Microbial Nutrition - Lecture notes Semester 1 of first year PDF

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Microbial Nutrition Microorganisms require food for synthesis of molecular constituents of the cell and as an energy supply. Viruses obtain “resources” Cyanobacteria/algae – photosynthesis Protozoa – ingest solid food particles Bacteria and fungi – typically saprophytic (Saprophytes are more generally plants, fungi, or micro-organisms more accurately called myco-heterotrophs because they actually parasitize fungi, rather than dead organic matter directly. They live on dead or decomposing matter.) -Receives nutrients in aqueous solution -Digestion outside cell -Secrete enzymes into environment Basic nutrients required Carbon source – usually organic Nitrogen source – N2, inorganic compounds (NH3) or amino acids Inorganic ions – phosphate, sulphate Mg2+,K+, Ca2+ Essential metabolites Water Nutritional categories of microorganisms All microorganisms (except viruses) can be divided into groups based on their nutrition and sources of: Carbon Energy Electrons (reducing power) Nutritional categories of microorganisms Carbon sources Organic -Heterotrophs – reduced, preformed organic molecules

Inorganic Autotrophs (self feeding)

-CO2 is sole or main C source

Rely on carbon fixed by autotrophs Energy sources: Chemical -Chemotrophs – Oxidise organic or inorganic molecules extract electrons from organic compounds -Lithotrophs (rock feeder) – extract electrons from reduced inorganic substances Ferric iron is highly insoluble and is produced by these bacteria Light -Phototrophs – light energy source in photosynthesis -Extract electrons from reduces inorganic substances Chemoheterotrophic microorganisms (chemorganoheterotrophs) • Use complex organic materials for carbon, energy and electron sources e.g. most bacteria, fungi, protozoa (and all higher animals) • Contribute to biogeochemical cycles • Most pathogenic microorganisms fall into this grouping • Many used in the food and pharmaceutical industry

Chemoautotrophic microorganisms (chemolithoautotrophs) • Use CO2 as carbon source • Use inorganic materials as energy and electron source Example bacterial species: Gallionella - iron oxidisers: often involved in spoilage of well water, water pipe blockages, precipitating ferric iron Nitrosomonas – “ammonia powered”, contributes to the Nitrogen cycle Photoautotrophs (Photolithoautotrophs) • Use sunlight as energy source, fix CO2 as carbon source, inorganic electron source e.g. all green plants, Cyanobacteria, green sulphur bacteria (Chlorobium), purple sulphur bacteria (Chromatium) Pho t o h e t e r o t r o p h s( Ph o t o o r g a n o he t e r o t r op h s ) •Us es u n l i g h ta se n e r g ys o ur c e , b u tc o mp l e xo r g a n i cma t e r i a l sa sc a r b ona nde l e c t r o n s o u r c e . •e . g .p ur p l en o n s u l p hu rb a c t e r i u m,Rh o d o s pi r i l l u m Pho t o s y n t h e s i s ed i ffe r e n t l yf r o mg r e e np l a n t s

Fuelling Reactions (Energy Generation in Bacteria)

How do bacteria obtain energy from organic nutrients? Respiration e.g. Escherichia coli growing on nutrient agar Fermentation e.g. Lactobacillus in yoghurt Respiration • Substrate oxidised and final electron acceptor is obtained from environment (exogenous) • Gives up to 38 molecules of ATPs per molecule of glucose • O2 used as terminal electron acceptor in aerobic respiration • Alternative electron acceptors used in anaerobic respiration Electron acceptors used in respiration

Obligate aerobe – cannot produce energy without oxygen Fermentation • No overall net oxidation • No TCA cycle or electron transport chain involvement • Uses an endogenous electron acceptor • Redox balance maintained via reduced products • Net yield of 2 molecules of ATP per molecule of glucose Respiration and Fermentation

How knowledge of bacterial metabolism is used in identification tests Catalase test • aerobic respiration results in toxic byproducts which catalase detoxifies • catalase-positive bacteria include strict aerobes and facultative anaerobes • catalase-negative bacteria include strict anaerobes and facultative anaerobes that only ferment and don’t respire aerobically Oxidase test • Detects the presence of cytochrome c oxidase in the electron transport chain • Uses the reagent, tetra-methylp-phenylenediamine dihydrochloride (electron rich), as an artificial electron donor for cytochrome c • When reagent is oxidised by cytochrome c, changes from colourless to dark blue/purple Carbohydrate Fermentation Tests • Detect the ability to ferment a specific carbohydrate • Fermentation of specific sugars used to differentiate enteric bacteria • End products acidic – test media contain pH indicators Phenol red medium Yellow = acid pH Red = approx. neutral...