Subgroup level differences of physiological activities in marine Lokiarchaeota

Area of Science:

• Microbiology
• Marine Ecology
• Biogeochemistry

Background:

• The Asgard archaeal superphylum is crucial for understanding eukaryotic origins.
• Lokiarchaeota are prevalent in marine sediments, but their in situ functions remain largely uncharacterized.
• Candidatus 'Prometheoarchaeum syntrophicum' is one of the few characterized Lokiarchaeota with known activities.

Purpose of the Study:

• To investigate the in situ metabolic activities of Lokiarchaeota in North Sea sediments.
• To differentiate the ecological roles and metabolic capabilities of distinct Lokiarchaeota subgroups.
• To understand the contribution of Lokiarchaeota to carbon cycling in marine environments.

Main Methods:

• Stable Isotope Probing (SIP) using 13C-labeled organic polymers, inorganic carbon, fermentation intermediates, and proteins.
• Incubation experiments with Helgoland mud area sediments.
• Metagenomic analysis to identify metabolic pathways.

Main Results:

• Lokiarchaeota class Loki-3 actively degraded lignin and humic acids mixotrophically, assimilating CO2, or heterotrophically utilized lactate.
• Lokiarchaeota class Loki-2 utilized proteins and inorganic carbon, and degraded bacterial biomass.
• Metagenomic data confirmed pathways for lactate and aromatic compound degradation in Loki-3, and protein degradation in Loki-2.

Conclusions:

• Lokiarchaeotal subgroups possess distinct metabolic capabilities, despite genomic overlaps.
• These metabolic differences indicate that Lokiarchaeotal subgroups occupy unique ecological niches within marine sediments.
• The findings enhance our understanding of microbial roles in marine carbon cycling and early life evolution.