symbiosis between two unicellular organisms looks like a eukaryote
Science | Examples abound of long-term mutually beneficial relationships between microorganisms and plants or animals. In contrast, only a few examples of such symbioses between unicellular partners are known. In a Perspective, Zehr highlights recent reports of unicellular symbioses in marine and fresh-water systems. In both cases, the cyanobacterial partner in the symbiosis has a much reduced genome and must thus always carry their symbiont. These systems resemble organelle evolution and may help to understand the evolutionary events that led to organelle formation in eukaryotic cells.