Microbial Growth and Nutrition Chapter 6

2 Microbial growth –Increase in a population of microbes Result of microbial growth is discrete colony –An aggregation of cells arising from single parent cell Reproduction results in growth How do bacteria grow?????

3 Chapter 6 Elements of Microbial Nutrition, Ecology and Growth Topics –Microbial Nutrition –Environmental Factors –Microbial Growth

4 Microbial Nutrition Chemical analysis Sources of essential nutrients Transport mechanisms

5 Bacteria are composed of different elements and molecules, with water (70%) and proteins (15%) being the most abundant. Table 7.2 Analysis of the chemical composition of an E. coli cell.

6 Sources of essential nutrients Required for metabolism and growth –Carbon source –Energy source

7 Carbon source Heterotroph (depends on other life forms) –Organic molecules –Ex. Sugars, proteins, lipids Autotroph (self-feeders) –Inorganic molecules –Ex. CO 2

8 Growth factors Essential organic nutrients Not synthesized by the microbe, and must be supplemented Ex. Amino acids, vitamins

9 Energy source Chemoheterotrophs Photoautotrophs Chemoautotrophs

10 Chemoheterotrophs Derive both carbon and energy from organic compounds –Saprobic decomposers of plant litter, animal matter, and dead microbes –Parasitic Live in or on the body of a host

11 Photoautotroph Derive their energy from sunlight Transform light rays into chemical energy Primary producers of organic matter for heterotrophs Primary producers of oxygen Ex. Algae, plants, some bacteria

12 Chemoorganic autotrophs Two types –Chemoorganic autotroph Derives their energy from organic compounds and their carbon source from inorganic compounds –Lithoautotrophs Neither sunlight nor organics used, rather it relies totally on inorganics

13 Methanogens are an example of a chemoautotroph. Fig. 7.1 Methane-producing archaea

14 Summary of the different nutritional categories based on carbon and energy source. Table 7.3 Nutritional categories of microbes by energy and carbon source.

15 Representation of a saprobe and its mode of action. Fig. 7.2 Extracellular digestion in a saprobe with a cell wall.

16 Transport mechanisms Osmosis Diffusion Active transport Endocytosis

17 Osmosis Diffusion of water through a permeable but selective membrane Water moves toward the higher solute concentrated areas –Isotonic –Hypotonic –Hypertonic

18 Representation of the osmosis process. Fig. 7.3 Osmosis, the diffusion of water through a selectively permeable membrane

19 Cells with- and without cell walls, and their responses to different osmotic conditions (isotonic, hypotonic, hypertonic). Fig. 7.4 Cell responses to solutions of differing osmotic content.

20 Diffusion Net movement of molecules from a high concentrated area to a low concentrated area No energy is expended (passive) Concentration gradient and permeability affect movement

21 A cube of sugar will diffuse from a concentrated area into a more dilute region, until an equilibrium is reached. Fig. 7.5 Diffusion of molecules in aqueous solutions

22 Facilitated diffusion Transport of polar molecules and ions across the membrane No energy is expended (passive) Carrier protein facilitates the binding and transport –Specificity –Saturation –Competition

23 Representation of the facilitated diffusion process. Fig. 7.6 Facilitated diffusion

24 Active transport Transport of molecules against a gradient Requires energy (active) Ex. Permeases and protein pumps transport sugars, amino acids, organic acids, phosphates and metal ions. Ex. Group translocation transports and modifies specific sugars

25 Endocytosis Substances are taken, but are not transported through the membrane. Requires energy (active) Common for eucaryotes Ex. Phagocytosis, pinocytosis

26 Example of the permease, group translocation, and endocytosis processes. Fig. 7.7 Active transport

27 Summary of the transport processes in cells. Table 7.4 Summary of transport processes in cells

28 Environmental Factors Temperature Gas pH Osmotic pressure Other factors Microbial association

29 Temperature For optimal growth and metabolism Psychrophile – 0 to 15 °C Mesophile- 20 to 40 °C Thermophile- 45 to 80 °C

30 Growth and metabolism of different ecological groups based on ideal temperatures. Fig. 7.8 Ecological groups by temperature

31 Example of a psychrophilic photosynthetic Red snow organism. Red snow

32 Figure 6.4 Microbial growth-overview

33 Gas Two gases that most influence microbial growth –Oxygen Respiration Oxidizing agent –Carbon dioxide

34 Oxidizing agent Oxygen metabolites are toxic These toxic metabolites must be neutralized for growth Three categories of bacteria –Obligate aerobe –Facultative anaerobe –Obligate anaerobe

35 Obligate aerobe Requires oxygen for metabolism Possess enzymes that can neutralize the toxic oxygen metabolites –Superoxide dismutase and catalase Ex. Most fungi, protozoa, and bacteria

36 Facultative anaerobe Does not require oxygen for metabolism, but can grow in its presence During minus oxygen states, anaerobic respiration or fermentation occurs Possess superoxide dismutase and catalase Ex. Gram negative pathogens

37 Obligate anaerobes Cannot use oxygen for metabolism Do not possess superoxide dismutase and catalase The presence of oxygen is toxic to the cell

38 Anaerobes must grow in an oxygen minus environment, because toxic oxygen metabolites cannot be neutralized. Fig Culturing technique for anaerobes

39 Thioglycollate broth enables the identification of aerobes, facultative anaerobes, and obligate anaerobes. Fig Use of thioglycollate broth to demonstrate oxygen requirements.

40 Oxygen 1. Obligate aerobes – Only aerobic growth, oxygen is required for growth (approx. 20%). 2. Facultative – both aerobic and anaerobic growth, oxygen can be used, but is not required, and oxygen does not hinder growth. (E. coli) 3. Obligate anaerobes- Only anaerobic growth, microbe is poisoned by oxygen, growth ceases. (Genus Clostridium)

41 pH Cells grow best between pH 6-8 (around pH7 = neutrophiles) Exceptions would be acidophiles (pH 0), and alkalinophiles (pH 10).

42 pH (measurement of acidity & alkalinity) 1. Neutrophiles - pH 6-8 (7.2 optimal) Most pathogens 2. Acidophiles - pH 0-6, Helicobacter pylori 3. Alkalinophiles - pH 8-12

43 Osmotic pressure Halophiles Requires high salt concentrations Withstands hypertonic conditions Ex. Halobacterium Facultative halophiles –Can survive high salt conditions but is not required –Ex. Staphylococcus aureus

44 Osmotic pressure (H 2 O) 1. Turgid – Bacterial cells don’t burst (lyse) because they have a cell wall. 2. Plasmolysis – Cell membrane shrinks away from the cell wall. 3. Halophiles – Require high concentrations of salt. (30% NaCl for bacteria from the dead sea, ordinary bacteria approx 1.5%)

45 Other factors Radiation- withstand UV, infrared Barophiles – withstand high pressures Spores and cysts- can survive dry habitats

46 Ecological association Influence microorganisms have on other microbes –Symbiotic relationship –Non-symbiotic relationship

47 Symbiotic Organisms that live in close nutritional relationship Types –Mutualism – both organism benefit –Commensalism – one organisms benefits –Parasitism – host/microbe relationship

48 An example of commensalism, where Staphylococcus aureus provides vitamins and amino acids to Haemophilus influenzae. Fig Satellitism, a type of commensalism

49 Non-symbiotic Organisms are free-living, and do not rely on each other for survival Types –Synergism – shared metabolism, not required –Antagonism- competition between microorganisms

50 Interrelationships between microbes and humans Can be commensal, parasitic, and synergistic Ex. E. coli produce vitamin K for the host

51 Associations and Biofilms –Biofilms Complex relationships among numerous microorganisms Develop an extracellular matrix –Adheres cells to one another –Allows attachment to a substrate –Sequesters nutrients –May protect individuals in the biofilm Form on surfaces often as a result of quorum sensing Many microorganisms more harmful as part of a biofilm

52 Figure 6.7 Plaque (biofilm) on a human tooth

53 Microbial Growth Binary fission Generation time Growth curve Enumeration of bacteria

54 Binary fission The division of a bacterial cell Parental cell enlarges and duplicates its DNA Septum formation divides the cell into two separate chambers Complete division results in two identical cells

55 Representation of the steps in binary fission of a rod-shaped bacterium. Fig Steps in binary fission of a rod-shaped bacterium.

56 Figure 6.17 Binary fission events-overview

57 Generation time The time required for a complete division cycle (doubling) Length of the generation time is a measure of the growth rate Exponentials are used to define the numbers of bacteria after growth

58 Representation of how a single bacterium doubles after a complete division, and how this can be plotted using exponentials. Fig The mathematics of population growth

59 Figure 6.18 Comparison of arithmetic and logarithmic growth-overview

60 Growth curve Lag phase Log phase Stationary phase Death phase

61 Lag phase Cells are adjusting, enlarging, and synthesizing critical proteins and metabolites Not doubling at their maximum growth rate

62 Log phase Maximum exponential growth rate of cell division Adequate nutrients Favorable environment

63 Stationary phase Survival mode – depletion in nutrients, released waste can inhibit growth When the number of cells that stop dividing equal the number of cells that continue to divide

64 Death phase A majority of cells begin to die exponentially due to lack of nutrients A chemostat will provide a continuous supply of nutrients, thereby the death phase is never achieved.

65 The four main phases of growth in a bacterial culture. Fig The growth curve in a bacterial culture.

66 Enumeration of bacteria Turbidity Direct cell count Automated devices –Coulter counter –Flow cytometer –Real-time PCR

67 The greater the turbidity, the larger the population size. Fig Turbidity measurements as indicators of growth

68 The direct cell method counts the total dead and live cells in a special microscopic slide containing a premeasured grid. Fig Direct microscopic count of bacteria.

69 A Coulter counter uses an electronic sensor to detect and count the number of cells. Fig Coulter counter

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