Thermodesulfobacteriota

The Thermodesulfobacteriota, or Desulfobacterota,^[4] are a phylum of anaerobic Gram-negative bacteria. Many representatives are sulfate-reducing bacteria,^[5] others can grow by disproportionation of various sulphur species,^[6] reduction or iron,^[7] or even use external surfaces as electron acceptors (exoelectrogens).^[8] They have highly variable morphology: vibrio, rods, cocci,^[4] as well as filamentous cable bacteria.^[9] Individual members of Desulfobacterota are also studied for their bacterial nanowires^[10] or syntrophic relationships.^[11]

Phylogenetic tree of prokaryotes based on ribosomal proteins and RNA polymerase^[12] Desulfobacterota are closely related to Pseudomonadota/Proteobacteria, Myxococcota, and Bdellovibrionota.

Thermodesulfobacteriota
Nitratidesulfovibrio vulgaris
Scientific classification
Domain:	Bacteria
Kingdom:	Pseudomonadati
Phylum:	Thermodesulfobacteriota Garrity & Holt 2021[1]
Classes[2]
"Ca. Anaeroferrophillalia" Murphy et al. 2021 "Ca. Anaeropigmentia" Murphy et al. 2021 "Ca. Dadabacteria"[3] Deferrisomatia Waite et al. 2020 Desulfarculia Waite et al. 2020 Desulfobaccia Waite et al. 2020 Desulfobacteria Waite et al. 2020 Desulfobulbia Waite et al. 2020 "Ca. Desulfofervidia" Waite et al. 2020 Desulfomonilia Waite et al. 2020 Desulfovibrionia Waite et al. 2020 Desulfuromonadia Waite et al. 2020 Dissulfuribacteria Waite et al. 2020 Syntrophia Waite et al. 2020 Syntrophobacteria Waite et al. 2020 Syntrophorhabdia Waite et al. 2020 Thermodesulfobacteria Hatchikian et al. 2002 "Ca. Zymogenia" Murphy et al. 2021
Synonyms[2]
Desulfobacterota Waite et al. 2020 "Ca. Dadabacteria" Hug et al. 2016 "Thermodesulfobacteraeota" Oren et al. 2015 Thermodesulfobacteria Garrity and Holt 2002

Taxonomy

The bacterial phylum Desulfobacterota has been created by merging: 1) the well-established class Thermodesulfobacteria, 2) the proposed phylum Dadabacteria, and 3) various taxa separated from the abandoned non-monophyletic class "Deltaproteobacteria" alongside three other phyla: Myxococcota, Bdellovibrionota, and SAR324.^[4]

Environment

In contrast to their close relatives, the aerobic phyla Myxococcota and Bdellovibrionota, Desulfobacterota are predominantly anaerobic.^[4] They likely retained their anaerobic lifestyle since before the Great Oxidation Event.^[13]

Three closely related classes within Desulfobacterota: Thermodesulfobacteria, Dissulfuribacteria, and Desulfofervidia,^[11] as well as the more distant Deferrisomatia, are exclusively thermophilic, while most members of other classes are mesophiles^[4] or even psychrophiles.^[14][15]

Metabolism

Sulfate-reducing bacteria (SRB) utilize sulfate as a terminal electron acceptor in a respiratory-type metabolism, coupled to the oxidation of organic compounds or hydrogen. By reducing sulfate, many Desulfobacterota species substantially contribute to the sulfur cycle.^[4]

Dissimilatory sulfate reduction

Microbial sulfur disproportionation (MSD) is a poorly known type of energy metabolism analogous to organic fermentation, where a single inorganic sulfur species of intermediate oxidation state is simultaneously oxidized and reduced, resulting in production of sulfide and sulfate. In Desulfobacterota, MSD is often present in species that also perform sulfate reduction.^[6]

Sulfur oxidation is rare among Desulfobacterota.^[16] However, several strains are known to perform this type of metabolism using diverse mechanisms. Strain MLMS-1 couples oxidation of sulfide to reduction of arsenate.^[17] Dissulfuribacter thermophilus (Dissulfuribacteria) oxidizes elemental sulfur with dissimilatory nitrate reduction to ammonium.^[18] Desulfurivibrio alkaliphilus (Desulfobulbia) couples oxidation of sulfide to the dissimilatory reduction of nitrate and nitrite to ammonium.^[16] Cable bacteria, closely related to D. alkaliphilus, oxidize sulfide using a long-distance electron transport to oxygen or nitrate reduction — see below.^[19]

Fe(III) minerals can be microbially reduced by Fe-reducing bacteria (FeRB) using a wide range of organic compounds or H₂ as electron donors. FeRB are widespread across Bacteria. Among Desulfobacterota, they are represented e.g. by the genus Geobacter (Desulfuromonadia).^[20]

Certain species of the families Geobacteraceae and Desulfuromonadaceae (Desulfuromonadia) are able to use external surfaces as electron acceptors to complete respiration.^[8][21][22] Species of the genus Geobacter use bacterial nanowires to transfer electrons to extracellular electron acceptors such as Fe(III) oxides.^[10]

Alternative Electron Transport Chain to move electrons to outer membrane of Geobacter Sulfurreducens

Certain species of the class Syntrophia use simple organic molecules as electron donors and grow only in the presence of H₂/formate-utilizing partners (methanogens or Desulfovibrio) in syntrophic associations.^[23]

The family Desulfobulbaceae contains two genera of cable bacteria: Ca. Electronema and Ca. Electrothrix. These filamentous bacteria conduct electricity across distances over 1 cm, which allows them to connect distant sources of electron donors and electron acceptors.^[9]

• 
  Cable bacteria in between two layers of sediment
• 
  Diagram demonstrating cable bacteria metabolism in surface sediment
• 
  Model representation of a cable bacteria cell

Notable species

• Desulfobulbus propionicus (Desulfobulbia), described in 1982 from mud samples in Germany, can serve as a biocatalyst in microbial electrosynthesis, i.e. the usage of electrons by microorganism to reduce carbon dioxide to organic molecules.^[24]
• Lawsonia intracellularis (Desulfovibrionia), described in 1995 from the intestines of pigs with proliferative enteropathy disease, is a highly pathogenic intracellular parasite.^[25][26]
• Oleidesulfovibrio alaskensis (Desulfovibrionia), described in 2004 from an oil well in Alaska, corrodes metals and reduces toxic radionuclides and metals such as uranium and chromium to less soluble and less toxic forms.^[27][28]
• Syntrophorhabdus aromaticivorans (Syntrophorhabdia), described in 2008 from industrial wastewater, is the first cultured anaerobe capable of degrading phenol to acetate in obligate syntrophic associations with a hydrogenotrophic methanogen.^[29]

• Dissulfuribacter thermophilus (Dissulfuribacteria), described in 2013 from a deep-sea hydrothermal vent, does not reduce sulfate and instead disproportionates elemental sulfur and other intermediate sulfur species.^[30]
• Ca. Desulfofervidus auxilii (Ca. Desulfofervidia), described in 2016 from Guaymas Basin sediments, is involved in the anaerobic oxidation of methane (AOM) together with archaeal syntrophic partners.^[11]

Microscopy

• 
  Thermodesulfobacterium hveragerdense
• 
  Nitratidesulfovibrio vulgaris
• 
  Caldimicrobium rimae
• 
  Thermodesulfobacterium hydrogeniphilum
• 
  Dissulfuribacter thermophilus
• 
  Thermodesulfatator indicus
• 
  Thermosulfurimonas dismutans
• 
  Thermodesulfobacterium commune
• 
  Thermodesulfatator atlanticus
• 
  Thermosulfuriphilus ammonigenes
• 
  Oleidesulfovibrio alaskensis
• 
  Ca. Electronema sp.
• 
  Taurinivorans muris
• 
  Taurinivorans muris
• 
  Geobacter sulfurreducens and its bacterial nanowires^[31]
• 
  Geobacter sulfurreducens

Phylogeny

See also: Bacterial taxonomy

The phylogeny is based on phylogenomic analysis:

120 marker proteins based GTDB 09-RS220[32][33][34]

Waite et al. 2020[2] Thermodesulfo Deferrisomatia Deferrisomatales "Dadaibacteria" Desulfuromonadia Geobacterales Desulfuromonadales Desulfomonilia Desulfomonilales Syntrophia Syntrophales Syntrophorhabdia Syntrophorhabdales Dissulfuribacteria Dissulfuribacterales "Thermodesulfobacteriia" Thermodesulfobacteriales Desulfobulbia Desulfobulbales "Desulfofervidia" "Desulfofervidales" Desulfovibrionia Desulfovibrionales Syntrophobacteria Syntrophobacterales Desulfobaccia Desulfobaccales Desulfarculia "Adiutricales" Desulfarculales Desulfobacteria Desulfatiglandales Desulfobacterales ‑bacteriota 16S rRNA based LTP_10_2024[35][36][37] Desulfobacterota G Syntrophorhabdia Syntrophorhabdales "Desulfuromonadota" Desulfuromonadia Geobacterales Desulfuromonadales Desulfobacterota_A Desulfovibrionia Desulfovibrionales "Desulfatiglandia" Desulfatiglandales Desulfomonilia Desulfomonilales Syntrophia Syntrophales Desulfobacterota Desulfobacteria Desulfobacterales Thermodesulfobacteriota "Thermodesulfobacteriia" Thermodesulfobacteriales Desulfobaccia Desulfobaccales Dissulfuribacteria Dissulfuribacterales Desulfarculia Desulfarculales Syntrophobacteria Syntrophobacterales Desulfobulbia Desulfobulbales "Deferrisomatota" Deferrisomatia Deferrisomatales

"Binatota" "Binatia" "Binatales" (Desulfobacterota B) "Deferrisomatota" Deferrisomatia Deferrisomatales (Desulfobacterota C) "Deferrimicrobiota" "Deferrimicrobiia" "Deferrimicrobiales" (Desulfobacterota E) Thermodesulfo "Zymogenia" "Zymogenales" "Anaeroferrophilia" "Anaeroferrophilales" Desulfuromonadia Geobacterales Desulfuromonadales Desulfomonilia Desulfomonilales Syntrophia Syntrophales Dissulfuribacteria Dissulfuribacterales "Thermodesulfobacteriia" Thermodesulfobacteriales Desulfobulbia Desulfobulbales Desulfovibrionia Desulfovibrionales "Desulfofervidia" "Desulfofervidales" "Desulfatiglandia" Desulfatiglandales Desulfobaccia Desulfobaccales Desulfarculia "Adiutricales" Desulfarculales Syntrophobacteria Syntrophobacterales Desulfobacteria Desulfobacterales ‑bacteriota Desulfobacterota G Syntrophorhabdia Syntrophorhabdales "Dadaibacteriota" "Dadabacteria" "Nemesobacterales" (Desulfobacterota D) "Acidulodesulfobacteriota" "Acidulodesulfobacteriia" "Acidulidesulfobacterales" (SZUA-79)

See also

• Sulfur cycle
• Exoelectrogen
• Cable bacteria
• Syntrophy
• Thermophile
• Bacterial nanowires
• Sulfate reducing bacteria