Sediment Bacterial Communities Reflect the History of a Sea Basin

Abstract

How entire microbial communities are structured across stratified sediments from the historical standpoint is unknown. The Baltic Sea is an ideal research object for historical reconstruction, since it has experienced many fresh- and brackish water periods and is depleted of dissolved oxygen, which increases the sediment's preservation potential. We investigated the bacterial communities, chemical elements (e.g. Cr, Pb Na, P, Sr and U) and sediment composition in a stratified sediment core dated by radiocarbon and spanning 8000 years of Baltic Sea history, using up-to-date multivariate statistics. The communities were analysed by 16S rRNA gene terminal restriction fragment length polymorphism. The communities of the deep Early Litorina and surface Late Litorina Sea laminae were separated from the communities of the middle Litorina Sea laminae, which were associated with elevated concentrations of U and Sr trace elements, palaeo-oxygen and palaeosalinity proxies. Thus, the Litorina Sea laminae were characterized by past oxygen deficiency and salinity increase. The communities of the laminae, bioturbated and homogeneous sediments were differentiated, based on the same historical sea phases, with correct classifications of 90%. Palaeosalinity was one of the major parameters that separated the bacterial communities of the stratified sediments. A discontinuous spatial structure with a surprising increase in community heterogeneity was detected in Litorina Sea sediments from 388 to 422 cm deep, which suggests that a salinity maximum occurred in the central Gulf of Finland app. 6200–6600 years ago. The community heterogeneity decreased from the surface down to 306 cm, which reflected downcore mineralization. The plateau of the decrease was in the app. 2000-year-old sediment layers. Bacterial community data may be used as an additional tool in ocean-drilling projects, in which it is important to detect mineralization plateaus both to determine historically comparable portions of sediment samples and historical events, such as sea-level rise culminations.

Remnants of marine bacterial communities can be retrieved from deep sediments in lakes of marine origin

“…Generally, batch cultures are known to be selective for fast-growing opportunistic bacteria, including Gammaproteobacteria (Eilers et al, 2000;Fuchs et al, 2000), and therefore, our results can be seen as a cultivation artefact. Nevertheless, Gammaproteobacteria are generally abundant members of sediment communities, both in freshwater and marine systems, including deep sediments Ye et al, 2009;Szabo et al, 2011), as well as Littorina Sea phase sediments from the Baltic Sea (Lyra et al, 2013). Thus, we do not see our results as a mere cultivation artefact but as evidence for a recruitment of marine bacteria from these very old sediments under the right conditions, even though we primarily enriched habitat generalists which can tolerate a broad range of salinities at the expense of habitat specialists that occur exclusively in marine systems.…”

“…Emeis et al, 2003;Andr en et al, 2011). It has been shown that such fluctuations can be followed in the composition of sediment bacteria at different depths (Lyra et al, 2013). However, it has not been demonstrated whether those bacteria are viable and able to grow under suitable environmental conditions.…”

Bacteria Contribute to Sediment Nutrient Release and Reflect Progressed Eutrophication-Driven Hypoxia in an Organic-Rich Continental Sea

“…Family Anaerolineaceae consists mainly of anaerobic fermenters [80]–[82] that have been found mostly in organic-rich environments such as anaerobic methanogenic sludges [80], [82], [83] or sediments [24], [84]. Recently, various anaerolineacean bacteria were detected in deep-core layers covering the last 8000 years of the Baltic Sea [85], which suggests that they may contribute to organic matter mineralization processes in the deeper biosphere. There are studies in which H 2 -producing Anaerolineaceae strains grew more rabidly in the presence of hydrogenotrophic methanogens [80], [82], [83].…”

Shift of grey seal subspecies boundaries in response to climate, culling and conservation

“…This shift was caused by gradual cooling and increased precipitation across northern Europe, which decreased the salinity and increased the winter ice cover of the Baltic Sea, resulting in marked changes in Baltic Sea diatom and bacterial communities and an overall decrease in primary productivity (Tuovinen et al 2008;Sepp€ a et al 2009;Witkowski et al 2009;Lyra et al 2013;Willumsen et al 2013). We hypothesize that the cooling was a major factor driving the reproductive isolation between North Sea and Baltic Sea grey seals: the former adjusting their breeding season and habitat to ice-free conditions in the North Sea, and the latter to a colder environment with annual periods of sea ice.…”