Particle-associated N₂ fixation by heterotrophic bacteria in the global ocean

Area of Science:

• Marine microbiology
• Biogeochemical cycles
• Oceanography

Background:

• Diazotrophs are crucial for global nitrogen availability.
• Marine nitrogen fixation was traditionally attributed to cyanobacteria in warm waters.
• Recent discoveries show widespread N2-fixing heterotrophic bacteria in the pelagic ocean.

Purpose of the Study:

• To elucidate the mechanisms enabling heterotrophic diazotrophs in cold, high-latitude waters.
• To determine the contribution of heterotrophic diazotrophs to the global marine nitrogen budget.
• To explain the ubiquitous distribution of N2-fixing heterotrophic bacteria.

Main Methods:

• Development and application of a data-driven, cell-based metabolic model.
• Analysis of nitrogen fixation capabilities across a range of environmental conditions.
• Estimation of global marine nitrogen fixation contributions.

Main Results:

• Heterotrophic bacteria within sinking particles can perform nitrogen fixation across diverse temperatures.
• This capability explains their widespread presence in various oceanic regions.
• Heterotrophic diazotrophs contribute approximately 10% to global marine nitrogen fixation.

Conclusions:

• Heterotrophic bacteria play a more significant role in marine nitrogen fixation than previously understood.
• Sinking particles provide a suitable niche for nitrogen fixation by heterotrophic bacteria.
• Current models of marine nitrogen cycling require revision to incorporate these findings.