Achaea

Figure 19.2 3

Figure 19.5 6

Crenarchaeota The name Crenarchaeota means “scalloped archaea.” - Are often irregular in shape All crenarchaeotes synthesize a distinctive tetraether lipid, called crenarchaeol. Figure 19.6 7

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 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 9

Crenarchaeota Sulfolobales - Include species that respire by oxidizing sulfur (instead of reducing it) - Found within hot springs - Sulfolobus solfataricus - A “double extremophile” - Grows at 80oC and pH 3 - Oxidizes H2S to sulfuric acid Figure 19.13 10

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 11

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 12

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 13

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 14

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 15

Great Salt Lake

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 17

Figure 19.31 18

Click box to launch animation Retinal-Based Photoheterotrophy Animation: Light-Driven Ion Pumps and Sensors Click box to launch animation

Halophilic prokaryotes

Halobacterium selinarum

H. salinarum glycoprotein cell wall

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 24