Thiomargarita namibiensis: King of the Bacteria
Ryan Cox

Someone with only a passing knowledge of science could probably tell you that bacteria are supposed to be tiny things, so small that you can’t see them without the aid of some pretty powerful magnification. So imagine the surprised look on the face of Heide Schulz, a biologist aboard the research vessel Petr Kottsov who was searching for sulfur reducing bacteria near Walvis Bay, Namibia, when she examined some sediment samples and noticed something peculiar: in the muck were organisms resembling a string of tiny pearls, most of which were from 0.1-0.3 mm (but some reaching up to 0.75 mm) in diameter, easily large enough to be viewed with just the naked eye.

So Dr. Schulz, curious as to the reason for the enormity of these bacteria (100 times bigger than the nearest competitor for the title of largest bacteria…roughly equivalent to comparing the largest of whales to a baby mouse), examined T. namibiensis more closely. What she discovered is that 98% of the interior of its cells was comprised of an enormous liquid vacuole. This vacuole is used to store both sulfur and nitrate, which is reduced by T. namibiensis to oxidize sulfide. The nitrate levels within each bacterium are up to 10,000 times greater than that of their environment, which translates to a lot of nitrate reducing potential for a large colony of T. namibiensis. Neighboring bacteria are connected through a common mucous sheath that keeps them aligned linearly, and the white clumps of sulfur within the cells are reflective, giving the bacteria a white color and contributing to its pearlesque appearance.

T. namibiensis’ large size, amazing as it is, is due to the size of its vacuole. However, the size of the vacuole imparts T. namibiensis with the ability to do some other amazing things as well. With such a large storage space for nitrate and sulfur, these bacteria are in essence able to “hold their breath” for up to 3 months without any additional intake of nutrients. With the wide variety of weather patterns, and with the accompanying changes in the amount of available nutrients, this feature plays a key role in the ability of these bacteria to survive for extended periods when starved of resources.

The coastal regions that T. namibiensis typically resides in are generally rich in phytoplankton, resulting in a large amount of biomass accumulation on the seafloor. Anaerobic bacteria then will oxidize this organic material, which results in large quantities of sulfide being released into the waters. Because of the abundance of resources in such an environment, T. namibiensis is ubiquitous, comprising up to 47g of biomass per square meter of seafloor. Due to this, it is a key role player in the oxidation of the high levels of sulfide, which otherwise would reach toxic levels in the seawater. The detoxifying of the sulfide in the seafloor sediments, coupled with the fact that nitrate from the water is reduced to accomplish this, shows the importance of T. namibiensis in keeping the deep sea waters they inhabit hospitable for the other organisms living there.

References

1. Jorgensen, Bo Barker et al. “The largest Bacterium: Scientist discovers new bacterial life form off the African coast.” Research News Release. Max Planck Society. August 4, 1999. http://www.mpg.de/english/illustrationsDocumentation/documentation/pressReleases/1999/news17_99.htm

2. “Thiomargarita.” MicrobeWiki. August 16, 2006. http://microbewiki.kenyon.edu/index.php/Thiomargarita

3. Wirsen, Carl. “Is Life Thriving Deep Below the Seafloor?” Oceanus. Woods Hole Oceanographic Institute. April 12, 2004. http://www.whoi.edu/oceanus/viewArticle.do?id=2497

*Disclaimer - This report was written by a student participaring in a microbiology course at the Missouri University of Science and Technology. The accuracy of the contents of this report is not guaranteed and it is recommended that you seek additional sources of information to verify the contents.

 

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