Well, the world celebrated the Birthday of Charles Darwin on the twelfth of February, a few days back. International Darwin’s Day was observed in many Universities and Colleges of the World where special events and conferences marked our tribute to one of the greatest naturalists and Scientists of our time. This unassuming man defied his fate so to speak and became a scientist instead of a clergyman, much against his father’s wishes.

Battling his intense fear of the sea, he undertook the now legendary voyage aboard the HMS Beagle, and collected and classified a colossal number of specimens, both plant and animal. In fact, he even collected mineral rocks and skeletal remains. So great was his passion for collection and identification, that he began observing details that had earlier been overlooked. From these details emerged a theory and he wrote his seminal work, “On The Origin of Species”.

The central idea of this theory was that all life forms tended to evolve from a previous form and hence in all probability, shared a common ancestor. To simplify this, suppose there existed an organism A. After a  few years slight changes in the genome of this organism occurred, which led to the formation of a species different from the original one. Thus, we have a branch-point, where the new species diverges from the older one and both species continue their existence. Both the species in their natural environments will continue to grow and adapt to the specific ecological niches. In doing so, after several thousand years, they may become so different from each other, that it would be difficult to imagine them being related. Nevertheless, they are evolutionarily related to one another. Another phenomenon might occur; namely selection of one species over the other. Natural environments are limiting for food, shelter and other resources with a large number of species fighting for a foothold. This intense competition leads to specialization of ecological niches. This simply means that various species try their best to make use of some unique resources so as to minimize competition; for example, if you consider the lowest o life forms, the bacteria, two different species living in the soil may have 2 completely different sources of food. This helps them to co-exist without impeding each other. However, this is not always possible and when the competition is too intense, any one species may be ‘Selected’ by nature to survive depending upon its relative fitness to exist in that environment. This fitness can be very simply defined in terms of some adaptational advantage of one species over the other. For example in a given environment, if two species of bacteria can use Lactose as a source of food, but one has in addition a tolerance to salt as well, then the second species is more likely to survive in an environment that has lactose and salt both as compared to the other one. If the environment suddenly turns more saline, the salt –tolerant organism will have a higher probability of survival than its counterpart. This forms the essence of the theory of natural selection.

“On the Evolution of Species was published in the year 1859 and it went on to becoming one of the most influential books of the time. The theory came to be widely accepted by the scientific community and overthrew many other popular streams of thought and Philosophy on evolution. Many of these theories had theological bases. The strong scientific backing of  Darwin’s ideas convinced most people about the soundness of his theory. Although as the body of scientific knowledge grew and more and more data on obscure species emerged, the Darwinian thought has been challenged more than once, the theory of evolution remains the single most important thought behind our attempts to explain our evolution on this planet. Today there are groups of scientists who have put Darwin in the perspective of genes, namely have explained or tried to the evolution of species in terms of genetics. This new breed of Darwinism has come to be known as Neo-Darwinism. Richard Dawkins is arguably the most well-known and witty of all neo-Darwinist writers. His series of books from ‘The selfish gene” to “Unweaving the Rainbow” make for a compelling read even for the skeptics. The debate is still raging and as more knowledge emerges it makes our theories seem painfully inadequate. However, that is a matter for another article.

What I felt was very apt for this week’s article was a paper published in the Scientific American on the second of this month. (February 2, 2010). The paper deals with the research of  Raymond Schuch from the Rockefeller University. His research revolves around Anthrax and Earthworms ! Strange huh! And what on earth has that got to do with Darwin anyway? Well, the connection is as strange to the scientists who discovered it as to us. Well I have already touched upon the competition between species aspect in terms of Survival of the fittest species. However, intense competition also leads to another phenomenon; interactions between species that are totally unrelated. These interactions may be positive (Symbiosis) or negative (Parasitism). The capacity of a species to form any such association might greatly increase its “fitness” in Darwinian terms for a particular environment.

One very interesting area of study is to study these types of interactions in species of Bacteria or viruses that are pathogenic to our species. These organisms are constantly evolving to better their pathogenic skills and even as we push the frontiers of medical science, we are still amazed at the apparent intelligence of these tiny adversaries of ours. The Anthrax study is a case in point. In the year 2002, researchers at the Rockefeller lab reported that they had found a way to fight the deadly Bacillus anthracis causative agent of Anthracis. This organism earned the dubious distinction of being the favourite bioweapon organism of terrorists. The organism is deadly and naturally researchers wanted to find a way out. In the journal Nature, scientists Fischetti and co-authors Raymond Schuch, Ph.D., and Daniel Nelson, Ph.D., reported the use of a Bacteriophage (a virus that attacks only bacteria) to combat this deadly germ. A drop of the virus containing fluid wiped out the entire population of the Anthrax germ growing in a test –tube. Actually the fluid contained an enzyme from the virus that allowed the virus to break open the bacterium so that the virus could escape. An extract of this enzyme was a potent tool against the Anthrax bug. What’s more, since it was an enzyme, it was highly specific, it would target only B. anthracis and nothing else. Also, in combination with another chemical, L-alanine, the extract can be used on the highly resistant endospore form of the bug.

A few years later, in 2009, the same set of authors continuing their work on this pathogen, reported a strange finding. That some of these bacterial viruses (phages) actually did not break open the cell they had infected (lyse: Such phages are known as lytic phages). Instead, these phages integrated into the genome of the bacterium and stayed there for generations (lysogenic phages). Now, while the concept of lysogenic phages was very much known, their actual role in the life cycle of this ubiquitous soil bacteria and its ability to survive for years in the soil was not suspected. In what looks like an evolutionary contract signed by the phage and the bacterium, they form a symbiotic association benefiting both of them!

And this is also where the earthworms come in! a few hundred year back prodigious microbiologist and chemist Louis Pasteur noticed a strange thing. The carcasses of livestock that dies of Anthrax were found teeming with earth worms. Being the genius he was, Pasteur speculated that these earthworms had something to do with the life cycle of B anthracis. Now after this long time, these researchers have confirmed his hunch. Picking up some earthworms from the soil and analyzing their gut flora may not be a very desirable task, but it certainly led to some fantastic results. The researchers found that, in the gut of these worms, a species of B. anthracis resided that had within its genome a lysogenic phage. This species had a greater lifespan than the normal Bacillus anthracis. Bacillus anthracis is not infective, it lies dormant in the soil as a resistant dormant body called the endospore. All techniques to isolate this bacterium have depended on heating soil samples to kill vegetative cells and isolate spores. However, now, it seems that the phage keeps the cell alive in vegetative form for years and years and the gut of the earthworm provides the required ecological niche. Apparently, the phage confers a higher life span on the cells. Also, it has the capacity to juggle the cell between the spore form and the vegetative form. It has always been assumed that when Bacillus anthracis is not infective, it lies dormant in the soil as a resistant dormant body called the endospore. All techniques to isolate this bacterium have depended on heating soil samples to kill vegetative cells and isolate spores. However, now, it seems that the phage keeps the cell alive in vegetative form for years and years and the gut of the earthworm provides the required ecological niche.

The cell being in vegetative form benefits the virus as it grows better in vegetative cells and if the environment turned particularly nasty they trigger events leading to spore formation. Using tiny little protein factors known as sigma factors, these viruses toggle the bacterial genome between these two states. Thus, the beauty is the cells of Bacillus anthracis can remain in the vegetative and infective state for longer time in the soil even away from a suitable host (usually livestock). This probably explains why many of these epidemic are cyclic in nature. Quoting Dr. Fischetti, “The finding has implications for the sequencing of genomes. What that means is that sequencing the genome may not be enough,” says Fischetti. “There are more than 1,000 known isolates of anthrax and there is little genetic variation between one isolate and the next. So at face value, it is a really boring genome. But what we see here is that the phage DNA, which works together with the anthrax genome, has always been overlooked.”

In the paper in the Scientific American in 2010, researchers from the same group have found that when Bacillus anthracis is induced to form vegetative cells, they also form Biofilms. Sticky layers of vegetative cells forming associations that enable them to tide over difficult environmental situations. These might also increase the pathogenicity of the organisms. Organisms in biofilms behave like a single unit, modifying their metabolism so that all species in the film can benefit. That this behaviour is controlled by phages in the genome has profound implications on our views about this disease and its epidemiology.

We have come a long way in trying to grasp disease and its molecular underpinnings. But this unique association between a virus and a bacterium might just alter our thinking about diseases and their cure forever. In the context of Darwin and his theory of natural selection, I think this piece of research pays a fitting tribute to the grand master of the Science of Evolutionary biology. So hail Darwin and the Earthworm ! !