Membrane Lipid Composition and Amino Acid Excretion Patterns of Methanothermococcus okinawensis Grown in the Presence of Inhibitors Detected in the Enceladian Plume

Abstract

Lipids and amino acids are regarded as important biomarkers for the search for extraterrestrial life in the Solar System. Such biomarkers may be used to trace methanogenic life on other planets or moons in the Solar System, such as Saturn’s icy moon Enceladus. However, little is known about the environmental conditions shaping the synthesis of lipids and amino acids. Here, we present the lipid production and amino acid excretion patterns of the methanogenic archaeon Methanothermococcus okinawensis after exposing it to different multivariate concentrations of the inhibitors ammonium, formaldehyde, and methanol present in the Enceladian plume. M. okinawensis shows different patterns of lipid and amino acids excretion, depending on the amount of these inhibitors in the growth medium. While methanol did not show a significant impact on growth, lipid or amino acid production rates, ammonium and formaldehyde strongly affected these parameters. These findings are important for understanding the eco-physiology of methanogens on Earth and have implications for the use of biomarkers as possible signs of extraterrestrial life for future space missions in the Solar System.

Experimental and Simulation Efforts in the Astrobiological Exploration of Exooceans

“…As a consequence, the abundance pattern of amino acids, i.e. the ratio of various amino acids to Gly, can be considered as a biosignature (Davila and McKay 2014;Creamer et al 2017;Klenner et al 2020a;Taubner et al 2019).…”

“…To alleviate this issue, high pressure reactors are used. For example, Taubner et al (2018) investigate the feasibility of methanogenic growth under simulated Enceladus conditions using a stainless steel Büchi reactor ( Fig. 5), which was continuously stirred.…”

“…These experiments include studies that examine material properties under subsurface conditions, e.g. the dynamics of ices, and high-pressure facilities used for both biotic (studies regarding microbial survival and biosignature production: Taubner et al 2018Taubner et al , 2019Foglia et al 2016;Schuerger and Nicholson 2016;Hazael et al 2017;Sharma et al 2002) and abiotic settings (studies exploring ice-water and water-silicate interactions: Vance and Brown 2008, 2013Mantegazzi et al 2012Mantegazzi et al , 2013. Further, investigations into environmental gradients are performed to broaden our understanding of the physical conditions on these icy worlds (More-Mutch et al submitted).…”

Microbial Diversity and Biosignatures: An Icy Moons Perspective

“…(1) The incorporation of cyclopentane rings along the isoprenoid chain as a function of fluctuating temperature (De Rosa et al 1980aRosa et al , 1980bErnst et al 1998;Uda et al 2001Uda et al , 2004 or pH (Shimada et al 2008) increases the packing efficiency of the membrane lipids (Gliozzi et al 1983), which increases membrane stability as a function of increasing temperature or salinity and decreasing pressure or pH, and consequently lowers membrane permeability (Chong et al 2012). 2The regulation of the tetraether-to-diether lipid ratio (Sprott et al 1991;Lai et al 2008;Matsuno et al 2009;Baumann et al 2018;Taubner et al 2019), since increasing tetraether lipids will stabilize membranes by forming monolayer-type membranes or domains in the membrane, and consequently helping to regulate the flux of solutes and protons across the membrane. 3The crosslinking of the two acyl-chains of the lipids yields macrocyclic archaeol or caldarchaeol derivatives by a covalent bond between the isoprenoid chains, which also reduces molecular motion to create a more closely packed structure and increases membrane stability, creating an efficient barrier against water, proton and solute leakage (Dannenmuller et al 2000;Mathai et al 2001).…”

Towards Determining Biosignature Retention in Icy World Plumes

“…The potential habitability of icy moons has led to studies addressing possible microbial survival and growth [17][18][19][20][21][22], as well as estimates of biomass concentrations [23][24][25] in these environments. The results show that, under certain conditions (degree of convection, mantle rheology, etc.…”