14 - Bacterial nutrition, media and cultivation Flashcards
VBNC
Viable but non culturable bacteria.
What is bacterial nutrition influenced by (and what determines culture media)
- Sources of external energy, electrons and carbon used for growth
- Diversity of chemicals needed to make bacterial cell components
- The need for growth factors
role of electrons in nutrition
- Electron flow in biological reactions generates energy (e.g. electron transport chain), and are needed to reduced molecules during biosynthesis (reduction of CO2 to form organic carbon)
Energy source of phototrophs
Light
energy source of chemotrophs
Exergonic chemical reactions (oxidation of organic or inorganic compounds)
Electron source of lithotrophs
(“rock eater’). Reduced inorganic molecules
Electron source of organotrophs
Organic molecules
Carbon source of autotrophs
CO2 - synthesised on its own
carbon source of heterotrophs
Organic molecules made by other organisms - synthesised on it’s own
What is carbon required for
Most cell structures and functional chemicals (e.g. DNA)
What is Nitrogen required for
Proteins, nucleic acid, some polysaccharides and lipids
What is hydrogen required for
All organic compounds
What is oxygen required for
Many organic compounds. Electron transport chain (respiration)
What is sulphur required for
S-amino acids and vitamins
What is phosphorus required for
Nucleic acids, phospholipids, ATP
What are cations required for
Enzymes and ribosomes
Compounds that are essential for growth but cannot be synthesised by bacteria
- All 20 amino acids
- Bases for making nucleic acids
- Vitamins
4 mechanisms of nutrient uptake
- Passive diffusion (ATP not required, small molecules only)
- Facilitated diffusion (ATP not required)
- Active transport (ATP required)
- Group translocation (ATP required, molecule is chemically modified during transport)
Facilitated diffusion
- Diffusion across the membrane involving carrier proteins
- ATP not required
Active transport
- Transport of solute molecules to higher concentrations (against concentration gradient) using transport proteins.
- ATP is required
steps of active transport
- After binding solute, the solute binding protein attaches to transporter and releases solute
- Energy released by hydrolysis of ATP. drives movement of solute across membrane
5 types of relationships to oxygen
- Obligate aerobes
- Obligate anaerobes
- Microaerophiles
- Facultative anaerobes
- Aerotolerant anaerobes
Obligate aerobes
Require oxygen for energy production and growth - suffocate without air
Microaerophiles
Mainly aerobic, damaged by atmospheric O2 (20%) and require 10% O2 for growth
Facultative anaerobes
Do not require O2 and can grow with or without it. (O2 more effective). Can perform both aerobic respiration and fermentation
Aerotolerant anaerobes
Tolerate oxygen but do not use it. Use fermentation only
obligate anaerobes
O2 is toxic, kills or inhibits growth. Use fermentation or anaerobic respiration
Types of temperature relationships
- Psychrophile
- Psychrotolerant
- Mesophile
- Thermophile
- Hyperthermophile
Psychrophile
- Cold environments
- 0, 15, 20ºC
Psychrotolerant
- Cold environments
- 0, 25, 35ºC
Mesophile
- Moderate temps
- Includes most human pathogens
- 15-20, 20-25, 45ºC
Thermophile
- high temps (hot springs)
- 45, 55-65, 85ºC
Hyperthermophile
- Very high temps (deep sea vents)
- 65, 80-100, 113ºC
2 common methods of culture media
- Liquid/broth culture (bacteria grown as a liquid suspension)
- Solid/plate culture (Bacteria grown on agar gel)
Agar media properties
- Carbohydrate extracted from red algae
- Dissolves at 90ºC and sets at 45ºC
- Easily sterilised
- Not degraded by bacteria
- Spread, streak or pour plate yield single isolated colonies
Basis for classification of media
- Chemical composition
- Physical nature
- Function
Chemical types of culture media
- Defined or synthetic
- Complex
Defined/synthetic media
Medium in which all ingredients can be defined with a chemical formula. Requires precise knowledge of growth requirements.
Complex media
- Medium containing some ingredients of unknown chemical composition
- Support growth of wide range of bacteria
- Used when nutritional requirements are unknown
Examples of complex media
Nutrient broth/agar, Tryptic Soy Broth/Agar (TSB/TSA), MacConkey Agar
What are complex media made of
Protein digests and meat extracts
What are the functional types of culture media
- Selective media
- Differential media
- Supportive (general purpose) media
- Enriched media
Selective media
Have ingredients which inhibit the growth of unwanted microbes, and favour the growth of specific organisms. (e.g. MacConkey agar uses bile salts and crystal violet to inhibit gram -‘ve but not gram +’ve and mannitol)
EXAMPLE of selective media: Pesticide degrading bacteria
- Pesticide supplied as sole C source
- Only bacteria capable of metabolising pesticide will grow
- Used to isolate rare micro-organisms
Differential media
Distinguish between different genera or species based on metabolic properties.
Many media are both selective and differential (e.g. S. aureus ferments mannitol, pH goes from red to yellow. others remain red.)
Supportive (general purpose) media
Support the growth of many microorganisms (e.g. TSB or TSA)
Enriched media
Blood and other nutrients added to general purpose media to encourage growth of fastidious microbes (e.g. Blood Agar shows alpha beta and gamma haemolysis)
Problems with cell uptake
–microbes can only take in dissolved molecules - they must take in nutrients
from dilute solutions into more concentrated cytoplasm in the cell i.e.
against a concentration gradient
–cytoplasmic membrane prevents passage of most substances
–there is an enormous variety of nutrients
–nutrient uptake mechanisms should be specific
Group translocation
transport of solute molecules to higher concentrations (against a
concentration gradient) in which the molecule is chemically-modified
during transport e.g. sugars are often phosphorylated during transport
Temperature as a regulator of growth
Mircobes cannot regulate their own temperatures, wholly influenced by the outside environment.
Temperature affects the membrane permeability of microbes to receive nutrients and excrete
