The Thermomicrobia is a group of
thermophilic
A thermophile is an organism—a type of extremophile—that thrives at relatively high temperatures, between . Many thermophiles are archaea, though they can be bacteria or fungi. Thermophilic eubacteria are suggested to have been among the earl ...
green non-sulfur
bacteria
Bacteria (; singular: bacterium) are ubiquitous, mostly free-living organisms often consisting of one biological cell. They constitute a large domain of prokaryotic microorganisms. Typically a few micrometres in length, bacteria were among ...
. Based on species ''Thermomicrobium roseum'' (type species) and ''Sphaerobacter thermophilus'', this bacteria class has the following description:
The class Thermomicrobia subdivides into two orders with validly published names: ''Thermomicrobiales''
Garrity and Holt 2001 and ''Sphaerobacterales''
Stackebrandt, Rainey and Ward-Rainey 1997. Gram negative. Pleomorphic, non-motile, non-spore-forming rods. Non-sporulating. No
diamino acid In chemistry, a diamino acid, also called a diamino carboxylic acid, is a molecule including a carboxylic acid and two amine functional groups. Diamino acids belong to the class of amino acids.
Biochemical function
Lysine is a proteinaceous diami ...
present. No peptidoglycan in significant amount. Atypical proteinaceous cell walls. Hyper-thermophilic, optimum growth temperature at 70-75 °C. Obligatory aerobic and chemoorganotrophic.
As thermophilic bacteria, members of this class are usually found in environments which are distant from human activity.
However, they have features like improved growth in antibiotics and CO oxidizing activity, making them interesting topics of research (e.g. for biotechnology application).
History
In 1973, a strain of rose-pink thermophilic bacteria was isolated from Toadstool Spring in Yellowstone National Park, which was later named ''Thermomicrobium roseum'' and proposed as a novel species of the novel genus ''Thermomicrobium''.
At that time the genus was categorized under family Achromobacteraceae, but it became a distinct phylum by 2001.
In 2004, it was proposed, on the basis of an analysis of genetic affiliations, that the Thermomicrobia should more properly be reclassified as a
class
Class or The Class may refer to:
Common uses not otherwise categorized
* Class (biology), a taxonomic rank
* Class (knowledge representation), a collection of individuals or objects
* Class (philosophy), an analytical concept used differentl ...
belonging to the phylum
Chloroflexota
The Chloroflexota are a phylum of bacteria containing isolates with a diversity of phenotypes, including members that are aerobic thermophiles, which use oxygen and grow well in high temperatures; anoxygenic phototrophs, which use light for photo ...
(formerly Chloroflexi). The bacteria ''Sphaerobacter thermophilus'' originally described as an Actinobacteria is now considered a Thermomicrobia.
In the same year, another strain of rose-pink thermophilic bacteria was isolated from Yellowstone National Park, which was named ''Thermobaculum terrenum''.
Later analysis based on genome put this species under Thermomicrobia class. However, the current standing of ''Thermobaculum terrenum'' is disputed.
In 2012, a thermo-tolerant nitrite-oxidizing bacterium was isolated from a bioreactor, which was named ''Nitrolancetus hollandica'' and proposed as a novel species later in 2014.
While it has nitrite-oxidizing activity, which is unique in the Thermomicrobia class, it is placed under the Thermomicrobia class based on 16s rRNA phylogeny.
In 2014, two thermophilic, Gram-positive, rod-shaped, non-spore-forming bacteria (strains KI3
T and KI4
T) isolated from geothermally heated biofilms growing on a tumulus in the Kilauea Iki pit crater on the flank of Kilauea Volcano (Hawai'i) were proposed as representatives of new species based on 16s rRNA phylogeny. The KI3
T strain, later named as ''Thermomicrobium carboxidum'', is closely related to ''Thermomicrobium roseum''. The KI4
T strain, later named as ''Thermorudis peleae'', was proposed as a type strain of new genus ''Thermorudis''.
In 2015, a thermophilic bacteria strain WKT50.2 isolated from geothermal soil in Waitike (New Zealand) was proposed to be a novel species, later named ''Thermorudis pharmacophila''. Phylogenic analysis based on 16s rRNA place it within Thermomicrobia class, as close relative to ''Thermorudis peleae''.
Characteristics
Living environment
Members of the class Thermomicrobia are broadly distributed across a wide range of both aquatic and terrestrial habitats. ''Thermomicrobium roseum'' was found in geothermally heated hot springs, ''Thermorudis pharmacophila'' and ''Thermobaculum terrenum'' from heated soils, and ''Thermomicrobium carboxidum'' and ''Thermorudis peleae'' from heated sediments
In addition, ''Sphaerobacter thermophilus'' was found in sewage sludge that went through thermophilic treatment.
The common features of their habitats include temperature ranging from around 65~75 °C and a pH around 6.0~8.0 (except for Nitrolancea hollandica which grow around 40 °C
).
Metabolism
Members of Thermomicrobia class have variation in their basic metabolism. ''Nitrolancetus hollandica'' has nitrifying activity that utilize NO
2− as energy source, which is unique in the whole
Chloroflexota
The Chloroflexota are a phylum of bacteria containing isolates with a diversity of phenotypes, including members that are aerobic thermophiles, which use oxygen and grow well in high temperatures; anoxygenic phototrophs, which use light for photo ...
phylum.
''Thermomicrobium spp.'' and ''Sphaerobacter thermophilus'' have constitutive CO oxidizing not found in other species in this class.
However, species of this class do share some features, as listed below:
* All members except ''Thermobaculum terrenum'' have inability to utilize some common
monosaccharide
Monosaccharides (from Greek ''monos'': single, '' sacchar'': sugar), also called simple sugars, are the simplest forms of sugar and the most basic units (monomers) from which all carbohydrates are built.
They are usually colorless, water-solub ...
s (e.g.
glucose
Glucose is a simple sugar with the molecular formula . Glucose is overall the most abundant monosaccharide, a subcategory of carbohydrates. Glucose is mainly made by plants and most algae during photosynthesis from water and carbon dioxide, using ...
,
fructose
Fructose, or fruit sugar, is a Ketose, ketonic monosaccharide, simple sugar found in many plants, where it is often bonded to glucose to form the disaccharide sucrose. It is one of the three dietary monosaccharides, along with glucose and galacto ...
, etc.) as sole carbon source''.''
The mechanisms behind this inability are currently unknown.
Antibiotic resistance
Members of Thermomicrobia class exhibit certain level of resistance against
metronidazole
Metronidazole, sold under the brand name Flagyl among others, is an antibiotic and antiprotozoal medication. It is used either alone or with other antibiotics to treat pelvic inflammatory disease, endocarditis, and bacterial vaginosis. It is ef ...
and/or
trimethoprim
Trimethoprim (TMP) is an antibiotic used mainly in the treatment of bladder infections. Other uses include for middle ear infections and travelers' diarrhea. With sulfamethoxazole or dapsone it may be used for ''Pneumocystis'' pneumonia in peop ...
, which are clinically relevant for humans. ''Thermomicrobium carboxidum'' and ''Thermorudis peleae'' show resistance against both of those antibiotics, while ''Sphaerobacter thermophilus'' shows resistance against only
metronidazole
Metronidazole, sold under the brand name Flagyl among others, is an antibiotic and antiprotozoal medication. It is used either alone or with other antibiotics to treat pelvic inflammatory disease, endocarditis, and bacterial vaginosis. It is ef ...
.
Interestingly, ''Thermomicrobium roseum'' and ''Thermorudis pharmacophila'' have an increased growth in both
metronidazole
Metronidazole, sold under the brand name Flagyl among others, is an antibiotic and antiprotozoal medication. It is used either alone or with other antibiotics to treat pelvic inflammatory disease, endocarditis, and bacterial vaginosis. It is ef ...
and
trimethoprim
Trimethoprim (TMP) is an antibiotic used mainly in the treatment of bladder infections. Other uses include for middle ear infections and travelers' diarrhea. With sulfamethoxazole or dapsone it may be used for ''Pneumocystis'' pneumonia in peop ...
, a rare trait even within antibiotic resistant bacteria.
The mechanisms behind are currently undocumented, and further study is required on this topic.
Cell envelope structure
Members of Thermomicrobia class have various
Gram-staining
In microbiology and bacteriology, Gram stain (Gram staining or Gram's method), is a method of staining used to classify bacterial species into two large groups: gram-positive bacteria and gram-negative bacteria. The name comes from the Danish bac ...
results. ''Thermomicrobium roseum'', ''Sphaerobacter thermophilus'' and ''Thermorudis pharmacophila'' are reported to be Gram-negative and have a typical layered
diderm cell envelope
The cell envelope comprises the inner cell membrane and the cell wall of a bacterium. In gram-negative bacteria an outer membrane is also included. This envelope is not present in the Mollicutes where the cell wall is absent.
Bacterial cell env ...
structure.
However, their cell envelope composition are atypical compared to typical Gram-negative bacteria. Cell envelope of ''Thermomicrobium roseum'' lacks significant amount of peptidoglycan, which is fundamental for typical Gram-negative bacteria, while being rich in protein.
Membrane lipids of ''Thermomicrobium roseum'' are mostly long chain
diol
A diol is a chemical compound containing two hydroxyl groups ( groups). An aliphatic diol is also called a glycol. This pairing of functional groups is pervasive, and many subcategories have been identified.
The most common industrial diol is e ...
s instead of glycerol-based lipids commonly found in bacteria. The same feature was found in ''Sphaerobacter thermophilus'' and ''Thermorudis pharmacophila.''
It was suggested that the high-protein and diol-based lipid composition are responsible for heat resistance of these bacteria.
Meanwhile, other members of Thermomicrobia class are reported to be Gram-positive and have typical monoderm cell envelope.
There are some possible explanations of the inconsistency of Gram-staining result within the class. For ''Thermorudis pharmacophila'', a possible explanation suggested by Houghton et al. is that it is actually an atypical
monoderm
In bacteriology, gram-positive bacteria are bacteria that give a positive result in the Gram stain test, which is traditionally used to quickly classify bacteria into two broad categories according to their type of cell wall.
Gram-positive bacte ...
bacterium, because its cell envelope contains amino acids usually associated with Gram-positive bacteria, have reaction to KOH,
vancomycin
Vancomycin is a glycopeptide antibiotic medication used to treat a number of bacterial infections. It is recommended intravenously as a treatment for complicated skin infections, bloodstream infections, endocarditis, bone and joint infections, ...
and
ampicillin
Ampicillin is an antibiotic used to prevent and treat a number of bacterial infections, such as respiratory tract infections, urinary tract infections, meningitis, salmonellosis, and endocarditis. It may also be used to prevent group B strepto ...
, and lacks genes responsible for diderm formation.
It is also suggested that further study is required to resolve this problem, since the inconsistent reports of cell envelope structure are found for the whole Chloroflexota phylum.
Phylogeny
Taxonomy
The currently accepted taxonomy is based on the
List of Prokaryotic names with Standing in Nomenclature
List of Prokaryotic names with Standing in Nomenclature (LPSN) is an online database that maintains information on the naming and taxonomy of prokaryotes, following the taxonomy requirements and rulings of the International Code of Nomenclature ...
(LPSN) and
National Center for Biotechnology Information
The National Center for Biotechnology Information (NCBI) is part of the United States National Library of Medicine (NLM), a branch of the National Institutes of Health (NIH). It is approved and funded by the government of the United States. The ...
(NCBI).
* Order
Thermomicrobiales Garrity & Holt 2002
** Family
Thermomicrobiaceae Garrity & Holt 2002
*** Genus ''
Thermomicrobium''
Jackson, Ramaley & Meinschein 1973
**** ''
T. carboxidum''
King & King 2014
**** ''
T. roseum''
Jackson, Ramaley & Meinschein 1973
*** Genus ''
Thermorudis''
King & King 2014
**** ''
T. peleae''
King & King 2014
**** ''
T. pharmacophila''
Houghton et al. 2015
* Order
Sphaerobacterales
''Sphaerobacter'' is a genus of bacteria. When originally described it was placed in its own subclass (Spahaerobacteridae) within the class Actinomycetota
The ''Actinomycetota'' (or ''Actinobacteria'') are a phylum of all gram-positive bac ...
Stackebrandt, Rainey & Ward-Rainey 1997
** Family
Sphaerobacteraceae
''Sphaerobacter'' is a genus of bacteria. When originally described it was placed in its own subclass (Spahaerobacteridae) within the class Actinomycetota. Subsequently, phylogenetic studies have now placed it in its own order Sphaerobacterales ...
Stackebrandt, Rainey & Ward-Rainey 1997
*** Genus ''
Sphaerobacter
''Sphaerobacter'' is a genus of bacteria. When originally described it was placed in its own subclass (Spahaerobacteridae) within the class Actinomycetota. Subsequently, phylogenetic studies have now placed it in its own order Sphaerobacterales ...
''
Demharter et al. 1989
**** ''
S. thermophilus''
Demharter et al. 1989
*** Genus ''
Nitrolancea''
Sorokin et al. 2014
**** ''
N. hollandica''
Sorokin et al. 2014
**** "''Ca.''
N. copahuensis"
Spieck et al. 2020
See also
*
List of bacteria genera This article lists the genera of the bacteria. The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI). However many taxonomic names are ...
*
List of bacterial orders
This article lists the orders of the Bacteria. The currently accepted taxonomy is based on the List of Prokaryotic names with Standing in Nomenclature (LPSN) and National Center for Biotechnology Information (NCBI)
and the phylogeny is based on 16S ...
Notes
References
{{Taxonbar, from=Q1349847
Chloroflexota