Chapter 7 Topics Microbial Nutrition Environmental Factors Microbial Growth

Microbial Nutrition Chemical analysis Sources of essential nutrients Transport mechanisms

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.

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

Carbon source Heterotroph (depends on other life forms) Organic molecules Ex. Sugars, proteins, lipids Autotroph (self-feeders) Inorganic molecules Ex. CO2

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

Energy source Chemoheterotrophs Photoautotrophs Chemoautotrophs

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

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

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

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

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

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

Transport mechanisms Osmosis Diffusion Active transport Endocytosis

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

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

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.

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

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

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

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

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

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

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

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

Environmental Factors Temperature Gas pH Osmotic pressure Other factors Microbial association

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

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

Example of a psychrophilic photosynthetic Red snow organism. Fig. 7.9 Red snow

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

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

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

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

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

Anaerobes must grow in an oxygen minus environment, because toxic oxygen metabolites cannot be neutralized. Fig. 7.10 Culturing technique for anaerobes

Thioglycollate broth enables the identification of aerobes, facultative anaerobes, and obligate anaerobes. Fig. 7.11 Use of thioglycollate broth to demonstrate oxygen requirements.

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

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

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

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

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

An example of commensalism, where Staphylococcus aureus provides vitamins and amino acids to Haemophilus influenzae. Fig. 7.12 Satellitism, a type of commensalism

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

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

Microbial Growth Binary fission Generation time Growth curve Enumeration of bacteria

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

Representation of the steps in binary fission of a rod-shaped bacterium. Fig. 7.13 Steps in binary fission of a rod-shaped bacterium.

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

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

Growth curve Lag phase Log phase Stationary phase Death phase

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

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

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

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.

The four main phases of growth in a bacterial culture. Fig. 7.15 The growth curve in a bacterial culture.

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

The greater the turbidity, the larger the population size. Fig. 7.16 Turbidity measurements as indicators of growth

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.

A Coulter counter uses an electronic sensor to detect and count the number of cells. Fig. 7.18 Coulter counter