Microbiology: A Systems Approach, 2 nd ed.

1. Microbiology: A Systems Approach, 2nd ed. Chapter 7: Microbial Nutrition, Ecology, and Growth

2. 7.1 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

4. Chemical Analysis of Microbial Cytoplasm

5. Sources of Essential Nutrients • Carbon sources • Nitrogen sources • Oxygen sources • Hydrogen sources • Phosphorus sources • Sulfur sources • Others

6. 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 CO2 as its carbon source (not nutritionally dependent on other living things)

7. Nitrogen Sources • Main reservoir- N2 • Primary nitrogen source for heterotrophs- proteins, DNA, RNA • Some bacteria and algae utilize inorganic nitrogenous nutrients • Small number can transform N2 into usable compounds through nitrogen fixation • Regardless of the initial form, must be converted to NH3 (the only form that can be directly combined with C to synthesize amino acids and other compounds)

8. Oxygen Sources • O is a major component of organic compounds • Also a common component of inorganic salts • O2 makes up 20% of the atmosphere

9. Hydrogen Sources • H is a major element in all organic and several inorganic compounds • Performs 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

10. Phosphorus (Phosphate) Sources • Main inorganic source of phosphorus is phosphate (PO43-) • Derived from phosphoric acid • Found in rocks and oceanic mineral deposits • Key component of all nucleotides • Phospholipids in cell membranes • Coenzymes

11. Sulfur Sources • Widely distributed throughout the environment in mineral form • Essential component of some vitamins • Amino acids- methionine and cysteine

12. 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 • Copper, cobalt, nickel, molybdenum, manganese, silicon, iodine, and boron- needed in small amounts by some microbes but not others

13. 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)

14. How Microbes Feed: Nutritional Types

15. Main Determinants of Nutritional Type • Sources of carbon and energy • Phototrophs- Microbes that photosynthesize • Chemotrophs- Microbes that gain energy from chemical compounds

16. 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 • Archaea • Some live in extreme habitats

17. Figure 7.1

18. 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)

19. Figure 7.2

20. 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

21. 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

22. 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

23. Figure 7.3

24. Osmotic Relationships • The osmotic relationship between cells and their environment is determined by the relative concentrations of the solutions on either side of the cell membrane • Isotonic: The environment is equal in solute concentration to the cell’s internal environment • No net change in cell volume • Generally the most stable environment for cells • Hypotonic: The solute concentration of the external environment is lower than that of the cell’s internal environment • Net direction of osmosis is from the hypotonic solution into the cell • Cells without cell walls swell and can burst • Hypertonic: The environment has a higher solute concentration than the cytoplasm • Will force water to diffuse out of a cell • Said to have high osmotic pressure

25. Figure 7.4

26. Adaptations to Osmotic Variations in the Environment • Example: fresh pond water- hypotonic conditions • Bacteria- cell wall protects them from bursting • Amoeba- a water (or contractile) vacuole that moves excess water out of the cell • Example: high-salt environment- hypertonic conditions • Halobacteria living in the Great Salt Lake- absorb salt to make their cells isotonic with the environment

27. 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

28. Figure 7.5

29. 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 facilitated diffusion 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

30. Figure 7.6

31. 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

32. Figure 7.7

33. 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

35. 7.2 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

36. Psychrophile • 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 psychrophiles- grow slowly in cold but have an optimum temperature above 20°C.

37. Figure 7.8

38. Figure 7.9

39. Mesophile • An organism that grows at intermediate temperatures • Optimum growth temperature of most: 20°C to 40°C • Temperate, subtropical, and tropical regions • Most human pathogens have optima between 30°C and 40°C

40. Thermophile • A microbe that grows optimally at temperatures greater than 45°C • Vary in heat requirements • General range of growth of 45°C to 80°C • Hyperthermophiles- grow between 80°C and 120°C

41. Gas Requirements • Atmospheric gases that most influence microbial growth- O2 and CO2 • Oxygen gas has the greatest impact on microbial growth • As oxygen enters into cellular reactions, it is transformed into several toxic products • Most cells have developed enzymes that go about scavenging and neutralizing these chemicals • Superoxide dismutase • Catalase • Essential for aerobic organisms

42. Several General Categories of Oxygen Requirements • Aerobe: can use gaseous oxygen in its metabolism and possesses the enzymes needed to process toxic oxygen products • Obligate aerobe: cannot grow without oxygen • Facultative anaerobe: an aerobe that does not require oxygen for its metabolism and is capable of growth in the absence of it • Microaerophile: does not grow at normal atmospheric concentrations of oxygen but requires a small amount of it in metabolism • Anaerobe: lacks the metabolic enzyme systems for using oxygen in respiration • Strict, or obligate, anaerobes: also lack the enzymes for processing toxic oxygen and cannot tolerate any free oxygen in the immediate environment and will die if exposed to it. • Aerotolerant anaerobes: do not utilize oxygen but can survive and grow to a limited extent in its presence

43. Figure 7.10

44. Figure 7.11

45. Carbon Dioxide • All microbes require some carbon dioxide in their metabolism • Capnophiles grow best at a higher CO2 tension than is normally present in the atmosphere

46. Effects of pH • Majority of organisms live or grow in habitats between pH 6 and 8 • Obligate acidophiles • Euglena mutabilis- alga that grows between 0 and 1.0 pH • Thermoplasma- archaea that lives in hot coal piles at a pH of 1 to 2, and would lyse if exposed to pH 7

47. Osmotic Pressure • Most microbes live either under hypotonic or isotonic conditions • Osmophiles- live in habitats with a high solute concentration • Halophiles- prefer high concentrations of salt • Obligate halophiles- grow optimally in solutions of 25% NaCl but require at least 9% NaCl for growth

48. Miscellaneous Environmental Factors • Nonphotosynthetic microbes tend to be damaged by the toxic oxygen products produced by contact with light • Some produce yellow carotenoid pigments to protect against the damaging effects of light by absorbing and dismantling toxic oxygen • Other types of radiation that can damage microbes are ultraviolet and ionizing rays • Barophiles: deep-sea microbes that exist under hydrostatic pressures ranging from a few times to over 1,000 times the pressure of the atmosphere • All cells require water- only dormant, dehydrated cell stages tolerate extreme drying

49. Ecological Associations Among Microorganisms • Most microbes live in shared habitats • Interactions can have beneficial, harmful, or no particular effects on the organisms involved • They can be obligatory or nonobligatory to the members • They often involve nutritional interactions

50. Symbiosis • A general term used to denote a situation in which two organisms live together in a close partnership • Members are termed symbionts • Three main types of symbionts • Mutualism: when organisms live in an obligatory but mutually beneficial relationship • Commensalism: the member called the commensal receives benefits, while its coinhabitant is neither harmed nor benefited • Satellitism: when one member provides nutritional or protective factors needed by the other • Parasitism: a relationship in which the host organism provides the parasitic microbe with nutrients and a habitat