Thiomargarita namibiensis is the World's Largest Bacterium

Posted on June 14, 2019

A recently discovered bacterium, Thiomargarita namibiensis, is the largest in the world. The bacterium is big enough to be visible to the naked eye. They can grow up to 3/4 mm wide in size. The images above show a light-photomicrograph of three cells of Thiomargarita with polarized light on the left and the visible bacterium on the body of a body (the white spot) in the image on the right.

Biologist Heide N. Schulz from the Max Planck Institute for Marine Microbiology in Bremen found the organisms in 1997 during a cruise with the Russian research vessel Petr Kottsov in sediments off the Namibian coast. The bacteria live from sulfide produced in the sea floor and store nitrate from the seawater in an "anaerobic lung."

Schulz's team says in the announcement, "Thiomargarita are not just rare and exotic microorganisms. They occur in high biomass of up to 47 g per square meter, thus playing an important role in the oxidation of the toxic sulfide in Namibian sediments. By coupling the oxidation of sulfide with the reduction of nitrate these bacteria use an energy source which is not accessible for most bacteria in the absence of oxygen. Their special trick, to "hold their breath" and wait until the nutrients become available, is an adaptation unique in the living world."

News of the giant sulfur bacterium was first published in 1999 in the journal Science. The researchers say some cells of thiomargarita as large as 0.75 mm (750 µm) were seen.

This video from Victoria Burgess helps explains how the gram negative bacterium have adapted to store sulfur and nitrate found in their unusually large vacuoles. The name Thiomargarita namibiensis means "sulfur pearl of Namibia."

MICROBES