Fluid inclusions from the deep Dead Sea sediment provide new insights on Holocene extreme microbial life

Abstract

The Dead Sea Deep Drilling Project allowed to retrieve a continuous sedimentary record spanning the two last glacial cycles. This unique archive, in such an extreme environment, has allowed for the development of new proxies and the refinement of already available paleoenvironmental studies. In particular, the interaction of the lake and sediment biosphere with elements and minerals that constitute paleoclimatic proxies has been emphasized. Although life is pushed to its extremes in the Dead Sea environment, several studies have highlighted the impact of microbial activity on this harsh milieu. The paradox is that the identity and means of adaptation of these organisms are largely ignored. We also know relatively little on the way this extreme ecosystem has evolved with time, and how it will react to growing pressure. Constraining this gap should allow to gain precision on the use of paleoenvironmental studies, and also assess the impact of human activity and climate change on a rare ecosystem. In this study, we use halite, the main evaporitic phase during arid periods in the Dead Sea basin and extract ancient DNA from their fluid inclusions, in order to characterize the ancient life of the Holocene Dead Sea. With the aid of an accurately designed protocol, we obtained fossil bacterial and archaeal 16S rRNA gene sequences that illustrate that the main microbial actors of the present Dead Sea have been present in the lake for a relatively long period, emphasizing the stability of this extreme environment. Additionally, we show that current phylotypes of the deep biosphere are present within the obtained fluid inclusions sequences, which would support seeding of the deep biosphere from the water column. Finally, we shed light on putative new actors of the sulfur cycle involving both archaea and bacteria, which could play an unexpected role in the reduction of sulfur species. Together, these data provide new research avenues for both geologists and biologists working in this extreme environment, and help understanding the evolution of the Dead Sea ecosystem with time.

Recycling of archaeal biomass as a new strategy for extreme life in Dead Sea deep sediments

“…2) instead suggests a bacterial origin of the WEs. Recent work on fluid inclusions allowed the retrieval of bacterial sequences in halite-dominated layers of the deep Dead Sea sediment (Thomas and Ariztegui, 2019). Our data would therefore support the development of bacteria upon archaeal necromass in the extreme environment of the Dead Sea subsurface.…”

Lake Sedimentary DNA Research on Past Terrestrial and Aquatic Biodiversity: Overview and Recommendations

“…However, none of these examples determined to what extent the identified communities represented dead, dormant, or metabolically active communities. Conversely, a recent study of Dead Sea sediments [157] illustrated a new pathway of carbon transformation in the subsurface and demonstrated how life can be maintained in extreme environments characterized by long-term isolation and minimal energetic resources.…”

Magnetic Properties of Late Holocene Dead Sea Sediments as a Monitor of Regional Hydroclimate

“…Nevertheless, sulfate‐reducing bacteria (SRB) activity has been detected in the Dead Sea water column, springs, and sediments from sulfur isotopic analyses of sulfide and sulfate (Bishop et al., 2013; Gavrieli et al., 2001; Häusler et al., 2014; Ionescu et al., 2012; Neev & Emery, 1967; Nissenbaum & Kaplan, 1976). Thomas and Ariztegui (2019) analyzed fluid inclusions from within halite and suggested that both archaea and bacteria are involved in the sulfur cycle in the Dead Sea. Overall, the high salinity and poor organic matter content limit MSR activity in the Dead Sea (Häusler et al., 2014; Ionescu et al., 2012; Thomas & Ariztegui, 2019; Thomas et al., 2016).…”

“…Thomas and Ariztegui (2019) analyzed fluid inclusions from within halite and suggested that both archaea and bacteria are involved in the sulfur cycle in the Dead Sea. Overall, the high salinity and poor organic matter content limit MSR activity in the Dead Sea (Häusler et al., 2014; Ionescu et al., 2012; Thomas & Ariztegui, 2019; Thomas et al., 2016).…”