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This overview delves into the fascinating world of Crenarchaeota and Euryarchaeota, two major groups of archaea known for their extraordinary adaptations. Crenarchaeota, often irregularly shaped, thrive in high temperatures and diverse conditions, producing unique lipids such as crenarchaeol. Key representatives include Desulforococcus mobilis and Sulfolobus solfataricus, which flourish in hot springs and hydrothermal vents. In contrast, Euryarchaeota, predominantly methanogens, inhabit anaerobic environments, contributing to methane production. Their unique biochemistry facilitates survival in diverse habitats, from wetlands to deep-sea sediments.
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Crenarchaeota The name Crenarchaeota means “scalloped archaea.” - Are often irregular in shape All crenarchaeotes synthesize a distinctive tetraether lipid, called crenarchaeol. Figure 19.6
Crenarchaeota Desulfurococcales - Lack cell walls, but have elaborate S-layer - Reduce sulfur at higher temperatures Desulforococcus mobilis - Hot springs Ignicoccus islandicus - Marine organism Figure 19.8
Crenarchaeota Barophilic hyperthermophiles - Grow near hydrothermal vents on the ocean floor - A common feature is the black smoker. - Crenarchaeotes that are vent-adapted: - Pyrodictium abyssi - Pyrodictium occultum Figure 19.9
Crenarchaeota Sulfolobales - Include species that respire by oxidizing sulfur (instead of reducing it) - Found within hotsprings - Sulfolobus solfataricus - A “double extremophile” - Grows at 80oC and pH 3 - Oxidizes H2S to sulfuric acid Figure 19.13
Crenarchaeota The crenarchaeote Cenarchaeum symbiosum inhabits the sponge Axinella mexicana. - The relationship is unclear, but they can be co-cultured in an aquarium for many years. Figure 19.17
Euryarchaeota: Methanogens Euryarchaeota means “broad-ranging archaea.” Are dominated by methanogens - All are poisoned by molecular oxygen and therefore require complete anaerobiosis. - Major substrates and reactions include: Carbon dioxide: CO2 + 4H2→ CH4 + 2H2O Acetic acid: CH3COOH → CH4 + CO2 Methanol: 4CH3OH → 3CH4 + CO2 + 2H2O Methylamine: 4CH3NH2 + 2H2O → 3CH4 + CO2 + 4NH3
Anaerobic Habitats for Methanogens Methanogens grow in: - Anaerobic soil of wetlands - Especially rice paddies - Landfills - Digestive tracts of animals - Termites - Cattle - Humans - Marine benthic sediments Figure 19.22A Figure 19.22B
Biochemistry of Methanogenesis Biochemical pathways of methanogens involve unique cofactors. - These transfer the hydrogens and increasingly reduced carbon to each enzyme in the pathway. Figure 19.25
Biochemistry of Methanogenesis The process fixes CO2 onto the cofactor methanofuran (MFR). - The carbon is then passed stepwise from one cofactor to the next, each time losing an oxygen to form water, or gaining a hydrogen carried by another cofactor. Figure 19.26
Euryarchaeota: Halophiles Main inhabitants of high-salt environments are members of the class Haloarchaea. Figure 19.28 - Their photopigments color salterns, which are used for salt production. - Most are colored red by bacterioruberin, which protects them from light. Halophilic archaea require at least 1.5M NaCl. Figure 19.29B
Animation: Light-Driven Ion Pumps and Sensors Retinal-Based Photoheterotrophy Click box to launch animation
Nanoarchaeota The smallest known euryarchaeotes. Nanoarchaeum equitans - Is an obligate symbiont of the crenarchaeote Ignicoccus hospitalis - Host and symbiont genomes have been sequenced, revealing extensive coevolution. Figure 19.36
