First insights into microbial degradation of organic matter in surface marine sediments from Potter Cove, Antarctica: the role of iron-reducing microorganisms

WILLIS PORATTI GRACIANA; AROMOKEYE DAVID A.; WUNDER LEA C.; YIN XIURAN; RICHTER-HEITMANN TIM; HENKEL SUSANN; VÁZQUEZ SUSANA; ELVERT MARCUS; MAC CORMACK WALTER.P; FRIEDRICH MICHAEL

Quilmes, Buenos Aires

Simposio; ISME Lat 2023 - 3er Simposio Latinoamericano de Ecología Microbiana; 2023

ISME; Universidad Nacional de Quilmes

In polar regions, global warming-induced glacial retreat exposes newly ice-free areas which are available for macroalgae colonization, intensifying their burial in marine surface sediments. Moreover, increasing amounts of iron-rich sediments are delivered to the marine ecosystem through meltwater inputs. Thus, fresh macroalgal detritus serve as primary organic matter (OM) source for microbial degradation and the iron oxides as terminal electron acceptors for microbial iron reduction. Potter Cove is a small fjord on the southwest of Isla 25 de Mayo (South Shetland Islands) at the northern tip of the West Antarctic Peninsula (WAP), where the environmental effects of climate change have increased in the last few decades at unprecedented rates. Microbial iron reduction has been proposed as the dominant terminal electron accepting process during OM degradation in the cove, especially in sediments close to newly-ice free areas. Therefore, we investigated the effect of macroalgal detritus on post-depositional microbial iron reduction in Potter Cove surface sediments and identified the potential key microorganisms involved in the food chain from macroalgae degraders to iron reducers. Sediment incubations were set up with macroalgal detritus as OM source, acetate as primary product of OM degradation and lepidocrocite as reactive iron oxide to mimic in situ conditions. Anthraquinone-2,6-disulfonic acid (AQDS) was also added to some treatments to stimulate the electron shuttling. Microbial iron reduction was stimulated by macroalgae and enhanced by up to 30-fold with AQDS. Acetate, formate, lactate, butyrate and propionate were detected as fermentation products from macroalgae degradation. By 16S rRNA gene sequencing, microorganisms such as Psychromonas, Marinifilum, Moritella, and Colwellia were detected as potential degraders and fermenters of macroalgae and fermentation products. Using RNA-SIP on specific sediment incubations we identified members of the class Deltaproteobacteria, including Desulfuromonadales Sva1033, Desulfuromonas, and Desulfuromusa, and Arcobacter as potential dissimilatory iron reducers. Our findings demonstrate that increasing burial of macroalgal detritus in an Antarctic fjord affected by glacier retreat intensifies early diagenetic processes such as iron reduction. Under a global warming scenario, the active microbial populations identified here will expand their environmental role, facilitate OM remineralization, and contribute to increased release of iron and CO2 from sediments.