DNA transfer through cell membranes in bacteria

DNA initiates polymorphic structural transitions in lecithin

The inverted micellar phase, obtained by treating lecithin and Ca(2+)-DNA complex with chloroform, was used as an intermediate step in the preparation of DNA-Ca(2+)-lecithin complex. DSC analysis demonstrated the involvement of a large fraction of lipid in the interaction with DNA. Freeze-fracture electron microscopy revealed (i) rod-like structures on the hydrophobic fracture surface of membranes and (ii) regular bundles of fibrils with a repeat distance of about 6 nm, which were located free in solution. Similar regular bundles of fibrils were also revealed by staining the samples with uranyl acetate. According to the suggested model, the observed structures are hexagonally packed inverted lipid tubes, with DNA located in their central cores. The possible biological relevance of the capability of Ca(2+)-DNA to initiate polymorphic phase transitions of lecithin is discussed.

Involvement of host cell energy in the transfection of Lactobacillus casei protoplasts with phage PL-1 DNA

Transfection of Lactobacillus casei ATCC 27092 protoplasts with phage PL-1 DNA was studied under various conditions. The process of transfection was dependent on the incubation temperature, and the apparent activation energy was calculated to be about 11 kcal/mol. Transfection was inhibited by treating the cells before protoplasting either with monoiodoacetate, N,N'-dicyclohexylcarbodiimide (DCCD), or NaN3, without affecting both the viability of uninfected cells and protoplasting. The addition of DCCD after mixing protoplasts and DNA had no influence on transfection efficiencies. The transfection of L. casei protoplasts with phage PL-1 DNA was considered to require cell energy such as proton-motive force, probably in the initial stages, although the direct involvement of cell energy in the transfer of DNA across the cell membrane is still unclear.

Nucleic acid transfer through cell membranes: towards the underlying mechanisms

Various cases of DNA (RNA) transfer through membranes of living cells are reviewed. They are classified into two major categories: those which occur in Nature (natural transfer) and those imposed by various physical and chemical treatments of cells (induced transfer). Among the examples of natural transfer surveyed are the transfer during bacterial conjugation, genetic transformation, viral infection of bacteria, and nuclear membrane trafficking. Consideration of the induced transfer is focused on the two methods most widely used at present to introduce foreign genetic information into pro- and eukaryotic cells: Ca2+ (and some other divalent cations)-induced and calcium phosphate-induced transfer, and transfer during electroporation of cells. Emphasis is made on the underlying mechanisms of transfer, or rather on what is currently known about them. Energetic aspects of transfer are also discussed and different tentative models of transfer are presented.

The susceptibility of conjugative resistance transfer in gram-negative bacteria to physicochemical and biochemical agents

Over thirty years of studies have established that conjugative transfer of plasmid-encoded resistance to drugs and heavy metals can take place at high frequency between various organisms under laboratory conditions. The detected transfer frequencies in soil, in aquatic environments, and in the urogenital and respiratory tracts of healthy animals and man have generally been low. However, the conversion of bacteria from susceptible to resistant to antibiotics has been observed often during antimicrobial therapy. This has formed a challenge for the antibacterial treatment of pathogenic bacteria and called for the evaluation of the extent of conjugative transfer in various environments. Several biochemical and physicochemical factors inhibit conjugation, show preferential toxicity against plasmid-bearing cells, or stimulate plasmid curing. These factors include various agents such as detergents, anesthetics, mutagens and antibiotics which affect membrane potential, membrane permeability, protein synthesis and the processing of DNA. The application of the data on these agents, summarized in this review, might be helpful in preventing drug multi-resistance from spreading. Also these data might be valuable in studies which use conjugation as a tool or which treat the molecular mechanisms involved in conjugation.