Alkanes increase the stability of early life membrane models under extreme pressure and temperature conditions

Mortality of mesozooplankton in an acidified ocean: Investigating the impact of shallow hydrothermal vents across multiple monsoonal periods

The shallow hydrothermal vents (HVs) of Kueishan Island are considered as a template for studying the extremes of sulfide-polluted and acidified water. The present study examined the biological and spatiotemporal aspects of mesozooplankton mortality in waters around this extreme HV environment. Zooplankton sample collection was carried out in three monsoonal periods and the results revealed that there was a significant decrease in the mortality of total mesozooplankton with increasing distance from the HVs. The overall mortality of mesozooplankton showed a significant negative correlation with sea surface temperature and pH. Particularly, mortality of copepods showed a significant negative correlation with pH, whereas it was significantly positive correlated with sea surface temperature in the southwest monsoon prevailing period. Overall, the results may imply a situation that zooplankton will encounter in the more acidified environment of a future ocean.

Residual Membrane Fluidity in Mycobacterial Cell Envelope Layers under Extreme Conditions Underlines Membrane-Centric Adaptation

One of the routes for adaptation to extreme environments is via remodeling of cell membrane structure, composition, and biophysical properties rendering a functional membrane. Collective studies suggest some form of membrane feedback in mycobacterial species that harbor complex lipids within the outer and inner cell wall layers. Here, we study the homeostatic membrane landscape of mycobacteria in response to high hydrostatic pressure and temperature triggers using high pressure fluorescence, mass and infrared spectroscopies, NMR, SAXS, and molecular dynamics simulations. Our findings reveal that mycobacterial membrane possesses unique and lipid-specific pressure-induced signatures that attenuate progression to highly ordered phases. Both inner and outer membrane layers exhibit phase coexistence of nearly identical lipid phases keeping residual fluidity over a wide range of temperature and pressure, but with different sensitivities. Lipidomic analysis of bacteria grown under pressure revealed lipidome remodeling in terms of chain length, unsaturation, and specific long-chained characteristic mycobacterial lipids, rendering a fluid bacterial membrane. These findings could help understand how bacteria may adapt to a broad spectrum of harsh environments by modulating their lipidome to select lipids that enable the maintenance of a fluid functional cell envelope.

The membrane regulator squalane increases membrane rigidity under high hydrostatic pressure in archaeal membrane mimics

Apolar lipids within the membranes of archaea are thought to play a role in membrane regulation. In this work we explore the effect of the apolar lipid squalane on the dynamics of a model archaeal-like membrane, under pressure, using neutron spin echo spectroscopy. To the best of our knowledge, this is the first report on membrane dynamics at high pressure using NSE spectroscopy. Increasing pressure leads to an increase in membrane rigidity, in agreement with other techniques. The presence of squalane in the membrane results in a stiffer membrane supporting its role as a membrane regulator.

Hybrid organic-inorganic structures trigger the formation of primitive cell-like compartments

Alkaline hydrothermal vents have become a candidate setting for the origins of life on Earth and beyond. This is due to several key features including the presence of gradients of temperature, redox potential, pH, the availability of inorganic minerals, and the existence of a network of inorganic pore spaces that could have served as primitive compartments. Chemical gardens have long been used as experimental proxies for hydrothermal vents. This paper investigates-10pc]Please note that the spelling of the following author name in the manuscript differs from the spelling provided in the article metadata: Richard J. G. Löffler. The spelling provided in the manuscript has been retained; please confirm. a set of prebiotic interactions between such inorganic structures and fatty alcohols. The integration of a medium-chain fatty alcohol, decanol, within these inorganic minerals, produced a range of emergent 3 dimensions structures at both macroscopic and microscopic scales. Fatty alcohols can be considered plausible prebiotic amphiphiles that might have assisted the formation of protocellular structures such as vesicles. The experiments presented herein show that neither chemical gardens nor decanol alone promote vesicle formation, but chemical gardens grown in the presence of decanol, which is then integrated into inorganic mineral structures, support vesicle formation. These observations suggest that the interaction of fatty alcohols and inorganic mineral structures could have played an important role in the emergence of protocells, yielding support for the evolution of living cells.

Alkanes as Membrane Regulators of the Response of Early Membranes to Extreme Temperatures

One of the first steps in the origin of life was the formation of a membrane, a physical boundary that allowed the retention of molecules in concentrated solutions. The proto-membrane was likely formed by self-assembly of simple readily available amphiphiles, such as short-chain fatty acids and alcohols. In the commonly accepted scenario that life originated near hydrothermal systems, how these very simple membrane bilayers could be stable enough in time remains a debated issue. We used various complementary techniques such as dynamic light scattering, small angle neutron scattering, neutron spin-echo spectroscopy, and Fourier-transform infrared spectroscopy to explore the stability of a novel protomembrane system in which the insertion of alkanes in the midplane is proposed to shift membrane stability to higher temperatures, pH, and hydrostatic pressures. We show that, in absence of alkanes, protomembranes transition into lipid droplets when temperature increases; while in presence of alkanes, membranes persist for longer times in a concentration-dependent manner. Proto-membranes containing alkanes are stable at higher temperatures and for longer times, have a higher bending rigidity, and can revert more easily to their initial state upon temperature variations. Hence, the presence of membrane intercalating alkanes could explain how the first membranes could resist the harsh and changing environment of the hydrothermal systems. Furthermore, modulating the quantity of alkanes in the first membranes appears as a possible strategy to adapt the proto-membrane behavior according to temperature fluctuations, and it offers a first glimpse into the evolution of the first membranes.

Hydrocarbon Desaturation in Cyanobacterial Thylakoid Membranes Is Linked With Acclimation to Suboptimal Growth Temperatures

The ability to produce medium chain length aliphatic hydrocarbons is strictly conserved in all photosynthetic cyanobacteria, but the molecular function and biological significance of these compounds still remain poorly understood. This study gives a detailed view to the changes in intracellular hydrocarbon chain saturation in response to different growth temperatures and osmotic stress, and the associated physiological effects in the model cyanobacterium Synechocystis sp. PCC 6803. We show that the ratio between the representative hydrocarbons, saturated heptadecane and desaturated heptadecene, is reduced upon transition from 38°C toward 15°C, while the total content is not much altered. In parallel, it appears that in the hydrocarbon-deficient ∆ado (aldehyde deformylating oxygenase) mutant, phenotypic and metabolic changes become more evident under suboptimal temperatures. These include hindered growth, accumulation of polyhydroxybutyrate, altered pigment profile, restricted phycobilisome movement, and ultimately reduced CO2 uptake and oxygen evolution in the ∆ado strain as compared to Synechocystis wild type. The hydrocarbons are present in relatively low amounts and expected to interact with other nonpolar cellular components, including the hydrophobic part of the membrane lipids. We hypothesize that the function of the aliphatic chains is specifically associated with local fluidity effects of the thylakoid membrane, which may be required for the optimal movement of the integral components of the photosynthetic machinery. The findings support earlier studies and expand our understanding of the biological role of aliphatic hydrocarbons in acclimation to low temperature in cyanobacteria and link the proposed role in the thylakoid membrane to changes in photosynthetic performance, central carbon metabolism, and cell growth, which need to be effectively fine-tuned under alternating conditions in nature.

Characterisation of a synthetic Archeal membrane reveals a possible new adaptation route to extreme conditions

It has been proposed that adaptation to high temperature involved the synthesis of monolayer-forming ether phospholipids. Recently, a novel membrane architecture was proposed to explain the membrane stability in polyextremophiles unable to synthesize such lipids, in which apolar polyisoprenoids populate the bilayer midplane and modify its physico-chemistry, extending its stability domain. Here, we have studied the effect of the apolar polyisoprenoid squalane on a model membrane analogue using neutron diffraction, SAXS and fluorescence spectroscopy. We show that squalane resides inside the bilayer midplane, extends its stability domain, reduces its permeability to protons but increases that of water, and induces a negative curvature in the membrane, allowing the transition to novel non-lamellar phases. This membrane architecture can be transposed to early membranes and could help explain their emergence and temperature tolerance if life originated near hydrothermal vents. Transposed to the archaeal bilayer, this membrane architecture could explain the tolerance to high temperature in hyperthermophiles which grow at temperatures over 100 °C while having a membrane bilayer. The induction of a negative curvature to the membrane could also facilitate crucial cell functions that require high bending membranes.