An acid-tolerant ammonia-oxidizing γ-proteobacterium from soil

Area of Science:

• Environmental microbiology
• Soil science
• Biogeochemical cycles

Background:

• Nitrification is crucial for soil fertility, converting ammonia to nitrate.
• Most known ammonia-oxidizing bacteria (AOB) are sensitive to acidic soil conditions.
• The microbial communities in acidic soils remain incompletely understood.

Purpose of the Study:

• To isolate and characterize acid-adapted ammonia-oxidizing bacteria (AOB) from acidic agricultural soils.
• To investigate the phylogenetic and physiological traits of novel AOB strains.
• To assess the role of these AOB in acidic soil nitrification.

Main Methods:

• Isolation and cultivation of AOB from acidic soil samples.
• Phylogenetic analysis using 16S rRNA gene sequencing.
• Determination of growth pH range and survival under extreme acidity.
• Genome sequencing and comparative analysis with known AOB.
• Quantitative PCR to assess gene abundance in soil.

Main Results:

• Isolation of a novel acid-adapted AOB, strain TAO100, belonging to Gammaproteobacteria.
• TAO100 thrives between pH 5-7.5 and survives pH 2 by forming aggregates.
• TAO100 is the first non-halophilic, soil-originated gammaproteobacterial AOB (γ-AOB).
• TAO100 possesses a smaller genome than other γ-AOB, lacking salt tolerance genes.
• TAO100's ammonia monooxygenase gene is highly abundant in acidic soils.

Conclusions:

• Strain TAO100 represents a significant discovery as a novel, acid-adapted AOB from soil.
• TAO100 is proposed as a new species, Candidatus Nitrosoglobus terrae, in a new genus.
• This finding highlights the importance of previously overlooked microbial groups in acidic soil ecosystems.
• TAO100 likely plays a substantial role in the nitrogen cycle of acidic agricultural soils.