Novel prosthecate bacteria from the candidate phylum Acetothermia

Area of Science:

• Microbiology
• Environmental Science
• Genomics

Background:

• Members of the candidate phylum Acetothermia are widespread but poorly understood regarding their physiology and ecological roles.
• This phylum is frequently detected in diverse environmental settings, including engineered ecosystems.

Purpose of the Study:

• To investigate the physiology and ecological significance of Acetothermia found in anaerobic digesters.
• To obtain the first closed genome for the phylum Acetothermia and elucidate its metabolic capabilities.
• To characterize the unique morphology of Acetothermia cells.

Main Methods:

• 16S rRNA gene amplicon sequencing to identify abundant operational taxonomic units.
• Differential coverage binning of metagenomes and long nanopore read scaffolding for genome assembly.
• Genome annotation and metabolic reconstruction.
• Fluorescence in situ hybridization, confocal laser scanning microscopy, Raman microspectroscopy, and atomic force microscopy for morphological analysis.

Main Results:

• An operational taxonomic unit belonging to Acetothermia was highly abundant in four full-scale anaerobic digesters.
• The first closed genome for Acetothermia was successfully reconstructed.
• Metabolic reconstruction indicated an anaerobic chemoheterotrophic lifestyle, fermenting peptides, amino acids, and sugars into acetate, formate, and hydrogen.
• Unusual cell morphology featuring a central rod with bipolar prosthecae was observed.

Conclusions:

• The study provides the first comprehensive genomic and physiological insights into the candidate phylum Acetothermia.
• The unique prosthecae are hypothesized to enhance nutrient uptake, conferring a competitive advantage in nutrient-limited environments.
• Acetothermia likely plays a significant role in the biogeochemical cycling within anaerobic digesters.