BIO-205 Chapter 8 F24 RMB Revisions Version 1 Microbiology OpenStax PDF

Chapter 8: Microbial Metabolism Microbiology OpenStax Slides compiled by Adronisha T. Frazier  Where do humans get energy? Nutrients from food! Sugar – including glucose, lactose Proteins – made of amino acids like Tryptophan Fats (which are lipids)...

Chapter 8: Microbial Metabolism Microbiology OpenStax Slides compiled by Adronisha T. Frazier  Where do humans get energy? Nutrients from food! Sugar – including glucose, lactose Proteins – made of amino acids like Tryptophan Fats (which are lipids) Image: https://nutritiondata.self.com/  Why do nutrients have energy? Nutrients are molecules with many chemical Glucose: each of the unlabeled bonds that store intersections of energy lines is a carbon Because typical atom nutrients have many bonds, they have a lot of energy Releasing all energy at once is excessive Cells instead rely on ATP to store and release energy in small, accessible chunks Image: https://www.biomol.com/media/image/b8/54/3f/G3050-  What is a bond? (Covalent) Chemical bond: Attractive force that links atoms together (with electrons) to form molecules. Each bond has an associated energy Therefore, molecules have an inherent energy Molecules generally broken down to obtain Glucose this energy! How can we transfer the  Chemical Reactions (1) Chemical reactions occur when atoms combine or change their bonding partners. Rearrangement of electrons! Combustion of propane (C3H8): C3H8 + 5 O2 -> 3 CO2 + 4 H2O + energy Image: https://chemicalreactions- propanegrill.weebly.com/about.html Each Black = sphere Carbon in this White = diagram Hydrogen represen Red = Oxygen ts an atom.  Reactants The starting and Products molecules of a chemical reaction are called reactants. The final molecules are called products. Combustion of propane (C3H8): C3H8 + 5 O2 [Reactants] -> 3 CO2 + 4 H2O [Products] + energy Reactants Products Each Black = sphere Carbon in this White = diagram Hydrogen represen Red = Oxygen ts an atom. Image: https://chemicalreactions- propanegrill.weebly.com/about.html  Metabolic Pathways Often, the product of one chemical reaction acts as the reactant of another chemical reaction, and this repeats in a chain. Connected chemical reactions are called metabolic pathways. The main way to collect energy is cellular respiration, which is composed of 3 metabolic pathways Image: https://www.pharmacy180.com/article/metabolic-pathways-3454/  Anabolism The biosynthesis of complex molecules from simple building blocks Accomplished via endergonic reactions (require energy to proceed) This was the major focus of Chapter 11 from last unit (and photosynthesis)  Catabolism Catabolism The breakdown of complex molecules into simpler ones Accomplished via exergonic reactions (release energy). Goals is to free up energy for other processes The major focus of this chapter  Question Which of the following cellular processes are anabolic? a. DNA Replication b. Transcription c. Translation d. Photosynthesis e. All of the above  Question Which of the following cellular processes are anabolic? a. DNA Replication b. Transcription c. Translation d. Photosynthesis e. All of the above  Catabolism AND Anabolism Catabolism provides energy (as ATP) for anabolism! If you want to build something up, you have to break something else down first! But what does this energy look like in practical terms?  Adenosine Triphosphate (ATP) Catabolism typically creates ATP. Anabolism uses it up. ATP is therefore often called the “energy currency” of the cell What makes ATP a good currency? ATP has 3 high energy phosphate groups ATP can easily lose 1 phosphate groups and become Adenosine Diphosphate (ADP) ATP can also lose 2 phosphate groups and become Adenosine Monophosphate (AMP) Cycle of Adenosine Triphosphate Figure 8.3 (credit: modification of work by Robert Bear, David Rintoul)  Why not just use the nutrients in food to DIRECTLY fuel cellular processes? 1. Cells have not evolutionarily evolved to do this. For instance, many enzymes specifically have to bind to ATP to work 2. Glucose has too much energy to use up all at once, so a lot of energy would be wasted When you “use up” ATP, you just break one or two bonds  Energy Transfer: Oxidation and Reduction Most of the energy stored in atoms and used to fuel cell functions is in the form of high-energy electrons. Reactions that remove electrons from donor molecules are oxidation reactions. Reactions that add electrons to acceptor molecules are reduction reactions. These two processes are OIL RIG: Oxidation Is ALWAYS coupled together Loss. Reduction Is (Redox reactions) Gain (of electrons). The following isQuestion something called a half- reaction: Na -> Na+ + e- Which of the following processes is e- is an electron happening here (from the perspective of the Na atom)? Can it occur completely in isolation? Note that the electrons are moving OUT of the atom. a. This is a reduction reaction, and it can occur on its own b. This is a reduction reaction, and it can only occur if an oxidation reaction simultaneously occurs c. This is an oxidation reaction, and it can occur on its own d. This is an oxidation reaction, and it can only occur if a reduction reaction simultaneously The following isQuestion something called a half- reaction: Na -> Na+ + e- Which of the following processes is e- is an electron happening here (from the perspective of the Na atom)? Can it occur completely in isolation? Note that the electrons are moving OUT of the atom. a. This is a reduction reaction, and it can occur on its own b. This is a reduction reaction, and it can only occur if an oxidation reaction simultaneously occurs c. This is an oxidation reaction, and it can occur on its own d. This is an oxidation reaction, and it can only occur if a reduction reaction simultaneously  Recognizing Oxidized and Reduced Molecules The Rule of Thumb: Molecules with more oxygen / less hydrogen are more oxidized Molecules with more hydrogen / less oxygen are more Image: https://oercommons.org/courseware/lesson/84552/student-old/  Recognizing Oxidized and Reduced Molecules During cellular respiration, we will ultimately turn all the molecules into CO2 (the most oxidized version of C possible), so we are slowly oxidizing things over time Image: https://bodell.mtchs.org/OnlineBio/BIOCD/text/chapter7/concept7.4.html The biological reactions we are about to discuss do not just happen by themselves. They need help from enzymes!  Enzyme Structure and Function A substance that helps speed up a chemical reaction without being changed is a catalyst. Enzymes are proteins that serve as catalysts for biochemical reactions inside cells. You need to catalyze every step of a metabolic pathway with an enzyme  How do enzymes work? Enzymes lower a reaction’s activation energy: the energy needed to form or break chemical bonds and convert reactants to products. Activation energy can come from heating the system.  What actually IS activation energy? Chemical reactions occur when atoms or molecules collide in the right orientation Activation energy is the collision energy required for a chemical reaction to occur Temperature is correlated to the average kinetic energy of molecules, so higher temperatures are more likely to lead to successful reactions Collision does not reach activation energy A B A B C A B C C Low energy collision No reaction 25 Affect of concentration on reaction rate Increased concentration means more total collisions More collisions at or above activation energy Increases the reaction rate A B C A B C A B C A B A C A B C B C A B C A A B C B C Even if the same percentage of reactions succeed, if there are more attempts, there are more successes!  How do enzymes affect reaction rate? Enzymes stabilize the transition state (make it easier to form) by orienting the reactants in ideal positions decrease the activation energy increase the reaction rate Collision reaches activation energy A A B C A B C B C Low energy collision Reaction occurs A Transition state stabilized by enzyme 28  Question Which of the following statements best describes the role of an enzyme? a. Enzymes slow down chemical reactions by increasing their activation energy b. Enzymes slow down chemical reactions by decreasing their activation energy c. Enzymes speed up chemical reactions by increasing their activation energy d. Enzymes speed up chemical reactions by decreasing their activation energy  Question Which of the following statements best describes the role of an enzyme? a. Enzymes slow down chemical reactions by increasing their activation energy b. Enzymes slow down chemical reactions by decreasing their activation energy c. Enzymes speed up chemical reactions by increasing their activation energy d. Enzymes speed up chemical reactions by decreasing their activation energy  Enzymes Catalyze Reactions 2 2 2 Image: https://www.bulbapp.com/u/background~536  Enzymes act upon highly specific substrates. Substrate: the reactant an enzyme acts upon Substrate molecules bind to active site of enzyme. Sometimes regulatory molecules bind to a separate allosteric site The 3D shape of the enzyme determines its specificity.  Enzyme Structure and Function Figure 8.6 According to the induced-fit model, the active site of the enzyme undergoes conformational changes upon binding with the substrate. Each individual step of a catabolic or anabolic pathway is catalyzed by an enzyme like this!  What else affects enzyme activity? Enzymes are subject to influences by local environmental conditions such as temperature, pH, and salt levels. Different enzymes may have different ideal conditions. Enzyme Inhibitors and Activators There are many kinds of molecules that inhibit or promote enzyme function, including: Competitive inhibitor Noncompetitive (allosteric) inhibitor Allosteric activators  Competitive Inhibitors Compete with the natural substrate for binding sites (binds to same sites). Usually look very similar to the natural substrate Degree of inhibition depends on concentrations of substrate and inhibitor. This is the only type of inhibition where this is true Noncompetitive inhibitors bind to enzyme at a different allosteric site (not the active site). Enzyme changes shape and alters the active site. Because only one inhibitor molecule is needed per enzyme for effective inhibition, the concentration of inhibitors needed for  Allosteric Activators Bind to allosteric sites that are far away from the active site They induce a shape change that increases the affinity of the enzyme’s active site(s) for its substrate(s). Example: cAMP is an allosteric activator of CAP Image: https://commons.wikimedia.org/wiki/File:OSC_Microbio_08_01_InhAct.jpg  Question The top molecule on the right is the typical substrate for an enzyme, folic acid. What type of inhibitor would you expect the bottom molecule, methotrexate, to be? a. Competitive inhibitor Image: https://en.m.wikipedia.org/wiki/File:Methotrexate_vs_folate.svg b. Noncompetitive inhibitor  Question The top molecule on the right is the typical substrate for an enzyme, folic acid. What type of inhibitor would you expect the bottom molecule, methotrexate, to be? a. Competitive inhibitor Image: https://en.m.wikipedia.org/wiki/File:Methotrexate_vs_folate.svg b. Noncompetitive inhibitor  Feedback Inhibition Cells have evolved also to use the products of their own metabolic reactions for feedback inhibition (negative feedback) of enzyme activity. Use of a pathway product to negatively regulate further production of that product. Enzyme Inhibitors Figure 8.9 (a) Binding of an allosteric inhibitor reduces enzyme activity, but binding of an allosteric activator increases enzyme activity. (b) Feedback inhibition, where the end product of the pathway serves as a noncompetitive inhibitor to an enzyme early in the pathway, is an important mechanism of allosteric regulation in cells.  Overview of Cellular Respiration Extensive enzyme pathways exist for breaking down carbohydrates to capture energy in ATP bonds. Energy Figure 8.4 Exergonic reactions are coupled to endergonic ones, making the combination favorable. Here, the endergonic reaction of ATP phosphorylation is coupled to the exergonic reactions of catabolism. Similarly, the exergonic reaction of ATP dephosphorylation is coupled to the endergonic reaction of polysaccharide formation, an example of anabolism.  Cellular Respiration Process by which energy is extracted from glucose and converted into a more accessible form (ATP) Energy Transfer 38 Total! Image: https://o.quizlet.com/bHNn-1l3VSs.F9A512jMxw_b.jpg  Stages of Cellular Respiration Cellular respiration is composed of four (three?) stages Glycolysis Transition Reaction / Pyruvate Oxidation / “Bridge Step” Sometimes just lumped in with Krebs Cycle Krebs Cycle / TCA Cycle / Citric Acid Cycle Electron Transport System / Electron Transport Chain  Cellular Respiration Process by which energy is extracted from glucose and converted into a more accessible form (ATP) Image: https://o.quizlet.com/bHNn-1l3VSs.F9A512jMxw_b.jpg  Glycolysis Glycolysis is the most common pathway for the catabolism of glucose EVERY living organism carries out some form of glycolysis, using the starting sugar glucose Evolved early in evolution! Glycolysis: 10-Step Process to Split glucose in half, make a little ATP Requirements: Glucose, ATP, NAD+, etc. 6-carbon glucose becomes 2 molecules of 3-carbon pyruvate Glucose + 2 NAD+ + 2 ATP -> 2 Pyruvate Net +2 NADH + 4 ATP of 2 ATP! You do not need to memorize this diagram Image: https://en.wikipedia.org/wiki/Glycolysis Glycolysis: 10-Step Process to Split glucose in half, make a little ATP Three main ideas to focus on for now: 1. Start with glucose, end with 2 pyruvates 2. Molecule split in half about halfway through the steps 3. Need 2 ATP to make 4 ATP x2 Image: https://en.wikipedia.org/wiki/Glycolysis Glycolysis: 10-Step Process to Split glucose in half, make a little ATP Requirements: Glucose, ATP, NAD+, etc. 6-carbon glucose becomes 2 molecules of 3-carbon pyruvate Glucose + 2 NAD+ + 2 ATP -> 2 Pyruvate + 2 The 2 NADH + 4 ATP NADH made here will also be relevant later. (NADH is where the Image: https://en.wikipedia.org/wiki/Glycolysis Glycolysis: 10-Step Process to Split glucose in half, make a little ATP Note: The standard type of glycolysis most common in microbes is called the Embden-Meyerhof-Parnas (EMP) pathway. Most Gram-Positive bacteria ONLY do this type Image: https://en.wikipedia.org/wiki/Glycolysis Phases of Glycolysis The EMP pathway consists of 2 distinct phases. 1: Energy Use 2 ATP Investment Phase Uses 2 ATP. Splits 6-carbon molecule into two phosphorylated 3- carbon molecules 2: Energy Payoff Phase Oxidizes those two molecules to Make 4 pyruvate. Produces 4 ATP.  Question Does glycolysis require ATP or make ATP? a. Glycolysis requires ATP b. Glycolysis makes ATP c. Glycolysis both requires AND makes ATP d. Glycolysis neither requires NOR makes ATP  Question Does glycolysis require ATP or make ATP? a. Glycolysis requires ATP b. Glycolysis makes ATP c. Glycolysis both requires AND makes ATP d. Glycolysis neither requires NOR makes ATP  Substrate-Level Phosphorylation The ATP made during glycolysis is a result of substrate-level phosphorylation Direct transfer of phosphate group from another molecule  Entner-Doudoroff (ED) Pathway An important alternative to the main EMP Pathway of Glycolysis Some G- bacteria, like opportunistic pathogen Pseudomonas aeruginosa, contain only the ED pathway Other G- bacteria, like E. coli, can use EITHER the ED pathway or the EMP pathway. Image: https://en.wikipedia.org/wiki/Entner%E2%80%93Doudoroff_pathw Pentose Phosphate Second Pathway (PPP) molecule in the A glycolytic pathway that glycolysis occurs in all cells pathway Branches off from glycolysis. The intermediates from the PPP are used for the Used biosynthesis of Used to to nucleotides and amino make make acids. nucleotides certain If a cell needs those most, amino it will primarily use the PPP acids If a cell needs energy most, it will primarily use glycolysis Image: https://en.wikipedia.org/wiki/Pentose_phosphate_pathw  How does a cell decide which metabolic pathway to use? If a cell needs amino acids and nucleotides the most, it will primarily use the PPP Also, if it does NOT need energy If a cell needs energy most, it will primarily use glycolysis Also, if it does NOT need amino acids and nucleotides Image: Kovářová J, Barrett MP. The Pentose Phosphate Pathway in Parasitic Trypanosomatids. Trends Parasitol. 2016;32(8):622-634. doi:10.1016/j.pt.2016.04.010  Cellular Respiration Process by which energy is extracted from glucose and converted into a more accessible form (ATP) Image: https://o.quizlet.com/bHNn-1l3VSs.F9A512jMxw_b.jpg  Pyruvate Oxidation (the “bridge reaction”) Pyruvate oxidized to acetate and CO2 Acetate binds to coenzyme A to form acetyl CoA 2 Pyruvate + 2 NAD+ -> 2 Acetyl CoA, 2 CO2, 2 NADH  Cellular Respiration Process by which energy is extracted from glucose and converted into a more accessible form (ATP) Image: https://o.quizlet.com/bHNn-1l3VSs.F9A512jMxw_b.jpg Krebs Cycle: Eight reactions completely oxidize the acetyl group to 2 molecules of CO2 (Also called Citric Acid Cycle or TCA Cycle) Requirements of Krebs Cycle Requirements: Acetyl-CoA, Oxaloacetate (OAA) that you usually have plenty of, NAD+, FAD, etc. 2 Acetyl CoA + 2 FAD + 6 NAD+ -> 4 CO2, 2 ATP, 2 FADH2, 6 NADH  Other details of Krebs Cycle Energy released is used to make GTP, NADH, and FADH2 GTP is easily converted into ATP Oxaloacetate FADH is another 2 is regenerated destination for in the last electrons in step, making redox reactions  Question Which of the following is NOT directly required to run the Krebs cycle? a. Acetyl CoA b. Oxaloacetate c. NAD+ d. Glucose e. Enzymes  Question Which of the following is NOT directly required to run the Krebs cycle? a. Acetyl CoA b. Oxaloacetate c. NAD+ d. Glucose e. Enzymes  Cellular Respiration Process by which energy is extracted from glucose and converted into a more Previous pathways and the accessible form (ATP) next pathway connected by NADH! Image: https://o.quizlet.com/bHNn-1l3VSs.F9A512jMxw_b.jpg  Over the course of Glycolysis, the Bridge Step, and Krebs Cycle, glucose is slowly oxidized to CO2. To accomplish this, something else must be reduced.  Energy Transfer: Oxidation and Reduction Most of the energy stored in atoms and used to fuel cell functions is in the form of high-energy electrons. Reactions that remove electrons from donor molecules are oxidation reactions. Reactions that add electrons to acceptor molecules are reduction reactions. These two processes are OIL RIG: Oxidation Is ALWAYS coupled together Loss. Reduction Is (Redox reactions) Gain (of electrons). Electron Carriers VERY common to gain or lose both a single proton (H) and 2 electrons A small class of compounds functions as electron carriers Shuttle high-energy electrons between compounds by acting as either oxidizing or Therefore, reducing agents reduced compounds tend in redox to have more H reactions. and oxidized compounds tend to have less H Electron Carriers VERY common to gain or lose both a single proton (H) and 2 electrons The main electron carriers are derivatives of nucleotides. Nicotinamide adenine dinucleotide (NAD) Nicotine adenine Therefore, dinucleotide reduced phosphate (NADP) compounds Flavin adenine tend to have more H and dinucleotide (FAD) oxidized compounds tend to have less H  Electron Transport System The electron transport system (ETS) is the last component of cellular respiration that is comprised of a series of membrane-associated protein complexes and associated electron carriers. Image: https://www.nature.com/scitable/content/the-electrochemical-proton-gradient-and-atp- synthase-14706672/  Electron Transport System: The Redox Reactions During these exergonic reactions, electrons from NADH and FADH2 are passed rapidly between protein complexes Each complex is slightly better at accepting electrons than the previous one Electrons are ultimately sent to oxygen, making water in the process  What gets used up and what is created in the (aerobic) ETS? 1. The NADH gives its electrons to the electron transport chain, thus being oxidized to NAD+ 2. The electrons have to ultimately go somewhere: the electrons go into the Final Electron Acceptor O2, and turn it into H2O 3. As we will see shortly, ADP is converted to ATP (As we also will see shortly, the redox reactions generate a membrane gradient.)  The Proton Motive Force Energy used to pump hydrogen ions (H+) across a membrane, so that there are more H+ outside the membrane than inside (active transport). The membrane is the inner mitochondrial membrane in eukaryotes. Cell membrane in prokaryotes. This membrane gradient of H+ is referred to as the Proton Motive Force (PMF).  Oxidative Protons want to bePhosphorylation equal in concentration on each side of membrane, but cannot do simple diffusion Protons flow back across the membrane through a channel protein, ATP synthase (Facilitated diffusion) The kinetic energy of H+ diffusion is ultimately transmitted to ATP Synthase, providing chemical energy for ATP  ATP Yield from Aerobic Respiration Mos t ATP mad e by ETC! Figure 8.16 summarizes the theoretical maximum yields of ATP from various processes during the complete aerobic respiration of one glucose molecule.  Question Which of the following molecules ultimately accepts the electrons at the very end of the electron transport chain (in human cells)? a. CO2 b. O2 c. ATP d. Complex IV e. ATP Synthase  Question Which of the following molecules ultimately accepts the electrons at the very end of the electron transport chain (in human cells)? a. CO2 b. O2 c. ATP d. Complex IV e. ATP Synthase Aerobic vs. Anaerobic Respiration In cellular respiration, electrons are transferred via various carriers to a final electron acceptor (FEA), which is either: Oxygen in aerobic respiration (makes the most ATP) Non-oxygen inorganic molecules like nitrate in anaerobic respiration (like below) Anaerob ic Image: https://en.wikipedia.org/wiki/Anaerobic_respirati Respirat  ATP From Anaerobic Electron Transport Systems Anaerobic electron transport systems make a little less ATP than aerobic electron transport systems However, they make more ATP than is made by fermentation Image: https://en.wikipedia.org/wiki/Anaerobic_respirati  Anaerobic Respiration: Ecology Some organisms perform reactions that others cannot. Differences in ETC are one reason for this! Some bacteria use ONLY nitrate as final electron acceptor, producing nitrogen gas (turn NO3 to N2). Plants can use nitrate and CANNOT use N2 – ecologically important! Some organisms (like E. coli) switch between using nitrate OR oxygen as their final electron acceptor Note: E. coli makes NH3, not N2  Fermentation Fermentation: alternative pathway to electron transport system. No further production of ATP beyond that produced during glycolysis. Fermenters produce a maximum of two ATP molecules per glucose (during glycolysis)  The Purpose of Fermentation If fermentation makes zero ATP, why do we do fermentation instead of doing nothing? Need to replenish NAD+ to continue doing glycolysis. Glycolysis: 10-Step Process to Split glucose in half, make a little ATP Requirements: Glucose, ATP, NAD+, etc. 6-carbon glucose becomes 2 molecules of 3-carbon pyruvate Glucose + 2 NAD+ + 2 ATP -> 2 Pyruvate + 2 NADH + 4 ATP If NAD+ runs out, no glycoly sis and no new energy ! Image: https://en.wikipedia.org/wiki/Glycolysis  Why not just perform the ETS (which also makes NAD+)? They are unable to! This is because of either or both of the following circumstances: 1. The cell lacks enough final electron acceptor (like O2) to carry out cellular respiration, because it is absent from the environment or has been used up. 2. The cell lacks genes to make appropriate machinery in the electron transport system or Krebs cycle. Image: https://www.wikihow.com/Reduce-Lactic-Acid-Build- up-in-Muscles  Aerobic respiration Some Energy makes the most Rankings energy, followed by anaerobic respiration  Question A wild-type E. coli cell with plenty of resources to spare needs a lot of energy as fast as possible. What will it likely rely on to obtain this energy? a. Aerobic respiration b. Anaerobic respiration c. Fermentation d. It is equally likely to use any of these processes  Question A wild-type E. coli cell with plenty of resources to spare needs a lot of energy as fast as possible. What will it likely rely on to obtain this energy? a. Aerobic respiration b. Anaerobic respiration c. Fermentation d. It is equally likely to use any of these processes  Lactic acid fermentation Performed by microorganisms and some complex organisms. Pyruvate is the electron acceptor One-step process. Does not make gas 2 Pyruvate + 2 NADH -> 2 Lactate and 2 NAD+ Reverse reaction occurs once O2 is abundant again  Ethanol Fermentation Alcohol (ethanol) fermentation produces ethanol. Two steps Releases gas (in the form of CO2) Use enzymes pyruvate decarboxylase and alcohol dehydrogenase 2 Pyruvate + 2 NADH -> 2 CO2 + 2 Ethanol + 2 NAD+  Types of Lactic Acid Bacteria (LAB) and their Applications Homofermentative LAB: lactic acid the only product Lactobacillus delbrueckii and S. thermophiles used in yogurt production. Heterofermentative LAB: product is a mixture of lactic acid, ethanol and / or acetic acid, and CO2. Leuconostoc mesenteroides helps sour vegetables like cucumbers and cabbage, producing pickles and Image: sauerkraut. https://commons.wikimedia.org/wi ki/File:Glasses_of_pickled_cucumbe rs_2.jpg  Many other fermentation methods occur in Table prokaryotes 8.3 Besides homolactic fermentation, most produce CO2 or hydrogen gas Common Fermentation Pathways Pathway End Products Example Microbes Commercial Products Acetone, butanol, Commercial solvents, Acetone-butanol-ethanol ethanol, CO Clostridium acetobutylicum 2 gasoline alternative Alcohol Ethanol, CO2 Candida, Saccharomyces Beer, bread Formic and lactic acid; ethanol; acetoin; 2,3 Butanediol butanediol; CO2; Klebsiella, Enterobacter Chardonnay wine hydrogen gas Butyric acid, CO2, Butyric acid Clostridium butyricum Butter hydrogen gas Lactic acid Lactic acid Streptococcus, Lactobacillus Sauerkraut, yogurt, cheese Acetic, formic, lactic, and Mixed acid succinic acids; ethanol, Escherichia, Shigella Vinegar, cosmetics, CO2, hydrogen gas pharmaceuticals Acetic acid, propionic Propionibacterium, Propionic acid acid, CO2 Bifidobacterium Swiss cheese too much about memorizing this page. The main takeaway is how many types of fermentati  Lactic Acid Bacteria are Important for Human Health They lower pH in various body parts, inhibiting pathogen growth When vaginal microbiota are reduced, pathogenic yeast can proliferate Are relevant for gastrointestinal health Are the primary component of probiotics. Image: https://my.clevelandclinic.org/health/diseases/5019-vaginal- yeast-infection  Using Fermentation to Identify Microbes Microbes can be differentiated according to the substrates they can ferment. Lactose: E. coli can ferment it (with gas). Salmonella cannot. Sorbitol: Pathogenic E. coli strain O157:H7 CANNOT ferment it. Other strains CAN. Mannitol: Staphylococcus aureus can ferment it. Other staphylococci Image: https://commons.wikimedia.org/wiki/File:Mannitol_Salt_Agar_with cannot. _growth_of_Staphylococcus_aureus_and_CoNS.jpg  Metabolic Pathways Are Interrelated and Regulated Metabolic pathways don’t operate in isolation; there is an interchange of molecules in and out of the pathways. Sources of carbon: carbohydrates, fats, and proteins.  Energy from Sugars & Lipids Polysaccharides are hydrolyzed to glucose → enters glycolysis Lipids are broken down to Glycerol → DHAP → glycolysis Image: https://en.wikipedia.org/wiki/Glycolysis Fatty acids → Acetyl CoA → Krebs cycle  Energy from Proteins Proteins are hydrolyzed to amino acids → glycolysis or Krebs cycle. Example: Glutamate is converted into α- ketoglutarate, an intermediate in the citric acid cycle.  Question Which of the following can feed into cellular respiration to make energy? a. Only glucose b. Only sugars c. Only sugars and fats d. Almost any type of nutrient, including sugars, fats, and proteins  Question Which of the following can feed into cellular respiration to make energy? a. Only glucose b. Only sugars c. Only sugars and fats d. Almost any type of nutrient, including sugars, fats, and proteins Acknowledgments "OpenStax Microbiology Slides" by Adronisha Frazier, Louisiana Community and Technical College System, Northshore Technical Community College is licensed under CC BY-SA 4.0