Microbial niche differentiation explains nitrite oxidation in marine oxygen minimum zones

Area of Science:

• Marine microbiology
• Biogeochemical cycling
• Oceanography

Background:

• Nitrite is crucial in the marine nitrogen cycle, influencing fixed nitrogen retention or loss.
• Nitrite oxidation to nitrate retains nitrogen, while reduction to gases leads to loss.
• Current models simplify nitrite oxidation using a single oxygen threshold.

Purpose of the Study:

• Investigate nitrite oxidation responses to varying nitrite and oxygen concentrations along a redox gradient.
• Identify niche differentiation in nitrite-oxidizing microbial communities.
• Assess the impact of these findings on marine nitrogen budget estimations.

Main Methods:

• Sampling from a Pacific Ocean oxygen minimum zone.
• Analyzing nitrite oxidation rates under different oxygen and nitrite conditions.
• Detecting nitrite-oxidizing bacteria using molecular methods.

Main Results:

• Nitrite oxidation responses varied significantly along the redox gradient.
• Oxygen addition fully inhibited nitrite oxidation in anoxic samples.
• Nitrite oxidation coupled with nitrogen loss occurred without oxygen consumption in anoxic waters.
• Novel nitrite-oxidizing bacteria clades were abundant in anoxic depths.

Conclusions:

• Niche differentiation of nitrite-oxidizing bacteria exists across redox gradients.
• Current models may inaccurately represent nitrogen cycling due to simplified nitrite oxidation parameters.
• Incorporating detailed mechanisms improves fixed nitrogen budget accuracy.