Chapter 6 Microbial Nutrition and Growth

Microbial Growth Microorganisms are found in the harshest of environments – Deep ocean – Volcanic vents – Polar regions – Other planets? Each species has limited environmental ranges in which it can grow – _______________________________(some can survive in boiling hot springs but cannot be cultivated at room temp) – _________________________

Growth Requirements Microbial growth – Result of microbial growth is discrete colony – __________________results in growth

Generation Time (Doubling Time) Time required for a cell to grow and divide Dependent on chemical and physical conditions 10 minutes to 3 hours or more E. coli - 20 minutes/10 hours Mycobacterium tuberculosis - 16 Hrs/48+ hours Example: – 10 cells of a food borne illness pathogen in potato salad, sitting for 4 hrs in a warm room, are capable of multiplying to more than 40,000 cells

Figure 6.20 Typical microbial growth curve Time Number of live cells (log)

Growth Requirements Organisms use a variety of nutrients for their energy needs and to build organic molecules for cellular structures Most common nutrients contain necessary elements such as ____________________ ________________________

Sources of Carbon – Organisms that utilize an inorganic source of carbon (carbon dioxide) – Make their own food – Catabolize organic molecules (proteins, carbohydrates, and fatty acids) – Obtain food from others

Growth Requirements Nutrients: Chemical and Energy Requirements – Oxygen requirements Aerobes Obligate Anaerobes Facultative anaerobes Aerotolerant anaerobes Microaerophiles

Oxygen Bacteria can be classified base on their oxygen requirements FT tube Absolute requirement for Oxygen Grow better when O2 is present but can grow without it Cannot grow/multiply in the presence of O2 Small O2 requirement, high concentrations are inhibitory Indifferent to O2 can grow in its presence but they do not use it to transform energy

Oxygen is lethal to some organisms All organisms produce superoxide ( O 2 -) Superoxide is toxic to cells (steals electrons) Superoxide must be neutralized

Superoxide dismutase O O H > H 2 O 2 + O 2 Hydrogen peroxide is also toxic to cells and it must be neutralized

Catalase 2 H 2 O > 2 H 2 O + O 2 Obligate Anaerobes lack: – Superoxide dismutase ( SOD ) – Catalase – Therefore oxygen is toxic to them and they cannot survive

Nitrogen Contained in many organic compounds – – 14% of dry weight of microbial cells Growth limiting nutrient – Growth ceases due to in sufficient N sources for proteins and nucleotides Acquisition of Nitrogen – Nitrate reduction to ammonium – Recycling nitrogen from their amino acids and nucleotides

Growth Requirements Physical Requirements – Temperature Effect of temperature on proteins – Effect of temperature on membranes of cells – If too low, _________________________________ – If too high, ______________________

Figure 6.4 Microbial growth-overview

Classifying organisms by temperature requirements – __________________(cold loving microbes ) -5C – 20C – _____________(moderate temp. loving microbes) 15 C - 45 C – __________________(heat loving microbes) 45C – 80C – ____________________ (Extreme heat loving) 70C +

Figure 6.5 Four categories of microbes based on temperature ranges for growth Psychrophiles Mesophiles Thermophiles Hyperthermophiles Growth rate Temperature (°C)

Figure 6.6 An example of psychrophile

Physical requirements: pH Most bacteria grow between pH pH 7.5 – ________________ ________________: above pH 8.5 ________________: below pH 5.5 Very few can grow at below pH 4.0 – many foods, such as sauerkraut, pickles, and cheeses are preserved from spoilage by acids produced during fermentation – There are microorganisms that grow in environments with a pH of less than one

Water All microorganisms require water for growth Certain environments may contain substances such as salt that interact with water molecules, which makes water unavailable.

Water If the solute concentration is higher in the medium than the cell? What happens? – Solute is the dissolved substance (salt, sugars,…)

Salt Halophiles (halo means salt) – ___________________: organisms that actually __________high salt concentrations – _____________________: ___________high salt concentrations Staphylococcus aureus: salt tolerant organism which colonizes human skin Opportunistic pathogen

Culturing Microorganisms Culture Media – Majority of prokaryotes have not been grown in culture medium Selective media Differential media Selective and Differential

Selective Media _____________the growth of some bacteria while ___________for the growth of others

Figure 6.12 An example of the use of a selective medium Fungal colonies Bacterial colonies pH 7.3pH 5.6

Differential Media Example: – Blood Agar Plates (TSA with 5% sheep blood) used to differentiate different __________________ – _________Hemolytic » » A green zone appears around the colony – _________Hemolytic » » Clear zone appears around the colony – _________Hemolytic » » No change to media

Selective and Differential Media Mannitol Salt Agar – _________________for ____________________ Mannitol is a ____________ Not all organisms can utilize this sugar – ____________for _______________organisms High salt concentration (7.5%) inhibits most bacteria – ___________Indicator

Eosin Methylene Blue (EMB) ______________for Gram Negative coliforms – Eosin makes this media _________for 2 major coliforms: E. coli and Enterobacter aerogenes

Why are the colonies on the left larger than the colonies in the middle?