Dr. Sebastian Rokitta, AWI biologist and lead author of the study

Dr. Sebastian Rokitta, AWI biologist and lead author of the study

In a recent study, scientists at the Alfred Wegener Institute, Helmholtz Centre for Polar and Marine Research (AWI) have determined the molecular mechanisms which microalgae apply in order to switch from rapid cell division to growth-arrest during times of acute nutrient deficiency.

The scientists’ laboratory experiments have been able to observe that calcifying microalgae in a state of nutrient deficiency initially tweak their metabolism to be more economic and efficient before, out of necessity, they even partially digest themselves. The molecular switches for these basic functions of cells are strikingly similar in all living things. Apparently, it is these switches, which, when malfunctioning in humans, cause cells to lose control of their division activity and potentially become cancer cells. The new findings are being published online this week in the journal Frontiers of Marine Science.

AWI biologist and co-author Dr. Bjöern Rost

AWI biologist and co-author Dr. Bjöern Rost

“Like all living things, algae depend on the nutrients phosphorus and nitrogen, which are introduced into coastal areas by rivers, or in the open ocean, and are carried up from depth by eddies. If the surface water is fertilized by such nutrients, a race for the precious elements begins in which the various algae compete for the nutrients. This race only ends when the nutrients which are necessary for cell division are exhausted and the algae are suddenly facing a famine situation,” explains Dr. Sebastian Rokitta, AWI biologist and lead author of the current study.

By using so-called microarrays, the scientists have been able to simultaneously observe the activity of more than 10,000 genes under different hunger scenarios. The new results show that the genetic programs which run in different hunger situations are largely the same in terms of arresting the cell division and are only slightly modified, depending on the particularly lacking nutrient, e.g., to switch on specific transporters and storage mechanisms. This strategy is very useful for the algae, since it greatly simplifies the management of the complex cellular apparatus.

What is striking is the close integration of nutrient availability and cellular energy supply in the algal metabolism. “Apparently, the triggered genetic programs also include molecular sensors that stop the cell division, so to speak, in case of low nutrient levels,” says the AWI biologist Dr. Bjöern Rost, who was also involved in the study.

The research results also demonstrate that, in the case of ongoing life-threatening nutrient starvation, the microalgae begin to “digest” their own cellular components, to ensure their survival as long as possible. They cannot maintain this process for very long, though. All those cells that destroy themselves through this emergency measure then unintentionally make their nutrient-containing components available to other algae as well as to their conspecifics.

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