Marine Cold Seep ANME-2/SRB Consortia Produce Their Lipid Biomass From Inorganic Carbon

Area of Science:

• Microbiology
• Biogeochemistry
• Geology

Background:

• Cold seeps host anaerobic methanotrophic archaea (ANME) and sulphate-reducing bacteria (SRB) that oxidize methane coupled to sulphate reduction.
• While ANME-SRB metabolic pathways are known, carbon assimilation into biomass and lipid biomarker functions are unclear.
• Understanding carbon flow is crucial for microbial ecology and biogeochemical cycling in these environments.

Purpose of the Study:

• To investigate carbon assimilation pathways in ANME-SRB consortia using lipid stable isotope probing.
• To determine the primary carbon source (methane vs. dissolved inorganic carbon) utilized by ANME and SRB for biomass production.
• To elucidate the functional roles of specific lipid biomarkers in ANME and SRB.

Main Methods:

• Lipid stable isotope probing (lipid-SIP) experiments using 13C-labeled methane (13CH4) and dissolved inorganic carbon (DI13C).
• Analysis of 13C incorporation into specific fatty acids (SRB) and isoprenoid lipids (ANME) in Astoria Canyon sediments.
• Calculation of carbon assimilation rates based on lipid-specific delta 13C values.

Main Results:

• Both ANME and SRB primarily assimilated dissolved inorganic carbon (DI13C) over methane (13CH4).
• SRB showed significantly higher DI13C assimilation (up to +417‰) compared to ANME (up to +126‰).
• Lipid analysis delineated biosynthetic pathways and identified crocetane as a potential membrane fluidity modulator.

Conclusions:

• ANME-SRB consortia preferentially utilize dissolved inorganic carbon for biomass synthesis.
• ANME may utilize additional carbon sources, possibly from SRB, beyond methane and inorganic carbon.
• Lipid biomarkers provide insights into microbial carbon assimilation, biosynthesis, and membrane function in cold seeps.