Reconstructing ecosystem functions of the active microbial community of the Baltic Sea oxygen depleted sediments

Abstract

Baltic Sea deep water and sediments hold one of the largest anthropogenically induced hypoxic areas in the world. High nutrient input and low water exchange result in eutrophication and oxygen depletion below the halocline. As a consequence at Landsort Deep, the deepest point of the Baltic Sea, anoxia in the sediments has been a persistent condition over the past decades. Given that microbial communities are drivers of essential ecosystem functions we investigated the microbial community metabolisms and functions of oxygen depleted Landsort Deep sediments by metatranscriptomics. Results show substantial expression of genes involved in protein metabolism demonstrating that the Landsort Deep sediment microbial community is active. Identified expressed gene suites of metabolic pathways with importance for carbon transformation including fermentation, dissimilatory sulphate reduction and methanogenesis were identified. The presence of transcripts for these metabolic processes suggests a potential for heterotrophic-autotrophic community synergism and indicates active mineralisation of the organic matter deposited at the sediment as a consequence of the eutrophication process. Furthermore, cyanobacteria, probably deposited from the water column, are transcriptionally active in the anoxic sediment at this depth. Results also reveal high abundance of transcripts encoding integron integrases. These results provide insight into the activity of the microbial community of the anoxic sediment at the deepest point of the Baltic Sea and its possible role in ecosystem functioning.

Metabolically-active obligate aerobes in anoxic (sulfidic) marine sediments

“…This supposition is corroborated by the reported identification of very low amount of mRNA in dormant laboratory cultures of Mycobacterium tuberculosis 39 , and revelation of strong positive correlation between the abundance of bacterial mRNAs involved in cell division and in situ concentration of bacterial cells cell, during the metatranscriptomic exploration of anaerobic Peru Margin sediments 40 . Notably, metatranscriptome analysis has also been used to delineate active prokaryotic community functions in O 2 -depleted sediments of Baltic Sea that are biogeochemically comparable with the ASOMZ sediments 41 .…”

Microbial trimethylamine metabolism in marine environments

“…Phylogenetic analysis revealed the presence of diverse methanogen communities distributed along the different geochemical zonations, including those from known TMA‐utilizers, for example, Methanococcoides and Methanosarcina (Zhuang et al ., ). Similarly, metatranscriptomic data from anoxic sediment in the Baltic Sea revealed that mcrA transcripts affiliated to Methanosarcina were highly abundant, suggesting a role of TMA‐dependent methanogenesis in the sediment (Thureborn et al ., ).…”

Prokaryotic Diversity and Distribution in Different Habitats of an Alpine Rock Glacier-Pond System

“…Interestingly, the relative abundance of such OTU decreases in shallower sediments, where other phylotypes occupy higher proportions of the cyanobacterial sequences pool. The presence and activity of Cyanobacteria in marine and lacustrine sediments at depths far higher than 3 m, where the penetration of solar radiation is limited, has been widely reported in literature [62][63][64][65]. Moreover, several studies described how microalgal and cyanobacterial community structure and diversity in freshwater lake sediments vary in relation to water depth, often as a consequence of disturbance events affecting shallow sediments, i.e.…”