Attachment between heterotrophic bacteria and microalgae influences symbiotic microscale interactions.

Area of Science:

• Microbiology
• Marine Biology
• Biotechnology

Background:

• The microalgal phycosphere, the zone surrounding algal cells, is crucial for interactions but challenging to study.
• Understanding these interactions is key for optimizing microalgal cultivation for biofuel production.

Purpose of the Study:

• To investigate the effects of bacteria on the carbon fixation of two biofuel-relevant microalgal species, Phaeodactylum tricornutum and Nannochloropsis salina.
• To quantify elemental exchanges at the single-cell level within the phycosphere.

Main Methods:

• Utilized stable isotope tracing and NanoSIMS (nanoscale secondary ion mass spectrometry) for high spatial resolution elemental analysis.
• Examined bacterial attachment and carbon fixation rates in P. tricornutum and N. salina under different conditions.

Main Results:

• P. tricornutum showed increased carbon fixation (64%) with bacterial attachment, with high bacterial colonization (92%-98%).
• N. salina exhibited decreased carbon fixation (10%) when associated with bacteria, with lower colonization (42%-63%).
• A specific bacterium (Haliscomenobacter sp. relative) acted as a mutualist for P. tricornutum, enhancing carbon fixation and nutrient uptake.

Conclusions:

• Algal species exhibit distinct responses to bacterial associations in the phycosphere.
• Phylogenetic identity and location of microbes dictate metabolic outcomes and elemental exchange.
• Harnessing mutualistic phycosphere interactions offers a promising strategy for enhancing microalgal productivity in engineering applications.