Mutualistic Interactions between Dinoflagellates and Pigmented Bacteria Mitigate Environmental Stress

Area of Science:

• Marine microbiology
• Symbiotic interactions
• Coral reef ecology

Background:

• Coral holobionts comprise hosts and diverse microorganisms, including Symbiodiniaceae dinoflagellates and bacteria.
• Interactions are vital for coral health, yet dinoflagellate-bacterial relationships are understudied.
• Climate change poses a threat to corals by stressing their symbiotic microalgae.

Purpose of the Study:

• To investigate dinoflagellate-bacterial interactions within the coral holobiont.
• To develop a method for manipulating coral microalgal microbiomes.
• To understand how these interactions mitigate environmental stress.

Main Methods:

• Developed KAS-antibiotic treatment to favor pigmented bacteria associated with cultured Symbiodiniaceae.
• Utilized 16S rRNA amplicon sequencing to identify bacterial communities.
• Employed culture-dependent and -independent techniques to study interactions.
• Assessed microalgal photosynthetic efficiency (F/F) under light stress.

Main Results:

• KAS treatment significantly increased pigmented bacteria (8-fold), identified as *Maribacter*.
• Microbiome-manipulated microalgae showed enhanced photosynthetic function under light stress.
• Demonstrated mutual protection: dinoflagellates protected bacteria from antibiotics, and bacteria protected microalgae from light stress via carotenoids.
• Identified a novel symbiotic relationship with mutual stress reduction.

Conclusions:

• Coral dinoflagellates and pigmented bacteria engage in a mutually beneficial symbiosis.
• This interaction enhances coral holobiont resilience to environmental stressors like light and antibiotics.
• Findings contribute to understanding coral holobiont function and inform conservation strategies for coral reefs.