Phage: Virii that use bacteria as hosts. Phages often kill their host immediately, these are often used as antibacterial agents. Others cause a permanent modification of the hosts DNA by the implantation/transmutation of RNA without causing death.

Phage and bacteria are in a constant evolutionary struggle for supremecy.

For much much much more information, see Greg Bear's newest book: Darwin's Radio.

Not to be confused with Star Trek's The Phage, an incredibly disfiguring disease (I'm still trying to work out the correlation).

Phage is name of the first virus that attacks Palm, and other Palm OS based devices.

When executed, the Phage virus fills the screen of the PalmOS based device with a dark gray box, terminates the application that is running and replicates itself (infects) other installed applications.

By most accounts, Phage is the first virus that is capable of infecting PDAs, or "Personal Digital Assistants", unlike several other well documented Trojans.

Phage is will also affect PDAs manufactured by Handspring (Visor), IBM (Workpad), TRG, and Symbol Technologies.

A PDA gets infected when Phage spreads from one Palm to another if infected files are shared via IR beaming or via "Hot Synching". At this time it does not appear that Phage can propogate itself (although it would be a cool hack to have Phage automatically enable beaming, and transfer itself to nearby Palms - I've thought of writing something like this since my Sony MagicCap days, and virii do not have to be destructive...).

The best solution to Phage, in the absence of proper anti-virus software is to completely restore the Palm OS device by means of using the HotSync manager. Set all HotSync conduits to "Desktop overwrites Handheld" and HotSynch with the Palm desktop.

Note that default settings for Palm OS backups does not include applications, so unless this setting has reset by the user, all installed applications will have to be re-installed.

bacteriophage therapy is the practice of administering phages as antibiotics. The bulk of the early work in this area was done by Felix d'Herelle at the Pasteur Institute in the early 20th century. His findings showed promise, but were the subject of much controversy in the medical community. The science of his day lacked the technology to identify, isolate, and prepare phages for medical use, so when conventional antibiotics were introduced in the 1940's, the study of phages as medicine all but ceased in the west.

Work continued in some of the Soviet block countries of Eastern Europe, and as antibiotic resistant bacteria have arisen in alarming numbers, medical researchers have begun to turn to institutions like the Polish Academy of Sciences in Wroclaw, Poland and the Bacteriophage Institute in Tblisi, Georgia for information.

There is much work still to be done before phages become a mainstream therapy for bacterial infections, but they hold good promise, and are once again being taken seriously by the world medical community.

This subject is discussed in greater detail at phage therapy.

PFY = P = phase

phage n.

A program that modifies other programs or databases in unauthorized ways; esp. one that propagates a virus or Trojan horse. See also worm, mockingbird. The analogy, of course, is with phage viruses in biology.

--The Jargon File version 4.3.1, ed. ESR, autonoded by rescdsk.

Phage are the viruses of bacteria. They are also called bacteriophage.

Phage are not alive in the strict sense of the word, they are basically only a lump of genetic material enclosed in a protecting shell, the so called capsid. This "head" is often geometrically shaped, ie icosahedral or octahedral. Additionally they may have a "tail" structure for the delivery of their payload.

They inject their DNA (mostly - there are some phage consisting of RNA as well) into a bacterium where it reprograms the whole cell machinery to assemble new phage. The cell then splits open and releases the progeny, which usually numbers several hundred. This is called a lytic cycle. Virulent phage enter it at once, temperate phage have the ability to integrate into the genome without killing the host. Thus they are replicated every time the host cell splits. This is termed lysogenic development. The so-called prophage may then begin a lytic cycle later on, when environment conditions worsen and bring about the possibility of the host cell dying.

Bacteria are not completely defenseless though. They have a kind of immune system, called restriction-modification system. Special enzymes, the restriction endonukleases, cut up all foreign DNA that enters the cell. How do they know it's foreign DNA? Well, because the cell's own DNA is protected by a small modification - it's methylated in a special pattern. Unfortunately some phage imitate that pattern, so there's no complete immunity. But a given phage cannot infect all strains of bacteria - it is host specific. Apart from that phage are also host specific in the sense that they need certain surface structures to attach. T4 for example can only attack E.coli cells, and some strains of E.coli more efficiently than others because it matches their methylation pattern better.

Phage vary greatly in their complexity. For example ΦX174 has only 5386 nucleotides (single stranded DNA) in 10 genes and a diameter of 25-30 nm, while T4 comes at a whopping 169000 base pairs (double stranded DNA) in more than 130 genes and is about 300 nm long. It also looks very spacy! See http://www.udel.edu/Biology/Wags/histopage/modelspage/t4.gif :)

As you can imagine, their ability to transfer DNA ("transduction") makes phage a valuable tool in genetic engineering.

Source: Biology of the prokaryotes / ed Lengeler, Drews, Schlegel / Thieme Verlag / 1999

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