2023-07-26 16:25:32
Blue-green algae, more appropriately called cyanobacteria, measure only fractions of a thousandth of a millimeter in their smallest variant. These picocyanobacteria are the tiniest photosynthetic organisms known—and by far the most numerous. However, they do not just appear as producers of organically bound carbon. Some also turn out to be consumers. An international research group led by Giovanna Capovilla and Rogier Braakman from the Massachusetts Institute of Technology in Cambridge discovered that they can even utilize chitin when they examined the genetic make-up of different picocyanobacteria.
Chitin is found in the whole body shell of crustaceans and other arthropods, which leave this outer skeleton as waste each time they molt. Like cellulose, chitin is made up of a long chain of glucose molecules. However, each sugar molecule is modified by a nitrogenous appendage. As a result, neighboring macromolecules are bound together so strongly that chitin is harder and more stable than cellulose.
The scientists found genes that provide enzymes for the breakdown of chitin in picocyanobacteria of the genus Synechococcus and the most primitive representatives of the more progressive genre Prochlorococcus. In the case of some cyanobacteria in miniature format, the corresponding gene assortment turned out to be complete. They can completely dissolve and ingest chitin particles. Like Capovilla and her colleagues in the Proceedings of the American National Academy of Science to reportmost genomes studied do not contain all the genes required to use chitin as a food source.
Where does the appetite for chitin come from?
The gene for the first step, in which the long chain of sugar molecules is broken down into small parts, is particularly rare. The degradation of chitin is probably often a joint effort by different microbes, for which not all those involved need to bring the complete tool kit. The degradation products can provide energy for the metabolism of the picocyanobacteria, but can also be directly incorporated into the construction of the cell wall, for example. The most modern versions of the genus Prochlorococcus, which specialize in high-intensity photosynthesis, have lost the ability to use chitin as an alternative energy source. And not only that, they also lack some genes for the recycling of building blocks that arise during the conversion and expansion of the cell wall.
Picocyanobacteria of the genus Synechococcus, seen here under the electron microscope, use the sun and chitin as an energy source. : Image: Science Photo Library
The most primitive representatives of Prochlorococcus Significantly, they live in ocean depths where light penetrates so little that photosynthesis alone is barely sufficient for life. With chitin as a source of carbon and energy, these picocyanobacteria can still grow and thrive there. Especially since they are ready at any time to start breaking down chitin: the necessary range of genes continuously provides building instructions for the enzymes in question.
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