Interaction and signalling between a cosmopolitan phytoplankton and associated bacteria

Area of Science:

• Marine microbiology
• Phytoplankton-bacteria interactions
• Biogeochemical cycles

Background:

• Marine microbial communities, particularly phytoplankton-bacteria consortia, significantly influence ocean ecosystems.
• Diatoms, major primary producers, interact with specific bacteria, but mechanisms remain largely unknown.
• Understanding these interactions is crucial for marine food web and biogeochemical cycle research.

Purpose of the Study:

• To elucidate the interaction mechanisms between a globally distributed diatom and its associated bacterial consortium.
• To identify specific bacterial species and molecules mediating diatom growth and nutrient exchange.
• To assess the prevalence of these signaling pathways in marine environments.

Main Methods:

• Culturing of a diatom-bacterial consortium.
• Metabolite analysis to identify exchanged compounds.
• Metatranscriptome analysis to study gene expression.
• Hormone quantification and synthesis pathway investigation.

Main Results:

• A Sulfitobacter species was identified as promoting diatom cell division.
• Bacterial indole-3-acetic acid (IAA) production, using diatom-secreted and endogenous tryptophan, was confirmed as the growth-promoting mechanism.
• A complex nutrient exchange was observed, involving diatom-excreted organosulfur compounds and bacterial ammonia.
• Widespread IAA production by Sulfitobacter-related bacteria in coastal environments was detected.

Conclusions:

• Marine diatom-Sulfitobacter interactions are mediated by infochemicals, specifically IAA, facilitating nutrient exchange and promoting diatom growth.
• This study highlights the role of hormone signaling in structuring marine microbial communities.
• The findings suggest that such infochemical-based interactions are prevalent in coastal marine ecosystems, impacting primary production and food webs.