BTE 102 Microbial World Lecture 4

Study Notes

Microbial growth involves an increase in the number of microorganisms through cell division, not an increase in cell size.
Growth is exponential under favorable conditions.

Temperature:
- Most microorganisms thrive at temperatures preferred by humans.
- Psychrophiles: Optimal growth at 15°C, maximal at 20°C, and minimal at 0°C.
- Mesophiles: Optimal growth between 30-40°C.
- Thermophiles: Optimal growth between 50-60°C.
Psychrophiles vs. Psychrotrophs:
- Psychrophiles are cold-loving and require temperatures typically at or below 15°C.
- Psychrotrophs can grow at lower temperatures but prefer warmer conditions.
pH Levels:
- Most bacteria flourish in the pH range of 6.5 to 7.5.
- Acidophiles tolerate acidic conditions.
- Alkaliphiles thrive in alkaline environments.
Osmotic Pressure:
- Hypertonic environments can lead to plasmolysis.
- Extreme halophiles require high osmotic pressure.
- Facultative halophiles can tolerate high osmotic pressure, while most microorganisms need nearly isotonic conditions.

Carbon:
- Essential for structural organic molecules; constitutes about half of a bacterial cell's dry weight.
- Chemoheterotrophs utilize organic carbon sources, while autotrophs use CO2.
Nitrogen:
- Comprises approximately 14% of a bacterial cell's dry weight; vital for nucleic acids and proteins.
- Bacteria often derive nitrogen from decomposing proteins or utilize NH4+ and NO3-.
- Nitrogen fixation converts atmospheric N2 into usable forms like nitrates and ammonium.
Sulfur:
- Important in amino acids, vitamins (e.g., thiamine, biotin).
- Obtained from decomposing sulfur-containing amino acids or using SO42- and H2S.
Phosphorus:
- Found in DNA, RNA, ATP, and cellular membranes; sourced from PO43-.
Trace Elements:
- Includes iron, copper, molybdenum, and zinc, required in small amounts as enzyme cofactors.
Organic Growth Factors:
- Organic compounds, including vitamins and amino acids, obtained from the environment.

Culture Medium:
- Nutrient-rich preparation designed to support microbial growth.
Inoculum:
- The introduction of microbes into the culture medium.
Culture:
- The result of microbial growth in or on the culture medium.
Criteria for Effective Culture Medium:
- Must contain appropriate nutrients, moisture, proper pH, suitable oxygen levels, be sterile, and allow for proper incubation temperature.
Agar:
- A complex polysaccharide used as a solidifying agent in culture media.
- Liquefies at 100°C and solidifies around 40°C, typically not metabolized by microbes.

Chemically Defined Media:
- Designed for autotrophic bacteria, with a known chemical composition.
Complex Media:
- Used for heterotrophic bacteria and fungi with variable chemical composition.
- Provided by extracts and digests of yeasts, meats, or plants, supplying the energy, carbon, nitrogen, and sulfur needs of organisms mostly through proteins.