Quantification of anaerobic thermophilic endospores in marine sediment by microcalorimetry, and its use in bioprospecting for gas and oil

Abstract

Endospores of anaerobic thermophilic bacteria (thermospores) are ubiquitous in cold marine sediments. These misplaced thermophiles likely originate from warm environments and are delivered to the seafloor by passive dispersal through the water column. The few studies of the abundance of thermospores that exist have only quantified a subset of the anaerobic metabolic types possibly present and the data density has been too low to address patterns of dispersal. Here, we introduce isothermal microcalorimetry as a fast tool to quantify the abundance of thermospores in environmental samples. We developed and tested the method on samples from the water column and sediment of Aarhus Bay, Denmark. The thermospores were stimulated to germinate and grow by heating the samples to 50°C inside an isothermal microcalorimeter and the metabolic heat production was followed across the exponential growth phase. The number of germinated thermospores was then calculated by dividing the total heat production rate by the cell specific heat production rate, empirically determined in parallel experiments. The abundance of thermospores in the water column of Aarhus Bay was 1.2 × 103−3.6 × 103 cells × mL−1 seawater. The abundance of thermospores in sediment in Aarhus Bay was 1.1 × 106−6.1 × 106 cells × mL−1 sediment and their half‐life was ∼70 yr. As application example we used isothermal microcalorimetry to test if thermospores were aggregated at a pockmark in Limfjorden (Denmark) with seepage of thermogenic gas and oil.

Historical Factors Associated With Past Environments Influence the Biogeography of Thermophilic Endospores in Arctic Marine Sediments

“…These studies have provided growing evidence in support of the hypothesis that many thermophilic endospores are derived from fluid flow expelled from marine deep biosphere ecosystems such as mid-ocean ridge venting systems and deeply buried hydrocarbon reservoirs, and are subsequently deposited to marine sediments via passive dispersal. Many thermophilic endospores identified in these studies are phylogenetically related to other organisms found at hydrothermal vents and/or hydrocarbon reservoirs (Hubert et al, 2009, 2010; Nielsen et al, 2017; Chakraborty et al, 2018). Additionally, the diversity of thermophilic endospores in a single cold sediment can be considerable (de Rezende et al, 2013; Müller et al, 2014; Chakraborty et al, 2018) and may be explained by different taxa originating from different warm sources.…”

Thermophilic endospores associated with migrated thermogenic hydrocarbons in deep Gulf of Mexico marine sediments

“…Besides these Clostridia , several other lineages of bacteria and archaea also inhabit oil reservoirs. Certain Thermotogae have only ever been found in oil reservoirs [ 75 – 77 ], an endemism suggesting that in principle they could also be cold sediment bioindicators for deeper reservoir environments if they are similarly ejected via hydrocarbon seeps and can in future also be detected at the seabed [ 13 , 78 , 79 ]. While it is not necessary that only spore-forming thermophiles would be subject to warm-to-cold upward transmigration, the results presented here reveal the ease with which thermospores can be studied as fingerprints of deep life and showcase petroleum geofluids as dispersal vectors connecting the deep and shallow biospheres.…”

A Review of Methods to Determine Viability, Vitality, and Metabolic Rates in Microbiology

“…The heat flow (or thermal power), expressed in W, is directly proportional to the metabolic activity (measured by other means such as oxygen consumption rate; for example, Brueckner et al, 2016 ). The passive and external measurement (through the thermopile placed below vials that are kept sealed) makes isothermal microcalorimetry well suited for measuring metabolic activity in general, but even more advantageous for solid and opaque samples (such as blood, soil, sediment, milk, and agar, for example; Alklint et al, 2005 ; Rong et al, 2007 ; Trampuz et al, 2007 ; Krišèiunaite et al, 2011 ; Nielsen et al, 2017 ).…”