A brain microbiome in salmonids at homeostasis

Area of Science:

• Microbiology
• Fish Biology
• Ecology

Background:

• Ectotherms exhibit unique interactions with microorganisms, with bacteria previously identified in teleost blood and organs.
• The presence and role of microbial communities within the healthy teleost brain remained unexplored.

Purpose of the Study:

• To investigate the existence and characteristics of bacterial communities in the healthy teleost brain.
• To compare brain bacterial communities with those in other tissues and explore their potential functions.

Main Methods:

• Culturomics was employed to isolate and identify bacteria from healthy trout brains.
• Comparative genomics was used to analyze potential adaptations of brain-associated bacteria.
• Microbiome analysis was performed on Chinook salmon at different life stages.

Main Results:

• A living bacterial community was identified in the healthy salmonid brain, with bacterial loads comparable to the spleen.
• Brain bacterial communities exhibited significant overlap in diversity with gut and blood communities (>50%).
• Comparative genomics revealed potential adaptations for niche colonization and polyamine biosynthesis in brain bacteria, and Chinook salmon brain microbiomes change with age.

Conclusions:

• The study redefines the physiological relationship between teleost brains and bacteria, revealing a previously unrecognized symbiosis.
• The brain microbiome may provide salmonids with a mechanism to sense and respond to environmental microbes.
• This discovery opens new avenues for understanding host-microbe interactions in aquatic vertebrates.