By Pooja Sainarayan

Local Journalism Initiative

As the seasons change, plants and animals all over the northern hemisphere have begun preparing for the cold winter months ahead. Using environmental cues, these multicellular organisms have complex proteins and the ability to form memories in order to sense the coming of the cold season. Interestingly, this ability to anticipate and prepare for the winter is not limited to complex organisms. Biologists have recently shown that at least one type of bacterium, the cyanobacteria, is capable of its own seasonal response, suggesting that this behaviour is a very innate and fundamental property of life.

Cyanobacteria, also known as blue-green algae are photosynthetic microscopic organisms that arise naturally in lakes, ponds, rivers and streams. The oldest known fossil dated 3.5 billion years old coming from Archaean rocks of western Australia are cyanobacteria. Considering that the oldest rocks are relatively only a litter older (3.8 billion years old), the cyanobacteria are indeed one of the oldest life forms on Earth. Since life was completely anerobic during the evolution of cyanobacteria, it is believed that these bacteria were directly responsible for the wiping out of anaerobic organisms and eventually resulting in The Great Oxidation event. The release of oxygen by these photosynthetic organisms was responsible for the earth’s atmospheric makeup, the origin of aerobic metabolism and ultimately, the evolution of multicellular organisms. It would not be wrong to say that we owe our existence to cyanobacteria. Although cyanobacteria helped to form and sustain our oxygen-filled atmosphere, its overgrowth, also known as “cyanobacteria bloom” can result in concentrations of toxins that are unsafe to the environment and living things. Of note, not all blue-green algae blooms are toxic. The reasons behind why some blooms produce toxins at any given time is not completely understood, which is why it is probably safe to avoid them altogether.

Cyanobacteria cells contain certain proteins that allow for photoperiod recognition. These proteins fall under the Kai family of proteins and are called KaiA, KaiB and KaiC, used by these bacteria to sense the hours of sunlight and darkness in a given day, called photoperiod. A group of researchers at Vanderbilt University hypothesized that the cyanobacteria’s photoperiod sensing may also extend to sense seasonal changes. To test this, the scientists grew cyanobacteria on a dish with summer-, intermediate- and winter- like conditions and then took cells from each condition to place into either a bucket of ice (0°C) or an incubator (30°C) for 2 hours. Afterwards, the cells were transferred back into the dish (30°C) to multiply for 5 days. The researchers measured the amount of cells that grew from the ice bucket versus the incubator and found that the cyanobacteria which were subjected to shorter photoperiod were up to three times better at surviving winter-like temperatures compared to those subjected to longer photoperiods. In addition, by removing the Kai-proteins and repeating the same experiments, the researchers demonstrated that the cyanobacteria could sense the shortening of days and prepare for the cold weather.

It is known that some cells can modify their fat composition on their cell walls to preserve their structure during colder temperatures. To understand whether a similar biochemical mechanism was occurring in the cyanobacteria, researchers chemically extracted the fats in the cells of cyanobacteria grown in winter conditions and measured the composition of these fats. This confirmed that the cells grown under the winter photoperiod conditions indeed increased their unsaturated fats to protect the integrity of their cell walls and avoid freezing. To sum it up, cyanobacteria rely on daily timekeeping to sense the shortening of days in order to biochemically prepare for the seasonal changes, known as photoperiodism. As photoperiodism was never observed in bacteria before, the researchers theorize that this ability likely evolved longer than we had previously thought and may even exist in other microorganisms.

The researchers also found that different genes were being used depending on the length of daylight. For instance, colder winter months brought about genes that increased metabolism to counteract the slower metabolic activity during winter. During the summer, genes implicated in protection against sun damage came into play. Apart from extending this research to other types of microorganisms and their ability to sense the seasons, it could also be particularly useful in detecting whether microorganisms responsible for toxic blooms can predict seasonal changes and to study the timing of these blooms to better control them. Further research into understanding photoperiodism in algae may serve to protect water habitats during blooms.