Thermocrinis ruber is a species of Gram-negative bacteria first discovered in Octopus Spring in Yellowstone National Park. It is a pink-filament-forming, hyperthermophilic bacterium growing in temperatures between 44 °C and 89 °C, with the optimal temperature being 80 °C. Its type strain is OC 1/4 [= DSM 12173] and OC14/7/2 [DSM No. 23557, AJ005640].
Etymology Thermocrinis ruber was named by Huber et al. The genus name, Thermocrinis, comes from the Greek word "therme" which means heat, and the Latin word "crinis", which means hair. The species name, ruber, comes from the Latin word for red. The species' full name illustrates how it forms red, filamentous strands that looks like hair in high temperature environments.
Morphology Thermocrinis ruber are Gram-negative, rod-shaped bacteria. T. ruber cells contain multiple flagella on one end of the cell. Cells are usually 1 to 3 μm long and 0.4 to 0.5 μm wide. T. ruber does not form spores, but can grow individually, as pairs, or in groups as pink filaments.
Taxonomy Thermocrinis ruber is a member of the Aquificales order and Aquificaceae family. The Aquificaceae family also include the Aquifex and Hydrogenobacter genera, which are the closest related genera to T. ruber. While T. ruber shares many characteristics with these two genera: being Gram-negative, rod-shaped, and autotrophs, there are still many differences that set it apart, which are described below. The Thermocrinis genus was created for this organism within the Aquificales order by Huber et al. Organisms of the Thermocrinis genus are defined as Gram-negative rods that are non-sporulating (i.e., do not form spores), and can form filaments in different mediums. Thermocrinis organisms can grow in temperatures up to 89 °C and mainly populate hot springs. There are four organisms in the Thermocrinis genus: T. ruber, T. albus, T. minervae, and T. jamiesonii, all of which are chemolithoautotrophs and hyperthermophiles found in hot springs
Nearest neighbors 16s ribosomal RNA sequencing was used to create a phylogenetic tree that showed T. ruber's close relations to organisms of the Aquifex and Hydrogenobacter genera, as well as to other organisms within the Thermocrinis genera. Evolutionary distance, a measure of how different two genomic sequences are, as well as Average Nucleotide Identity, a measure of how many nucleotides two organisms share, was used to determine close neighbors.
Thermocrinis albus Thermocrinis albus is an obligate autotroph (i.e., only uses carbon dioxide as a carbon source) found in an Icelandic hot spring and it has a distance of 5.1% phylogenetic distance to T. ruber. This implies that although it is within the same genus as T. ruber, it may be long to a different lineage.
Thermocrinis minervae Thermocrinis minervae was isolated from a Costa Rican hot spring and it has a 95.7 % 16s RNA sequence similarity to T. ruber.
Thermocrinis jamisonii Thermocrinis jamiesonii was isolated from Great Boiling Spring in Nevada and it has a 97.10 % 16s RNA sequence similarity to T. ruber.
Hydrogenobacter hydrogenophilus Hydrogenobacter hydrogenophilus is a Gram-negative thermophile isolated from a thermal spring in Kamchatka. It has an 84.62% Average Nucleotide Identity similarity to T. ruber.
Aquifex pyrophilus Aquifex pyrophilus is a Gram-negative, hyperthermophilic rod isolated from marine sediments in Kolbeinsey Ridge, Iceland. A. pyrophilus are chemolithoautotrophs and the Aquifex genus was created for this organism. The evolutionary distance between T. ruber and Aquifex pyrophilus is 12.8%
Hydrogenbacter thermophilus Hydrogenobacter thermophilus is an obligate chemolithotrophic, Gram-negative thermophile isolated from hot springs within Japan. The evolutionary distance between T. ruber and Hydrogenbacter thermophilus TK-6 is 6.5%.
Discovery Thermocrinis ruber was discovered in Octopus Spring in Yellowstone National Park, Wyoming. Microbiologist Thomas Brock found that the pink filaments in the hot springs were living organisms in the 1960s when he found they contained proteins and nucleic acids. Thomas Brock initially investigated the microorganisms in Yellowstone Park after a report by ES Kempner found that blue-green algae from the park could grow in temperatures up to 73 °C. Brock took multiple samples at varying times from Mushroom Spring and found that the microorganisms could photosynthesize most efficiently at the temperature they were collected from. Any variance in temperature decreases their efficiency, implying that they have developed mutations that allow them to adapt to the temperatures they grow in. With this discovery, he discovered hyperthermophiles, microorganisms that thrive at higher temperatures. Later, he discovered the pink filaments near White Creek that were in temperatures of 88 °C. He used spectrophotometry to analyze the filaments by wavelength and discovered they were chemotrophic (i.e., used chemicals for energy), as they contained no chlorophyll and could not photosynthesize. While he discovered the existence of T. ruber in these pink filaments, he did not continue research and analysis on them.
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