Bacterial immunity (Introduction)

by David Turell , Wednesday, February 11, 2015, 14:39 (3573 days ago)

Special complex techniques:-https://www.quantamagazine.org/20150206-crispr-dna-editor-bacteria/-This is the sentience dhw's favorite researchers talk about. All in the bacteria's genetic tool kit and all done at a molecular level automatically. To me this is anything but God-given, being too complexly specified to be the result of chance: -"Koonin knew that microbes are not passive victims of virus attacks. They have several lines of defense. Koonin thought that CRISPR and Cas enzymes provide one more. In Koonin's hypothesis, bacteria use Cas enzymes to grab fragments of viral DNA. They then insert the virus fragments into their own CRISPR sequences. Later, when another virus comes along, the bacteria can use the CRISPR sequence as a cheat sheet to recognize the invader-"To test Koonin's hypothesis, Barrangou and his colleagues infected the milk-fermenting microbe Streptococcus thermophilus with two strains of viruses. The viruses killed many of the bacteria, but some survived. When those resistant bacteria multiplied, their descendants turned out to be resistant too. Some genetic change had occurred. Barrangou and his colleagues found that the bacteria had stuffed DNA fragments from the two viruses into their spacers. When the scientists chopped out the new spacers, the bacteria lost their resistance.-"As Wiedenheft, Doudna and their colleagues figured out the structure of Cas enzymes, they began to see how the molecules worked together as a system. When a virus invades a microbe, the host cell grabs a little of the virus's genetic material, cuts open its own DNA, and inserts the piece of virus DNA into a spacer.-"As the CRISPR region fills with virus DNA, it becomes a molecular most-wanted gallery, representing the enemies the microbe has encountered. The microbe can then use this viral DNA to turn Cas enzymes into precision-guided weapons. The microbe copies the genetic material in each spacer into an RNA molecule. Cas enzymes then take up one of the RNA molecules and cradle it. Together, the viral RNA and the Cas enzymes drift through the cell. If they encounter genetic material from a virus that matches the CRISPR RNA, the RNA latches on tightly. The Cas enzymes then chop the DNA in two, preventing the virus from replicating.-"As CRISPR's biology emerged, it began to make other microbial defenses look downright primitive. Using CRISPR, microbes could, in effect, program their enzymes to seek out any short sequence of DNA and attack it exclusively."