Potential impacts of climate change on the marine sediment microbiota of the West Antarctic Peninsula

WILLIS PORATTI GRACIANA; WUNDER LEA C.; AROMOKEYE DAVID; VÁZQUEZ SUSANA; FRIEDRICH MICHAEL; MAC CORMACK WALTER

Mendoza

Simposio; Congreso SAIB 2022. Reunión Anual Edición LVIII. Simposio de Microbiología; 2022

SAIB

Rapid warming has affected the Western Antarctic Peninsula (WAP) strongly over the last 50 years, resulting in glacier retreat at unprecedented rates. Consequently, increasing amounts of iron(III) oxides accumulate in areas close to the retreating glaciers and a rapid rise in the mean air temperature by 0.17°C per decade has been recorded over the last decades. Microbial iron reduction of insoluble iron(III) oxides linked to organic matter oxidation can produce dissolved iron in pore water and contribute to the total benthic Fe2+ fluxes, which is then exported to the Southern Ocean, known for being limited in primary productivity. Depending on the availability of organic matter and electron donors, iron reduction can out-compete sulfate reduction in marine sediments. However, little is known about of iron and sulfur geochemical cycles and organic matter degradation in Antarctic sediments and particularly how these microbial populations are affected by the environmental change observed in the region. Therefore, our aim is to elucidate the ecology of iron-reducing microbial communities, and their environmental controls in Antarctic marine sediments. Our study site, Potter Cove on Isla 25 de Mayo (King George Island, South Shetland Island) is one of the most biodiverse coastal Antarctic regions, ASPA 132 (Antarctic Specially Protected Area 132) and has been the focus of several multidisciplinary studies over the last decades. Here, we focus on hots spots of environmental change at Potter Cove including sediment sites that have been newly exposed due of receding glaciers, accumulating iron oxides and high dissolved iron concentrations compared to typical sulfidogenic sites as a reference, indicative of sulfate reduction. For that, factors that are potentially controlling iron and sulfate reducing microorganisms will be discussed, such as electron donor type and availability, electron acceptor availability, terrigenic inputs and temperature variations. As key outcomes, we found that macroalgae degradation fuels microbial iron reduction in Potter Cove. The main bacterial degraders of macroalgae are members of the genus Psychromonas and that members of the Sva1033 clade (order Desulfuromonadales) are responsible of the last steps of organic matter degradation coupled to iron reduction. In addition, temperature increase will strongly affect iron reduction rates in the Cove, which may be accompanied by shift in dominant iron reducing populations.