Micr20010 Lecture 6 2024 PDF

MICR20010 Lecture 6 Bacterial Physiology and Metabolic Diversity Dr. Jennifer Mitchell Microbiology School of Biomolecular and Biomedical Science  Lecture 5 Microbial Growth and Physiology Growth of Bacteria – Bacteria Divide by Binary Fi...

MICR20010 Lecture 6 Bacterial Physiology and Metabolic Diversity Dr. Jennifer Mitchell Microbiology School of Biomolecular and Biomedical Science  Lecture 5 Microbial Growth and Physiology Growth of Bacteria – Bacteria Divide by Binary Fission – Growth of Bacteria on Solid Medium – Growth of Bacteria in Liquid Medium Growth Phases of liquid Bacterial Culture Measurements of Bacterial Growth Direct Measurements of Bacterial Growth: Indirect Measurements of Bacterial Growth: Growth Requirements  Learning Outcomes Metabolic diversity Chemical basis of energy production Simplified model of energy production Energy storage and release Chemotrophs Phototrophs Chemotrophs – Chemoorganotrophs – Chemolithotrophs Autotrophs Heterotrophs Photosynthesis  Carbon and Energy All cells need carbon and energy sources for their metabolic activities Different microorganisms have evolved every conceivable means of obtaining carbon and energy This results in significant metabolic diversity Hence microbes have been able to colonise environmental habitats which are too extreme for other life forms. https://www.teagasc.ie/news--events/daily/other/the-soil-microbiome-and-soil-health.php  Chemical Basis of Energy Production 1. Chemical reactions used to generate energy 2. Specifically chemical reactions involving the release of electrons 3. Electrons have stored energy and when an atom or molecule loses that electron (becomes oxidized) that energy is released 4. Oxidation: atom or molecule loses one or more electrons 5. Reduction: atom or molecule gains those electrons. 6. Energy sources are oxidised to release electrons which have stored energy 7. Energy generated is stored in the form of ATP OIL RIG Oxidation Is Loss of electrons Reduction Is Gain of electrons  Simplified Model of Energy Production Light e- e- ATP oxidised Iron Enzymes e- e- e- e- idised s ox yme Glucose Enz Example of simple oxidation reaction: Fe2+ ⇋ Fe3+ + e- Ferrous iron Ferric iron  ENERGY Energy Storage: Used to trap energy released from chemical reactions Energy stored as high-energy phosphate bond Inorganic phosphate group attached to adenosine diphosphate (ADP) Adenosine triphosphate (ATP) The energy currency of the cell Energy Release: Phosphate enzymatically removed from ATP to release energy  How to get Energy? Chemotrophs: Derive energy from chemicals Chemotrophs – Chemoorganotrophs (Use organic chemicals) – Chemolithotrophs (Use inorganic chemicals) Phototrophs – Derive energy from light  Chemoorganotrophs Derive energy from organic chemicals Organic chemicals are compounds containing carbon All cells require carbon as a major nutrient, hence these chemicals are a good source of carbon and energy for chemoorganotrophs 1000’s of different organic chemicals present on Earth ALL can be broken down by microorganisms to derive energy  How do chemoorganotrophs derive energy from organic chemicals? Answer: Oxidation of the compound releases electrons, which are ultimately used to generate ATP. Electrons have stored energy and when an atom or molecule loses that electron (becomes oxidized) that energy is released Oxidation: atom or molecule loses one or more electrons Reduction: atom or molecule gains those electrons. Energy sources are oxidised to release electrons which have stored energy Aerobes Some chemoorganotrophs can only produce energy in the presence of oxygen Anaerobes Microbes that can only produce energy in the absence of oxygen Facultative anaerobes Microbes that produce energy in the presence or absence of oxygen  Methanogens Livestock produce significant amounts of methane as part of their normal digestive processes. Some feed additives can inhibit the microorganisms that produce methane in the rumen and subsequently reduce methane emissions. Ruminant livestock – cattle, sheep, buffalo, goats, deer and camels – have a fore-stomach (or rumen) containing microbes called methanogens, which are capable of digesting coarse plant material and which produce methane as a by-product of digestion (enteric fermentation): this methane is released to the atmosphere by the animal belching. https://www.agric.wa.gov.au/climate-change/carbon-farming-reducing-methane- emissions-cattle-using-feed-additives#:~:text=Feed%20additives%20or%20supplements%20can  Supplements Methane-reducing feed additives and supplements inhibit methanogens in the rumen, and subsequently reduce enteric methane emissions. Methane-reducing feed additives and supplements are most effective when grain, hay or silage is added to the diet, especially in beef feedlots and dairies.  Reducing Methane Methane-reducing feed additives and supplements can be: synthetic chemicals natural supplements and compounds, such as tannins and seaweed fats and oils. Feeding one type of seaweed at 3% of the diet has resulted in up to 80% reduction in methane emissions from cattle.  Active inhibitors trihalomethanes, such as bromoform, which is an active ingredient that decreases methane emissions Tannins  Benefits: The reduced volume of methane formation may lead to better efficiency of feed utilisation, given that methane emissions represent a gross energy loss from feed intake of about 10%.  Chemolithotrophs Derive energy from inorganic chemicals Inorganic chemicals are compounds which do not contain carbon, e.g. H2, H2S, Fe2+ These inorganic compounds are oxidised to release electrons for ATP synthesis However all cells require carbon as a major nutrient  Chemolithotrophs Name Examples Source of energy and electrons Respiration electron acceptor Iron bacteria Acidithiobacillus ferrooxidans Fe2+ (ferrous) → Fe3+ (ferric) + e- O2 → H2O Nitrosifying bacteria Nitrosomonas NH3 (ammonia) → NO2- (nitrite) + e- O2 → H2O Nitrifying bacteria Nitrobacter NO2- (nitrite) → NO3- (nitrate) + e- O2 → H2O Chemotrophic purple sulfur S2 (sulfide) → S0 (sulfur) + e- O2 → H2O bacteria Halothiobacillaceae Sulfur-oxidizing bacteria Chemotrophic S0 (sulfur) → Sulfate (SO2−4) + e- O2 → H2O Rhodobacteraceae Aerobic hydrogen bacteria Cupriavidus metallidurans H2 (hydrogen) → H2O (water) + e- O2 → H2O Thiobacillus denitrificans Thiobacillus denitrificans S0 (sulfur) → Sulfate (SO2−4) + e- NO3- (nitrate) Sulfate-reducing bacteria: H2 (hydrogen) → H2O (water) + e- Sulfate (SO2−4) Hydrogen bacteria Sulfate-reducing bacteria: Desulfotignum PO3−3 (phosphite) → PO3−4 Sulfate (SO2−4) Phosphite bacteria phosphitoxidans (phosphate) + e- Methanogens Archaea H2 → H2O + e- CO2 (carbon dioxide) Carboxydothermus carbon monoxide (CO) → carbon Carboxydotrophic bacteria dioxide (CO2) + e- H2O (water) → H2 (hydrogen) hydrogenoformans  Chemolithotrophs Chemolithotrophs obtain carbon from CO2 – autotrophy Ecological niche and competition Lithotrophy is advantageous because organisms deriving energy from inorganic compounds do not have to compete with chemoorganotrophs. In addition some of their energy sources (H2, H2S) are waste products from the chemoorganotrophs  Heterotrophs and Autotrophs Heterotrophs Microbial cells which use one or more organic compounds as their carbon source are called heterotrophs Autotrophs Microbial cells which use CO2 as their carbon source are called autotrophs – CO2 fixation or Calvin cycle  Autotrophs Autotrophs are called primary producers because they produce organic matter from CO2 in the air. Chemoorganotrophs and other organisms can ultimately use this organic matter by feeding on the autotrophs or their waste products All organic matter on the planet has been synthesised from CO2 by autotrophs  Phototrophs Use light as energy source Phototrophs contain pigments which allow them to use light as an energy source These pigments give the cells colour  Photosynthesis Phototrophs obtain energy from light using photosynthesis Photosynthesis involves reactions in which ATP is generated Oxygenic photosynthesis – oxygen is produced as a bi-product Anoxygenic photosynthesis – no oxygen is produced What are the Pigments in Phototrophic Cells? Chlorophylls Carotenoids  Chlorophylls Green colour Similar to the pigments responsible for photosynthesis in plants Phototrophic bacteria contain chlorophylls called bacteriochlorophylls In plant cells photosynthesis takes place in chloroplasts In bacteria photosynthesis takes place in a specially developed cytoplasmic membrane.  Carotenoids Yellow, red, brown and green colours Carotenoids are closely associated with bacteriochlorophyll but play no direct role in photosynthesis Transfer light energy to bacteriochlorophyll Carotenoids have a photoprotective role Photosynthetic Bacteria  Further Reading Brock Biology of Microorganisms Chapter 5 “Nutrition, Laboratory Culture and Metabolism of Microorganisms”