July 24, 2013
How Purple Bacteria Could Survive Alien Light
April Flowers for redOrbit.com - Your Universe Online
Purple bacteria, which have been around longer than most other organisms on the planet, contain pigments that allow them to use sunlight as their energy source. Neil Johnson, a University of Miami (UM) physicist who studies these magenta microbes, recently discovered they can also survive in the presence of extreme alien light.
Johnson, head of the inter-disciplinary research group in complexity in the College of Arts and Sciences at UM, led a team of international scientists whose work reveals new possibilities for life on earth and elsewhere in the universe.
"The novelty of our work is that despite all the effort aimed at finding planets outside our solar system where life might exist, people have ignored the fact that photosynthesis - and hence life on Earth - isn't just about having the right atmosphere and light intensity," Johnson says. "Instead, as we show, a crucial missing ingredient is how the light arrives at the organism."
The findings of this study could also be applied to a scenario in which our own sun develops wild fluctuations in intensity and in a situation in which bacteria are subject to extreme artificial light sources in the laboratory. They might also prove beneficial in the effort to engineer a new generation of designer light-harvesting structures.
The researchers used a mathematical model to calculate the probability of survival when the bacteria is subjected to bursts of light. This is similar to what might be experienced if the light source were an unstable star. On average, the total amount of light was the same as what the bacteria would normally receive. Since the organisms would receive the light in such an unusual pattern, however, the researchers wondered under which circumstances the bacteria could survive.
"It's like saying we know we need to bring home a certain amount of food per week, but what happens if all of the food is delivered in one day? You might not be able to store all of it," Johnson says. "Maybe some food would get spoiled, or maybe you wouldn't have time to use it all," he says. "The light is like food for the bacteria, and the issue is the amount of food and the timing with which you bring it in."
Light is delivered in packets of photons, which purple bacteria process in places called reaction centers. These centers are where the energy of the photons fuels the production of metabolic materials. According to Johnson, this is similar to asking what happens when food arrives in the kitchen in an irregular way.
"The reaction center, like any kitchen, can't do a thousand things at once. They can only handle one photon at a time," Johnson says. "The new chemicals made in the process take some time to diffuse. Otherwise, it results in a buildup of chemicals that can kill the bacteria," he says. "Since we are concluding this from statistical calculations, we can say it's very unlikely that the bacteria will survive."
The research team was surprised to find while many seemingly innocuous changes in the way the light arrives at the organisms end up being fatal, the bacteria could survive a sudden deluge of photons. The key factor in surviving such extreme conditions is that the organisms have many reaction center "kitchens," allowing the photons to spread out naturally, leaving each reaction center enough time to recover.
"Ultimately the chemicals have time to diffuse and that is what saves it," Johnson says. "On the average the bacteria is therefore getting what it needs from the reaction centers."
The team suspects purple bacteria are not the only organisms to use this mechanism and they plan to expand future research to other photosynthetic life forms.