Bacteria by Trudy M. Wassenaar

Author:Trudy M. Wassenaar [Wassenaar, Trudy M.]
Language: eng
Format: epub
Publisher: John Wiley & Sons
Published: 2011-11-02T21:00:00+00:00

Chapter 16

Record Holders

Record holders usually receive more attention than the group that collectively is most common, the modal. Since our knowledge of the bacterial world is skewed, a lot remains unknown to this day, both about the modal and the record holders of microbial communities. Records are bound to be broken as new discoveries are made, and the modal may shift as we learn more about what is common. Nevertheless, here is an attempt to present the currently known winners from a variety of contests.

Bacteria are usually small, so we will start with size. Being big is a problem for bacteria, as they need to take up their food through passive diffusion, and the bigger a body is, the smaller is its surface to volume ratio. In other words, a small bacterium has a larger surface, relatively speaking, which allows more efficient traffic of solutes. An example of an exceptionally big bacterium is Epulopiscium fishelsoni, a Firmicute isolated from the guts of tropical fish; it must be literally living in its food, as it can grow to 0.6-mm-long rods, and must diffuse its food despite its unfavorable dimensions. However, it is not yet breaking the records.

The biggest bacterium known to date is Thiomargarita namibiensis, a Gram-negative Proteobacterium that lives in mud on the sea floor off the Namibian coast. These bacterial giants measure 0.75 mm, making their individual cells easily visible to the naked eye. They grow in chains and look like little white beads of a pearl string against the dark mud, which gave them their name (margaron is Greek for pearl). These bacteria need sulfur, and can grow so big since they store their food inside their own cells, in specialized sacs called vacuoles. Similar bacteria were found off the coast of northern Chile, where immense mats of white hairlike growth were discovered to be made of giant sulfur-eating bacteria. They were one of the many discoveries of the Census of Marine Life project, which aims to catalogue all ocean life. The findings published so far have already revolutionized our view on biological diversity. It is now estimated that microbes may make up 90% of all marine biomass, and there may be 10 times as many species as previously suspected.

The smallest bacteria are easily 15,000 times smaller than these microbial giants. The miniatures are generally described as “nanobacteria” but that is not a taxonomic term; it only refers to their size. Nanobacteria measure at most a few ten-thousandth of a millimeter (0.2 µm, which is the same as 200 nm) and can be either eubacteria or archaea. The archaeal Thermodiscus maritimus, a Crenarcaheote which lives in the ocean, looks like a microscopic flying saucer; their disk-shaped cells have a diameter of only 0.2 µm, and a thickness of 0.1 µm. A number of nanoscale archaea that turned out to be related to each other were combined into a separate phylum, called Nanoarchaeota, which form a separate deep branch of the Archaea domain. The first discovered Nanoarchaeota grew like

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