Microbial Growth and Nutrition Chapter 6 How do

Microbial Growth and Nutrition Chapter 6

How do bacteria grow? ? ? • 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 2

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

Microbial Nutrition • Chemical analysis • Sources of essential nutrients • Transport mechanisms 4

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. 5

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

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

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

Energy source • Chemoheterotrophs • Photoautotrophs • Chemoautotrophs 9

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 10

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 11

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 12

Methanogens are an example of a chemoautotroph. Fig. 7. 1 Methane-producing archaea 13

Summary of the different nutritional categories based on carbon and energy source. Table 7. 3 Nutritional categories of microbes by energy and carbon source. 14

Representation of a saprobe and its mode of action. Fig. 7. 2 Extracellular digestion in a saprobe with a cell wall. 15

Transport mechanisms • • Osmosis Diffusion Active transport Endocytosis 16

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

Representation of the osmosis process. Fig. 7. 3 Osmosis, the diffusion of water through a selectively permeable membrane 18

Cells with- and without cell walls, and their responses to different osmotic conditions (isotonic, hypertonic). Fig. 7. 4 Cell responses to solutions of differing osmotic content. 19

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 20

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 21

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 22

Representation of the facilitated diffusion process. Fig. 7. 6 Facilitated diffusion 23

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 24

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

Example of the permease, group translocation, and endocytosis processes. Fig. 7. 7 Active transport 26

Summary of the transport processes in cells. Table 7. 4 Summary of transport processes in cells 27

Environmental Factors • • • Temperature Gas p. H Osmotic pressure Other factors Microbial association 28

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

Growth and metabolism of different ecological groups based on ideal temperatures. Fig. 7. 8 Ecological groups by temperature 30

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

Figure 6. 4 Microbial growth-overview 32

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

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

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 35

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 36

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

Anaerobes must grow in an oxygen minus environment, because toxic oxygen metabolites cannot be neutralized. Fig. 7. 10 Culturing technique for anaerobes 38

Thioglycollate broth enables the identification of aerobes, facultative anaerobes, and obligate anaerobes. Fig. 7. 11 Use of thioglycollate broth to demonstrate oxygen requirements. 39

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) 40

p. H • Cells grow best between p. H 6 -8 (around p. H 7 = neutrophiles) • Exceptions would be acidophiles (p. H 0), and alkalinophiles (p. H 10). 41

p. H (measurement of acidity & alkalinity) 1. Neutrophiles - p. H 6 -8 (7. 2 optimal) Most pathogens 2. Acidophiles - p. H 0 -6, Helicobacter pylori 3. Alkalinophiles - p. H 8 -12 42

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 43

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% Na. Cl for bacteria from the dead sea, ordinary bacteria approx 1. 5%) 44

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

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

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

An example of commensalism, where Staphylococcus aureus provides vitamins and amino acids to Haemophilus influenzae. Fig. 7. 12 Satellitism, a type of commensalism 48

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 49

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

• 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 51

Figure 6. 7 Plaque (biofilm) on a human tooth 52

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

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 54

Representation of the steps in binary fission of a rod-shaped bacterium. Fig. 7. 13 Steps in binary fission of a rod-shaped bacterium. 55

Figure 6. 17 Binary fission events-overview 56

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 57

Representation of how a single bacterium doubles after a complete division, and how this can be plotted using exponentials. Fig. 7. 14 The mathematics of population growth 58

Figure 6. 18 Comparison of arithmetic and logarithmic growth-overview 59

Growth curve • • Lag phase Log phase Stationary phase Death phase 60

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

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

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 63

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. 64

The four main phases of growth in a bacterial culture. Fig. 7. 15 The growth curve in a bacterial culture. 65

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

The greater the turbidity, the larger the population size. Fig. 7. 16 Turbidity measurements as indicators of growth 67

The direct cell method counts the total dead and live cells in a special microscopic slide containing a premeasured grid. Fig. 7. 17 Direct microscopic count of bacteria. 68

A Coulter counter uses an electronic sensor to detect and count the number of cells. Fig. 7. 18 Coulter counter 69

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