Haloarchaea as Promising Chassis to Green Chemistry.

Climate change and the scarcity of primary resources are driving the development of new, more renewable and environmentally friendly industrial processes. As part of this green chemistry approach, extremozymes (extreme microbial enzymes) can be used to replace all or part of the chemical synthesis stages of traditional industrial processes. At present, the production of these enzymes is limited by the cellular chassis available.

Phytoplanktonic species in the haloalkaline Lake Dziani Dzaha select their archaeal microbiome.

Microorganisms are key contributors of aquatic biogeochemical cycles but their microscale ecology remains largely unexplored, especially interactions occurring between phytoplankton and microorganisms in the phycosphere, that is the region immediately surrounding phytoplankton cells. The current study aimed to provide evidence of the phycosphere taking advantage of a unique hypersaline, hyperalkaline ecosystem, Lake Dziani Dzaha (Mayotte), where two phytoplanktonic species permanently co-dominate: a cyanobacterium, Arthrospira fusiformis, and a green microalga, Picocystis salinarum. To assay phycospheric microbial diversity from in situ sampling, we set up a flow cytometry cell-sorting methodology for both phytoplanktonic populations, coupled with metabarcoding and comparative microbiome diversity.

sp. nov., isolated from nodules of a wide range of native legumes across the Australian continent.

Bradyrhizobia are particularly abundant in Australia, where they nodulate native legumes growing in the acidic and seasonally dry soils that predominate in these environments. They are essential to Australian ecosystems by helping legumes to compensate for nutrient deficiencies and the low fertility of Australian soils. During a survey of Australian native rhizobial communities in 1994-1995, several genospecies were identified, among which genospecies B appeared to be present in various edaphic and climatic conditions and associate with a large range of leguminous hosts across the whole continent.

Molecular Rearrangements in Protomembrane Models Probed by Laurdan Fluorescence.

Lipid membranes are a key component of living systems and have been essential to the origin of life. One hypothesis for the origin of life assumes the existence of protomembranes with ancient lipids formed by Fischer-Tropsch synthesis. We determined the mesophase structure and fluidity of a prototypical decanoic (capric) acid-based system, a fatty acid with a chain length of 10 carbons, and a lipid system consisting of a 1:1 mixture of capric acid with a fatty alcohol of equal chain length (C10 mix).

The Exploration of the Lipidome Reveals the Widest Variety of Phosphoglycolipids in Thermococcales.

One of the most distinctive characteristics of archaea is their unique lipids. While the general nature of archaeal lipids has been linked to their tolerance to extreme conditions, little is known about the diversity of lipidic structures archaea are able to synthesize, which hinders the elucidation of the physicochemical properties of their cell membrane. In an effort to widen the known lipid repertoire of the piezophilic and hyperthermophilic model archaeon , we comprehensively characterized its intact polar lipid (IPL), core lipid (CL), and polar head group compositions using a combination of cutting-edge liquid chromatography and mass spectrometric ionization systems.

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.

Membrane adaptation in the hyperthermophilic archaeon Pyrococcus furiosus relies upon a novel strategy involving glycerol monoalkyl glycerol tetraether lipids.

Microbes preserve membrane functionality under fluctuating environmental conditions by modulating their membrane lipid composition. Although several studies have documented membrane adaptations in Archaea, the influence of most biotic and abiotic factors on archaeal lipid compositions remains underexplored. Here, we studied the influence of temperature, pH, salinity, the presence/absence of elemental sulfur, the carbon source and the genetic background on the lipid core composition of the hyperthermophilic neutrophilic marine archaeon Pyrococcus furiosus.

Acid Hydrolysis for the Extraction of Archaeal Core Lipids and HPLC-MS Analysis.

Lipid membranes are essential cellular elements as they provide cellular integrity and selective permeability under a broad range of environmental settings upon cell growth. In particular, Archaea are commonly recognized for their tolerance to extreme conditions, which is now widely accepted to stem from the unique structure of their lipids. While enhancing the stability of the archaeal cell membrane, the exceptional properties of archaeal lipids also hinder their extraction using regular procedures initially developed for bacterial and eukaryotic lipids.

Non-Polar Lipids as Regulators of Membrane Properties in Archaeal Lipid Bilayer Mimics.

The modification of archaeal lipid bilayer properties by the insertion of apolar molecules in the lipid bilayer midplane has been proposed to support cell membrane adaptation to extreme environmental conditions of temperature and hydrostatic pressure. In this work, we characterize the insertion effects of the apolar polyisoprenoid squalane on the permeability and fluidity of archaeal model membrane bilayers, composed of lipid analogues. We have monitored large molecule and proton permeability and Laurdan generalized polarization from lipid vesicles as a function of temperature and hydrostatic pressure.

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.

Complete Genome Sequence of sp. Strain BDV5419, Representative of Australian Genospecies L.

We report the complete genome sequence of sp. strain BDV5419, representative of genospecies L, which symbiotically associates with the Australian native legume and is expected to represent a novel species. The complete genome sequence provides a genetic reference for this Australian genospecies.

Complete Genome Sequence of sp. Strain BDV5040, Representative of Widespread Genospecies B in Australia.

We report the complete genome sequence of sp. strain BDV5040, representative of genospecies B, which symbiotically associates with legume hosts belonging to all three Fabaceae subfamilies across the Australian continent. The complete genome sequence provides a genetic reference for this Australian genospecies.

Apolar Polyisoprenoids Located in the Midplane of the Bilayer Regulate the Response of an Archaeal-Like Membrane to High Temperature and Pressure.

Archaea are known to inhabit some of the most extreme environments on Earth. The ability of archaea possessing membrane bilayers to adapt to high temperature (>85°C) and high pressure (>1,000 bar) environments is proposed to be due to the presence of apolar polyisoprenoids at the midplane of the bilayer. In this work, we study the response of this novel membrane architecture to both high temperature and high hydrostatic pressure using neutron diffraction.

High-Temperature Behavior of Early Life Membrane Models.

Origin of life scenarios generally assume an onset of cell formation in terrestrial hot springs or in the deep oceans close to hot vents, where energy was available for non-enzymatic reactions. Membranes of the protocells had therefore to withstand extreme conditions different from what is found on the Earth surface today. We present here an exhaustive study of temperature stability up to 80 °C of vesicles formed by a mixture of short-chain fatty acids and alcohols, which are plausible candidates for membranes permitting the compartmentalization of protocells.

New Insights Into DNA Repair Revealed by NucS Endonucleases From Hyperthermophilic Archaea.

Hyperthermophilic Archaea (HA) thrive in high temperature environments and their genome is facing severe stability challenge due to the increased DNA damage levels caused by high temperature. Surprisingly, HA display spontaneous mutation frequencies similar to mesophilic microorganisms, thereby indicating that the former must possess more efficient DNA repair systems than the latter to counteract the potentially enhanced mutation rates under the harsher environment. Although a few repair proteins or enzymes from HA have been biochemically and structurally characterized, the molecular mechanisms of DNA repair of HA remain largely unknown.

Novel Intact Polar and Core Lipid Compositions in the Model Species, and , Reveal the Largest Lipid Diversity Amongst Thermococcales.

Elucidating the lipidome of Archaea is essential to understand their tolerance to extreme environmental conditions. Previous characterizations of the lipid composition of species, a model genus of hyperthermophilic archaea belonging to the Thermococcales order, led to conflicting results, which hindered the comprehension of their membrane structure and the putative adaptive role of their lipids. In an effort to clarify the lipid composition data of the genus, we thoroughly investigated the distribution of both the core lipids (CL) and intact polar lipids (IPL) of the model and, for the first time, of , the sole obligate piezophilic hyperthermophilic archaeon known to date.

In Search for the Membrane Regulators of Archaea.

Membrane regulators such as sterols and hopanoids play a major role in the physiological and physicochemical adaptation of the different plasmic membranes in Eukarya and Bacteria. They are key to the functionalization and the spatialization of the membrane, and therefore indispensable for the cell cycle. No archaeon has been found to be able to synthesize sterols or hopanoids to date.

Complete Genome Sequences of 11 Type Species from the Genus of Hyperthermophilic and Piezophilic Archaea.

We report here the genome sequences of the type strains of the species , , , , , , , , , and , as well as the prototype of a possible type strain of a novel species, strain P6.

Complete Genome Sequence of the Hyperthermophilic Piezophilic Archaeon NCB100 Isolated from the Rebecca's Roost Hydrothermal Vent in the Guaymas Basin.

Members of the order are common inhabitants of high-temperature hydrothermal vent systems (black smokers) that are represented in clone libraries mostly by isolates from the genus. We report the complete sequence of a novel species from the genus, strain NCB100, which has been isolated from a flange fragment of the Rebecca's Roost hydrothermal vent system in the Guaymas Basin.

Membrane homeoviscous adaptation in the piezo-hyperthermophilic archaeon Thermococcus barophilus.

The archaeon Thermococcus barophilus, one of the most extreme members of hyperthermophilic piezophiles known thus far, is able to grow at temperatures up to 103°C and pressures up to 80 MPa. We analyzed the membrane lipids of T. barophilus by high performance liquid chromatography-mass spectrometry as a function of pressure and temperature.

Homeoviscous Adaptation of Membranes in Archaea.

Because membranes play a central role in regulating fluxes inward and outward from the cells, maintaining the appropriate structure of the membrane is crucial to maintain cellular integrity and functions. Microbes often face contrasted and fluctuating environmental conditions, to which they need to adapt or die. Membrane adaptation is achieved by a modification of the membrane lipid composition, a strategy termed homeoviscous adaptation.