Question

What is a chemolithotroph? How does a lithotroph get energy? Explain how the electron transport chain of the lithotrophs works: describe specifically how it is used to extract energy and reducing power from H,, HS and from Fe 2. Include drawings. What types of environments do these organisms tend to live in? How efficient is their metabolism, relative to organotrophs? Bonus: Give the genus and species name of one organism of each type: hydrogen oxidizer, sulfide oxidizer, and iron oxidizer.

please answer in detailed explanation!

Answer 1

• Chemolithotrophs- These are microbes that obtain electrons for electron transport chain from the oxidation of inorganic molecules.
  
• Their sources of energy are hydrogen, reduced nitrogen compounds, reduced sulfur compounds, and ferrous iron.

AG" (kcal/mole) I - 56.6 -17.4 H₂ + 2 2 02 H2O NO2 + 1 2 + NO3- NH + 150, +NO + H2O + 2H+ So + 1 O2 + H2O H₂804 - 65.0 -118.5 S202 - +202 + H₂O 2504²- + 2H+ - 223.7 - 11.2 2Fe2+ + 2H+ + IO2 + 2Fe 3+ +H2O

Chemolithotrophs remove electrons from a substrate (oxidized in the cell) that is put into respiratory chains and enters into electron transport chain that will produce ATP by phosphorylation. Electron acceptor is mostly Oxygen.

Energy yield is always lower than a glucose molecule because NADH that donates electrons has more negative reduction potential. In oxidative phosphorylation, P: O ratio is 1.0. Since less ATP is produced, large amount of organic material needs to be oxidized for energy needs.

Autotrophic chemolithotrophs fix CO₂ into carbohydrates for which it requires 3 ATP and 2 NADPH for every molecule fixed.

Inorganic energy é and cedron source Electron transport I chain L PME ATPT osudative phosphorylation e CNADPH) ATP I Carbon source Coften CO₂) ADP+P; - Biosynthesis

Hydrgen Oxidation:

Hydrogen oxidizing bacteria oxidize hydrogen

They grow under microaerophilic conditions because the hydrogenase enzyme that is used in hydrogen oxidation is inhibited by oxygen, but oxygen is still a terminal electron acceptor. Hydrogen (H₂) can be used as a source of energy both anaerobically and aerobically. Aerobically, membrane bound hydrogenase oxidizes hydrogen, pumping out protons by electron transfer to various cytochromes and quinones.

In many other, a second cytoplasmic hydrogenase generates NADH, that fixes carbon dioxide through Calvin Cycle.

Sulfur Oxidation:

Sulfur oxidation uses oxidation of reduced sulfur compounds such as sulfide (H₂S), inorganic sulfur (S₀), and thiosulfate (S₂O₂⁻³) to form sulfuric acid (H₂SO₄).

Inorganic sulfur being stored either inside or outside of the cell until needed.

It is a two step process occurs because sulfide is a better electron donor than inorganic sulfur or thiosulfate. A greater number of protons are translocated across the membrane. Sulfur-oxidizing organisms use reverse electron flow to generate reducing power for carbon dioxide fixation via the Calvin cycle—a process in which electrons are pushed against their thermodynamic gradient to produce NADH. In biochemical terms, enzyme sulfite oxidase is used to convert reduced sulfur compounds to sulfite (SO₂⁻³) and, sulfate (SO₂⁻⁴).

SULPHUR - OXIDISING BACTERIA Li Direct oxidation of sulfite : So rulfite oxidase SO² + 2e i) Formation of adenosine s' phosphoulfate : 250 2- + ZAMP QAPS + 2Pi 2AD 250,2- +AMP + 2 Pi - 2ApS + 46 2ADP + 2004- AMP + ATP 250,- + ATP + 4e" 2H₂S + O₂ - Sulfide 25 + 2H₂O onidation

Iron Oxidation:

Ferric iron (Fe³⁺) is a well-known anaerobic terminal electron acceptor. Electron flow makes use of ferric iron reductase ending in oxygen or nitrate.

Ferrous iron is a soluble form of iron that is stable at extremely low pHs or under anaerobic conditions. Ferrous iron is oxidized immediately to the ferric (Fe³⁺) form and is hydrolyzed abiotically to insoluble ferric hydroxide (Fe(OH)₃) at low pH and aerobic conditions.

Acidophiles, eg., Acidithiobacillus ferrooxidans oxidize iron at low pH acidic environments..

Microaerophiles- that live at the oxic-anoxic interfaces oxidizes ferrous iron at cirum-neutral pH. These micro-organisms example., Gallionella ferruginea

Anaerobic photosynthetic bacteria eg., Rhodopseudomonas, use ferrous iron to produce NADH for autotrophic carbon dioxide fixation by the use of enzyme rusticyanin.

• Lithotrophs live in waste water, volcanoes, deep sea ocean vents, the atmosphere, mines, seawater, fresh water.
• Lithotrophs derive energy from inorganic compounds whereas organotrophs obtain them from organic compounds, which allows lithotrophs to be used for bioremediation purposes due to their reverse electron flow process.

Hydrogen Oxidizer: Hydrogenobacter thermophilus

Sulfide Oxidizer: Halothiobacillus neapolitanus

Iron Oxidizer: Shewanella putrefaciens