We compared plasmid DNA production in 13 strains of Escherichia coli in shake flasks using media containing glucose or glycerol. DNA yield from either carbon source showed small correlation with maximum growth rate. Three strains, SCS1-L, BL21 and MC4100, were selected for a controlled exponential fed-batch process at a growth rate of 0.14 h(-1) to an optical density of about 70, followed by a four-hour heat treatment. Prior to heat treatment, SCS1-L generated 15.4 mg DNA/g, BL21 generated 11.0 mg DNA/g and MC4100 generated 7.9 mg DNA/g, while after heat treatment the strains attained DNA yields, respectively, of 18.0, 15.0 and 6.8 mg/g. The strains also varied in their percentage of supercoiled DNA after heat treatment, with SCS1-L averaging 66% supercoiled, BL21 17% and MC4100 40%. We further investigated the two strains that yielded the highest percentage of supercoiled DNA (SCS1-L and MC4100) at a higher growth rate of 0.28 h(-1). At this condition, a slightly lower DNA yield was generated faster, and the percentage of supercoiled DNA increased. Heat treatment improved DNA yield, and surprisingly did so to a greater extent at the higher growth rate. As a consequence of these factors, higher growth rates might be advantageous for DNA production.

Innate immune responses against viral infection, especially the induction of type I interferon, are critical for limiting the replication of the virus. Although it has been shown that DNA can induce type I interferon, to date no natural DNA ligand of a virus that induces type I interferon has been described. Here we screened the genome of murine gammaherpesvirus 68 with mutations at various genomic locations to map the region of DNA that induces type I interferon. A repetitive region termed the 100-base-pair repeat region is a ligand that is both necessary and sufficient for the viral genomic DNA to induce type I interferon. A region colinear with this ligand in the genome of Kaposi's sarcoma-associated herpesvirus also induces type I interferon. We have thus defined a repetitive region of the genomes of gammaherpesviruses as the first natural DNA virus ligand that induces type I interferon.The innate immune system is a highly efficient defense system of multicellular organisms that is critical in protection against microorganisms. With its families of evolutionarily conserved receptors, the innate immune system recognizes and responds to ligands containing molecular patterns that are indicative of a particular microorganism type. These pathogen-associated molecular patterns (PAMPs) are unique to the type of microorganism that is being encountered, and the innate immune system responds to these PAMPs with the appropriate induction of signals (15,28). For example, when the innate immune system encounters a viral PAMP, the quintessential innate response is to induce the release of type I interferon (IFN) (23).IFNs were first described in the 1950s, when it was found that cells exposed to inactivated viruses secrete a chemical that interferes with the replication of subsequent viral infections (12,13,30). These secreted chemicals were proteins that were named "interferons" for their ability to "interfere" with viral infection. IFNs are recognized by the type I interferon receptor and signal in both autocrine and paracrine manners to induce the transcription of a number of specific genes (7, 33, 36). The IFN-induced gene products work in concert to produce an antiviral state making the cell refractory to further viral infection, to potentiate the cell to undergo apoptosis upon the stress of a viral infection, or to activate the adaptive arm of the immune response (20,22,32,45,50). Induction of IFN is key to mounting a proper and robust immune response to a viral infection (46).For most of the years since the discovery of IFN, the mechanisms by which viral PAMPs are recognized and induce the production of IFN remained unknown. New virions are created through viral parasitization of the cellular transcription and translation machinery; consequently, most protein components of viruses are effectively host derived and not hypothesized to be effective PAMPs. On the other hand, viral genomic RNA and DNA are often highly structured and represent nucleic acid species not typically found in a host cell or in particular subce...