Lecture 7 - The Archaea

what are archaea?

• these are very simple cells; hence they look like bacteria under the microscope

• Not membrane-bound in the nucleus (the chromosome)

• they have no nucleus and a circular chromosome

• they have the same structure as bacteria

archaea vs bacteria

• archaea and bacteria diverged and formed separate domains

archaea cell morphology

• Round shaped (cocci with flagella)

• Rod shaped (short bacillus)

• Lobed cocci

• Squared

• filamentous

archaea cell wall composition considerably varies. explain how

• polysaccharides

• protein

• glycoproteins - protein with sugar molecules attached. e.g. halococcus salifodiniae

• so they contain a mixture of all these macromolecules

• no cell wall

• contain methanochondtiotin e.g. methanosarcina barker

what do archaeal cell walls not contain

peptidoglycan

methanochondriotin

this is found in cartilage. it is very tough and is found in archaea, giving them a tough cell wall

pseudomurein vs peptidoglycan

• pseudomurein is structurally similar to peptidoglycan, although contains some significant differences

• Peptidoglycan - long sugar molecules; polymers of them

• Pseudomurein - consists of a different sugar, hence different compounds are formed. it is also insensitive to penicillin

s-layer

• this is the most common cell wall in archaea

• it is a crystalline structure of proteins or glycoproteins. it can also accompany other cell wall components

how are archaeal cell membranes unique?

• bonded by ether linkages and some by ester linkages

• the lipid tail is not a fatty acid and these tails vary in structure

• an ether linkage bonds the lipid tail and glycerol

• the lipids can form monolayers and impart distinct membrane properties

what are lipid monolayers?

 

a single, one-molecule-thick film of amphiphilic lipid molecules that forms at an interface

hami

• these are pill-like structures used for attachment

• Uses these hooks to pull itself towards whatever it wants to go to

• Used to attached to each other or to other cells, forming a biofilm

archaella

• the archaea have unique flagella

• these rotate to drive mobility

• they are smaller than bacterial flagella

how do archaea reproduce?

binary fission

archaeal metabolism diversity

• aerobic

• anaerobic

• phototrophic (simply using energy from the sunlight - no photosynthesis nor CO2 fixation(

extremophiles - the 3 types

• hyperthermophiles

• methanogens

• extreme halophiles

these were originally identified in extreme environments

note that not all archaea are extremophiles

halophile habitat and structure

• salt lakes, fish, salted food

• they require 9-32% NaCl for growth

• they are resistant to high salt concentrations

• the halophile cytoplasm is osmotically balanced

how is halophile cytoplasm osmotically balanced?

• K+ cations are accumulated and imported, which balances the osmotic forces (cell concentration) and maintains cell water content (hence preventing it from dehydrating)

halophile cell structure

• contains a glycoprotein cell wall, which is complexed with Na+ cations

• this is required for cell wall integrity

more types of extremophiles

• thermophiles and hyperthermophiles (growth optima is >100 degrees + found on the inner walls of submarine volcanic habitats)

• psychrophiles - found in cold regions

• barophiles - found at the bottom of the ocean and are resistant to extreme pressures

growth optima

archaea have a high optimal growth temperature

autoclaving

• all microorganisms will be destroyed under certain conditions

• they kill endospores after 15 mins at 121 degrees celsius

• Hence it's the most optimal and utilised sterilisation method

are archaea pathogenic?

no