Cyanobacteria originated photosynthesis and were innovators in using cellular greenhouses to do so. They also evolved the ability to flexibly capture whatever light was available to them – an adaptive optimality that changed the world.

Unlike heterotrophic prokaryotes, cyanobacteria have internal membranes to house their photosynthetic energy factories. These flattened sacs are called thylakoids. Plants inherited this architecture: photosynthesizing in specialized plastids.

By releasing oxygen as a byproduct of photosynthesis, cyanobacteria converted Earth’s early reducing (oxygen-depriving) atmosphere into an oxidizing one, creating the Great Oxygenation Event 2.4 billion years. This caused the “rusting” of Earth, which dramatically changed the composition of life on the planet, beginning with the near extinction of then-ubiquitous anaerobic organisms. Even today, with plants aplenty on land, cyanobacteria still contribute half of Earth’s oxygen production.

Cyanobacteria adapted to survive in all sorts of water bodies, whether salty or not. In the ocean, cyanobacteria rise to the surface during the day to collect sunlight and sink at night in respite. They naturally time their energy cycles to match their diurnal activity.

Cyanobacteria keep a 10-nanometer diameter protein that acts as a pocket watch. This protein accurately maintains time of day regardless of temperature or noise in the environment.

Sunlight was much weaker billions of years ago, and not every cyanobacterium gets an ideal spot for sunbathing. So, cyanobacteria intelligently adapted to optimal garnering of the wavelengths most available. “When cyanobacteria live in low-light conditions, they switch from using the visible light that is most conducive to growth to harvesting the weaker, far-red sunlight that filters down to them,” remarked American molecular biologist Donald Bryant.

A specific protein surveys the wavelengths of light coming in and tells colleagues to modify the photosynthetic apparatus accordingly. An estimated 1/8th of Earth’s oxygen comes from these highly adaptive cyanobacteria.

Once other life took to harvesting cyanobacteria for food, these molecular mavens started manufacturing poisons to ward off predation. Cyanotoxins are some of the most powerful poisons known, including ones which can cause rapid death in animals via respiratory failure. Such savvy – knowing precisely how to kill unrelated species – came from comprehending alien biology.

A localized force of coherence guides organisms toward adaptations which may enhance survival. This is the modus operandi of biological evolution. Cyanobacteria illustrate the wiles of this knowledgably creative coherence.


Ishi Nobu, The Web of Life, BookBaby (2019).

Christopher Gisriel et al, “The structure of Photosystem I acclimated to far-red light illuminates an ecologically important acclimation process in photosynthesis,” Science Advances (5 February 2020).

Scientists solve structure enabling cyanobacteria to thrive in low light,” (5 February 2020).