Viruses Pass Major Test to Enter Ranks of Living

Viruses with their own immune systems can kill bacteria, and could be key in fighting superbugs.

Viruses can acquire fully functional immune systems, according to new research that bolsters the controversial theory that viruses are living creatures.

Until now, scientists thought that viruses existed only as primitive particles of DNA or RNA, and therefore lacked the sophistication of an immune system.

The study, published in the journal Nature, is the first to show that a virus can indeed possess an immune system, not to mention other qualities commonly associated with complex life forms.

The belief that viruses are living creatures "stems from the fact that viruses have their own complex genome, they replicate to make more of themselves, and they are evolving," co-author Andrew Camilli of the Tufts University School of Medicine told Discovery News.

The use of a complex immune system "doesn't prove" that viruses are living beings, "but it does add to the argument," he said.

Living organisms are typically defined as being capable of vital functions, such as the ability to grow and adapt to the environment over successive generations. Viruses are now on the fence between being considered a biological entity and an actual living creature.

Camilli and his colleagues focused their investigation on a viral predator of cholera bacteria. This type of virus is known as a bacteriophage ("phage" for short).

Lead author Kimberley Seed, a postdoctoral fellow in Camilli's lab, was analyzing DNA sequences of phages taken from stool samples of Bangladesh cholera patients. She was surprised to find genes for a functional immune system previously only found in some types of bacteria.

To verify the discovery, she and her colleagues used phages both with and without the immune system to infect a new strain of cholera bacteria. Only the virus harboring the immune system readily killed the cholera bacteria.

Not only can some viruses have an immune system; some also can steal them from bacteria.

The scientists found that viruses can capture immunity genes from bacteria during a phase when "the viral genome is being replicated into dozens of copies within the infected host cell," Camilli explained. The virus therefore steals an immune system from the bacteria. This benefits the phage virus.

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"The immune system allows the phage to target and destroy specific inhibitory genes of the host cell by literally cutting the target genes into pieces," Seed told Discovery News. By disarming these genes, "the phage essentially disarms the host cell, and can then proceed with the infection and kill the host cell."

While we tend to associate both viruses and bacteria with health threats, that is not always the case. In this instance, the virus winds up on the side of humans.

Camilli explained that "phages are killers of bacteria. If the species of bacteria they happen to kill is a human pathogen, then the phage is doing us a favor."

The researchers hope that this activity could battle "superbugs," which are bacteria with a resistance to most are all current antibiotics.

Mammals, including humans, possess immune systems that, unlike those of bacteria, are encoded on much larger pieces of DNA.

"It would be very difficult, if not impossible, for a virus to capture (such an immune system)," Camilli said.

"A second consideration is that the virus has to have a good use for the captured immune system in order to hang onto it," he added. "In the case of a phage, we have shown that it can use the captured immune system to good effect. This may or may not be true for another type of immune system, should a virus be able to capture it."

Sylvain Moineau, a professor in the Department of Biochemistry, Microbiology and Bioinformatics at Université Laval, is one of the world's leading experts on bacteriophages. Moineau told Discovery News that the discovery of a phage with an immune system "is a remarkable finding. Phages always seem to find a way to impress us."

Moineau and colleague Manuela Villion remind that phages are among the most abundant biological entities on the planet, outnumbering their bacterial hosts tenfold. Whether they and other viruses represent living organisms, however, is still up for debate.

A bacteriophage

Rarely has anyone looked at a potentially fatal infectious disease and exclaimed, "Now, that is a thing of beauty." One sculptor, however, has taken bacteria and viruses from their invisible world and placed them in ours.

Artist Luke Jerram has created a collection of glass artwork in the shape microorganisms -- bacteria and viruses no less that have the potential to infect or even kill human beings. By bringing these microscopic marauders to the light, Jerram demystifies these otherwise unknowable microorganisms. And using glass as a medium reinforces not only the fragility of the work, but also our own in the face of these diseases.

In this slide show, take a closer look at some of the highlights from Jerram's glass microbiology collection.

Turning HIV into a work of art is a seemingly impossible task. The virus is responsible for the deaths of an estimated 34 million people worldwide since the epidemic was first reported in 1981, according to UNAIDS, the joint United Nations Programme on HIV/AIDS.

The HIV virus sculpture was the first Jerram built for his collection.

If there's one disease that has plagued humankind throughout its history, it's malaria. In 2010, the World Health Organization estimated that more than 200 million people were infected with the disease, mostly in poverty-stricken regions of sub-Saharan Africa, but also parts of South America and Southeast Asia.

Malaria is transmitted through mosquito bites. Mosquito nets, insect repellant and pesticides are all effective means of prevention, but only for those with the available resources and access to afford them.

Looking at this spindly sculpture might make you the slightest bit queasy, and for good reason. E. coli is represented by this glass artwork. Although most E. coli strains are in fact harmless to humans, the strains we're most acquainted with are the ones that cause food poisoning.

This alien-looking sculpture is actually T4 Bacteriophage, a virus that targets E. coli bacteria.

Bacteriophages are small viruses that attach to the cell membrane of bacteria. The virus injects its DNA into the bacteria, which then produces replicas of the virus, filling the bacterium until it bursts.

If this model is giving you that nostalgic feeling of plagues past, you might not be surprised to find out that this work represents Severe acute respiratory syndrome, or SARS.

SARS made global headlines in 2003 when people in 37 countries and nearly reached pandemic levels. Although coverage of the illness was widely criticized for overstating the threat, nearly 9,000 were infected with the disease, with had a nearly 10 percent fatality rate.

Swine flu, shown here, was another contagious disease that drew global attention that Jerram selected for his exhibition, but this time it was personal. According to his website, Jerram came down with swine flu and constructed the sculpture "with a fever whilst swallowing my Tamiflu tablets every few hours."

Swine flu, or H1N1 strain of the influenza virus, made global headlines in 2009 as the next potential major flu epidemic. Though common among pigs, swine flu is rarely transmitted among humans. When it does infect a human, however, the symptoms associated with the virus, typical of other flu strains, are particularly acute.

Given just how common the Human Papilloma Virus (HPV) is among humans, you'd think this virus, pictured here, wouldn't be so controversial. In fact, it isn't, but the use of a vaccine to prevent the infection, which can lead to certain kinds of cancers in women.

Because the virus can be transmitted sexually, however, the idea of vaccinations, particularly compulsory ones for children -- the vaccine is in fact intended only for people 25 and younger -- generated a considerable pushback, despite the obvious benefits of the treatment.

Hand, foot and mouth disease might not get a lot of press, but these disease outbreaks are in fact fairly common, particularly among infants and children. Occasionally, they can be fatal. Symptoms are similar to the flu, with the exception of sores that can appear all over the body, but particularly the hands, feet and mouth of the carrier.

This final entry is an unrealized future mutation for a disease that doesn't exist yet. Look for it in a contaminated water main, food source or loving pet near you. (But seriously, don't.)