Skip to content
Quick Guides

Microbiology - Microbial Cultivation and Growth

Preview 5 of 15 pages

See the first 5 pages exactly as they appear in the document.

  1. Page 1
    Read page 1 as text

    Study Guide Microbiology – Microbial Cultivation and Growth 1. Growth Requirements for Microorganisms One of the defining features of microorganisms is their ability to grow and multiply , forming large populations. Microbial growth occurs when cells increase in size and then divide. For this growth to happen successfully, microorganisms need specific chemical and physical conditions . 1.1 Chemical Requirements for Microbial Growth To grow and survive, microorganisms must obtain a variety of chemical substances from their environment. Water and Carbon • Water is essential for all life processes. • Almost all organic compounds in microorganisms — such as proteins, carbohydrates, fats, and lipids — contain carbon . • About 50% of the dry weight of a bacterial cell is carbon . Sources of carbon: • Organic carbon from environmental materials • Carbon dioxide (CO ₂ ) from the atmosphere Microorganisms that use CO ₂ as their carbon source include: • Chemoautotrophs – obtain energy from chemical reactions • Photoautotrophs – obtain energy from sunlight through photosynthesis Nitrogen and Phosphorus • Nitrogen is required for making:

  2. Page 2
    Read page 2 as text

    Study Guide o Proteins o Amino acids o DNA and RNA Some bacteria can use nitrogen directly from the air. These are called nitrogen - fixing bacteria , such as: • Rhizobium • Azotobacter • Phosphorus is essential for: o Nucleic acids o Phospholipids in cell membranes o ATP production Oxygen Requirements Microorganisms vary greatly in their oxygen needs: • Aerobic organisms o Require oxygen o Use oxygen as the final electron acceptor in cellular respiration • Anaerobic organisms o Grow without oxygen o Often produce gases like hydrogen sulfide or methane o Some pathogens, such as Clostridium species, are anaerobic • Facultative organisms o Can grow with or without oxygen • Microaerophilic organisms o Require low levels of oxygen • Capnophilic organisms o Grow best in environments with high carbon dioxide levels

  3. Page 3
    Read page 3 as text

    Study Guide 1.2 Trace Elements and Growth Factors Microorganisms also require small amounts of trace elements , including: • Iron • Copper • Zinc These are often needed for enzyme synthesis . Some microorganisms require organic growth factors , such as: • Vitamins • Amino acids • Purines • Pyrimidines 1.3 Physical Requirements for Microbial Growth In addition to chemicals, physical conditions strongly influence microbial growth. Temperature Enzyme activity depends on temperature, so microorganisms are classified based on their preferred temperature range. • Psychrophiles o Prefer cold temperatures o About 0°C to 20°C • Mesophiles o Prefer moderate temperatures o About 20°C to 40°C o Most human pathogens fall into this group

  4. Page 4
    Read page 4 as text

    Study Guide • Thermophiles o Prefer high temperatures o Above 40°C F igure 1 Three types of bacteria and the temperature environments in which they thrive . Each microorganism has: • A minimum growth temperature • A maximum growth temperature • An optimum growth temperature , where growth is fastest

  5. Page 5
    Read page 5 as text

    Study Guide pH (Acidity and Alkalinity) The pH of the environment affects enzyme function and growth. • Most bacteria grow best at pH 6.5 – 7.5 • Human tissues have a pH of 7.0 – 7.2 , which supports many bacteria • Acidophiles o Prefer acidic conditions (pH ≤ 6.0) o Found in foods like yogurt and sauerkraut o Molds and yeasts often belong to this group 1.4 Osmotic Pressure and Salt Concentration Microbial growth is also influenced by osmotic pressure , which depends on salt concentration. • Normal cytoplasmic salt concentration ≈ 1% • When external salt concentration is also 1%, conditions are ideal Effects of imbalance: • High external salt o Water leaves the cell o Cell shrinks and may die (used in food preservation) • Low external salt o Water enters the cell o Cell may swell and burst Halophiles Microorganisms that tolerate or require high salt concentrations are called halophiles . Examples include: • Diatoms • Dinoflagellates • Many marine bacteria, fungi, protozoa, and algae These organisms thrive in salty environments such as oceans and salt lakes.

10 more pages in the full document

Unlock it once and it stays in your library, ready to chat with or turn into flashcards.

Unlock the full document

More Microbiology study materials

See all

Study this document with CramX

Once it is in your library, every tool can work from it.