Here is more about Thiomargarita magnifica, a sulfur-metabolising bacterium which is visible to the naked eye. Its genome is enormous as well, with 11 million bases and 11,000 genes, containing more than half a million copies of some sequences of DNA.
Here is the research paper, “A centimeter-long bacterium with DNA compartmentalized in membrane-bound organelles”.
Cells of most bacterial species are around 2 µm in length, with some of the largest specimens reaching 750 µm. Using fluorescence, x-ray, and electron microscopy in conjunction with genome sequencing, we characterized Ca. Thiomargarita magnifica, a bacterium with an average cell length greater than 9,000 µm that is visible to the naked eye. We found that these cells grow orders of magnitude over theoretical limits for bacterial cell size through unique biology, display unprecedented polyploidy of more than half a million copies of a very large genome, and undergo a dimorphic life cycle with asymmetric segregation of chromosomes in daughter cells. These features, along with compartmentalization of genomic material and protein synthesis in membrane-bound organelles, indicate gain of complexity in the Thiomargarita lineage, and challenge traditional concepts of bacterial cells.