Elements of Microbial Nutrition, Ecology, and Growth
Microbial Nutrition
Reference: https://sites.google.com/site/rccmicrobiology/chapter-7-elements-of-microbial-nutrition-ecology-and-growth
- Nutrition: process in which chemical substances are acquired from the environment and used in cellular activities such as metabolism and growth.
- Essential nutrient: any substance that is required by an organism.
- Macronutrients: required in large quantities and play principle roles in cell structure and metabolism.
- Micronutrients & trace elements: manganese, zinc, and nickel and required in minute amounts and important in enzyme function and maintenance of protein structure.
- Organic nutrient: molecules containing hydrogen and carbon.
- Chemical Analysis of Microbial Cytoplasm
- 70% water.
- Protein next prevalent.
- 97% of dry cell weight comes from organic compounds.
- 96% of cell composed of 6 elements (CHNOPS).
- Carbon Sources
- Heterotroph: organism that must obtain it's carbon in an organic form.
- Dependent on other life forms.
- Autotroph: organism that must obtain carbon in an inorganic form (CO2).
- Not dependent on other life forms.
- Nitrogen Sources
- Indispensable to the structure of proteins, DNA, RNA, and ATP.
- Nitrogen needs to be converted to NH3 to combine with carbon to synthesize amino acids and other compounds.
- Oxygen Sources
- Component of carbohydrates, lipids, and proteins.
- Important role of structural and enzymatic functions of the cell.
- Essential for metabolism in many organisms.
- Hydrogen Sources
- Hydrogen roles overlap:
- Maintaining pH.
- Forming bonds between molecules.
- Serving as the source of free energy in oxidation-reduction reactions of respiration.
- Phosphorus Sources
- Main inorganic source is phosphate (PO4^-3) derived from phosphoric acid.
- Important for energy transfers.
- Sulfur Sources
- Rock and sediments can contain sulfates, sulfides, hydrogen sulfide gas, and elemental sulfur.
- Essential for some vitamins (B1) and amino acids cysteine and methionine.
- Cysteine contributes to shape and structural stability of proteins with disulfide bonds.
- Other Nutrients Important for Microbial Metabolism
- Potassium
- Sodium
- Calcium
- Magnesium
- Iron
- Growth Factors: Essential Organic Nutrients
- Growth factor: organic compound that can not be synthesized by an organism such as an amino acid, nitrogen base, or vitamin.
- Essential amino acids: required amino acids that must be obtained from food.
- Autotrophs and Their Energy Source
- Energy sources: sunlight vs inorganic compounds.
- Photoautotrophs: sunlight for energy.
- Chemoautotrophs: inorganic compounds for energy.
- Methanogens: produce methane as a product from respiration.
- 4H2 + CO2 --> CH4 + 2H2O
- Lithoautotrophes: chemoautotrophes that use inorganic minerals.
- Heterotrophs
- Chemoheterotrophs: use carbon and energy from organic compounds.
- Aerobic Respiration
- Glucose[(CH2O)n] + O2 --> CO2 + H2O + Energy (ATP)
- Saprobes: feed on organic detritus from dead organisms.
- Rigid cell walls.
- Can't engulf large food particles.
- Release enzymes to extracellular environment and digest molecules into smaller ones that can pass freely through the cell wall.
- Obligate saprobes: can only live in organic matter and not a live host.
- Facultative saprobe: lives in organic matter and can infect host.
- Opportunistic pathogen: infection to host when host is compromised.
- Parasites: derive nutrients from the cells or tissues of a host.
- Pathogens: parasites inclined to cause damage to tissues or death.
- Ectoparasites: live outside the body.
- Endoparasites: live inside the body.
- Obligate parasites: unable to live outside the body.
- Ex: Apicomomplexa protozoa.
- Passive transport: does not require direct energy.
- Diffusion: movement from a area of high density/concentration to an area of lower density/concentration.
- Osmosis: movement of water, in a system in which is selectively or differentially permeable, from lower concentration are to a higher concentration area.
- Hypotonic solution: low solute solution, high solute in membrane.
- Cell will lyse (burst).
- Some organisms adapt by using water, or contractile, vacoule to siphon excess water out.
- Isotonic:
- Equal amounts of solute.
- Hypertonic solution: high solute solution, low solute in membrane
- Cell undergoes plasmolysis or crenation.
- Facilitated diffusion: does not use energy but must bind to specialized membrane proteins.
- Ex: Glucose binds to permease in the membrane to transport.
- Active Transport
- Required energy.
- Pumps: rapidly carry ions across the membrane.
- Group translocation: couples the transport of the nutrient with its conversion of the substance for use inside the cell.
- Endocytosis: Eating and Drinking by Cells
- Endocytosis: cell carrying substances into the cell.
- Encloses substance while forming vacuole.
- Phagocytosis: ingesting of whole cells or large solid matter.
- Done by amoebas and certain white blood cells.
- Pinocytosis: ingestion of liquids, such as oils or large molecules in solution.
- Temperature Adaptations
- Minimum temperature: lowest temperature that permits continued growth and metabolism.
- Anything bellow, activities are inhibited.
- Maximum temperature: highest temperature at which growth and metabolism can proceed.
- Anything above, activities are inhibited.
- Optimum temperature: small range of temperature that promotes the fastest rate of growth and metabolism.
- Some range between minimum and maximum.
- Ecology Groups
- Psychrophiles: optimum temperature bellow 15 degrees Celsius.
- Mesophiles: optimum temperature for most between 20 to 40 degrees Celsius.
- Thermoduric microbes: can survive short-term exposure to high temperatures.
- Contain mechanisms such as cysts or endospores.
- Thermophile: optimum temperature above 45 degrees Celcius.
- How Microbes Process Oxygen
- Oxygen is used by phagocytes to kill bacteria.
- Toxic forms of oxygen: superoxide ion, peroxides, hydroxyls.
- Most cells have enzymes to protect themselves by neutralizing these chemicals.
- Two-step process:
- 1. O2- + O2- + 2H+ --superoxide dismutase--> H2O2 + O2
- 2. H2O2 + H2O2 --catalase--> 2H2O + O2
- If unable to convert toxic oxygen, organism must live in a non-oxygen environment.
- Aerobe Groups
- Obligate aerobe: organism cannot grow without oxygen.
- Facultative anaerobe: organism capable to grow with oxygen, but it can adapt to fermentation when without oxygen.
- Microaerophile: organism requires small amount of oxygen.
- Obligate anaerobe: organism cannot grow with the presence of oxygen.
- Aerotolerant anaerobes: organisms do not use oxygen but can survive to a limited extent in its presence.
- Produce peroxidase and M++ to protect themselves.
- Capnophile: require higher levels of CO2 than normally present in atmosphere.
- Effects of pH
- Acidophile: organism that likes acidic environments.
- Neutrophile: organism that likes neutral environments.
- Alkalophile: organism that likes basic environments.
- Osmotic Pressure
- Halophiles: organism that likes high concentration environments (salt).
- Osmophile: organism that can withstand and grow at high osmotic pressure.
- Barophile: organism that can withstand extreme pressures.
- Dormant cell stages survive because of their inactivity of enzyme production which require water for enzyme production.
- Symbiotic
- Mutualism: both members benefit.
- Commensalism: commensal benefits, other member not harmed.
- Parasitism: parasite is dependent and benefits, host is harmed.
- Non-symbiotic
- Synergism: members cooperate and share benefit.
- Antagonism: some members are inhibited or destroyed by others.
- Members of a community compete.
- Binary fission: division of bacteria cells.
- Generation, or doubling, time: time required to complete fission cycle (parents cell to two new daughter cells).
- N_f = N_i * 2^n
- Stages In The Normal Growth Curve
- Lag phase: "flat period" were it seems little growth occurs.
- Cells are not multiplying at their maximum rate.
- Newly inoculated cells require a period of adjustment, enlargement, and synthesis.
- Exponential Growth (log) Phase
- Period of maximum rate of cell division.
- Actively growing cells are more vulnerable to conditions that disrupt cell metabolism and binary fission.
- Stationary Growth Phase
- Survival mode in which cells stop growing or grow slowly.
- Death Phase
- Curve dips downward.
- Turbidity: observation of a media going from clear to turbid indicating the population growth which can be measured with sensitive instruments.
- Enumeration of Bacteria
- Direct, or total, cell count: counting the number of cells microscopically.
- Cytometer is used to count by counting a calibrated sample size.
- Coulter counter: flows through pipette and is counted by an electronic sensor.
Reference: https://sites.google.com/site/rccmicrobiology/chapter-7-elements-of-microbial-nutrition-ecology-and-growth