Home About us Contact
|
Home About us Contact | ||
|
|
||
Plasmid Loss (plasmid + loss)
Selected AbstractsOptimal mixing to improve the performance of batch and continuous fermentations with recombinant Escherichia coliJOURNAL OF CHEMICAL TECHNOLOGY & BIOTECHNOLOGY, Issue 4 2005Venkata SRK Ganduri Abstract Fermentations with genetically altered bacteria tend to lose plasmids as the fermentation progresses. Methods such as two-stage cultivation, cell recycle and the addition of antibiotics are commonly used to enhance plasmid stability. Here we examine a different method, the regulation of mixing in the bioreactor. In particular, large bioreactors are considered where uniform mixing is difficult to achieve and the probability of plasmid loss varies with the specific growth rate. For both batch and continuous cultivations of Escherichia coli C600 gal K containing the plasmid pBR Eco gap, it is seen through a model that both modes of operation exhibit high plasmid stability and cell growth when the broth is incompletely mixed, and mixing near and away from the point of inoculation are unequal. Thus, the natural incomplete mixing in large bioreactors may be utilized to improve plasmid stability. A practical method to implement this idea is suggested. Copyright © 2005 Society of Chemical Industry [source] Tryptophanase in sRNA control of the Escherichia coli cell cycleMOLECULAR MICROBIOLOGY, Issue 1 2007Dhruba K. Chattoraj Summary The field of gene regulation underwent a major revolution with the discovery of small non-coding RNAs (sRNAs) and the various roles they play in organisms from bacteria to man. Escherichia coli has more than 60 sRNAs that are transcribed primarily from intergenic regions. They usually target the leader region of mRNAs and prevent their translation. Protein targets are relatively rare. In this issue of Molecular Microbiology, Chant and Summers provide an example of a totally unexpected protein target. They show that dimers of plasmid ColE1 make an sRNA that interacts directly with the enzyme tryptophanase and enhances its affinity for its substrate, tryptophan. A breakdown product, indole, then arrests cell division until the dimers are resolved to monomers. The monomerization helps to prevent plasmid loss. Targeting a catabolic enzyme to buy time for recombination is an amazing example of adaptation, which illustrates the power of a selfish element (a plasmid in this case) to exploit the host cell machinery to its advantage. [source] The RepA protein of plasmid pSC101 controls Escherichia coli cell division through the SOS responseMOLECULAR MICROBIOLOGY, Issue 2 2001Hanne Ingmer Although plasmid copy number varies widely among different plasmid species, normally copy number is maintained within a narrow range for any given plasmid. Such copy number control has been shown to occur by regulation of the rate of plasmid DNA replication. Here we report a novel mechanism by which the pSC101 plasmid also can detect an imbalance between the cellular level of its replication protein, RepA, and plasmid-borne RepA binding sites to inhibit bacterial DNA replication and delay host cell division when RepA is in relative excess. We show that delayed cell division occurs by RepA-mediated induction of the SOS response and can be reversed by over-expression of the host DNA primase, DnaG. The effects of RepA excess are prevented by introducing a surfeit of RepA binding sites. The mechanism reported here may help to limit variation in plasmid copy number and allow repopulation of cells with plasmids when copy number falls , potentially pre-empting plasmid loss in cultures of dividing cells. [source] Stability of recombinant plasmids on the continuous culture of Bifidobacterium animalis ATCC 27536BIOTECHNOLOGY & BIOENGINEERING, Issue 2 2003Antonio González Vara Abstract Bifidobacterium animalis ATCC 27536 represents among bifidobacteria a host-model for cloning experiments. The segregational and structural stabilities of a family of cloning vectors with different molecular weights but sharing a common core were studied in continuous fermentation of the hosting B. animalis without selective pressure. The rate of plasmid loss (R) and the specific growth rate difference (,,) between plasmid-free and plasmid-carrying cells were calculated for each plasmid and their relationship with plasmid size was studied. It was observed that both R and the numerical value of ,, increased exponentially with plasmid size. The exponential functions correlating the specific growth rate difference and the rate of plasmid loss with the plasmid molecular weight were determined. Furthermore, the smallest of the plasmids studied, pLAV (4.3-kb) was thoroughly characterized by means of its complete nucleotide sequence. It was found that it contained an extra DNA fragment, the first bifidobacterial insertion sequence characterised, named IS 1999. © 2003 Wiley Periodicals, Inc. Biotechnol Bioeng 84: 145,150, 2003. [source] | ||||||||||