens to a non-plasmid strain of Escherichia coli was studied. The transferred Ti-plasmid was found to be exposed to deletions and formed a wide range of derivatives with a size ranging from 3-4 kb to 50 kb, maintained in E. coli due to ColE1-replicon. The Ti-plasmid is also inserted into the chromosome of the recipient bacterium with at least a 100-fold lower frequency than the formation of deletional derivatives. It was shown that the induction of vir genes controlling the transfer of T-DNA into plants has no appreciable effect on the efficiency of obtaining transconjugates in mating with E. coli. The deletion of the genetic material of megaplasmids with the inserted functional site OriV ColE1, as a result of the conjugative transfer from cells of different bacteria to the cells of E. coli, was proposed for molecular cloning.

Agrobacterium tumefaciens↗

PubMed1999

Peripheral blood CD14(+) cells from healthy subjects carry a circular conformation of latent cytomegalovirus genome.

The majority of the human population harbors latent cytomegalovirus. Although CD14(+) peripheral blood mononuclear cells have been implicated as sites of latency, the conformation of the latent viral genome in these cells is unknown. In this study, the conformation of viral genomic DNA was assessed in CD14(+) cells from healthy virus seropositive carriers using an electrophoretic separation on native agarose gels in combination with polymerase chain reaction detection. Here we show that the viral genome migrates as a circular plasmid with a mobility equivalent to a circular 230-kb Shigella flexneri megaplasmid marker. Neither linear nor complex or integrated forms of the viral genome were detected. This report provides further evidence that the CD14(+) cell population is an important site of viral latency in the naturally infected human host. Detection of the viral genome as a circular plasmid during latency suggests that this virus maintains its genome in a manner analogous to other herpesviruses where latent viral genome conformation has been studied.

Carrier State↗

PubMed2026

Ecological and evolutionary implications of a mobile genetic element-rich haloarchaeon with unique osmotic resilience.

We isolated a novel halophilic archaeon, strain DSL9, representing the proposed new species Haloliberatus hailidukes gen. nov., sp. nov., from Dishui Lake, China. Unlike most obligate halophiles, DSL9 survives in low salinity, even distilled water, without lysis. Genomic analysis revealed dual salinity adaptation strategies: salt-in and compatible solutes, including a complete trehalose biosynthesis pathway. The strain harbors multiple plasmids, notably a 111,311 bp large plasmid (pHdsl9-3) encoding replication (Orc1/Cdc6, SSB), transcription (TFIIB), transmission (T4SS cluster, ArdC-like protein), and recombination (XerA) modules. pHdsl9-3 provides auxiliary functions such as defense, genome diversification, ion detoxification, and suggests active horizontal gene transfer. Similar elements are widespread in Halobacteriales, highlighting their role in haloarchaeal genetic diversity and plasticity. The encoded XerA hinted at a function beyond DNA dimer resolution, suggesting it may have been adapted by other archaeal mobile genetic elements. These findings underscore the need to investigate plasmid-driven evolution and environmental adaptation mechanisms in haloarchaea.IMPORTANCEThis study reports the isolation and characterization of DSL9, a novel halophilic archaeon from a freshwater lake. Remarkably, DSL9 defies the typical obligate halophilic lifestyle by surviving in low-salinity environments, including distilled water, without cell lysis. A key discovery is the identification of a 111,311 bp large plasmid harboring essential modules for replication, transcription, transmission, and integration. Widespread distribution of similar elements across Halobacteriales suggests their crucial role in haloarchaeal genetic diversity and plasticity, warranting further study of plasmid-mediated evolution and adaptation strategies.

Lakes↗