How bacteria made this Planet Habitable for Humans. Sergio Sañudo Wilhelmy University of Southern California

Transcription

1 How bacteria made this Planet Habitable for Humans Sergio Sañudo Wilhelmy University of Southern California

2 What I m going to tell you How important is a group of bacteria that makes possible human life on this planet by: Producing bio available nitrogen Producing dissolved oxygen

3 The Central Dogma Information is stored in DNA (gives directions) The information in DNA is copied into RNA (delivers the message) The information in RNA guides the production of Proteins that do ALL the work

4 Why central dogma?

5 What are proteins? Although genes get a lot of attention, it s the proteins that perform most life functions and even make up the majority of cellular structures. Proteins are large, complex molecules made up of smaller subunits called amino acids. Chemical properties that distinguish the 20 different amino acids cause the protein chains to fold up into specific three dimensional structures that define their particular functions in the cell.

6 Aminoacids

7 How many proteins? So far, biochemists have identified more than 875,000 proteins and the three dimensional shape of 7,000. The longest human protein is Titin with 34,350 amino acids. It is the protein that keeps your heart beating. We don t know yet how many proteins are in the human body.

8 From amino acids to proteins Titin 34,500 amino acids

9 The relevance of Nitrogen Human Oxygen 65.0 Carbon 18.5 Hydrogen 9.5 Nitrogen 3.3 Calcium 2.0 Phosphorous 1.1 Potassium 0.35 Sulfur 0.25 Sodium 0.15 Chlorine 0.15 Magnesium 0.05 Iron Iodine The proportions by mass of different elements

10 Where is the Nitrogen needed for Protein synthesis? Human Oxygen 65.0 Carbon 18.5 Hydrogen 9.5 Nitrogen 3.3 Calcium 2.0 Phosphorous 1.1 Potassium 0.35 Sulfur 0.25 Sodium 0.15 Chlorine 0.15 Magnesium 0.05 Iron Iodine Seawater Oxygen 88.3 Hydrogen 11.0 Chlorine 1.9 Sodium 1.1 Magnesium 0.1 Sulfur 0.09 Potassium 0.04 Calcium 0.04 Carbon Silicon Nitrogen Strontium Nitrogen 78% Oxygen 21% Other 1% Earth s Crust Oxygen 46.6 Silicon 27.7 Aluminum 8.1 Iron 5.0 Calcium 3.6 Sodium 2.8 Potassium 2.6 Magnesium 2.1 Other 1.5 elements

11 But we don t breathe Nitrogen Nitrogen 78% Oxygen 21% Other 1% Nitrogen fixation, the transformation of N 2 (gas) to a biologically useful form is often touted as the great evolutionary invention that allowed life to prosper on Earth

12 Abiotic Nitrogen Fixation N N + 2 CO 2 Lightning 2 NO + 2 CO Nitrogen gas Fixed Nitrogen

13 The Organism that Made it all possible Only a small group of cyanobacteria called diazotrophs can fix Nitrogen

14 Evolution of Nitrogenases

15 Cyanobacteria

16 Nitrogen fixation estimates Estimates of global ocean nitrogen fixation range from 60 to 200 million metric tons of N per year

17 How is the nitrogen returned to the atmosphere?

18 Importance of Denitrification Bacterial denitrification is the reverse process of nitrogen fixation that returns nitrogen to the atmosphere. Without denitrification, N 2 would be completely removed from the atmosphere in only about 20 million years.

19 N2

20 Implications for life on other planets: let s follow the Nitrogen Saturn s moon Titan: Nitrogen 98.4% Methane 2% Frozen water Mars Nitrogen 2.7% CO %

21 Resilience of microorganisms Chroococcidiopsis, one of the most primitive cyanobacteria, and another bacteria, Deinococcus radiodurans, are capable of withstanding up to 1000 times the radiation released in Hiroshima with no loss of viability.

22 How about Intelligent life?

23 The energetic cost of a large brain A large brain requires lots of energy as ATP (adenosine triphosphate). In a human body at rest, ATP molecules are formed and reformed at a rate of about 9 X10 20 molecules per second, equivalent to a turnover rate of 65 kg per day with much higher rates than this during periods of activity. Human brain makes about 2% of the person s weight but it consumes 20% of the body s energy at rest.

24 The energetic cost of a large brain The only element than can produce that much energy is OXYGEN (for typical adult male; 380 liters of O 2 per day or 7600 liters of air per day)

25 Anaerobic versus aerobic energy production Anaerobic metabolism glucose (6C) + 2ADP + 2Pi = 2ATP + 2 lactic acid (3C) + heat Aerobic metabolism glucose (6C) + oxygen + 36ADP + 36Pi = 36ATP + 6CO2 (1C) + heat + water

26 Oxygenic photosynthesis

27 The uniqueness of oxygenic photosynthesis Electrons are transferred from a donor to an acceptor that is reduced down a thermodynamic gradient (they lose energy) Photosynthesis visible solar radiation The energy from the flow of electrons is used to produce a proton gradient across membranes to produce ATP.

28 Evolution of Chlorophylls Another protein containing 17 polypeptides subunits with metal and pigment cofactors and over 45,000 atoms

29 Chlorophylls evolution and non oxygenic photosynthesis Cyanobacteria/Plants have both photosynthetic apparatus and Chlorophyll a

30 Oxygenic Photosynthesis Cyanobacteria From greennon sulfur bacteria (Chloroflexus aurantiacus) From greensulfur bacteria (Chlorobium)

31 Life with Oxygen The utilization of O 2 as a substrate for energy production is not without risk. A fraction of electrons escape the respiratory chain producing toxic oxidants (e.g. superoxide anion) that destroy proteins and DNA.

32 Evolution of Superoxide Dismutases Superoxide dismutases converts the superoxide anion radical into hydrogen peroxide and oxygen reducing its toxicity.

33 Anybody out there? Our life on the Earth s Surface based on solar energy and photosynthesis may be the exception rather than the rule as it requires liquid water, sunlight and very distinct enzymes formed during several billions of evolution

34 Evolution of metabolic pathways Oxic More complex biochemical networks Anoxic Oxygen is not a prerequisite for life. Anaerobic organisms are still very abundant.

35 The Earth was transformed when cyanobacteria invented photosynthesis Comparison of planetary atmospheres Gas Venus Earth Mars Earth (no life) (life) CO 2 (%) O 2 (%) TP (bars) Surface T( 0 C)

36 Human presence: % of Earth s Life History If All life history can be reduced to 24 hours: Humans have been here for about 4 seconds

37 Some Final Thoughts One of the huge species, Homo sapiens, got remarkably self important. But when, to his surprise, a virus or climate change wiped him out, most of life on Earth took no notice at all.

38 The King of Spain was correct If the Lord Almighty had consulted me before embarking on the Creation, I would have recommended something simpler Alfonso X de Castilla y Leon ( )

39 After all, the Earth is a very unique place because of cyanobacteria

40 END of the talk

41 The uniqueness of oxygenic photosynthesis Photosynthesis Oxidation-removal of electrons: (Oxygen is the most powerful stripper of electrons). Electrons are transferred to an acceptor that is reduced down a thermodynamic gradient (they lose energy) The energy from the flow of electrons is used to produce a proton gradient across membranes to produce ATP.