Environmental Breviatea harbour mutualistic Arcobacter epibionts

Area of Science:

• Microbiology
• Protistology
• Symbiosis Research

Background:

• Breviatea are ancient, free-living unicellular protists distantly related to animals and fungi, often possessing anaerobic lifestyles due to ancient low-oxygen oceanic conditions.
• The specific interactions and metabolic dependencies of Breviatea with other microorganisms remain largely unexplored.

Purpose of the Study:

• To characterize a newly discovered breviate, Lenisia limosa, and its associated microbial partners.
• To elucidate the nature and molecular mechanisms of the interaction between L. limosa and its colonizing bacteria, identified as relatives of Arcobacter.

Main Methods:

• Cultivation of the novel breviate Lenisia limosa.
• Physiological experiments to determine the basis of the L. limosa-Arcobacter association.
• Whole-genome sequencing and differential proteomics to analyze molecular changes in both organisms.
• Re-analysis of existing transcriptomic data from other Breviatea species.

Main Results:

• The association between L. limosa and Arcobacter is a mutualistic symbiosis driven by hydrogen transfer, benefiting both partners.
• L. limosa exhibits increased fitness due to a novel NAD(P)H-accepting hydrogenase, expressed only in the presence of Arcobacter.
• Arcobacter upregulates proteins typically involved in animal cell colonization ('virulence factors') in response to Lenisia, suggesting a dual role for these factors in both pathogenesis and mutualism.

Conclusions:

• Mutualistic interactions between Breviatea and hydrogen-consuming Arcobacter may be widespread.
• Molecular mechanisms originally identified in virulence contexts can be repurposed to facilitate beneficial symbiotic relationships.
• This study reveals a novel microbial partnership and highlights the adaptability of bacterial 'virulence' factors.