Metabolism of Extremophiles

Transcription

1 1 Microbial Metabolism Metabolism of Extremophiles Ching-Tsan Huang ( 黃慶璨 ) Office: Agronomy Building, Room 111 Tel: (02) cthuang@ntu.edu.tw

2 Extremophiles 2 Definition Inhabit some of earth's most hostile environments of temperature (-2ºC to 15ºC and 60ºC to 120ºC) salinity (3-5 M NaCl) ph (<4 and >9) pressure (>400 atmospheres).

3 Halophiles Thermophiles 3 Extreme Acidophiles

4 Diverse Environments 4

5 Enzyme activity Extreme Temperatures 5 Classification Psychrophile 0 ~ 20 o C Mesophile 20 ~ 40 o C Thermophile 40 ~ 80 o C Hyperthermophile > 80 o C Microbial growth at high temperature Increase proportion of saturated lipids in membranes Increase enzyme stability under high temperatures Effect of temperature on microbial activities Too high disintegrate the cell membranes Too low freeze or gel the cell membranes In general, the Q 10 for enzyme is near o C Temperature Q 10

6 Atmospheric pressure Extreme Pressure Change in atmosphere pressure Microbial activity Extremely low AP Water evaporation Oxygen limitation Hydrostatic pressure Hydrostatic pressure increases 1 atm for every 10 m of depth. 1 ~ 400 atm has no or little effect on microbial activity. Barotolerant and Barophilic Osmotic pressure Hypertonic habitats water move into microbial cells expand and rupture cells Hypotonic habitats water move out microbial cells dehydrate and shrivel cells Osmotolerant and Osmophilic 6

7 Extreme Saline Salinity Affect osmotic pressure Denature proteins by disrupt the tertiary structure Dehydrate cells Halotolerant and halophilic Achieve osmotic pressure balance with high intracellular concentration of glycerol or potassium chloride. Water activity The amount of water actually available for microbial use Depends on the number of moles of water and solute, as well as the activity coefficients for water the particular solute. Water Holding Capacity (WHC) Aerobic soil microorganisms: 50 ~ 70% WHC c.a ~ 0.99 aw 7

8 Ionizing radiation rays and x-rays Radiation radio waves low levels of irradiation mutation high dose destroy nucleic acids and enzymes cell death Ultraviolet radiation 260 nm: the most germicidal wavelength the adsorption maximum of DNA UV-induce dimerization Visible light radiation Wavelength increase g rays x-rays UV light visible light infrared microwaves Energy increase 8

9 9 Characteristics of Archaea Cell walls: lack peptidoglycan (like eukaryotes). Fatty acids: the archaea have ether bonds connecting fatty acids to molecules of glycerol. Complexity of RNA polymerase: both archaea and eukaryotes have multiple RNA polymerases that contain multiple polypeptides. Protein synthesis: various features of protein synthesis in the archaea are similar to those of eukaryotes but not of bacteria. Metabolism: various types of metabolism exist in both archaea and bacteria that do not exist in eukaryotes Methanogenesis occurs only in the domain Archaea.

10 10 Archaeal Cell Walls can stain gram positive or gram negative Stains positive often thick homogeneous layer Stains negative often surface layer of protein or glycoprotein lack muramic acid lack D-amino acids resistant to lysozyme and b-lactam antibiotics some contain pseudomurein peptidoglycan-like polymer others contain other polysaccharides, proteins or glycoproteins

11 Archaeal Lipids and Membranes 11 Bacteria/Eucaryotes fatty acids attached to glycerol by ester linkages Archaea branched chain hydrocarbons attached to glycerol by ether linkages some have diglycerol tetraethers

12 12 Genetics and Molecular Biology Chromosomes one chromosome per cell closed circular double-stranded DNA generally smaller than bacterial chromosomes Have few plasmids mrnas may be polygenic, no evidence of splicing trnas contain modified bases not found in bacterial or eukaryotic trnas Ribosomes 70S, shapes differ from bacteria and eukaryotes

13 Metabolism 13 Extreme Halophiles Thermophiles use modified Entner-Doudoroff for glucose catabolism Methanogens do not catabolize glucose significantly pyruvate acetyl CoA catalyzed by pyruvate oxidoreductase use reverse Embden- Meyerhoff for gluconeogenesis functional TCA cycle have respiratory chains no TCA cycle no respiratory chains use reverse Embden- Meyerhoff for gluconeogenesis biosynthetic pathways similar to those of other organisms some fix nitrogen some use glycogen as major reserve material some use glycogen as major reserve material

14 14 ED: Entner-Doudoroff EM: Embden-Meyerhof

15 Glucose degradation via the EMP pathway known for most Bacteria and Eukarya (classical) and the modified EMP versions reported for Archaea. Bräsen C et al. Microbiol. Mol. Biol. Rev. 2014;78:89-175

16 Taxonomy 16

17 17 Crenarchaeota Most are extremely thermophilic Many are acidophiles Many are sulfur-dependent for some, used as electron acceptor in anaerobic respiration for some, used as electron source (chemolithotrophs) Almost all are strict anaerobes Grow in geothermally heated water or soils that contain elemental sulfur Include organotrophs and lithotrophs (sulfur-oxidizing and hydrogen-oxidizing)

18 Euryarchaeota Methanogens anaerobic environments rich in organic mater e.g. animal rumens, anaerobic sludge digesters Halobacteria aerobic, respiratory, chemoheterotrophs with complex nutritional requirements Thermoplasms Thermoacidophiles, lack cell walls Extremely thermophilic S o -metabolizers optimum growth temperatures C strictly anaerobic; reduce sulfur to sulfide; motile by flagella Sulfate-reducers extremely thermophilic, irregular coccoid cells use sulfate, sulfite, or thiosulfite as electron acceptor 18

19 19 Methanogenesis From CO 2 From methyl compound From acetate CH 4 CH 4 CH 4

20 Sulfate reduction