Notes:
1) The importance to know the requirements for microbial growth is to slow down the growth of microbes and use to culture the microbes.
2) Growth referring to the number of cells, not the size. Tolerance refers to the microbes able to survive under conditions in which they cannot grow. For example, thermophile is different with thermotolerant. The optimum temperature of thermophile is 55 degree celcius while the optimum temperature of thermotolerant is 30 degree celcius but they still able to survive at 55 degree celcius.
3) The physical requirements for microbial growth is light, temperature, water activity, pH and osmotic pressure. Water activity refers to the amount of water that can be found in substrate that just enough for them to grow.
4) Phototroph require light to carry out photosynthesis. The intensity and wavelength absorbed by different microbes are based on the pigments they have.
5) Subdivision of groups based on growth temperature:
- Psychrophiles
Optimum temperature: 15 degree celcius
Maximum temperature: 20 degree celcius
- Psychrotrophs
Optimum temperature: 20-30 degree celcius
Maximum temperature: 35 degree celcius
- Mesophiles
Optimum temperature: 25-35 degree celcius
Maximum temperature: 45 degree celcius
- Thermophiles
Optimum temperature: 50 to 55 degree celcius
Maximum temperature: 80 degree celcius
- Hyperthermophiles
Optimum temperature: 85-100 degree celcius
Maximum temperature: 113 degree celcius
6) Acidophiles grow between pH 0-6, Neutrophiles grow between pH 6-7.5, Alkaliphiles grow between 8-11.5
7) Most of the bacteria survive in higher water activity habitat (the water activity of bacteria is 0.91-0.97). Most of the fungus surive in lower water activity habitat ( the water activity of fungus is 0.81-0.88). If bacteria live in hypertonic solution, they will undergo plasmolysis. If bacteria live in hypotonic solutioon, they will undergo lysis.
8) Microorganisms that require some NaCl for growth are halophiles. Mild halophiles require 1-6% salt (>0.2M of salt), moderate halophiles require 6-15% salt; extreme halophiles that require 15-30%(>2M of salt) NaCl for growth are found among the archaea. Bacteria that are able to grow at moderate salt concentrations, even though they grow best in the absence of NaCl, are called halotolerant.
9) The chemical requirements for microbial growth are water, carbon, special growth factors, trace elements, oxygen, nitrogen, phosphorus and sulfur.
10) Water is important to dissolve nutrients and carry out cellular functions in microbes. Autotroph uses carbon dioxide as carbon source and heterotroph uses organic molecules as carbon source.
11) Oxygen is require for the growth of certain bacteria but not all bacteria.
a) Obligate aerobes: need oxygen for growth
b) Facultative anaerobe: grow best in the presence of oxygen but can grow in the absence of oxygen.
c) Obligate anaerobes: oxygen is not require for growth
d) Aerotolerant anaerobes: only anaerobic condition. Oxygen is not required for growth but can suvive and tolerate in the presence of oxygen
e) Microaerophiles: only aerobic condition. Oxygen is required in concentrations lower than those in air.
- Singlet oxygen
- is a normal molecular oxygen that has been boosted into a high-energy state
- Superoxide free radicals
- SOD converts the superoxide free radicals into molecular oxygen and hydrogen peroxide
- Peroxide anion
- Hydroxyl radical
13) Trace elements such as Fe, Mg, Mn, Cu and Zn are important for enzyme function because they are part of enzyme and cofactors. They used to maintain the protein structure.
Activities: Quizzes and introduction of green sulfur bacteria, purple sulfur bacteria, green non-sulfur bacteria, purple non-sulfur bacteria
My own explorace：
1) Although halophiles are "osmophiles" (and halotolerant organisms are "osmotolerant") the term osmophiles is usually reserved for organisms that are able to live in environments high in sugar. Organisms which live in dry environments are called xerophiles.
2) Cyanobacteria are aquatic and photosynthetic. They consist of phycocyanin and chlorophyll a. They can convert inert atmospheric nitrogen into organic form such as nitrate or ammonia. These fixed form of nitrogen are need by plants for growth.
3) Green sulfur bacteria can be in rod, spiral and sphere shape. They are photolithotrophic, obligate phototrophs or strict aerobes.They consist of bacteriochlorophyll c,d or e and small amount of chlorophyll a.
4) Green non-sulfur bacteria is thermophilic and gram negative bacteria. They are anoxygenic phototrophic. Their source of electons are hydrogen, hydrogen sulfide and thiosulfate. They are photoheterotrophs. They consist of bacteriochlorophyll c,d or e and carotenoids.
5) Purple sulfur bacteria is photoautotrophic gram negaive bacteria. They are in rod shaped. They need oxygen to survive but only can live in low oxygen environment.
6) Purple non-sulfur bacteria is anoxygenic phototrophic. Their energy source is light and carbon source is organic compound. They only can tolerate small concentraion of sulphur. They also can undergo aerobic chemoheterotrophy in the absence of light.
Reflection:
Each bacteria have their specific growth requirements. We can't use the same way to culture every bacteria. Based on their specific growth requirements, those bacteria can be categorised into different group such as halophile, thermophile and xerotolerant. Next week we gonna learn isolation and culturing, maintaining and preserving microbes based on the growth requirements of each bacteria.
No comments:
Post a Comment