Viruses Are Alive and Are Oldest Living Creatures
Viruses have just joined the tree of life in a dramatic way -- they even predate modern cells.
Viruses have been difficult to classify, with some scientists arguing that they are just nonliving bits of DNA and RNA, yet new research not only finds that they are very much alive, but that they also emerged before the first modern cells.
Viruses have therefore just been placed on the tree of life, occupying the senior-most spot right at the bottom of the tree. They are not "animal, vegetable or mineral," as the saying goes, but exist within their own unique group, according to a new study.
"For now, we call it the 'viral supergroup,' just short of 'superkingdom' or 'domain,' which are words that are quite charged with meanings," Gustavo Caetano-Anoll's of the University of Illinois and the Carl R. Woese Institute for Genomic Biology told Discovery News. He co-authored the study, published this week in the journal Science Advances.
Arshan Nasir, who is Caetano-Anollés' graduate student and also worked on the study, added that "viruses are living. They simply have an atypical mode of living that is slightly different from ours. They are not fully independent. Instead, they move in and out of our bodies, stealing the resources and producing their offspring. In short, we need to broaden how we define life and its associated activities."
Viruses are challenging to study because the sequences that encode their genomes are subject to rapid change. As a result, the scientists elected to study what are known as "folds": the structural building blocks of proteins that give proteins their complex, three-dimensional shapes.
The scientists compared fold structures across different branches on the tree of life, reconstructing the evolutionary history of the folds and of the organisms whose genomes code for them. The researchers did this for 5,080 organisms representing every branch of the tree of life, including 3,460 viruses.
They identified 442 protein folds shared between cells and viruses, and 66 that are unique to viruses.
Nasir said that "a large number of viral genes are nothing like we have seen so far in the cellular world. They are most likely new genes created by viruses."
The researchers theorize that viruses evolved at a time when primordial cells were extruding genetic material, which viruses could then acquire. Most viruses then gained the ability to encapsulate themselves in protective protein coats, called capsids, which became more sophisticated over time. Capsids allowed viruses to become infectious to cells that had previously resisted them.
Viruses, Caetano-Anollés said, "can be visualized as cells that have lost and lost genetic material in exchange for reaping the benefits of their interactions with other cells."
As Nasir said, however, viruses also likely generate their own new genes, with some viruses becoming gigantic. On the tiny end of the spectrum there are viruses like Ebola, which only has seven genes. On the larger end are more recently discovered mimiviruses that have genomes as big, or bigger than, those of parasitic bacteria.
Andrew Camilli, a professor of molecular biology and microbiology at Tufts University, agrees that viruses are "living creatures."
"This belief stems from the fact that viruses have their own complex genome, they replicate to make more of themselves, and they are evolving," he told Discovery News.
Camilli even found that viruses acquire their own immune systems. He said that once viruses that attack bacteria "capture" an immune system, they can then disarm the host cell, "and can then proceed with the infection and kill the host cell."
Such research on viruses is allowing scientists to better understand the life cycles and evolution of these entities, with a future goal of managing viruses with more targeted, effective approaches.
For now, the researchers at least hope the argument that viruses are not alive is itself dead.
As Nasir said, "We commonly use phrases like 'how to kill viruses' in common day language. You can't kill something that is not alive, literally speaking."
Viruses are alive, researchers confirm.
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.)