NEW WORLDS: Cyanobacteria’s automatic sunshade

Due to the importance of this process, these organisms have developed mechanisms that protect them from overexposure to sunlight.

By JUDY SIEGEL-ITZKOVICH
Yellow Wagtail bird (photo credit: ITSIK MAROM)
Yellow Wagtail bird
(photo credit: ITSIK MAROM)
Photosynthesis, in which plants use sunlight, carbon dioxide glucose and water to create gluclose, is also vital in the animal kingdom – not only for organisms that perform photosynthesis themselves, but for all living things. This is because even animals that do not perform photosynthesis consume glucose.
Due to the importance of this process, these organisms have developed mechanisms that protect them from overexposure to sunlight. Just as film in pre-digital cameras can be overexposed, natural photosynthetic systems are also liable to become impaired as a result of overexposure, leading to the death of the organism.
One of these defense mechanisms has now been revealed in a study conducted by Prof. Noam Adir and doctoral student Dvir Harris of the Technion-Israel Institute of Technology’s Schulich Faculty of Chemistry, in collaboration with Dr. Diana Kirilovsky and her laboratory at I2BC-CEA, in France. The article was published in PNAS, the official scientific journal of the US National Academy of Sciences.
The defense mechanism was deciphered in cyanobacteria (formerly known as blue-green algae). The main player in this mechanism is OCP – a protein that changes its structure and color in response to intense light and blocks the flow of energy that reaches the center of the photosynthetic reaction.
This occurs by means of a reaction between the active species of OCP and phycobilisome (PBS) the protein complex that functions as a light harvesting antenna in the cyanobacteria.
Adir and his team discovered how bacteria protect their photosynthetic system from overexposure by blocking the energy.
“In effect, the protein acts as a biological switch. In response to strong light, part of the protein penetrates into the PBS and changes its structure, thereby diverting the flow of energy to the reaction centers. According to experiments done by the Kirilovsky lab, this defense mechanism blocks more than 90 percent of the sun’s radiation. As soon as the radiation diminishes, the protein returns to its normal state and the flow of energy resumes.”
BATS USE HEAVY WINGS TO LAND UPSIDE DOWN How do bats manage to roost upside down on cave ceilings or tree limbs? They need to perform an aerobatic feat unlike anything else in the animal world. In an article recently published in the PLoS Biology scientific journal, researchers from Brown University in Rhode Island have shown that extra mass in bats’ beefy wings makes the maneuver possible.
Compared to birds and insects, bats have heavy wings for their body size. Those comparatively cumbersome flappers might seem to reduce maneuverability, but new research shows that bats’ extra wing mass makes possible an unusual feat of aerobatics – the ability to land upside down.
“Bats land in a unique way,” said biologist Dr. Sharon Swartz.
“They have to go from flying with their heads forward to executing an acrobatic maneuver that puts them head down and feet up. No other flying animal lands the same way as bats do.”
But exactly how they are able to generate the forces necessary to perform those maneuvers hadn’t been clear.
When they come in to land they’re not moving very fast, which makes it hard to generate the aerodynamic forces needed to reorient themselves, so the question is, how do bats get themselves in position to land? Using a special flight enclosure, high-speed cameras and some sophisticated computer modeling, the researchers showed that it has a lot to do with wing mass and inertia. Bats’ wings are heavy, hand-like assemblages of bone, muscles, joints, tendons and skin. By throwing that extra wing weight around in very precise ways, bats generate inertial forces in order to reorient themselves, rather than relying on the aerodynamic forces generated by pushing against the air.
It’s similar to the way high divers shift their weight to perform flips and twists or cats reorient themselves to land feet-down when they fall.
Videos of bats in flight showed that as they approach the ceiling, they retract one of their wings ever so slightly toward their bodies, while flapping the other at full extension. With each wing beat in that asymmetric configuration, the bats rotate a half turn, helping to put them in position to meet the mesh feet first. In subsequent trials, the researchers removed the mesh from the ceiling, leaving the bats nothing to grab on to. Video of those trials showed that, after attempting to land, the bats performed a similar rolling maneuver using their wings in order to reorient themselves for forward flight.
The research sheds light on the basic biology that helps bats fly and land the way they do, but also may be useful in the development of human-made flying machines such as drones or robotic vehicles.