Prokaryote Nutrition and Growth

Describe features of symbiosis (1)

Bacteria may be free-living in symbiotic association. Commensalism - bacterium uses larger organism as its physical environment, acquiring nutrients etc. but not directly from the other organism. Such bacteria in humans are called normal flora

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Describe features of symbiosis (2)

Mutualism - bacterium and larger organism have a mutually beneficial relationship. Normal gut flora digesting complex carbohydrates. Parasitism - bacterium live at the expensive of larger organism. Disease causing parasites are pathogens

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Describe features of symbiosis (3)

Some commensal organisms are also appropriate pathogens. Normal flora might be in places where it shouldn't be e.g. gut flora on skin (infection). No bacteria should be in the blood. Parasitism/infection - bacteria which cause disease

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Describe features of symbiosis (4)

Shouldn't be in the body. Poor immune system (e.g. chemotherapy, increased use of steroids) - increased risk of infection (change in flora). Colonisation - organism co-exists with humans. Contamination - e.g. spores, spread infection

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What is the difference between colonisation and contamination? (1)

Time length (longer for colonisation), able to remove contamination quickly (e.g. hand hygiene). Infection - cause tissue damage. Contamination of MRSA e.g. direct contact. Cut/open wound, spores enter broken skin (infection/inflammation)

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What is the difference between colonisation and contamination? (2)

Important to understand context of samples e.g. see if clinical features match to detection of bacteria (e.g. fever, ill, infection). Differentiate between normal flora and pathogens. Patients may get antibiotics when it is not necessary

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What are the sources and uses of macronutrients? (1)

Carbon (CHOs, CO2, CH4, oil, plastics). Hydrogen (H+ source and electrons for energy metabolism). Autotrophs need H to reduce CO2 to H2O, heterotrophs obtain H from organic molecules.

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What are the sources and uses of macronutrients? (2)

Nitrogen (constituent of amino acids, nucleotides, phospholipids cell wall components, sources - amino acids, NH4+, NO3-, N2). Sulphur (for cysteine/methionine, B vitamins (biotin, thiamine), sources - organic molecules, SO4 2-, SH reduction)

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What are the sources and uses of macronutrients? (3)

Phosphorus (for production of ATP, PO4 3- in culture media provides buffering capability). Oxygen (required for synthesis of organic molecules, anaerobes/aerobes, terminal electron acceptor of electron transport in anaerobes, O2 toxic in anaerobes)

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What are the sources and uses of macronutrients? (4)

Aerobic bacteria are able to oxidise carbon sources which are reduced (methane, propane). Anaerobe cytoplasm provides reducing environment to action of prodrug antibiotic metronidazole

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What are the oxygen requirements for different species? (1)

Obligate aerobe (completely dependent on atmospheric O2 for growth e.g. Mycobacterium spp.).Facultative anaerobe (doesn't require O2 for growth but grows better in its presence e.g. E.coli)

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What are the oxygen requirements for different species? (2)

Aerotolerant anaerobe (grows equally will in presence/absence of O2 e.g. Streptococcus pyogenes). Obligate anaerobe (dies in presence of O2 e.g. Clostridium spp.)

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What are the oxygen requirements for different species? (3)

Microaerophile (requires 2-10% O2 for growth, damaged by atmospheric O2 e.g. Treponema pallidum

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Describe features of micronutrients (1)

Potassium (common enzyme co-factor). Sodium (used with Cl for osmoregulation of cells, needed for Na dependent transport processes). Magnesium (integral part of photosynthetic pigments, common enzyme co-factor for ATPase)

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Describe features of micronutrients (2)

Iron (found in haem containing proteins (e.g cytochromes catalase), secrete siderophores (chelators) to scavenge for environmental iron (III). Cobalt (constituent of Vit B12)

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Describe features of micronutrients (3)

Trace elements - substances needed only in very small quantities as enzyme co-factors e.g. copper, zinc, molybdenum, nickel, tungsten, selenium

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What is passive diffusion?

Small non-polar molecules and uncharged polar molecules diffuse across membrane

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What is facilitated diffusion?

Passage across cell membrane down concentration gradient via transport protein (permease). Not ideal for bacteria in environments with low concentration of nutrients

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Describe features of active transport

ATP binding cassette transporter. Transporter receives substrate from binding protein. ATP hydrolysis facilitates entry. Utilisation of proton motive force (PMF) for transport. Proton gradient across membrane provides energy for transport

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What are the environmental preferences for different types of bacteria? - Temperature (1)

Psychrophile (grows well at 0 degrees Celsius, optimum growth at 15 degrees Celsius e.g. Bacillus psychrophilus). Psychotroph (can grow at 0-7 degrees Celsius, optimum growth at 25 degrees Celsius e.g. Listeria monocytogenes)

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What are the environmental preferences for different types of bacteria? - Temperature (2)

Mesophile (optimum growth at 20-45 degrees Celsius e.g. E.coli, Neisseria gonorrhoea). Thermophile (optimum growth at 55-65 degrees Celsius e.g. Geobacillus stearothermophilus)

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What are the environmental preferences for different types of bacteria? - Solute and water activity

Osmotolerant (grows over wide range of solute concentrations e.g. Staphylococcus aureus). Halophile (requires high NaCl conc, >0.2 M e.g. H.pylori)

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What are the environmental preferences for different types of bacteria? - pH

Acidophile (growth optimum between pH 0-5.5 e.g. H.pylori). Neutrophile (growth optimum between 5.5-8.0). Alkalophile (growth optimum between 8.5-11.5)

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Describe features of bacterial growth (1)

Bacterial growth refers to an increase in population rather than individual size. Cells divide by binary fission after replication of their genome to produce cloned daughter cells. E.coli can reproduce every 20 min (1 cell becomes 1 billion in 10h)

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Describe features of bacterial growth (2)

Mutation rate may introduce resistance. E.g. CF sputum samples, find different species, bacterial growth

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Describe features of generation time (1)

N0 (number of bacteria at early stage of exponential growth). Nt (number of bacteria present after period of exponential growth). t (time interval between N0 and Nt). n (number of generations)

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Describe features of generation time (2)

Nt = N0 x 2^n. n = (log Nt - log N0) /log 2. Generation time = t/n. Plot log n (number of cells) against time (minutes). (E.g. Q)

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What is the lag phase?

Adaptation to medium, little increase in cell numbers, cells are metabolically active, increase in ATP production, increased biosynthesis. Bacteria get used to surroundings, prepare for growth cycle

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What is the log phase? (1)

After cells have adapted to medium they undergo rapid cell division at regular rates (generation time). Population doubling each generation time. Exponential/logarithmic growth. Antibiotics are active against highly metabolic active cells

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What is the log phase? (2)

Need bacteria to actively grow in order for antibiotics to be effective

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What is the stationary phase? (1)

Nutrients limited. Certain requires inorganics such as O2 decrease. Toxic waste concentrations increase. Cell metabolism decreases. Population static. Some cells may become metabolically inactive (quiescence). Some antibiotics become ineffective

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What is the stationary phase? (2)

Negative acceleration. Cells may become dormant again until lag phase occurs (more nutrients or cell numbers/population demand decreases)

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What is the death phase? (1)

Medium becoming less supportive. More cells die than being produced. May be due to antibiotics (might get death phase after log phase and before stationary phase). Change in environment/no longer have nutrients/toxic environment

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What is the death phase? (2)

Population decreases if source decreases, supply/demand. May return to log phase again if source of nutrient remains (no decrease). Antibiotics given as a course during phase, due to PK of drugs

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What is the death phase? (3)

Also allows bacteria to return to log phase where antibiotics are effective

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What are primary metabolites?

Produced during log phase, growth, products essential for cell growth e.g. amino acids, nucleotides, lipids, CHO, proteins etc, (substrate decreases, products increase as cell number increases)

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What are secondary metabolites?

Produced at onset of stationary phase or as a result of quorum sensing, alkaloids, antibiotics, pigments, toxins, pheromones, virulence factors etc (substrate decreases, products rapidly increase as cell number increases)

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Prokaryote Nutrition and Growth

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