For the first time in at least a billion years, two lifeforms have merged into a single organism.
The process, called primary endosymbiosis, has only happened twice in the history of the Earth, with the first time giving rise to all complex life as we know it through mitochondria. The second time that it happened saw the emergence of plants.
Now, an international team of scientists have observed the evolutionary event happening between a species of algae commonly found in the ocean and a bacterium.
From the Science paper, https://www.science.org/doi/10.1126/science.adk1075
Editor’s summary
Many partnerships have been formed between nitrogen-fixing microbes and carbon-fixing eukaryotes that need nitrogen to grow. The possibility of a eukaryote with a nitrogen-fixing organelle derived from endosymbiosis, which is called a nitroplast, has been speculated. Studying a marine alga with a cyanobacterial endosymbiont, Coale et al. used soft x-ray tomography to visualize cell morphology and division of the alga, revealing a coordinated cell cycle in which the endosymbiont divides and is split evenly, similar to the situation for plastids and mitochondria in these cells (see the Perspective by Massana). Proteomics revealed that a sizable fraction of the proteins in this structure are encoded by and imported from the alga, including many that are essential for biosynthesis, cell growth, and division. These results offer a fascinating view into the transition from an endosymbiont into a bona fide organelle. —Michael A. Funk