Saturday, October 16, 2010

A Bug's Life

Microbes have been in the news lately, for deeds both good and bad. Considering that we share our planet with at least five million trillion trillion bacteria, to say nothing of viruses and other microorganisms, it’s probably a good thing that we’re paying attention to what these invisible creatures can do.

The vast oil spill in the Gulf of Mexico caused by the Deepwater Horizon explosion has been in the public eye for the past several months. While corporate executives, politicians and the general public engaged in heated debate about failed attempts to cap the gushing oil well, an unnoticed cleanup crew had already moved into place. The release of natural gas from the damaged oil well served as a signal for bacteria like Vibrio and Alcanivorax that can literally “eat” oil, using them as fuel to survive and in the process breaking down these complex molecules into much simpler components like carbon dioxide.

Large bacterial communities have now arisen at the spill site and the first detailed analysis of these populations was published a few days ago in the prestigious journal Science, raising hopes that bacteria could be used to effectively mop up the oil spill.
Over eight hundred thousand gallons of chemical dispersant have been used to break the oil into smaller droplets that bacteria can effectively use. Scientists hope to eventually generate a single artificial organism that can work as a sponge to soak up spilt oil. Although a long and lengthy process, microbial ecologists studying the spill maintain that bacterial degradation is the only way to completely remove all traces of oil from the ocean.

From breaking down hydrocarbons to making them; a biotech company in the United States has just won a patent on a genetically engineered bacterium that uses sunlight and carbon dioxide to produce alkanes, ingredients of diesel fuel. These bacteria lead an exceptionally Spartan lifestyle, requiring only sunlight, carbon dioxide and water and growing on water unfit for human consumption or on agriculturally unsuitable land. One can imagine the fuel of the future being churned out in vast greenhouses as these bacteria silently perform their own brand of alchemy, churning out fuel for the entire planet literally from thin air.

Whether it’s cleaning up humanity’s messes or feeding our limitless demand for energy, microbes would appear to be our allies. But recent research into some of the world’s deadliest diseases conclusively proves otherwise. The human immunodeficiency virus (HIV), one of the worst modern scourges, originates from a monkey ancestor, the simian immunodeficiency virus (SIV). Given that HIV has caused over 25 million deaths to date and a cure is yet to be found, studying the origins of this virus has significant medical implications.

SIV infection in monkeys is benign, with infected animals remaining perfectly healthy.
But at some point in history, SIV made a giant leap from monkeys into humans, and turned into a lethal virus that dismantled the human immune system, leaving its host fatally vulnerable to infection. The question of how and when the virus made its species-spanning leap remains one of the enduring mysteries in the field of HIV research.

The answers to that question just got a lot more complicated, thanks to a new finding also published in Science; as it turns out, SIV is a lot older than first estimated. Instead of a few hundred years, the virus has been infecting monkeys for over thirty thousand years, implying that humans and infected monkeys have been co-existing for much longer than initially expected. Presumably, humans were exposed to SIV at several points during this timespan; why didn’t the virus make the jump then? We may never have a clear answer as to what made a harmless monkey virus turn into one of the most feared microbes of the 20th century. 

And viruses aren’t the only microbes capable of travelling from animals to humans. We can now add Plasmodium falciparum, one of the deadliest human parasites, to that list. The causative agent of malignant malaria, P. falciparum accounts for 91% of all malarial infections worldwide and 90% of malaria-associated deaths. While it was known that P. falciparum also originated in monkeys, the exact type of primate involved remained unclear. That issue was resolved on September 22 with the finding that P. falciparum moved to humans from gorillas. Intriguingly, it seems that the parasite crossed the gorilla-human divide only once; a single trans-species infection was sufficient to allow the evolution of P. falciparum into a lethal human parasite.

While HIV and P. falciparum are among the best known pathogens to move from animals to humans, plenty of other exotic microorganisms (think Ebola and anthrax) are carried by animals as well. It’s unnerving to think that humans and animals could peacefully co-exist for millennia before a single invisible hitchhiker could latch on to an unsuspecting human and give rise to a deadly new human pathogen. Who knows what else is lurking out there? And so, while we revel in the hoops that we can make microbes jump through, it’s wise to remember that the tables can always be turned.

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