Microbial Nutrition and Growth Microbial Nutrition Nutrition a
Microbial Nutrition and Growth
Microbial Nutrition • Nutrition: a process by which chemical substances (nutrients) are acquired from the environment and used in cellular activities • All living things require a source of elements such as C, H, O, P, K, N, S, Ca, Fe, Na, Cl, Mg- but the relative amounts vary depending on the microbe • Essential Nutrient: any substances that must be provided to an organism – Macronutrients: Required in relatively large quantities, play principal roles in cell structure and metabolism (ex. C, H, O) – Micronutrients: aka trace elements, present in smaller amounts and involved in enzyme function and maintenance of protein structure (ex. Mn, Zn, Ni) • Nutrients are processed and transformed into the chemicals of the cell after absorption • Can also categorize nutrients according to C content – Inorganic nutrients: A combination of atoms other than C and H – Organic nutrients: Contain C and H, usually the products of living things
Chemical Analysis of Microbial Cytoplasm
Sources of Essential Nutrients • • Carbon sources Nitrogen sources Oxygen sources Hydrogen sources Phosphorus sources Sulfur sources Others
Carbon Sources • The majority of C compounds involved in normal structure and metabolism of all cells are organic • Heterotroph: Must obtain C in organic form (nutritionally dependent on other living things) • Autotroph: Uses inorganic CO 2 as its carbon source (not nutritionally dependent on other living things)
Nitrogen Sources • Main reservoir- N 2 • Primary nitrogen source for heterotrophsproteins, DNA, RNA • Some bacteria and algae utilize inorganic nitrogenous nutrients • Small number can transform N 2 into usable compounds through nitrogen fixation • Regardless of the initial form, must be converted to NH 3 (the only form that can be directly combined with C to synthesize amino acids and other compounds)
Oxygen Sources • O is a major component of organic compounds • Also a common component of inorganic salts • O 2 makes up 20% of the atmosphere
Hydrogen Sources • H is a major element in all organic and several inorganic compounds • Performs overlapping roles in the biochemistry of cells: – Maintaining p. H – Forming hydrogen bonds between molecules – Serving as the source of free energy in oxidationreduction reactions of respiration
Phosphorus (Phosphate) Sources • Main inorganic source of phosphorus is phosphate (PO 43 -) – Derived from phosphoric acid – Found in rocks and oceanic mineral deposits • Key component in nucleic acids • Also found in ATP • Phospholipids in cell membranes and coenzymes
Sulfur Sources • Widely distributed throughout the environment in mineral form • Essential component of some vitamins • Amino acids- methionine and cysteine
Other Nutrients Important in microbial Metabolism • • Potassium- protein synthesis and membrane function Sodium- certain types of cell transport Calcium- stabilizer of cell walls and endospores Magnesium- component of chlorophyll and stabilizer of membranes and ribosomes • Iron- important component of cytochrome proteins • Zinc- essential regulatory element for eukaryotic genetics, and binding factors for enzymes • Cooper, cobalt, nickel, molybdenum, manganese, silicon, iodine, and boron- needed in small amounts by some microbes but not others
Growth Factors: Essential Organic Nutrients • Growth factor: An organic compound such as an amino acid, nitrogenous base, or vitamin that cannot be synthesized by an organism and must be provided as a nutrient • For example, many cells cannot synthesize all 20 amino acids so they must obtain them from food (essential amino acids)
How Microbes Feed: Nutritional Types
Main Determinants of Nutritional Type • Sources of carbon and energy • Phototrophs- Microbes that photosynthesize • Chemotrophs- Microbes that gain energy from chemical compounds
Autotrophs and Their Energy Sources • Photoautotrophs – Photosynthetic – Form the basis for most food webs • Chemoautotrophs – Chemoorganic autotrophs- use organic compounds for energy and inorganic compounds as a carbon source – Lithoautotrophs- rely totally on inorganic minerals – Methanogens- produce methane from hydrogen gas and carbon dioxide • Archae • Some live in extreme habitats
Figure 7. 1
Heterotrophs and Their Energy Sources – Majority are chemoheterotrophs that derive both carbon and energy from organic compounds • Saprobes – Free-living microorganisms – Feed primarily on organic detritus from dead organisms – Decomposers of plant litter, animal matter, and dead microbes – Most have rigid cell wall, so they release enzymes to the extracellular environment and digest food particles into smaller molecules » Obligate saprobes- exist strictly on dead organic matter in soil and water » Facultative parasite- when a saprobe infects a host, usually when the host is compromised (opportunistic pathogen)
Other Chemoheterotrophs • Parasites – Derive nutrients from the cells or tissues of a host – Also called pathogens because they cause damage to tissues or even death – Ectoparasites- live on the body – Endoparasites- live in organs and tissues – Intracellular parasites- live within cells – Obligate parasites- unable to grow outside of a living host
Transport Mechanisms for Nutrient Absorption • Cells must take nutrients in and transport waste out • Transport occurs across the cell membrane, even in organisms with cell walls
The Movement of Water: Osmosis • Osmosis: Diffusion of water through a selectively permeable membrane • The membrane is selectively permeable- having passageways that allow free diffusion of water but can block certain other dissolved molecules • When the membrane is between solutions of differing concentrations and the solute is not diffusible, water will diffuse at a fast rate from the side that has more water to the side that has less water
The Movement of Molecules: Diffusion and Transport • Diffusion: When atoms or molecules move in a gradient from an area of higher density or concentration to an area of lower density or concentration – Random thermal movement of molecules will eventually distribute the molecules from an area of higher concentration to an area of lower concentration – Evenly distributes the molecules – Diffusion of molecules across the cell membrane is largely determined by the concentration gradient and permeability of the substance – Simple or passive diffusion is limited to small nonpolar molecules or lipid soluble molecules
Facilitated Diffusion • Utilizes a carrier protein that binds a specific substance, changes the conformation of the carrier protein, and the substance is moved across the membrane • Once the substance is transported, the carrier protein resumes its original shape • Carrier proteins exhibit specificity • Saturation: The rate of a substance is limited by the number of binding sites on the transport proteins • Competition: When two molecules of similar shape can bind to the same binding site on a carrier protein
Active Transport • Nutrients are transported against the diffusion gradient or in the same direction as the natural gradient but at a rate faster than by diffusion alone • Requires the presence of specific membrane proteins (permeases and pumps) • Requires the expenditure of energy • Items that require active transport: monosaccharides, amino acids, organic acids, phosphates, and metal ions • Specialized pumps- an important type of active transport • Group translocation: couples the transport of a nutrient with its conversion to a substance that is immediately useful inside the cell
Figure 7. 7
Endocytosis: Eating and Drinking by Cells • A form of active transport • Transporting large molecules, particles, lipids, or other cells • Occurs in some eukaryotic cells • The cell encloses the substance in its cell membrane, simultaneously forming a vacuole and engulfing it • Phagocytosis- amoebas and certain white blood cells; ingesting whole cells or large solid matter • Pinocytosis- Transport of liquids such as oils or molecules in solution
Environmental Factors that Influence Microbes • Temperature Adaptations – Microbial cells cannot control their temperature, so they assume the ambient temperature of their natural habitat – The range of temperatures for the growth of a given microbial species can be expressed as three cardinal temperatures: • Minimum temperature: the lowest temperature that permits a microbe’s continued growth and metabolism • Maximum temperature: The highest temperature at which growth and metabolism can proceed • Optimum temperature: A small range, intermediate between the minimum and maximum, which promotes the fast rate of growth and metabolism – Some microbes have a narrow cardinal range while others have a broad one – Another way to express temperature adaptation- to describe whether an organism grows optimally in a cold, moderate, or hot temperature range
Psychophile • A microorganism that has an optimum temperature below 15°C and is capable of growth at 0°C. • True psychrophiles are obligate with respect to cold and cannot grow above 20°C. • Psychrotrophs or facultative psychrophilesgrow slowly in cold but have an optimum temperature above 20°C.
Figure 7. 8
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