Prochlorococcus Cells Rely on Microbial Interactions Rather than on Chlorotic Resting Stages To Survive Long-Term...

Area of Science:

• Marine microbiology
• Ocean biogeochemical cycles
• Cyanobacteria physiology

Background:

• Microorganisms survive nutrient stress via resting cells with low metabolic activity.
• Cyanobacteria and phytoplankton use chlorosis (pigment loss) to form resting stages.
• Prochlorococcus is a dominant phytoplankton globally, crucial for ocean biogeochemical cycles.

Purpose of the Study:

• Investigate chlorosis-like processes in Prochlorococcus under stress.
• Determine Prochlorococcus viability and survival mechanisms during nutrient starvation.
• Understand the ecological role of microbial interactions in Prochlorococcus survival.

Main Methods:

• Axenic laboratory cultures of Prochlorococcus strain MIT9313.
• Induction of stress conditions to observe chlorosis.
• Nanoscale secondary ion mass spectrometry (NanoSIMS) to measure carbon (C) and nitrogen (N) uptake.
• Coculture experiments with Alteromonas macleodii HOT1A3.

Main Results:

• Prochlorococcus exhibits a chlorosis-like process under multiple stress conditions.
• Chlorotic Prochlorococcus cells show reduced metabolic activity (C and N uptake).
• Chlorotic Prochlorococcus cells are not viable axenically but survive for months in coculture with Alteromonas macleodii.

Conclusions:

• Prochlorococcus survival during nutrient starvation depends on symbiotic relationships with heterotrophic bacteria.
• Reliance on bacterial symbionts, not resting cell formation, is key to Prochlorococcus's ecological success.
• Microbial interactions significantly influence ocean biogeochemical cycles at a global scale.