MICROBIOLOGY-62-69.pdf

MICROBIAL NUTRITION Bacteria require a constant influx of certain substances from their habitat Organisms use a variety of nutrients for their energy needs and to build organic molecules and cellular structures All organisms require...

MICROBIAL NUTRITION Bacteria require a constant influx of certain substances from their habitat Organisms use a variety of nutrients for their energy needs and to build organic molecules and cellular structures All organisms require a source of elements such as carbon, hydrogen, oxygen, phosphorous, potassium, nitrogen, sulfur, calcium, iron, sodium, chloride, magnesium, and certain other elements Microbes obtain nutrients from variety of sources Nutrition - Process by which chemical substances (nutrients) are acquired from the environment and used for cellular activities Essential nutrient - Any substance that must be provided to an organism - Two categories of essential nutrients: ○ Macronutrients ○ Micronutrients or Trace elements Macronutrients - Required in relatively large quantities and play principal roles in cell structure and metabolism ○ Carbon ○ Nitrogen ○ Oxygen ○ Hydrogen Micronutrients - Also known as trace elements - Present in much smaller amounts - Involved in enzyme function and maintenance of protein structure  - Need very little amount but critical to cell function - Often used as enzyme cofactors ○ Manganese ○ Cobalt ○ Zinc ○ Molybdenum ○ Nickel ○ Copper Organic nutrients - Contain carbon and hydrogen atoms and are the products of living things - Simple organic molecules such as methane - Large polymers (carbohydrates, lipids, proteins, nucleic acids) Inorganic nutrient - Atom or simple molecule that contains a combination of atoms other than carbon and hydrogen - Found in the crust of the earth, bodies of water, and the atmosphere Essential Nutrients - Chemicals that are necessary for particular organisms, which they cannot manufacture by themselves ○ Carbon ○ Phosphate ○ Hydrogen ○ Sulfur ○ Oxygen ○ Nitrogen  a. Carbon - Is a fundamental macronutrient for bacteria and serves as the primary building block for all cellular components - Needed for the skeleton or backbone of all organic molecules and molecules serving as carbon sources normally also contribute both oxygen and hydrogen atoms - Bacteria utilize carbon for various essential processes, including energy production, synthesis of cellular structures, and metabolism. b. Nitrogen - Main reservoir is nitrogen gas (N2) - 79% of earth’s atmosphere is N2 - Part of the structure of proteins, DNA, RNA & ATP – these are the primary source of N for heterotrophs - Some bacteria & algae use inorganic N nutrients (NO3-, NO2-, or NH3) - Some bacteria can fix N2 - Regardless of how N enters the cell, it must be converted to NH3, the only form that can be combined with carbon to synthesis amino acids, etc c. Oxygen - Major component of carbohydrates, lipids and proteins - Plays an important role in structural & enzymatic functions of cell - Component of inorganic salts (sulfates, phosphates, nitrates) & water - O2 makes up 20% of atmosphere - Essential to metabolism of many organisms d. Hydrogen - Major element in all organic compounds & several inorganic ones (water, salts & gasses) - Gasses are produced & used by microbes - Roles of hydrogen Maintaining pH Forming H bonds between molecules Serving as the source of free energy in oxidation-reduction reactions of respiration e. Phosphorous - Component of phospholipid membranes, DNA, RNA, ATP, and some proteins - Main inorganic source is phosphate (PO4-3) derived from phosphoric acid (H3PO4) found in rocks & oceanic mineral deposits - Key component of nucleic acids, essential to genetics - Serves in energy transfers (ATP) f. Sulfur - Widely distributed in environment, rocks, sediments contain sulfate, sulfides, hydrogen sulfide gas and sulfur - Component of sulfur-containing amino acids, disulfide bonds critical to tertiary structure of proteins (a.a. methionine& cysteine), and in vitamins (thiamin and biotin) - Contributes to stability of proteins by forming disulfide bonds Other Important Nutrients Sodium (Na) - Important for certain types of cell transport Calcium (Ca) - Stabilizer of cell wall and endospores of bacteria Magnesium (Mg) - Component of chlorophyll and a stabilizer of cell membranes and ribosomes Iron (Fe) - Important component of the cytochrome proteins of cell respiration Zinc (Zn) - Essential regulatory element for eukaryotic genetics  Copper, Cobalt, Nickel, Molybdenum, Manganese, Silicon, Iodine, and Boron are needed in small amounts by some microbes, but not others Other chemical requirements ○ Trace elements – only required in small amounts; usually found in sufficient quantities in tap water ○ Growth factors – necessary organic chemicals that cannot be synthesized by certain organisms (vitamins, certain amino acids, purines, pyrimidines, cholesterol, NADH, and heme) Growth Factors - Organic compounds, required in very small amount and then only by some cells Amino acids - Needed for protein synthesis Purines and pyrimidines - For nucleic acid synthesis Vitamins - Small organic molecules that usually make up all or part enzyme cofactors, and only very small amounts are required for growth Nutritional Types of Microorganisms 1. Carbon source a. Autotroph - Can use CO2 as a sole carbon source (Carbon fixation) b. Heterotroph - Requires an organic carbon source; cannot use CO2 as a carbon source 2. Energy Source a. Phototroph - Uses light as an energy source b. Chemotroph - Uses energy from the oxidation of reduced chemical compounds 3. Electron (Reduction potential) Source a. Organotroph - Uses reduced organic compounds as a source for reduction potential b. Lithotroph - Uses reduced inorganic compounds as a source for reduction potential Two Kinds of Bacterial Heterotrophs 1. Saprobes - Free living organisms that feed on organic detritus from dead organisms - Decomposers of plant litter, animal matter, and dead microbes - Recycle organic nutrients 2. Parasites - Derive nutrients from the cells or tissues of a living host - Pathogens - Cause damage to tissues or even death - Range from viruses to helminths - Less strict parasites can be cultured artificially - If provided with the correct nutrients and environmental conditions - The vast majority of microbes causing human disease are chemoheterotrophs ○ Ectoparasites - Live on the body ○ Endoparasites - Live in the organs and tissues a. Intracellular parasites - Live within cells such as the leprosy bacillus and the syphilis spirochete b. Obligate parasites - Unable to grow outside of a living host How Microbes Eat: Transport Mechanisms The process of moving molecules into or out of cells Transport of necessary nutrients occurs across the cell membrane, even in organisms with cell walls The driving force of transport is atomic and molecular movement a. Passive transport - Do not require energy, substances exist in a gradient and move from areas of higher concentration towards areas of lower concentration ○ Diffusion ○ Facilitated diffusion - Requires a carrier ○ Osmosis - Water b. Active transport - Require energy and carrier proteins, gradient independent ○ Carrier-mediated active transport ○ Group translocation - Transported molecule chemically altered ○ Bulk transport - Endocytosis, Exocytosis, Pinocytosis Nutrient Transport Processes 1. Simple Diffusion - Movement of substances directly across a phospholipid bilayer, with no need for a transport protein - Movement from high to low concentration - No energy expenditure (e.g. ATP) from cell - Small uncharged molecules may be transported via this process, e.g. H2O, O2, CO2 2. Facilitated Diffusion - Movement of substances across a membrane - with the assistance of a transport protein - Movement from high ® low concentration - No energy expenditure (e.g. ATP) from cell - The rate of diffusion across selectively permeable membranes is greatly increased by the use of carrier proteins, sometimes called permeases, which are embedded in the plasma membrane.  - Two mechanisms: ○ Channel Proteins ○ Carrier Proteins Diffusion - All molecules (solid, liquid, or gas) are in continuous movement - As temperature increases, molecular movement becomes faster - In any solution, including cytoplasm, these moving molecules cannot travel very far without having collisions with other molecules - As a result of these collisions, the directions of colliding molecules are altered and unpredictable - If the solute is more concentrated in one area than another, the thermal movement will eventually distribute the molecules evenly - Diffusion of molecules across the cell membrane is largely determined by the concentration gradient and permeability of the substance The Movement of Water: Osmosis Osmosis - The diffusion of water through a selectively, or differentially, permeable membrane - Has passageways that allow free diffusion of water, but block certain other dissolved molecules - When the membrane is placed between solutions of differing concentrations of solute and the solute cannot pass through the membrane, water will diffuse at a faster rate from the side that has more water to the side that has less water - This will continue until the concentration of water is equalized on both sides of the membrane - Living membranes generally block the entrance and exit of larger molecules and permit the free movement of water - Most cells are surrounded by some free water and the amount of water entering or leaving has a major impact on cellular activities and survival - This osmotic relationship between cells and their environment is determined by the relative concentrations of the solutions on either side of the cell membrane Active transport - Transport of solute molecules to higher concentrations, or against a concentration gradient, with the use of metabolic energy input - Features of active transport: The transport of nutrients against the diffusion gradient Movement from low to high concentration - Movement of substances across a membrane with the assistance of specific membrane proteins (permeases and pumps) - The expenditure of energy (e.g. ATP or ion gradients) from cell ○ Examples of substances transported actively are monosaccharides, amino acids, organic acids, phosphates, and metal ions Active Transport systems in bacteria 1. ATP-binding cassette transporters (ABC transporters) - Active in bacteria, archaea and some eukaryotes - The target binds to a soluble cassette protein (in periplasm of gram-negative bacterium, or located bound to outer leaflet of plasma membrane in gram- positive bacterium). The target-cassette complex then binds to an integral membrane ATPase pump that transports the target across the plasma membrane  a. Cotransport systems - Transport of one substance from a low to high concentration as another substance is simultaneously transported from high to low ○ For example: lactose permease in E. coli: As hydrogen ions are moved from a high concentration outside to low concentration inside, lactose is moved from a low concentration outside to high concentration inside b. Group translocation system - A molecule is transported while being chemically modified ○ Phosphoenolpyruvate: sugar ○ Phosphotransferase systems (PTS) ○ PEP + sugar (outside) to pyruvate + sugar-phosphate (inside) The best-known group translocation system is the phosphoenolpyruvate: sugar phosphotransferase system (PTS), which transports a variety of sugars into prokaryotic cells while Simultaneously phosphorylating them using phosphoenolpyruvate (PEP) as the phosphate donor The phosphoenolpyruvate: sugar phosphotransferase system of E. coli. The following components are involved in the system: phosphoenolpyruvate, PEP; enzyme 1, E I; the low molecular weight heat-stable protein, HPr; enzyme 11, E II,- and enzyme III, E III 2. Iron uptake by siderophores - Low molecular weight organic molecules that are secreted by bacteria to bind to ferric iron (Fe3+); necessary due to low solubility of iron; Fe3+-siderophore complex is then transported via ABC transporter - Siderophore-iron complex is then transported back into the bacterial cell through specific receptors Bulk transport: Endocytosis and Exocytosis - Processes that involve the movement of large particles, macromolecules, or fluids into (Endocytosis) or out of (Exocytosis) a cell by engulfing them in vesicles formed from the cell membrane - Transport of large molecules, particles, liquids, or other cells across the cell membrane requiring the expenditure of energy - Cell encloses the substance in its membrane - Simultaneously forms a vacuole and engulfs the substance ○ Phagocytosis - Accomplished by amoebas and white blood cells - Ingest whole cells or large solid matter ○ Pinocytosis - Ingestion of liquids such as oils or molecules in solution