Ch 6 Microbial Nutrition and Growth

Essential nutrient

Any substance an organism must be given because it cannot make it

Macronutrient

Nutrient needed in large amounts (examples: carbon, nitrogen, phosphorus, sulfur, potassium, magnesium, calcium, iron)

Micronutrient (trace element)

Nutrient needed in tiny amounts, often as enzyme helpers (examples: zinc, copper, manganese, molybdenum, cobalt)

Growth factor

Organic compound an organism cannot make and must obtain (examples: amino acids, vitamins)

Fastidious

Requires many growth factors or complex nutrients to grow

Autotroph

Uses CO2 as its carbon source

Heterotroph

Uses organic compounds as its carbon source

Chemoheterotroph

Gets both carbon and energy from organic compounds

Saprobe

Free living decomposer that feeds on dead organic matter using exoenzymes

Parasite

Gets nutrients from the tissues of a living host

Ectoparasite

Lives on the surface of a host

Endoparasite

Lives inside a host

Intracellular parasite

Lives inside host cells

Obligate parasite

Cannot grow outside a host

Facultative parasite

Can live as a parasite or independently (opportunistic)

Exoenzyme

Enzyme secreted outside the cell to break down large molecules into absorbable pieces

Why saprobes need exoenzymes

They must digest large dead organic matter outside the cell before they can absorb it

Simple diffusion

Passive movement of molecules across the membrane from high to low concentration with no energy

Facilitated diffusion

Passive movement from high to low concentration through specific carrier proteins; no energy needed

Active transport

Carrier proteins pump molecules, even against the gradient, using ATP or proton motive force; requires energy

Which transport requires energy

Active transport (facilitated diffusion does not)

Osmosis

Diffusion of water through a selectively permeable membrane

Isotonic

Solute concentration equal inside and outside the cell; no net water movement

Hypotonic

Lower solute concentration outside; water moves into the cell, which swells and may burst (the cell wall usually prevents bursting)

Hypertonic

Higher solute concentration outside; water leaves the cell and it shrinks (plasmolysis)

Plasmolysis

Cytoplasmic membrane shrinks away from the cell wall in a hypertonic environment

Where microbes are usually found

Slightly hypotonic or isotonic environments

Osmophile

Lives in habitats with high solute concentration

Halophile

Requires high salt, about 9 to 25 percent

Facultative halophile

Does not require salt but tolerates it

Superoxide dismutase

Converts toxic superoxide radicals into hydrogen peroxide and oxygen

Catalase

Converts hydrogen peroxide into water and oxygen

Technique to study oxygen needs

Fluid thioglycollate medium (or an agar deep tube)

Obligate aerobe

Requires oxygen; grows at the top of the tube

Obligate anaerobe

Killed by oxygen; grows at the bottom of the tube

Facultative anaerobe

Grows with or without oxygen; grows throughout the tube, best near the top

Microaerophile

Needs low oxygen; grows a little below the surface

Neutrophile

Grows best at pH 6 to 8 (example: Helicobacter pylori neutralizes acid with urease)

Acidophile

Requires low pH, below 5.5 (examples: molds, yeasts, Thermoplasma)

Alkalinophile

Requires high pH, above 8.5 (found in soda lakes and deserts)

Cardinal temperatures

The minimum, optimum, and maximum temperatures for growth of an organism

Psychrophile

Grows at 0 degrees C, optimum below 15 degrees C; rarely pathogenic; found in snowfields, polar ice, oceans

Psychrotolerant

Grows slowly in cold, optimum 15 to 30 degrees C; refrigerator spoilage organisms (Listeria monocytogenes, Yersinia enterocolitica)

Mesophile

Optimum 20 to 40 degrees C; most human pathogens (example: Staphylococcus aureus)

Thermophile

Grows at 45 degrees C and above; found in compost piles, soil, hot springs

Extreme thermophile

Grows at very high temperatures (above about 65 to 80 degrees C); found in hydrothermal vents

Binary fission

Bacterial reproduction in which one cell copies its chromosome and divides into two

Generation time

Time it takes for a population to double

Growth curve

Graph of population size over time in a closed culture

Closed culture

Culture with no nutrients added and no waste removed

Lag phase

Cells adjust to new conditions; little or no division

Exponential (log) phase

Cells divide at the maximum rate; most susceptible to environmental changes, toxins, and control agents

Stationary phase

Growth rate equals death rate because of waste buildup and nutrient depletion

Death phase

Cells die faster than they divide, often exponentially

Viable

Alive and able to reproduce

Viable nonculturable (VNC) cells

Alive but do not grow on culture media

Why VNC cells are a concern

They can be missed by culture tests and may revive and cause disease

Plate count

Dilute the sample, grow colonies on solid media, and count them (30 to 300 colonies per plate is accurate); counts only viable cells; slow and assumes each colony came from one cell

Direct count

Count cells under a microscope with a counting chamber or by an electronic counter; fast but counts living and dead cells

Turbidity

Measure cloudiness with a spectrophotometer; fast and easy but needs a dense culture and cannot tell living from dead cells

Spectrophotometer

Instrument that measures how much light a sample absorbs or transmits

Polymerase chain reaction (PCR)

Detects and can quantify specific microbial nucleic acid; fast and specific but does not show whether cells are alive