Genome-based reclassification of the genus Thermoanaerobacter: taxonomic emendations and new combinations

Noureddine Bouras; Guendouz Dif; Saïd Belghit; Scott V Nguyen; Jonathan L Jacobs; Omrane Toumatia; Sherif S Ebada; Imen Nouioui

doi:10.1016/j.anaerobe.2026.103027

Genome-based reclassification of the genus Thermoanaerobacter: taxonomic emendations and new combinations

Anaerobe. 2026 Mar:97:103027. doi: 10.1016/j.anaerobe.2026.103027. Epub 2026 Jan 23.

Authors

Noureddine Bouras¹, Guendouz Dif², Saïd Belghit³, Scott V Nguyen⁴, Jonathan L Jacobs⁴, Omrane Toumatia⁵, Sherif S Ebada⁶, Imen Nouioui⁷

Affiliations

¹ Laboratoire de Valorisation et Conservation des Ecosystèmes Arides (LVCEA), Faculté des Sciences de la Nature et de la Vie et Sciences de la Terre, Université de Ghardaia, B.P. 455, Ghardaïa, Algeria; Laboratoire de Biologie des Systèmes Microbiens (LBSM), Ecole Normale Supérieure Cheikh Mohamed El Bachir El Ibrahimi, BP 92, Kouba, Algiers, Algeria. Electronic address: bouras.noureddine@univ-ghardaia.edu.dz.
² Laboratoire de Biologie des Systèmes Microbiens (LBSM), Ecole Normale Supérieure Cheikh Mohamed El Bachir El Ibrahimi, BP 92, Kouba, Algiers, Algeria; École Normale Supérieure Taleb Abderrahmane de Laghouat, Département des Sciences Naturelles, BP 4033, Laghouat, 03000, Algeria.
³ Laboratoire de Valorisation et Conservation des Ecosystèmes Arides (LVCEA), Faculté des Sciences de la Nature et de la Vie et Sciences de la Terre, Université de Ghardaia, B.P. 455, Ghardaïa, Algeria.
⁴ American Type Culture Collection (ATCC), Manassas, VA, USA.
⁵ Laboratoire de Biologie des Systèmes Microbiens (LBSM), Ecole Normale Supérieure Cheikh Mohamed El Bachir El Ibrahimi, BP 92, Kouba, Algiers, Algeria.
⁶ Department of Pharmacognosy, Faculty of Pharmacy, Ain Shams University, Cairo, Egypt.
⁷ Leibniz-Institut DSMZ - German Collection of Microorganisms and Cell Cultures, Inhoffenstraße 7B, 38124, Braunschweig, Germany.

PMID: 41581727
DOI: 10.1016/j.anaerobe.2026.103027

Abstract

Objective: The genus Thermoanaerobacter is comprised of strictly anaerobic, thermophilic, rod-shaped bacteria predominantly isolated from geothermal environments. Due to phylogenetic and taxonomic overlaps among certain species, this study aims to clarify the taxonomic status of key Thermoanaerobacter members through genome-based analyses.

Methods: We conducted a comprehensive taxonomic re-evaluation using multiple genomic metrics, including digital DNA-DNA hybridization (dDDH), average nucleotide identity (ANI via FastANI), average amino acid identity (AAI), and percentage of conserved proteins (POCP). These analyses were supported by 16S rRNA gene sequencing and genome-based phylogenomic reconstruction.

Results: Genome-based metrics and phylogenomic analyses revealed several taxonomic inconsistencies within the genus. As a result, Thermoanaerobacter thermohydrosulfuricus is redefined to include Thermoanaerobacter ethanolicus subsp. thermohydrosulfuricus, Thermoanaerobacter ethanolicus subsp. siderophilus, Thermoanaerobacter ethanolicus subsp. ethanolicus and Thermoanaerobacter ethanolicus subsp. indiensis under Thermoanaerobacter thermohydrosulfuricus subsp. thermohydrosulfuricus subsp. nov., while Thermoanaerobacter wiegelii is assigned to Thermoanaerobacter thermohydrosulfuricus subsp. wiegelii subsp. nov., comb. nov. Thermoanaerobacter pseudethanolicus, Thermoanaerobacter brockii subsp. finnii, and Thermoanaerobacter brockii subsp. lactiethylicus DSM 9801^T were reclassified as Thermoanaerobacter brockii. Additionally, Thermoanaerobacter mathranii, Thermoanaerobacter italicus, and Thermoanaerobacter pentosaceus are reclassified as Thermoanaerobacter thermocopriae.

Conclusions: This study supports a taxonomic rearrangement within Thermoanaerobacter, refining species boundaries based on robust genomic evidence. The proposed changes enhance the taxonomic resolution and phylogenetic consistency of thermophilic anaerobic bacteria within this genus.

Keywords: Average nucleotide identity (ANI); Digital DNA-DNA hybridization (dDDH); Genomic analysis; Reclassification; Thermoanaerobacter.

MeSH terms

DNA, Bacterial / genetics
Genome, Bacterial*
Genomics
Nucleic Acid Hybridization
Phylogeny
RNA, Ribosomal, 16S / genetics
Sequence Analysis, DNA
Thermoanaerobacter* / classification
Thermoanaerobacter* / genetics

Substances

RNA, Ribosomal, 16S
DNA, Bacterial