Here are some interesting finding from a new report:
QUOTE: ...in the system of Prochlorococcus and virus P-SSP7, an unprecedented 41 of the bacteria's 1,717 genes were upregulated. That is, the researchers detected increased quantities of the messenger RNA encoded by these genes in the cell during the infection process. The upregulation of so many host genes during infection is a phenomenon unseen before in the world of bacteriology.
Moreover, many of the host genes upregulated during infection are among those that are found in genomic islands in the host, variable regions that appear to be hot-spots for genetic exchange between bacterial hosts and viruses. In this case, some of the genes that have been transferred back and forth encode for proteins that affect the bacteria's ability to adapt to changes in environmental factors, such as nutrient deprivation and light stress. The scientists hypothesize that modifications made to the bacterial genes when they were in the virus led to new versions of the proteins that may provide the bacteria with an increased ability to withstand environmental changes. It is also possible that multiple copies of a gene provide some benefit.
Another unusual occurrence is that the viral genome contains genes transferred from bacterial hosts that encode energy-producing proteins, including photosynthesis genes that cyanobacteria need for metabolism and DNA replication. Although these genes are positioned far apart in the viral genome, they are transcribed at the same time during infection rather than in the usual left-to-right order. This leads the researchers to surmise that the virus is trying to keep its host alive longer so that the host continues to provide the energy needed for the virus's own DNA replication.
Lindell and Chisholm believe the most plausible scenario to explain the gene upregulation and gene trading is that the bacterium activates certain genes in response to infection as a means of self-protection. The virus has "learned" to use those genes to its own advantage and so incorporates them into its own genome. Later, when infecting another bacterium, the virus upregulates those genes itself to facilitate its own reproduction within the host bacterium. When a bacterium survives an infection, those viral modified genes are incorporated back into the bacterial DNA in genome islands, making that bacterium and its descendants more likely to survive in the harsh ocean environment.
"These viral parasites cooperate with their hosts during infection, providing proteins that probably function within host metabolic pathways, to squeeze every bit of energy out them before killing them off," said Lindell. "Yet on evolutionary scales, such host-pathogen interactions are influencing the evolution of gene content in both host and virus, which in turn is likely impacting their ability to colonize new niches." UNQUOTE.
Source: http://www.sciencedaily.com/releases/2007/09/070905134534.htm |
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