Spatially structured bacterial interactions alter algal carbon flow to bacteria

Area of Science:

• Marine microbial ecology
• Biogeochemical cycles
• Phytoplankton-bacteria interactions

Background:

• Phytoplankton are crucial for global carbon fixation, with microbial food webs controlling carbon fate.
• A mechanistic understanding of how heterotrophic bacteria interactions influence this process is lacking.

Purpose of the Study:

• Investigate how bacteria-bacteria interactions affect the remineralization and biomass incorporation of photosynthetically fixed carbon.
• Quantify the impact of bacterial competition and facilitation on algal carbon drawdown.

Main Methods:

• Utilized bacterial isolates grown on diatom exudates.
• Employed exometabolomics and genome-scale metabolic modeling to assess resource competition.
• Used single-cell isotope tracing in a custom cultivation system to track carbon fate.

Main Results:

• Pairwise bacterial interactions showed more benefits than predicted, with 30% exhibiting facilitative effects.
• Highly competitive primary bacterial strains reduced secondary strain carbon drawdown by 51% at the single-cell level.
• Facilitative primary strains increased total algal-derived carbon assimilation 7.6-fold compared to competitive strains.

Conclusions:

• The spectrum of bacterial interactions, from competitive to facilitative, directly influences algal carbon drawdown.
• Bacterial community structure and interactions are critical regulators of marine carbon cycling.