Lecture 6 - Bacterial Nutrition, Media, and Transport.pdf

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University of Toronto St. George
Cell and Systems Biology
William Navarre

MGY377H © Lisa | Page 13 L E C T U R E 6 : B A C T E R I A L N U T R I T I O N , M E D I A , & T R A N S P O R T BACTERIAL NUTRITION  the nutritional requirements of a bacterium such as E. coli are revealed by the cell’s elemental composition, which consists of C, H, O, N, S, P, L, Mg, Fe, Ca, Mn, & traces of Zn, Co, Cu, & Mo  these elements are found in the form of water, inorganic ions, small molecules, & macromolecules which serve either a structural or functional role in the cells  macronutrients: required in large amounts (not to be confused w NRG source, these are for incorporation into the cell)  micronutrients: required in trace amounts  major elements, their sources, & fxs in bacterial cells: % of dry Element Source Function weight Carbon 50 organic compounds or CO 2 main constituent of cellular material H2O, organic compounds, constituent of cell material & cell water2 O serves as an Oxygen 20 CO , O electron acceptor in aerobic respiration 2 2 Nitrogen 14 NH 3 NO 3 organic constituent of amino acids, nucleic acids nucleotides, & compounds, N 2 coenzymes H O, organic compounds, Hydrogen 8 2 main constituent of organic compounds & cell water H 2 inorganic phosphates constituent of nucleic acids, nucleotides, phospholipids,LPS, Phosphorus 3 (PO4) teichoic acids SO , H S, S , organic sulfurconstituent of cysteine, methionine, glutathione, several Sulfur 1 4 2 compounds coenzymes main cellular inorganic cation & cofactor for certain Potassium 1 potassium salts enzymes Magnesium 0.5 magnesium salts inorganic cellular cation, cofactor for certain enzymatic rxs Calcium 0.5 calcium salts inorganic cellular cation, cofactor for certain enzymes & a component of endospores component of cytochromes & certain non-heme iron- Iron 0.2 iron salts proteins & a cofactor for some enzymatic rxs CARBON SOURCE FOR BACTERIAL GROWTH  the C requirements of organisms must be met by organic carbon (a chemical compound w a C-H bond) or by CO 2 1. heterotrophs: organisms that use organic C such as AAs, FAs, organic acids, sugars, nitrogen bases, aromatic compounds, etc. 2. autotrophs: organisms that use CO as a s2le source of C for growth ENERGY SOURCES FOR BACTERIAL GROWTH  all living organisms require a source of NRG 1. phototrophs: organisms that use radiant NRG (light) 2. chemoorganotrophs: organisms that use an organic form of C 3. lithotrophs: organisms that use inorganic compounds MGY377H © Lisa| Page 213 MAJOR NUTRITIONAL TYPES OF PROKARYOTES Nutritional type Energy source Carbon source Example Photoautotrophs light CO 2 Cyanobacteria, some Purple & Green Bacteria Organic Some Purple & Green Photoheterotrophs light compounds Bacteria Chemoautotrophs or Inorganic compounds A few Bacteria & many Lithotrophs (Lithoautotrophs) ex. H2, NH3, NO2, H2S CO 2 Archaea Chemoheterotrophs or Organic compounds Organic Most Bacteria, some Heterotrophs compounds Archaea OTHER MACRONUTRIENTS  bacterial cell is 12% N, N is a key element in proteins, nucleic acids, & other constituents -  inorganic form such as NH ,3nitrate (NO )3 AAs, or nitrogen gas (N 2 nitrogen-fixing bacteria)  P (lipids), S, K, Mg, Ca, Na are also considered macronutrients – they have many essential fxs in cells MICRONUTRIENTS (IRON)  iron is a key micronutrient, w major roles in cellular respiration (cytochrome, iron-sulfur proteins in electron transport), nitrogenases, etc.  bacteria have several systems for uptake of Fe that involve siderophores (solubilizes Fe)  the ability to acquire Fe is often considered a virulence mechanism for pathogens (no Fe  infx can be controlled)  our bodies have multiple systems to bind & transport Fe, essentially competing for Fe w pathogens  imp aspect of our immune defense: 1) iron-chelating agents (ex. Lipochalin-2 in gut) 2) iron-transporting systems (ex. NRAMP1 in phagosome of macrophages) GROWTH FACTORS  growth factors are organic compounds  required in small amounts by cells  they fulfill specific roles in biosynthesis  the need for a growth factor results from either a blocked or missing metabolic pathway in the bacterial cell (can’t make the component, need it from envmt)  growth factors are organized into 3 categories: 1. purines & pyrimidines – required for synthesis of nucleic acids (DNA & RNA) 2. amino acids – required for the synthesis of proteins 3. vitamins – needed as coenzymes & functional groups of certain enzymes MGY377H © Lisa| Page 313  p-Aminobenzoic acid is a precursor of folic acid  bacteria need to make folic acid which is a precursor for nucleotide biosynthesis  there is a drug that mimics this folic acid biosynthetic pathway  humans need to take vitamins to get folic acid (we can’t make it) CULTURE OF BACTERIA  cross-feeding bw Staphylococcus aureus & Haemophilus influenzae growing on blood agar  Haemophilus influenzae was first streaked on to the blood agar plate followed by a cross streak w Staphylococcus aureus  H. influenzae is a fastidious bacterium (doesn’t grow everywhere) which requires both hemin & NAD for growth  small amount of bacteria grow in the regions close to the cross  there is sufficient hemin in blood for growth of Haemophilus, but the medium is insufficient in NAD  S. aureus produces NAD in excess of its own needs & secretes it into the medium, which supports the growth of Haemophilus as satellite colonies  culture of bacteria allows identification, characterization, & ability to establish links to disease (ex. Koch’s postulates)  medium must contain all required nutrients, correct growth envmt (temp, O conc) 2  most bacteria (99%) on earth can’t be cultured yet ex. most bacteria in our gut can’t be cultured (only subgroups – gut microbiome)  culture media for the growth of bacteria: 1. liquid media – used for growth of pure batch cultures 2. solidified media – used widely for the isolation of pure cultures, for estimating viable bacteria populations, & a variety of other purposes  agar: polysaccharide from red algae, used as solidifying agent  used when there is a mixture of culture & want to purify specific type of colony MGY377H © Lisa Zh| Page 4  types of culture media (6): 1. chemically-defined medium – the exact chemical composition is known, usually composed of pure chemicals off the shelf 2. complex medium – the exact chemical constitution of the medium is not known, contains digests of animal/plant products such as milk, yeast, or beef ex. LB  complex medium (LB) for the growth of fastidious bacteria (pH 6.6): Component Amount Function of component Beef extract 1.5 g source of vitamins & other growth factors Yeast extract 3.0 g source of vitamins & other growth factors Peptone 6.0 g source of amino acids, N, S, & P Glucose 1.0 g C & NRG source Agar 15.0 g inert solidifying agent water 1000 ml 3. minimal medium – provides only the exact nutrients (including any growth factors) needed by the organism for growth  minimal medium for the growth of Bacillus megaterium (ex of a chemically-defined medium): Component Amount Function of component sucrose 10.0 g C & NRG source K2HPO 4 2.5 g pH buffer, P & K source KH2PO 4 2.5 g pH buffer, P & K source (NH 4 2PO 4 1.0 g pH buffer, N & P source MgSO ·7H O 0.20 g S & Mg source 4 2 2+ FeSO4·7H2O 0.01
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