Experimental principle Some bacteria have the ability to synthesize amylase and can secrete extracellular amylase. Amylase can hydrolyze starch into maltose and glucose. After starch hydrolysis, it will no longer turn blue when meeting iodine. Lipase produced by bacteria can break down the fat in the medium to produce glycerol and fatty acids. Fatty acids can lower the pH of the medium, and can be tested by adding neutral red as an indicator to the oil and fat medium. The neutral red indicator range is pH6.8 (red) ~ 8.0 (yellow). When bacteria break down fat to produce fatty acids, red spots appear in the culture medium around the colony. Some bacteria secrete proteases to break down gelatin and produce small molecules. If the bacteria have the ability to decompose gelatin, the culture medium can change from the original solid state to the liquid state. Milk contains mainly lactose, casein and other ingredients. The use of milk by bacteria mainly refers to the decomposition and utilization of lactose and casein. Litmus is often added to bovine milk as acid-base indicator and redox indicator. Litmus is lilac when neutral, red when acidic, blue when alkaline, and partially or completely decolored when reduced. There are three situations in which bacteria use milk: (1) Acid coagulation: After fermentation of lactose by bacteria, a lot of acid is produced, which makes litmus milk turn red. When the acidity is very high, it can make milk coagulate. This is called acid coagulation. (2) The coagulation effect of rennet: some bacteria can secrete rennet to coagulate casein in cow's milk, which occurs in a neutral environment. Usually this bacterium also has the ability to hydrolyze proteins, so it produces ammonia and other alkaline substances, making litmus blue. (3) Peptoneization: Casein is hydrolyzed to make the milk into a clear and transparent liquid. Peptoneization can be carried out under acidic or alkaline conditions, generally litmus pigments are reduced and faded. Experimental Materials 1. Living materials: E. coli, Bacillus subtilis, Staphylococcus aureus, Enterobacter aerogenes, Alcaligenes viscolactis, Pseudomonas aeruginosa Psudomonas aeruginosa and Proteus vularis. 2. Medium: starch medium: beef extract peptone medium plus 0.2% soluble starch; fat medium: beef extract peptone medium plus peanut oil 10mL, 0.6% neutral red aqueous solution 1mL; gelatin liquefaction medium: peptone 5g, Gelatin 100 ～ 150g, water 1000mL, pH 7.2 ～ 7.4, sterilized at 115 ℃ for 20min. Litmus milk medium: 100g milk powder, 0.075g litmus, 1000 mL water, pH 6.8, sterilized at 121 ° C for 15 min. 3. Reagent: Lugol's iodine solution. Experimental supplies Plates, inoculation rings, alcohol lamps, test tubes, inoculation needles, etc. experimental method (1) Starch hydrolysis test 1. Prepare the starch medium plate: Pour the starch medium after cooling to about 50 ° C into a sterile plate and make it into a flat plate after solidification. 2. Inoculation: Use a marker to divide the bottom of the plate into two parts, write the bacterial name on each part, use the inoculation ring to take a small amount of bacteria to be tested, and point to the center of the corresponding part on the surface of the medium The species should be Bacillus subtilis as a control strain. ★ Can you explain the reason? 3. Cultivation: Place the plate after inoculation in a 28 ° C incubator for 24 hours. 4. Detection: Take out the plate, open the lid of the plate, add a small amount of iodine solution onto the plate, and gently rotate to make the iodine solution evenly cover the entire plate. A colorless transparent circle around the colony indicates that the starch has been hydrolyzed, indicating that the bacteria has the ability to decompose starch. The size of the transparent circle can be used to indicate the strength of the test strain's ability to hydrolyze starch. (2) Oil and fat hydrolysis test 1. Place the flask containing the oil medium in a boiling water bath to melt it, take it out and shake it well to distribute the oil evenly, and then pour it into a sterile plate to be solidified into a flat plate. 2. Inoculation: Inoculate on both sides of the same dish, one of which is Staphylococcus aureus as a control bacteria. Incubate in a 37 ° C incubator for 24 hours. After taking out, observe the color of the flat moss. If red spots appear, it means that the fat has been hydrolyzed. This reaction is a positive reaction. The size of the red spot indicates the strength of the tested strain in hydrolyzing fat. (3) Gelatin liquefaction test 1. Inoculation: Inoculate E. coli or Enterobacter aerogenes in gelatin medium by puncture inoculation method. 2. Cultivation: Incubate in a 20 ° C incubator for 48h. If the bacteria are not long at 20 ℃, they should be cultured at the optimum temperature. 3. Observation result: Observe whether the medium is liquefied and its shape after liquefaction. Because gelatin solidifies below 20 ° C and liquefies itself above 25 ° C, if bacteria are cultivated above 20 ° C, they should be observed in an ice bath during observation. If gelatin is liquefied by bacteria, even at low temperatures It won't set again. (4) litmus milk test 1. Inoculation: Inoculate Alcaligenes lactis and Pseudomonas aeruginosa into litmus milk medium. 2. Cultivation: Incubate the inoculated test tube at a constant temperature of 37 ° C for 7 days, and keep a non-inoculated litmus milk medium as a control. 3. Observation of results: Take out the culture, take the test tube without inoculation of any bacteria as a control, and observe the changes after inoculation of different bacteria.
Polycarbonate (referred PC) is a polymer molecular chain containing a carbonate group, an ester group according to the structure can be divided into aliphatic, aromatic, aliphatic - aromatic and other types. Which due to the aliphatic and aliphatic - aromatic polycarbonate lower mechanical properties, thereby limiting its application in engineering terms. Currently, only the aromatic polycarbonate obtained industrial production. Due to the special nature of the polycarbonate structure, it has now become the top five fastest growing engineering plastics in general engineering plastics.
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Biochemical reactions in microbial identification