Scientists observed a rare occurrence of primary endosymbiosis between marine algae and a bacterium, an event not seen for over one billion years. The endosymbiotic event involves one microorganism engulfing another, leading to the development of organelles like mitochondria and chloroplasts in host cells.

Such symbiotic events have greatly influenced evolution, with only three known instances leading to significant breakthroughs in the development of complex life forms. The first endosymbiosis event 2.2 billion years ago gave rise to mitochondria, and a subsequent event a billion years ago resulted in the evolution of chloroplasts in more advanced cells.

The recent laboratory observation suggests the potential formation of a new organelle, with the algae using a bacterium to convert atmospheric nitrogen into ammonia.