Haloalkaliphilic denitrifiers-dependent sulfate-reducing bacteria thrive in nitrate-enriched environments

Area of Science:

• Microbial Ecology
• Environmental Microbiology
• Biogeochemical Cycles

Background:

• Sulfate-reducing bacteria (SRB) are crucial in global carbon, nitrogen, and sulfur cycles.
• Saline-alkali environments, expanding due to human activity, present unique challenges for SRB.
• The impact of environmental nitrate on SRB in these extreme conditions is not well understood.

Purpose of the Study:

• To investigate how SRB respond to nitrate stress in saline-alkali environments.
• To elucidate the mechanisms underlying nitrate inhibition and relief of SRB activity.
• To explore the microbial interactions involved in nitrogen and sulfur cycling under stress.

Main Methods:

• Long-term enrichment of saline-alkali lake sediment using anaerobic filter reactors.
• Gradual addition of nitrate to evaluate SRB response and sulfate reduction inhibition.
• Mass balance analysis to determine the priority of nitrate versus sulfate reduction.
• Metatranscriptomic analysis to assess gene expression changes in SRB and denitrifying bacteria (DB).

Main Results:

• Nitrate addition progressively inhibited sulfate reduction.
• Increased hydraulic retention time mitigated nitrate inhibition.
• Nitrate reduction occurred prior to sulfate reduction.
• Key energy metabolism genes in SRB were down-regulated, contrary to previous hypotheses.
• Nitrate addition strongly activated denitrification genes in DB, leading to rapid nitrate removal and relief of SRB inhibition.

Conclusions:

• Haloalkaliphilic SRB exhibit a dependency on denitrifying bacteria (DB) to cope with nitrate stress.
• Nitrate inhibition of SRB is relieved through the cooperative action of DB.
• This study expands understanding of microbial interdependencies in nitrogen and sulfur cycling within extreme environments.