Quantitative microbial taxonomy across particle size, depth, and oxygen concentration.

Area of Science:

• Marine microbiology
• Oceanography
• Biogeochemistry

Background:

• Marine particles are crucial for carbon sequestration and microbial habitats.
• The East Pacific Rise (EPR) offers unique environments, including an Oxygen Deficient Zone (ODZ) and hydrothermal vent plumes, for studying microbial ecology.
• Understanding microbial community structure in relation to particle size and depth is vital for marine carbon cycling.

Purpose of the Study:

• To quantify microbial diversity and abundance across various marine particle size fractions.
• To investigate the relationship between microbial community composition, particle size, and ocean depth.
• To explore microbial distribution in the ODZ and hydrothermal vent plume regions of the EPR.

Main Methods:

• Particles were separated into seven size fractions (0.2-1.2 to >500 μm).
• Bacterial 16S rRNA gene sequencing was performed on size-fractionated samples.
• Bacterial abundance was quantified per microgram of carbon and per liter of seawater.

Main Results:

• Bacterial abundance per microgram of carbon and per liter significantly increased on particles >180 μm in the deep water column.
• Microbial communities showed significant variation based on particle size and depth.
• Free-living microbes were also found on particles, and particle-attached microbes were present in free-living fractions, indicating community exchange.
• Bacterial abundance increased in the ODZ, while hydrothermal vent plume regions showed distinct microbial distributions across particle sizes.

Conclusions:

• Microbial community composition is strongly influenced by particle size and depth.
• Findings support models of high exchange rates between particle-attached and free-living microbial communities.
• The study provides quantitative insights into microbial distribution across diverse marine particle environments.