MadSci Network: Cell Biology
Query:

Re: The largest unicellular organism

Date: Mon Jun 7 12:28:16 1999
Posted By: Michael Onken, MadSci Admin
Area of science: Cell Biology
ID: 928557042.Cb
Message:

I assume from your post that you are referring to Thiomargarita namibiensis, a massive sulfur-bacterium that lives in the oceanic silt off the coast of Namibia (Southwestern Africa). These bacteria attain their size (up to 0.8 mm) by storing excess nitrates in a huge vacuole that occupies most of the cell - without this vacuole, the bacterium is not much larger than a normal cell. While this is the largest bacterium yet discovered, it is far from the largest unicellular organism. That prize goes to the plasmodial slime molds, members of the eukaryotic Kingdom Protista. The best studied slime mold, Physarum polycephalum, grow to about 20 cm across, and is a single cytoplasm with millions of nuclei throughout its "body" (called a "Coenocyte"). These molds have given scientists unique insights into several intracellular processes. One of its cousins, Fuligo septica, created a scare it Dallas, Texas in 1973, when a single organism nearly a meter across convinced locals that an alien invasion was underway. Furthermore, depending on how strictly one adheres to the definition of cellularity, the largest organism in the world is a 10,000 Kg fungus, Armillaria bulbosa, from Michigan, which has septa throughout its branches (hyphae) that look cellular, although the cytoplasm is continuous throughout the organism.


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