Archaea Cell Biology PDF

2-8: Unique aspects of Archaea cell biology Lecture Overview: • Overview of archaea cell biology and how it differs (or is similar to) bacteria, archaea cell membranes, archaea cell walls, archaea flagella/surface appendages. • Asgard archaea….our distant relatives? • Textbook: Chapter 2 What’s th...

2-8: Unique aspects of Archaea cell biology Lecture Overview: • Overview of archaea cell biology and how it differs (or is similar to) bacteria, archaea cell membranes, archaea cell walls, archaea flagella/surface appendages. • Asgard archaea….our distant relatives? • Textbook: Chapter 2 What’s the difference between Bacteria and Archaea?? o Similar in some superficial (and important) ways - prokaryotes, usually single cell, overall similar sizes/morphologies o Evolutionarily, Archaea domain shares a more recent common ancestor with Eukarya than with Bacteria o Fundamental aspects of the cell biology differ o Archaea DNA-related biology/processes (chromosome structure, replication, transcription, translation) more similar to eukaryotes than to bacteria o There is a lot we don’t yet know about archaea – most have not been isolated and cultured, only known via environmental DNA sequencing Unique cell membranes of Archaea (see next slide) o Bacteria/Eukarya – ester-linked lipids. Archaea – ether-linked o Bacteria/Eukarya – Lipids are fatty acids. Archaea – isoprenoid o Archaea lipids contain side branches and rings o Some archaea produce transmembrane phospholipids - a lipid monolayer – similar to bilayer, but lipid tails are joined o Archaea’s unique membrane structure is thought to be important for its ability to survive harsh environments. More robust structure. Archaea membrane structures Bacteria (reminder) Textbook figs 2.1 & 2.3 Archaea: Cell walls o Variation in how the cell wall is put together depending upon the environmental niche o For majority of archaea – proteinaceous S-layers act as the cell wall (in bacteria, S-layers act as supplementary structures…not generally thought of as part of the cell wall) o Other archaea use variable proteinaceous or carbohydrate structures o Rare archaea have a second membrane (nothing link LPScontaining membrane of Gram-negative bacteria) o A few archaea lack a cell wall altogether. For others, cell envelope not yet characterized/understood. Archaeal cell walls - Pseudomurein o A small subset of Archaea produce a cell wall that is similar to bacterial cell walls o Made of a similar polymer called pseudomurein. Lacks D-amino acids, different sugar linkage, NAM replaced with N-acetyltalosainuronic acid. o Remarkably, thought to have evolved independently from peptidoglycan synthesis!! Peptidoglycan reminder (all bacterial cell walls) Pseudomurein produced by certain archaea Unique archaea appendages o Some unique appendages have been found in some archaea o This includes the hamus (hami, plural) – fix cells to a surface or to other cells to mediate biofilm formation o Proteinaceous “grappling hook” Textbook Fig 2.19 Archaea motility - archaellum o Archaea swimming motility via an analogous flagellum-like apparatus (but functionally/ evolutionarily distinct) o Propeller-like appendage that sticks out, rotation by a motor drives movement – also can be chemotactic. o Simpler - fewer proteins. Driven by ATP hydrolysis (not PMF) o Filament built from inside out (opposite of flagellum filament). Related to (evolved from?) Type IV pilus o Generally (not always) archaea swim more slowly than bacteria. Textbook Fig 2.19 An unusual (or typical?) archaea: Haloquadratum walsbyi • Extreme halophile found in hyper-saline lakes with saturating salt concentrations – requires ~4x [salt] in seawater to grow • First identified in 1980…took ~25 years to culture in lab • (commonly produces PHA granules and gas vesicles) • Very unique morphology – very thin squares. High surface to volume ratio. Zenke et al, Front. Microbio., 2015 Evolution of Eukarya: The endosymbiotic theory What do we know about this archaeal organism? ⍺-Proteobacterium Textbook Fig. 13.10 Asgard archaea Nature, 2015 Identification of the first “Asgard archaea” – archaea the appear to bridge the gap between archaea & eukaryotes “missing link” Nature, 2017 Identification of an expanded collection of Asgard archaea – many new “eukaryotic” functions/complexity Nature, 2020 Culturing an Asgard archaea in the lab. Took 12 years of culturing/ enrichment. Doubling time > 2 weeks (<30 mins for E. coli) Asgard archaea • Superphylum of Archaea – multiple distinct sub-phyla have been identified (genome sequenced). Lokiarchaeota was first. • Found in anaerobic marine sediments • Contain many Eukaryote-specific proteins – show signs of eukaryote-like cell biology features (such as vesicle trafficking) • Some phylogenetic trees place Eukarya within Archaea lineage…are we just a branch of the Archaea domain of life? ZarembaNiedzwiedzka et al, Nature, 2017 Asgard archaea • Superphylum of Archaea – multiple distinct sub-phyla have been identified (genome sequenced). Lokiarchaeota was first. • Found in anaerobic marine sediments • Contain many Eukaryote-specific proteins – show signs of eukaryote-like cell biology features (such as vesicle trafficking) • Some phylogenetic trees place Eukarya within Archaea lineage…are we just a branch of the Archaea domain of life? ZarembaNiedzwiedzka et al, Nature, 2017