Giant: Meet a bacterium that is visible to the naked eye

Meet Thiomargarita magnifica. It is 5,000 times larger than most bacteria, which typically measure two micrometres in size. “To put it into context, it would be like a human encountering another human as tall as Mount Everest,” Jean-Marie Volland from the US Department of Energy Joint Genome Institute and one of the scientists behind the discovery, said in a press briefing June 21, 2022. Volland and his team announced their discovery in the journal Science. Photo: Lawrence Berkeley National Laboratory

Thiomargarita magnifica was discovered in 2009 by Olivier Gros, a marine biology professor at the Université des Antilles. He spotted long white filaments on sunken leaves in the waters of mangrove forests in the southern Caribbean Sea. Photo: Lawrence Berkeley National Laboratory

DNA analysis revealed that the Caribbean giant is indeed a bacterium belonging to the genus Thiomargarita, a group of giant bacteria that consume sulphur to produce energy. The species gets its name from the Latin magnus, which means big. This single-celled bacteria has dethroned Thiomargarita namibiensis, a 750- micrometres-long giant of the same genus. Photo: Lawrence Berkeley National Laboratory

Thiomargarita magnifica’s size is not the only odd feature. Its DNA is enclosed in a pouch or a compartment called “pepins,” meaning seeds in French. This packaging is unheard of in the bacteria kingdom, where DNA moves about freely within the cell. The new bacterial species has opened our eyes to unexplored microbial diversity, Shailesh Date, Chief Executive Officer at Laboratory for Research in Complex Systems, said in the press meeting. Photo: Lawrence Berkeley National Laboratory

The species contain hundreds of thousands of copies of DNA. They are also not pathogenic to humans, according to the research team. Photo: Lawrence Berkeley National Laboratory

There is a lot that remains to be understood. According to Gros, they have not been able to detect the species in the last two months. “We need to check if they show seasonality,” he said during the press briefing. Others highlighted that they do not yet know why the bacteria evolved to such proportions, if the size puts them at an advantage, or if it comes with costs. Researchers hope to find answers to them and more. Photo: Lawrence Berkeley National Laboratory