Microbial Physiology Past Paper PDF

MICROBIAL PHYSIOLOGY 1 There is significant reduction of total ATP CHAPTER 10: FERMENTATION...

MICROBIAL PHYSIOLOGY 1 There is significant reduction of total ATP CHAPTER 10: FERMENTATION yield from fermentation of pyruvate → (Oct. 20, 2024 – Session 5) glucose ○ Because NADH2 & FADH not further 5.1 Fermentation 1 oxidized in ETC Ethanolic, Acetogenic Fermentation 2 ○ Pyruvate not converted to Acetyl-CoA; instead serves as OA for NADH Butanediol & Mixed-Acid Fermentation 2 NADH is oxidized to NAD+ w/ pyruvate (& Butyrate Fermentation 3 its derivatives) as terminal e- acceptor Propionate, Amino Acid Fermentation 4 Energy Efficiency 5 Homofermenters – only acid as product ○ Assimilate glucose exclusively through glycolytic pathway ○ Pyruvate does not continue to Kreb’s Fermentation Anaerobic catabolism Organic compound is both an e- donor & e- acceptor Energy (ATP) generation mainly by substrate-level phosphorylation O2 not involved (end products as e- Heterofermenters – different products acceptors) ○ LAB, Leuconostoc, Mycobacterium sp. ○ Fermentation can happen in the presence/absence of O2 MICROBIAL PHYSIOLOGY 2 Kinds of Fermentation Acetogenic Fermentation 1.) Lactate Fermentation 2.) Ethanol Fermentation 3.) Acetogenic Fermentation Pyruvate + 4H+ → Acetate 4.) Mixed-acid & Butanediol Fermentation Acetogens – can grow either: 5.) Butyrate Fermentation ○ Chemoorganotrophically – by sugar fermentation Ethanolic Fermentation *2CH3COOH = acetic acid Substrate: Hexose (glucose) / Pyruvate ○ Chemolithotrophically – by reduction 1. Glucose undergoes glycolysis → 2 Pyruvate of CO2 → Acetate w/ H2 2. 2Pyruvate decarboxylated to 2 acetaldehyde ○ Pyruvate decarboxylase – E1 of Pyruvate Dehydrogenase Complex; Makes Pyruvate → Acetyl-CoA Substrate: Hexose (glucose) / Pyruvate 3. 2 Acetaldehyde reduced to 2 Ethanol 1. Glucose undergoes glycolysis → 2 Pyruvate ○ Alcohol dehydrogenase – conversion ○ Yields 2 NADH of alcohols, aldehydes, ketones by 2. 2 Pyruvate (3C) → 2 Acetate (2C) reducing 2 NAD+ → NADH; ○ Yields 2 acetate + 2CO2 & 4H+ Responsible for alcohol tolerance ○ 2CO2 can be converted to 1 Acetate (Ethanol → Acetaldehyde) (CO2 + 4H+ from glycolysis + 4H+ from Products: 2 EtOH; 2 CO2; 2 ATP pyruvate to acetate) Products: 3 Acetate; 3H+ ; 4 ATP Butanediol & Mixed-Acid Fermentation A.) Mixed-Acid Fermentation Common to enteric bacteria & anaerobic fungi Wood-Ljungdahl-Pathway Substrate: Hexose (glucose)/ Pyruvate ○ An ethanolic fermentation 1. Glucose undergoes glycolysis → Pyruvate ○ Also “Reductive Acetyl-CoA Pathway” 2. PEP decarboxylation → OAA → 2 reductions ○ Requires Corrinoid iron/sulfur protein = formation of Succinate (CFeSP) 3. Pyruvate reduction = formation Lactate ○ Reduction 4. Pyruvate decarboxylation → Acetyl-CoA = formation of Formate ○ Pyruvate formate lyase 5. Pyruvate → Acetyl-CoA → Ethanol Products: Succinate, Lactate, Formate, Ethanol, Acetate; CO2 ; H2 MICROBIAL PHYSIOLOGY 3 Points to Remember: Enteric bacteria (facultative anaerobes) undergo changes as part of adaptation to anaerobic growth: No O2; Terminal reductases replace oxidases in ETC TCA modified to become a reductive pathway (TCA reversed) ○ a-ketoglutarate dehydrogenase & succinate dehydrogenase occur at low levels ○ Succinate dehydrogenase replaced by fumarate reductase Pyruvate–formate lyase substituted for pyruvate dehydrogenase ○ Cells oxidize Pyruvate → Acetyl-CoA & formate (instead of Acetyl-CoA, CO2, NADH) Bacteria carry out a mixed-acid/ butanediol fermentation B.) Butanediol Fermentation Substrate: Hexose (glucose)/ 2 Pyruvate a-acetolactate – 1st intermediate ○ a-acetolactate synthase Acetoin → 2,3-butanediol ○ Needs 1 NADH ○ 2 Pyruvate needed to make 1 2,3-butanediol Product: One 2,3-butanediol Butyrate Fermentation Substrate: Hexose (glucose)/ Pyruvate 1. Glucose undergoes glycolysis → 2 Pyruvate 2. Pyruvate decarboxylated → Acetyl-CoA ○ Pyruvate ferredoxin oxidoreductase 3. Acetyl-CoA → Acetoacetyl-CoA 4. Acetoacetyl-CoA reduced → B-Hydroxybutyryl-CoA 5. B-Hydroxybutyryl-CoA reduced → Butyryl-CoA 6. Butyryl-CoA → Butyrate ○ Donate P = Yield ATP Product: Butyrate MICROBIAL PHYSIOLOGY 4 Amino Acid Fermentation Also “Stickland reaction” – oxidation of 1 AA and reduction of another AA Co-catabolism of alanine & glycine ○ Alanine: e- donor; undergoes oxidation ○ Glycine e- acceptor Starting: Alanine & Glycine 1. Alanine oxidized → Pyruvate 1. Glycine reduced → Acetyl-P 2. Pyruvate → Acetyl-P 3. Acetyl-P → Acetate ○ Substrate-level phosphorylation ○ Yield ATP Products: 3 Acetate; CO2 ; 3 NH4+; 3 ATP Propionate Fermentation (Succinate-Propionate Pathway) Lactate undergoes oxidation reactions Starting: 3 Lactate 1. 3 Lactate → 3 Pyruvate ○ Lactate dehydrogenase 2. 3 Pyruvate → Acetate ○ w/ substrate-level phosphorylation ○ Yield ATP 2. 3 Pyruvate → 2 succinate 3. Succinate → Succinyl-CoA → Methylmalonyl-CoA → Propionyl-CoA → 2Propionate ○ CoA in Propionyl-CoA recycled to make Succinyl-CoA again Products: 2 Propionate; Acetate; CO2 ; H2O; 3 ATP MICROBIAL PHYSIOLOGY 5 Energy Efficiency N = # of ATP formed EATP = E in 1 high E phosphoanhydride bond Ereact = E released as heat in the chemical reaction (total free energy yield) Example 1: Under standard conditions, Ereact= -686 kcal/mol of glucose and EATP = -7.3 kcal/mol. From the chemical reaction for the formation of ATP, we see that 36 molecules are formed. Therefore, we calculate the efficiency as: Only about 38.3% of the energy released from the reaction of glucose w/ oxygen is captured in ATP bonds. Ethanolic-CO2 Fermentation: – Total free energy yield = -238.8 kJ/mole glu – Total E value for ATP = -63.6 kJ Efficiency = (-63.6/-238.8) (100) = 26.6% Lactate Fermentation: Efficiency = (-63.6/-196.8) (100) = 32.3% (more efficient) MICROBIAL PHYSIOLOGY 6 CHAPTER 11: PHOTOSYNTHESIS (Oct. 20, 2024 – Session 5) 5.2 Photosynthesis 6 Photosynthetic System Components 6 Photosystems 8 Photosynthesis *Carotenoids usually present Autotrophs – grow w/ CO2 as C source Photosynthetic System Components Photoautotrophy – light energy used to reduce CO2 to organic compounds 1.) Light-harvesting molecules Photoheterotrophy – light energy used to Carotenoids (Crt) reduce organic carbon to organic Phycobilins (Phy) compounds Bacteriochlorophylls (Bchl) Generally, C reduction to cell material Chlorophylls (Chl) Energy from ATP ○ Oxygenic & purple anoxygenic e- come from NADH or NADPH phototrophs – Chl/Bchl do NOT exist freely Anoxygenic Oxygenic ○ Chl/Bchl attached to proteins & housed within membranes to form Purple & Green Algae, MOS photo complexes (50-300) bacteria Cyanobacteria e- H2S, molecular H 2.) Reaction Centers H2O donor (reduced S) Only small number of reaction centers Carbon CO2 CO2 participate directly to ATP synthesis Surrounded by many light harvesting Energy ADP → ATP ADP → ATP Chl/Bchl ○ Light harvesters have “antenna Product SO42- ½ O2 pigments” also “light harvesting pigments” that funnel energy intro reaction centers Arrangement beneficial for low light MICROBIAL PHYSIOLOGY 7 Chromatophores / Lamellae Bchls whose distribution runs along lines Membrane vesicle/ membrane sac absorb other regions in visible and infrared In purple bacteria Different pigments = different phototrophs Membrane arrangement that houses in same habitat = not competing for same photosynthetic pigments wavelength of light = peaceful coexistence ○ Photosynthetic pigments integrated into internal membrane systems that Accessory Pigments arise from invaginations of CM NOT required for photosynthesis Thylakoid A.) Carotenoids/ Carotenes In cyanobacteria Most widespread accessory pigment Photosynthetic pigments also in lamellar Firmly embedded in membrane membranes Hydrophobic Resemble thylakoid of chloroplast in algae ○ Long chain of hydrocarbon Typically yellow, red, brown, green Chlorophyll & Bacteriochlorophyll ○ Absorb blue Required for photosynthesis ○ Responsible for red, purple, pink, Related to tetrapyrroles green, yellow, brown in anoxygenic ○ Parent structures of cytochromes, but phototrophs contain Mg cofactor instead of Fe Function as light harvesters also but ○ Cytochrome = Fe in center; primarily as photoprotective agents Chlorophyll = Mg in center ○ Bright light can be harmful = catalyze Contain specific constituents on photooxidation reactions = produce tetrapyrrole ring & a hydrophobic alcohol toxic forms of O2 ○ Alcohol anchors chlorophyll into ○ Singlet O = spontaneously oxidize membrane photo complexes = nonfunctional B.) Phycobiliproteins Main light harvesting systems in cyanobacteria & red algae chloroplast (descendants of cyanobacteria) Consist of red or blue-green linear tetrapyrroles also “bilins” ○ Bilins bound to protein Red phycobilin is also “phycoerythrin” Chlorophyll a – transmits/shows green ○ Absorbs strongly at 515 nm (visible ○ Absorbs red & blue light spectrum) ○ Seen at 680, 430 nm Blue phycobilin is also “phycocyanin” ○ E.g. Cyanobacteria ○ Absorbs strongly at 620 nm Bacteriochlorophyll a Allophycocyanin ○ Seen at 870, 805, 590, 360 nm ○ Absorbs strongly at 650 nm ○ Absorption depends on arrangement ○ In direct contact w/ photosynthetic in membrane membrane ○ E.g. Most purple bacteria ○ Surrounded either by phycocyanin and/or phycoerythrin Phycobiliproteins assemble into aggregates as “phycobilisomes” that attach to cyanobacterial thylakoids Energy transfer: Phycobilisomes → RC Allow growth in low light (under water) MICROBIAL PHYSIOLOGY 8 Chlorosomes B.) Noncyclic Photophosphorylation In anoxygenic green S & nonsulfur bacteria “Z” scheme – if light hits P680 RC, ○ E.g. Chlorobium, Chloroflexus reduction potential decreases = more Giant antenna systems but are NOT negative = e- passes through ETC = ATP attached to proteins generated via PMF Contain Bchl c, d, e arranged in dense ○ P680 RC BEFORE being exposed to arrays along axis of structure light is more positive Contain also FMO protein External e- donor required to repeat ○ H2O 3.) Electron Transport Chain Arrangement of protein complexes in purple bacteria = PMF Photosystems Cyanobacteria can do anoxygenic phototrophy A.) Cyclic Photophosphorylation by using PSI despite having Chl a In purple bacteria ○ Occurs in heterosis – oxygen Excitons – where transfer of light from inactivates nitrogenous enzymes antennae to RC takes place Heterosis – makes sure enzyme system is P870 – RC of purple bacteria NOT exposed to oxygen ○ Degrade PSII ensuring O2 is not reproduced as by product ○ Allow ATP production w/ PSI PSII – higher or more positive e- potential, thus appreciate any help such as from H2O