Bacterial Biogeography across the Amazon River-Ocean Continuum.

Area of Science:

• Microbiology
• Environmental Science
• Ecology

Background:

• The Amazon river-ocean continuum is a dynamic environment with limited research on microbial biodiversity.
• Understanding microbial community structure is crucial for ecosystem function in this large tropical system.

Purpose of the Study:

• To investigate spatial and temporal patterns of microbial biodiversity across the Amazon river-ocean continuum.
• To identify key environmental drivers structuring microbial communities in river, plume, and coastal ocean environments.

Main Methods:

• Amplicon sequencing of 16S rRNA genes in whole water and size-fractionated samples.
• Analysis of microbial communities along the lower Amazon River, Tapajós River tributary, and plume/coastal ocean.
• Co-occurrence network analysis to understand community assembly and interactions.

Main Results:

• Riverine microbial communities varied by tributary but were homogeneous in the mainstem, tracking seasonal river discharge.
• Two distinct seasonal microbial communities were identified in the river, linked to discharge levels.
• Plume communities showed spatial variation driven by salinity, but other factors like nutrients and phytoplankton composition were also critical.
• Co-occurrence networks revealed distinct assemblages in different zones, indicating immigration and species sorting in the plume.

Conclusions:

• River discharge and salinity are major drivers of microbial community structure across the Amazon river-ocean continuum.
• The Amazon system supports distinct seasonal riverine and transitional plume microbial communities.
• Comparing Amazon microbial patterns to temperate and arctic systems highlights the universal importance of discharge and salinity.