Unexpected microbial rhodopsin dynamics in sync with phytoplankton blooms

Area of Science:

• Marine microbiology
• Ocean biogeochemistry
• Phototrophic metabolism

Background:

• Surface ocean harbors diverse microbial communities crucial for global productivity.
• Rhodopsin phototrophs are a dominant metabolic group, suggesting significant ecological roles.
• Previous research linked rhodopsin to nutrient-poor environments, but its role in productive waters remained unclear.

Purpose of the Study:

• To investigate the dynamics and significance of rhodopsin phototrophy in a productive marine upwelling system.
• To determine the relationship between rhodopsin concentrations and environmental factors in nutrient-rich waters.

Main Methods:

• Monthly measurements of retinal (a rhodopsin chromophore) in the Southern California Bight.
• Correlation analysis with chlorophyll concentrations and heterotrophic bacterial abundances.
• Metagenomic sequencing to identify dominant rhodopsin-harboring taxa.

Main Results:

• Rhodopsin levels peaked during the spring phytoplankton bloom, correlating with high chlorophyll.
• Abundances of heterotrophic bacteria, especially Flavobacteriales, strongly correlated with rhodopsin concentrations.
• Flavobacteriales dominated the rhodopsin gene pool during peak rhodopsin levels.

Conclusions:

• Rhodopsin phototrophy plays a substantial role in productive marine ecosystems.
• This finding expands the known importance of rhodopsin beyond oligotrophic environments.
• Flavobacteriales are key contributors to light-driven energy capture in productive upwelling systems.