The Ability of Microbial Community of Lake Baikal Bottom Sediments Associated with Gas Discharge to Carry Out the Transformation of Organic Matter under Thermobaric Conditions

Abstract

The ability to compare the composition and metabolic potential of microbial communities inhabiting the subsurface sediment in geographically distinct locations is one of the keys to understanding the evolution and function of the subsurface biosphere. Prospective areas for study of the subsurface biosphere are the sites of hydrocarbon discharges on the bottom of the Lake Baikal rift, where ascending fluxes of gas-saturated fluids and oil from deep layers of bottom sediments seep into near-surface sediment. The samples of surface sediments collected in the area of the Posolskaya Bank methane seep were cultured for 17 months under thermobaric conditions (80°C, 5 MPa) with the addition of complementary organic substrate, and a different composition for the gas phase. After incubation, the presence of intact cells of microorganisms, organic matter transformation and the formation of oil biomarkers was confirmed in the samples, with the addition of Baikal diatom alga Synedra acus detritus, and gas mixture CH4:H2:CO2. Taxonomic assignment of the 16S rRNA sequence data indicates that the predominant sequences in the enrichment were Sphingomonas (55.3%), Solirubrobacter (27.5%) and Arthrobacter (16.6%). At the same time, in heat-killed sediment and in sediment without any additional substrates, which were cultivated in a CH4 atmosphere, no geochemical changes were detected, nor the presence of intact cells and 16S rRNA sequences of Bacteria and Archaea. This data may suggest that the decomposition of organic matter under culturing conditions could be performed by microorganisms from low-temperature sediment layers. One possible explanation of this phenomenon is migration of the representatives of the deep thermophilic community through fault zones in the near surface sediment layers, together with gas-bearing fluids.

Seasonal and spatial variation in the sediment bacterial community and diversity of Lake Bosten, China

“…Based on changes in the bacterial content and microflora structure of lake sediments, the relationship between microorganisms and the environment can be shown. Therefore, exploring the bacterial community composition and environmental impact factors in sediments from different geographical locations is of great significance to understand the evolution and function of lake microecological systems and to control eutrophication and control lakes .…”

Experimental equipment for Lake Baikal deep biosphere microorganism’s exploration and some results obtained using this equipment

“…), which could be transferred to the surface sediments with gas-saturated material from depths of several kilometres (Pavlova et al, 2019a). In cultivated samples of bottom sediments from methane seeps characterized by presence of a fluid convection loop we detected typical mesophilic inhabitants of bottom sediments with a "flexible" metabolism (Bukin et al, 2016;Pavlova et al, 2016). This composition probably allows adapting to the changes in environmental conditions during the burial of individual bottom sediment layers and the circulation of fluid flows.…”

“…The experiments have shown that long-term cultivation of microbial communities from bottom sediments of methane seeps Goloustnoye and Posolsk Bank, which were enriched with detritus of the Baikal diatom Synedra acus and CH 4 :H 2 :CO 2 gas mixture, leads to the destruction of algal biomass and formation of petroleum biomarkers, such as retene or gammacerene (Bukin et al, 2016;Pavlova et al, 2016). These data indicate the involvement of microorganisms in the formation of retene during the destruction of diatoms under milder than pyrolysis conditions.…”

“…We have shown the ability of some taxa from Lake Baikal deep bottom sediment layers to survive under conditions typical for protocatagenesis, as well as in typical involvement known for these taxa in organic matter transformation locations. The metagenomic analysis of DNA samples before and after the experiments allowed us to characterize the dominant and minor components of microbial communities and identify the putative main participants in the observed processes inhabiting deep bottom sediments of Lake Baikal (Bukin et al, 2016;Pavlova et al, 2016;Pavlova et al, 2019a). We have noticed that different geochemical conditions of bottom sediments associated with hydrocarbon discharge determine different compositions of microbial communities and, hence, the transformation degree of organic matter as well as spectrum of compounds resulting from the destruction of organic matter under thermobaric conditions.…”

“…Loci subject to analysis were amplified by polymerase chain reaction (PCR) and subsequently used for massive parallel sequencing libraries preparation and analysis on Illumina MiSeq platform (SB RAS Genomics Core Facility, Novosibirsk). Massive parallel sequencing and phylogenetic analysis were performed as described previously (Bukin et al, 2016).…”