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

Quantitative analysis of amino acid excretion by Methanothermobacter marburgensis under N2-fixing conditions

Methanogenic archaea (methanogens) possess fascinating metabolic characteristics, such as the ability to fix molecular nitrogen (N2). Methanogens are of biotechnological importance due to the ability to produce methane (CH4) from molecular hydrogen (H2) and carbon dioxide (CO2) and to excrete proteinogenic amino acids. This study focuses on analyzing the link between biological methanogenesis and amino acid excretion under N2-fixing conditions. Among five hydrogenotrophic, autotrophic methanogens, Methanothermobacter marburgensis was prioritized and further cultivated in closed batch cultivation mode under N2-fixing conditions. M. marburgensis was grown on chemically defined minimal medium with different concentrations of ammonium in a H2/CO2/N2 atmosphere. This enabled the quantification of ammonia uptake, N2-fixation, amino acid excretion and the conversion of H2/CO2 to CH4. To quantify N2-fixation rates in a mass balance setting a novel method has been established. The method utilizes the pressure drop below a certain threshold pressure in closed batch cultivation mode - the threshold pressure for N2-fixation (THpN2fix). Using the THpN2fix method, volumetric N2-fixation rates of M. marburgensis as high as 0.91 mmol L-1 h-1 were determined. Excretion of amino acids was found with highest detected values of glutamic acid, alanine, glycine and asparagine. The highest total amino acid excretion of 7.5 µmol L-1 h-1 was detected with H2/CO2/N2 at an ammonium concentration of 40 mmol L-1. This study sheds light on the link between methanogenesis, biological N2-fixation, and proteinogenic amino acid excretion. The concomitant production of amino acids and CH4 could become of biotechnological relevance in an integrated approach coupling biomethanation and N2-fixation in a biorefinery concept.

Methanogens and what they tell us about how life might survive on Mars

Space exploration and research are uncovering the potential for terrestrial life to survive in outer space, as well as the environmental factors that affect life during interplanetary transfer. The presence of methane in the Martian atmosphere suggests the possibility of methanogens, either extant or extinct, on Mars. Understanding how methanogens survive and adapt under space-exposed conditions is crucial for understanding the implications of extraterrestrial life. In this article, we discuss methanogens as model organisms for obtaining energy transducers and producing methane in a simulated Martian environment. We also explore the chemical evolution of cellular composition and growth maintenance to support survival in extraterrestrial environments. Neutral selective pressure is imposed on the chemical composition of cellular components to increase cell survival and reduce growth under physiological conditions. Energy limitation is an evolutionary driver of macromolecular polymerization, growth maintenance, and survival fitness of methanogens. Methanogens grown in a Martian environment may exhibit global alterations in their metabolic function and gene expression at the system scale. A space systems biology approach would further elucidate molecular survival mechanisms and adaptation to a drastic outer space environment. Therefore, identifying a genetically stable methanogenic community is essential for biomethane production from waste recycling to achieve sustainable space-life support functions.

Unraveling the multiplicity of geranylgeranyl reductases in Archaea: potential roles in saturation of terpenoids

The enzymology of the key steps in the archaeal phospholipid biosynthetic pathway has been elucidated in recent years. In contrast, the complete biosynthetic pathways for proposed membrane regulators consisting of polyterpenes, such as carotenoids, respiratory quinones, and polyprenols remain unknown. Notably, the multiplicity of geranylgeranyl reductases (GGRs) in archaeal genomes has been correlated with the saturation of polyterpenes. Although GGRs, which are responsible for saturation of the isoprene chains of phospholipids, have been identified and studied in detail, there is little information regarding the structure and function of the paralogs. Here, we discuss the diversity of archaeal membrane-associated polyterpenes which is correlated with the genomic loci, structural and sequence-based analyses of GGR paralogs.

Lipidomics and Comparative Metabolite Excretion Analysis of Methanogenic Archaea Reveal Organism-Specific Adaptations to Varying Temperatures and Substrate Concentrations

Methanogenic archaea possess diverse metabolic characteristics and are an ecologically and biotechnologically important group of anaerobic microorganisms. Although the scientific and biotechnological value of methanogens is evident with regard to their methane-producing physiology, little is known about their amino acid excretion, and virtually nothing is known about the lipidome at different substrate concentrations and temperatures on a quantitative comparative basis. Here, we present the lipidome and a comprehensive quantitative analysis of proteinogenic amino acid excretion as well as methane, water, and biomass production of the three autotrophic, hydrogenotrophic methanogens Methanothermobacter marburgensis, Methanothermococcus okinawensis, and Methanocaldococcus villosus under varying temperatures and nutrient supplies. The patterns and rates of production of excreted amino acids and the lipidome are unique for each tested methanogen and can be modulated by varying the incubation temperature and substrate concentration, respectively. Furthermore, the temperature had a significant influence on the lipidomes of the different archaea. The water production rate was much higher, as anticipated from the rate of methane production for all studied methanogens. Our results demonstrate the need for quantitative comparative physiological studies connecting intracellular and extracellular constraints of organisms to holistically investigate microbial responses to environmental conditions. IMPORTANCE Biological methane production by methanogenic archaea has been well studied for biotechnological purposes. This study reveals that methanogenic archaea actively modulate their lipid inventory and proteinogenic amino acid excretion pattern in response to environmental changes and the possible utilization of methanogenic archaea as microbial cell factories for the targeted production of lipids and amino acids.

Quantitative Analysis of Core Lipid Production in Methanothermobacter marburgensis at Different Scales

Archaeal lipids have a high biotechnological potential, caused by their high resistance to oxidative stress, extreme pH values and temperatures, as well as their ability to withstand phospholipases. Further, methanogens, a specific group of archaea, are already well-established in the field of biotechnology because of their ability to use carbon dioxide and molecular hydrogen or organic substrates. In this study, we show the potential of the model organism Methanothermobacter marburgensis to act both as a carbon dioxide based biological methane producer and as a potential supplier of archaeal lipids. Different cultivation settings were tested to gain an insight into the optimal conditions to produce specific core lipids. The study shows that up-scaling at a constant particle number (n/n = const.) seems to be a promising approach. Further optimizations regarding the length and number of the incubation periods and the ratio of the interaction area to the total liquid volume are necessary for scaling these settings for industrial purposes.

Hyperthermophilic methanogenic archaea act as high-pressure CH4 cell factories

Bioprocesses converting carbon dioxide with molecular hydrogen to methane (CH₄) are currently being developed to enable a transition to a renewable energy production system. In this study, we present a comprehensive physiological and biotechnological examination of 80 methanogenic archaea (methanogens) quantifying growth and CH₄ production kinetics at hyperbaric pressures up to 50 bar with regard to media, macro-, and micro-nutrient supply, specific genomic features, and cell envelope architecture. Our analysis aimed to systematically prioritize high-pressure and high-performance methanogens. We found that the hyperthermophilic methanococci Methanotorris igneus and Methanocaldococcoccus jannaschii are high-pressure CH₄ cell factories. Furthermore, our analysis revealed that high-performance methanogens are covered with an S-layer, and that they harbour the amino acid motif Tyr^α444 Gly^α445 Tyr^α446 in the alpha subunit of the methyl-coenzyme M reductase. Thus, high-pressure biological CH₄ production in pure culture could provide a purposeful route for the transition to a carbon-neutral bioenergy sector.

Archaea Biotechnology

Archaea are a domain of prokaryotic organisms with intriguing physiological characteristics and ecological importance. In Microbial Biotechnology, archaea are historically overshadowed by bacteria and eukaryotes in terms of public awareness, industrial application, and scientific studies, although their biochemical and physiological properties show a vast potential for a wide range of biotechnological applications. Today, the majority of microbial cell factories utilized for the production of value-added and high value compounds on an industrial scale are bacterial, fungal or algae based. Nevertheless, archaea are becoming ever more relevant for biotechnology as their cultivation and genetic systems improve. Some of the main advantages of archaeal cell factories are the ability to cultivate many of these often extremophilic organisms under non-sterile conditions, and to utilize inexpensive feedstocks often toxic to other microorganisms, thus drastically reducing cultivation costs. Currently, the only commercially available products of archaeal cell factories are bacterioruberin, squalene, bacteriorhodopsin and diether-/tetraether-lipids, all of which are produced utilizing halophiles. Other archaeal products, such as carotenoids and biohydrogen, as well as polyhydroxyalkanoates and methane are in early to advanced development stages, respectively. The aim of this review is to provide an overview of the current state of Archaea Biotechnology by describing the actual state of research and development as well as the industrial utilization of archaeal cell factories, their role and their potential in the future of sustainable bioprocessing, and to illustrate their physiological and biotechnological potential.

Towards Determining Biosignature Retention in Icy World Plumes

With the discovery of the persistent jets of water being ejected to space from Enceladus, an understanding of the effect of the space environment on potential organisms and biosignatures in them is necessary for planning life detection missions. We experimentally determine the survivability of microbial cells in liquid medium when ejected into vacuum. Epifluorescence microscopy, using a lipid stain, and SEM imaging were used to interrogate the cellular integrity of E. coli after ejected through a pressurized nozzle into a vacuum chamber. The experimental samples showed a 94% decrease in visible intact E. coli cells but showed a fluorescence residue in the shape of the sublimated droplets that indicated the presence of lipids. The differences in the experimental conditions versus those expected on Enceladus should not change the analog value because the process a sample would undergo when ejected into space was representative. E. coli was selected for testing although other cell types could vary physiologically which would affect their response to a vacuum environment. More testing is needed to determine the dynamic range in concentration of cells expected to survive the plume environment. However, these results suggest that lipids may be directly detectable evidence of life in icy world plumes.

Experimental and Simulation Efforts in the Astrobiological Exploration of Exooceans

The icy satellites of Jupiter and Saturn are perhaps the most promising places in the Solar System regarding habitability. However, the potential habitable environments are hidden underneath km-thick ice shells. The discovery of Enceladus' plume by the Cassini mission has provided vital clues in our understanding of the processes occurring within the interior of exooceans. To interpret these data and to help configure instruments for future missions, controlled laboratory experiments and simulations are needed. This review aims to bring together studies and experimental designs from various scientific fields currently investigating the icy moons, including planetary sciences, chemistry, (micro-)biology, geology, glaciology, etc. This chapter provides an overview of successful in situ, in silico, and in vitro experiments, which explore different regions of interest on icy moons, i.e. a potential plume, surface, icy shell, water and brines, hydrothermal vents, and the rocky core.