Microbial Nutrition PDF Fall 2024

Microbial Nutrition Nutrition: – Nutrients are acquired from the environment and used for cellular activities Essential nutrient: – Any substance, whether in elemental or molecular form that must be provided to an organism  Macronutrients: – Required in relatively large quant...

Microbial Nutrition Nutrition: – Nutrients are acquired from the environment and used for cellular activities Essential nutrient: – Any substance, whether in elemental or molecular form that must be provided to an organism  Macronutrients: – Required in relatively large quantities – Play principal roles in cell structure and metabolism Micronutrients (trace elements): – Present in smaller amounts – Involved in enzyme function and maintenance of protein structure  Inorganic nutrients: – Simple molecule that contains a combination of atoms other than carbon and hydrogen Organic nutrients: – Contain carbon and hydrogen atoms – Usually the product of living things  Carbon Sources Heterotroph: – An organism that must obtain its carbon in organic form – Dependent on other life forms – Most carbon sources exist in a form that is simple enough for absorption – Many carbon sources must be digested by the cell in order to be absorbed  Autotroph: – “Self-feeder” – Organism that uses inorganic CO2 as its carbon source – Have the capacity to convert CO2 into carbon compounds – Not dependent on other living things  Nitrogen Sources Indispensable to DNA, RNA, and ATP. – Primary nitrogen source for heterotrophs – Must be degraded into basic building blocks in order to be utilized Regardless of the source, nitrogen must be converted to NH3 before it enters the cell. – This is the only form that can be directly combined with carbon to synthesize amino acids and other compounds  Oxygen Sources Oxygen plays an important role in the structural and enzymatic functions of the cell. – Major component of carbohydrates, lipids, nucleic acids and proteins Common component of inorganic salts.  Hydrogen Sources Overlapping roles in the biochemistry of cells: – Maintaining pH – Forming hydrogen bonds between molecules – Serving as the source of free energy in oxidation-reduction reactions of respiration Phosphorous (Phosphate) Sources Main inorganic source is phosphate (PO4). – Derived from phosphoric acid (H3PO4) – Found in rocks and oceanic mineral deposits Key component of nucleic acids. – Essential to genetics of cells and viruses  Sulfur Sources Widely distributed throughout the environment in rocks and sediments. Essential component of vitamins and amino acids methionine and cysteine. – Form disulfide bridges that help determine the shape and structural stability of proteins  Essential Organic Nutrients Growth factor: – An organic compound such as an amino acid, nitrogenous base, or vitamin that cannot be synthesized by an organism – must be provided by the environment  How Microbes Feed: Nutritional Types Phototroph: microbes that photosynthesize. Chemotroph: microbes that gain energy from chemical compounds.  Autotrophs and Their Energy Sources Photoautotrophs: – Capture energy from light rays and transform it into chemical energy that can be used for cell metabolism – Produce organic molecules that can be used by themselves and heterotrophs Photosynthetic Bacteria Oscillatoria cyanobacteria  cyanobacteria Unlike eukaryotic plants and algae, cyanobacteria are prokaryotic organisms. They lack a membrane bound nucleus, chloroplasts, and other organelles found in plants and algae. Instead, cyanobacteria have a double outer cell membrane and folded inner thylakoid membranes that are used in photosynthesis. contain the pigments phycoerythrin and phycocyanin, which are responsible for their blue-green color. Anoxygenic photosynthetic bacteria are photoautotrophs (synthesize food using sunlight) that don't produce oxygen Anoxygenic bacteria are different than cyanobacteria they do not have chlorophyll to absorb light. They contain bacteriochlorophyll, which is capable of absorbing shorter wavelengths of light than chlorophyll. tend to be found in deep aquatic zones where shorter wavelengths of light are able to penetrate.  Autotrophs and Their Energy Sources Chemoautotrophs: – Chemoorganic autotrophs: Use organic compounds for energy and inorganic compounds as a carbon source – Lithoautotrophs: Require neither sunlight nor organic nutrients and rely totally on inorganic materials This process is accomplished through oxidation and ATP synthesis. Lithoautotrophs are able to fix carbon dioxide (CO2) through the Calvin cycle, a metabolic pathway in which carbon enters as CO 2 and leaves as glucose. This group of organisms includes sulfur oxidizers, nitrifying bacteria, iron oxidizers, and hydrogen oxidizers.  Autotrophs and Their Energy Sources Methanogens: – Chemoautotrophs that produce methane from hydrogen gas and carbon dioxide – Formed in anaerobic, hydrogen-containing microenvironments – Archaea are methanogens that live in ocean vents and hot springs – Methane can be used as a fuel and plays a role as a greenhouse gas.  Heterotrophs and Their Energy Sources Chemoheterotrophs: – Derive both carbon and energy from organic molecules – Organic molecules processed through respiration or fermentation and produces ATP  Heterotrophs and Their Energy Sources Aerobic respiration: – Principal energy-yielding pathway in animals, protozoa, fungi, and aerobic bacteria – Glucose and oxygen are reactants, and carbon dioxide is given off – Earth’s balance of energy and metabolic gases is dependent on this reaction – Complementary to photosynthesis  Heterotrophs and Their Energy Sources Saprobes: – Free-living microorganisms that feed primarily on organic material from dead organisms. Parasites: – Derive nutrients from the cells or living tissues of a host.  Saprobic Microorganisms Decomposers of plant litter, animal matter, and dead microbes. – Important in recycling of organic materials. Most saprobes have a rigid cell wall and cannot engulf large particles of food. – Bacteria and fungi Release enzymes into the environment to digest food into smaller particles that can be transported into the cell. Saprobic Microorganisms  Parasitic Microorganisms Live on or in the body and cause some degree of harm to the host. – Considered pathogens because they can damage tissues and cause death. – Ectoparasites: live on the body. – Endoparasites: live in organs and tissues. – Intracellular parasites: live within cells. – Obligate parasites: unable to live outside of a living host.  The Movement of Molecules: Diffusion and Transport Diffusion: – The movement of molecules in a gradient from an area of higher density or concentration to an area of lower density or concentration – Diffusion across a cell membrane is determined by the concentration gradient and the permeability of the substance. The Movement of Water: Osmosis Osmosis: The movement of water across a selectively permeable membrane. – The membrane is selectively or differentially permeable: has passageways that allow the passage of water but not other substances. Osmosis  Osmosis Isotonic conditions: – The external environment is equal to the cell’s internal environment – Diffusion of water proceeds at the same rate on both sides of the cell – Generally the most stable environments for cells; already in an osmotic steady state with the cell  Osmosis Hypotonic conditions: – Solute concentration of the external environment is lower than that of the cell’s internal environment – Pure water is the most hypotonic environment because it has no dissolved solutes – The net direction of osmosis is from the hypotonic solution into the cell – Cells without walls can swell and burst  Osmosis Hypertonic conditions: – Environment outside the cell has a slightly higher concentration of solutes than inside the cell – High osmotic pressure forces water to diffuse out of the cell – Limits the growth of microbes – Principle behind using concentrated salt and sugar solutions to preserve food.  Adaptations to Osmotic Variations in the Environment Isotonic conditions pose little stress on cells. Hypotonic environments: – Bacteria and amoeba living in fresh pond water – Bacteria: cell wall protects cells from bursting – Amoeba: utilize a contractile vacuole that constantly moves excess water out of the cell; requires energy  Adaptations to Osmotic Variations in the Environment Hypertonic environments: – Cells must restrict the loss of water to the environment or increase the salinity of the internal environment – Halobacteria: – Absorb salt to make their cells isotonic with the environment Have a physiological need for a high salt concentration in their environments.  Adaptations to Osmotic Variations in the Environment Facilitated diffusion: – Mediated transport – Utilizes a carrier protein that will bind a specific substance Transport Processes in Cells  Adaptations to Osmotic Variations in the Environment Saturation: – The rate of transport of a substance is limited by the number of binding sites on the transport proteins – The rate of transport increases as the rate of substance concentration until all of the binding sites are occupied.  Adaptations to Osmotic Variations in the Environment Competition: – Two molecules of the same shape can bind to the same binding site on the carrier protein – The chemical with the higher binding affinity or the chemical in higher concentration will be transported at a greater rate.  Active Transport Features of Active Transport: – Transports nutrients against a concentration gradient or with a concentration gradient at a faster rate – Presence of specific membrane proteins: permeases and pumps – Expenditure of energy  Endocytosis Endocytosis: – Transport of large molecules, particles, or liquids across the cell membrane by certain eukaryotes – Requires the expenditure of energy – Phagocytosis: endocytosis by amoebas and certain white blood cells that ingest whole cells or large solid matter – Pinocytosis: entry of oils or molecules in solution into the cell Transport in Cells  Environmental Factors That Influence Microbes – Heat – Cold – Gases – Acid – Radiation – Osmotic pressure – Hydrostatic pressure – Other microbes Range of temperatures for a given microbial species 1. Minimum temperature: – The lowest temperature that permits a microbe’s continued growth and metabolism.  Temperature 2. Maximum temperature: – Highest temperature at which growth and metabolism can proceed – If the temperature rises slightly above maximum, growth will stop – If the temperature continues to rise, enzymes and nucleic acids will become denatured, or permanently inactivated.  Temperature 3. Optimum temperature: – Intermediate temperature range between minimum and maximum – Promotes the fastest rate of growth and metabolism – Small chemical differences in bacterial membranes which affect their fluidity allow them to thrive at different temperatures. Temperature  Temperature Psychrophiles: – Organisms that have an optimum temperature below 15°C – Capable of growth at 0°C – Cannot grow above 20°C – Facultative psychrophiles: grow slowly in the cold, but have an optimum temperature between 15 – 30°C.  Temperature Mesophiles: – Majority of medically significant organisms – Individual species can grow from 10 – 50°C – Optimum growth temperature: 20 – 40°C – Most human pathogens: 30 – 40°C – Thermoduric microbes survive short exposure to high temperatures; common contaminants of heated or pasteurized foods.  Temperature Thermophiles: – Grow optimally at temperatures above 45°C – Live in soil and water associated with volcanic activity, compost piles – Range from 45 – 80°C.  Gases (O2, CO2, N2) Microbes fall into one of three categories: – Those that use oxygen and can detoxify it – Those that can neither use oxygen nor detoxify it – Those that do not use oxygen but can detoxify it  How Microbes Process Oxygen Superoxide ion (O2-), hydrogen peroxide (H2O2), and hydroxyl radicals (OH-): – Destructive metabolic byproducts of oxygen – Cells use enzymes to scavenge and neutralize them Superoxide dismutase. is an enzyme that catalyzes the superoxide (O2−) radical into either ordinary molecular oxygen (O 2) or hydrogen peroxide (H2O2). Catalase. It catalyzes the decomposition of hydrogen peroxide to water and oxygen. It is a very important enzyme in protecting the cell from oxidative damage by reactive oxygen species (ROS). How Microbes Process Oxygen Aerobe (aerobic organism): – Can use gaseous oxygen in its metabolism – Possesses the enzymes needed to process toxic oxygen products – Obligate aerobe: an organism that cannot grow without oxygen. How Microbes Process Oxygen Facultative anaerobe: – An aerobe that does not require oxygen for its metabolism – Capable of growth in the absence of oxygen – Metabolizes by aerobic respiration when oxygen is present – Adopts anaerobic metabolism (fermentation) when oxygen is absent. How Microbes Process Oxygen Microaerophile: – Does not grow at normal atmospheric conditions of oxygen – Requires a small amount of oxygen in its metabolism. How Microbes Process Oxygen Anaerobe: – Lacks the metabolic enzyme systems for using oxygen in respiration – Strict or obligate anaerobes cannot tolerate free oxygen and will die in its presence Live in highly reduced habitats such as lakes, oceans, and soil How Microbes Process Oxygen Aerotolerant anaerobes: – Do not utilize oxygen – Can survive and grow to a limited extent in its presence – Not harmed by oxygen because they possess alternative mechanisms for breaking down peroxides and superoxide.  How Microbes Process Oxygen Capnophiles: – Grow best at a higher CO2 tension than is normally present in the atmosphere – Important in the isolation of some pathogens – Incubation is carried out in a CO2 incubator that provides 3 – 10% CO2 – Campylobacter jejuni is now recognized as one of the main causes of bacterial foodborne disease in many developed countries – In 2004, a capnophilic bacterium was characterized that appears to require carbon dioxide.  pH Obligate acidophiles: – Require an acidic environment for growth – Molds and yeasts tolerate acid and are common spoilage agents of pickled foods Alkalinophiles: – Live in hot pools and soils that contain high levels of basic minerals – Bacteria that decompose urine create alkaline conditions  Osmotic Pressure Obligate Halophiles: – Require high concentrations of salt for growth – Have significant modifications to their cell walls and membranes and will lyse in hypotonic habitats Facultative halophiles: – Resistant to salt, even though they do not normally reside in high-salt environments  Radiation Protective measures against radiation: – Yellow carotenoid pigments absorb and dismantle toxic oxygen – Other microbes use enzymes to overcome the damaging effects of UV radiation on DNA  Hydrostatic Pressure Barophiles: – Deep sea microbes that exist in pressures up to 1000x atmospheric pressure – So strictly adapted to high pressures that they rupture when exposed to normal atmospheric pressure Associations Between Organisms Symbiosis: a general term used to denote a situation in which two organisms live together in a close partnership. Mutualism: exists when organisms live in an obligatory but mutually beneficial relationship. Associations Between Organisms Commensalism: – Commensal: receives benefits – Coinhabitant: neither harmed nor benefitted Associations Between Organisms Parasitism: – Host: provides the parasitic microbe with nutrients and a habitat – Parasite: multiplication of the parasite usually harms the host to some extent Antagonism: – Arises when members of a community compete – One microbe secretes chemical substances into the surrounding environment that inhibit or destroy other microbes Associations Between Organisms Antibiosis: The production of inhibitory compounds, such as antibiotics. Mold secreting penicillin, destroying bacteria. Synergism: – An interrelationship between two or more free- living organisms that benefits both but is not necessary for their survival.