Lec 13 and 14 PDF

PowerPoint® Lecture Presentations CHAPTER 3, 14, 15 Microbial Metabolism and Metabolic Diversity & Functional Diversity FERMENTATION © 2018 Pearson Education, Inc. FERMENTATION: •Lactobacilli: makers of cheese and sauerkrautlactic acid production • Saccharomyces: ethanol production Cataboli...

PowerPoint® Lecture Presentations CHAPTER 3, 14, 15 Microbial Metabolism and Metabolic Diversity & Functional Diversity FERMENTATION © 2018 Pearson Education, Inc. FERMENTATION: •Lactobacilli: makers of cheese and sauerkrautlactic acid production • Saccharomyces: ethanol production Catabolic diversity of prokaryotes Fermentation • So in terms of microbial metabolism ask yourself.. • Where are the electrons coming from? Organic or inorganic or through light activation? • Where are the electrons going? What is the terminal electron acceptor? Oxygen or some other compound? • Where is the carbon coming from? Organic or inorganic (CO2)? 1. Where electrons coming from? 2. Where electron going? 3. Source of C? glycolysis Glucose Pyruvate Lactic acid Anaerobic Ethanol Acetyl CoA TCA cycle FERMENTATION glucose But reduced electron carriers such as NADH generated here ATP generated here! Substrate level phosphorylation during glycolysis. pyruvate No oxygen or other terminal electron acceptor! So where do the electrons go? glucose But reduced electron carriers such as NADH generated here ATP generated here! Substrate level phosphorylation during glycolysis. pyruvate From here you can make lactic acid, ethanol and other fermentation products! No oxygen or other terminal electron acceptor! Lecture Overview This lecture looks more into detail on fermentation and fermentation products, particularly lactic acid production and its utility as a food preservative and flavour enhancer in cheeses. We will also look into detail on fermentation and fermentation products, specifically ethanol production. Lecture Objectives After this lecture and reading appropriate portions of the text, the student should be able to describe the pathway for the catabolism of glucose to pyruvate (glycolysis) and pyruvate to lactic acid or ethanol. Microorganisms and Concepts Lactobacillus sp. Penicillium sp. Propionobacterium shermanii Enterobacter cloacae Saccharomyces sp. Candida albicans • ethanol • lactic acid • fermentation • regeneration of NAD • antibiotics and disease • heterofermentation vs homofermentation • respiration vs fermentation Brevibacterium sp. Klebsiella sp. Leuconostoc sp. Lecture- Lactobacilli: makers of cheese and sauerkraut Non-sporulating Gram+ bacteria Staphylococcus, Streptococcus, Lactobacillus, Leuconostoc Most species of this non-spore-forming bacterium ferment glucose or lactose (glucose+galactose) into lactic acid, hence the name Lactobacillus. -Aerotolerant anaerobes. -The most common application of Lactobacillus is industrial, specifically for dairy production. Fermented Foods Overview • Fermentation=treatment with microbes • Biochemical defn= reduction of pyruvate or a derivative of pyruvate – Microbes digest food first – Preserves food – Alcohol, acid buildup – Makes food digestible • Breaks down indigestible fibers – Adds nutrients • Microbially-produced vitamins Lactic acid as a fermentation production Acidic Dairy Fermentation • Milk coagulated by bacteria to form curds – Lactose digested, fermented to lactic acid • Cheese, yogurt safe for lactose-intolerant people – Proteases (rennet) cuts up milk protein • Coagulates curd to make harder cheeses – Further fermentation Propionibacterium produces CO2 gas Fermentation by Penicillium mold Other Acidic Animal Product Fermentations • Lactobacillus – Yogurt, kefir, sausage • Lactococcus – Buttermilk, sour cream • Streptococcus – Yogurt, kefir • Others – fish, many types of sausage Acidic Vegetable Fermentations • Soybeans – Microbes remove harmful elements – Rhizopus: Tempeh – Aspergillus: Miso, Soy sauce • Cabbage, cucumbers, olives – Pickling: Fermentation in brine (high salt) • Leuconostoc: Sauerkraut, pickles, olives, kimchi -This genus also contains several bacteria that make up part of the natural flora of the vagina. -Because of their ability to derive lactic acid from glucose, these bacteria create an acidic environment which inhibits growth of many bacterial species that lead to urogenital infections. -Lactobacillus is generally harmless to humans, rarely inciting harmful infections or diseases. Inoculation and Milk Ripening -The basis of cheesemaking relies on the fermentation of lactose (=glucose+galactose) by lactic acid bacteria (LAB). -LAB produce lactic acid which lowers the pH and in turn assists coagulation, helps prevent spoilage and pathogenic bacteria from growing, contributes to cheese texture, flavour and keeping quality. -LAB also produce growth factors which encourages the growth of non-starter organisms, and provides lipases and proteases necessary for flavour development during curing. -Streptococcus for buttermilk -aroma production (biacetyl and volatile acids) from Leuconostoc -tangy flavour in sausages to lactic acid bacteria -curd is produced by acidity and enzyme rennet -microorganisms added to curd for specific cheeses: -mold spores, Penicillium roqueforti----> blue cheese Penicillium camamberti-->Brie, Camembert -Brick and Limberger cheese surface rubbed with Brevibacterium linens. -Swiss-->Proprionibacterium shermanii produces proprionic acid and CO2. https://www.youtube.com/watch?v=jMAlToEYHJM Sauerkraut -As Leuconostoc is a heterofermentative lactic acid bacterium, much gas (carbon dioxide) accompanies the acid production during this stage. -The pH continues to drop, strains of Lactobacillus succeeds the Leuconostoc. -The complete fermentation, then, involves a succession of three major groups or genera of bacteria, a succession governed by the decreasing pH. -Throughout the fermentation, it is critical that oxygen be excluded. The presence of oxygen would permit the growth of some spoilage organisms, particularly the acid-loving molds and yeasts. Homolactic or homofermentative bacteria Heterolactic or heterofermentative bacteria Respiration Fermentation Fermentation -ATP generated only during glycolysis. -electrons are transferred (with protons) from reduced coenzymes (i.e. NADH) to pyruvic acid or its derivatives -organic molecule is the final electron acceptor -only 2 ATP molecules for each molecule of glucose as opposed to 38 for aerobic respiration. -how can microbes grow with so little ATP production? COOC=O CH3 Pyruvate NADH H+ NAD COOHCOH CH3 Lactate Reduction of pyruvate to lactate. NAD accepts two electrons: therefore one proton is covalently Associated, and one is ionically associated, with NAD. Ethanol Saccharomyces cerevisiae -Facultative anaerobe -Reproduce by budding -Cell wall composed of B-1,3 and B-1,6 glucan and mannan Fermentation The incomplete oxidation of an organic compound under anaerobic conditions. Oxidation- loss of electrons to - NAD à NADH. This happens in glycolysis--- glucose -> pyruvate. How do you recycle the NADH back to NAD??? That is, where do you dump the electrons? In respiration the electrons go to oxygen via the electron transport chain. No electron transport chain under anaerobic conditions !! Electrons dumped onto pyruvate or an intermediate of pyruvate. Fermentation results in a excess of NADH -Accumulation of NADH causes a problem for anaerobes. -They have too much of it and it prevents further oxidation of substrate due to a lack of an NAD+ pool to accept electrons. -In many fermentation pathways, the steps after energy generation are performed in part to get rid of the NADH. Energy is derived from Substrate-Level Phosphorylation (SLP) -The substrate is converted to a phosphorylated compound and subsequently the high energy phosphate is transferred to ATP Phosphoenolpyruvate is converted to pyruvate with the formation of ATP. The phosphate hilighted in red is transferred from PEP to ATP. In fermentation , ATP synthesis occurs as a result of substrate-level phosphorylation. An intermediate substrate becomes “high energy” and eventually transfer phosphate from ADP to ATP In respiration, the cytoplasmic membrane is energized by the proton motive force which leads to ATP formation. Proton motive force is coupled to ATP formation and energy transferred by membrane bound ATP synthase. Oxidation of NADH. Acetaldehyde is reduced to ethanol (the active ingredient in alcoholic beverages). This is the final step in yeast fermentation of glucose to ethanol. 43 - Yeast infection is a very common problem. Approximately 75% of all women have at least one yeast infection in their lifetime. WHAT IS IT? - Yeast cells are normally present in the vagina, mouth, gastrointestinal tract and other areas of the body. A type of yeast called Candida albicans is the organism responsible for most vaginal yeast infections. -Normally, these yeast cells are kept in check by healthy bacteria (Lactobacillus). A yeast infection occurs when the normal balance in the vagina changes, and the yeast cells overgrow. WRONG!!!! http://www.youtube.com/watch?v=dZCDI_V7IoU&playn ext=1&list=PL3C1F413A92D177DA&feature=results_mai n Overgrowth has several possible causes. -One cause may be a change in hormone levels. - A second possible cause may be antibiotics. Antibiotics can reduce the bacteria (Lactobacillus) that keep the yeast in check, allowing the yeast to overgrow. - Substances that may irritate the vaginal area include chlorine in swimming pools, nylon underwear, douching and even scented toilet paper. -A fourth cause may be a change in blood sugar. Yeast thrives on sugar. If there is higher level of sugar in the blood, then yeast tend to overgrow. That is one reason why yeast infections may be more common in diabetics. -A fifth cause may be a lowered resistance to infection. Candida albicans Candida albicans -Candida albicans is a dimorphic fungus that grows at 37oC. -In some circumstances, however, the same strains of C. albicans that grow as harmless commensals can become pathogenic, invading the mucosa and causing significant damage. - disease termed thrush - this is common in newborn babies, perhaps resulting from passage through an infected birth canal. - Candida can adhere to denture resin, and high sugar levels in the diet can also increase the adhesion by enhancing the production of a mannoprotein adhesive on the yeast cell surface. From which the cells can bud and be disseminated.