Microbiology Lab | Starch Hydrolysis Test (via Amylase) — Transcript

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1. 0:00welcome back to microbiology lab my name
2. 0:02is Kevin tow cough and in this video
3. 0:03we're going to discuss the starch
4. 0:05hydrolysis test also simply refer to as
5. 0:07the starch test so first of all some
6. 0:10species of bacteria are capable of
7. 0:13performing what's called starch
8. 0:14hydrolysis now another term for starch
9. 0:17that you may have heard in other classes
10. 0:19or textbooks is amylose and some
11. 0:22bacteria can actually hydrolyze or break
12. 0:25down this amylose into individual
13. 0:28disaccharides and monosaccharides in
14. 0:30fact here's the reaction that we're
15. 0:32going to be looking at today so starch
16. 0:35can be broken down into glucose which is
17. 0:37our monosaccharides and other small
18. 0:40disaccharides and so on and so forth and
19. 0:42this is accomplished via an enzyme
20. 0:44called amylase in fact you may have seen
21. 0:47amylase in a class like a and P and a
22. 0:50demean physiology because we two
23. 0:51actually possess this enzyme and starch
24. 0:54is a giant polysaccharide it's a giant
25. 0:57polymer of individual glucose units and
26. 1:00this enzyme amylase can break it down
27. 1:02into small dice a carides and then the
28. 1:05monosaccharides glucose and in the case
29. 1:08of bacteria they can actually do this
30. 1:11reaction in order to produce glucose and
31. 1:13disaccharides and then therefore they
32. 1:15can actually use those pieces to produce
33. 1:17energy in catabolism all right now only
34. 1:21some species of bacteria actually have
35. 1:24this enzyme amylase so the ones that do
36. 1:26would be amylase positive the ones that
37. 1:28do not have this enzyme would be amylase
38. 1:31negative we can actually use what's
39. 1:33called the starch hydrolysis test in
40. 1:35order to determine whether or not the
41. 1:37species of bacteria in question have
42. 1:39this enzyme amylase alright so what we
43. 1:42do is we actually have a set of very
44. 1:44similar to what you see here on this
45. 1:46plate except it won't look like this yet
46. 1:49so what we do is we plate two species of
47. 1:52bacteria one on one side of the plate
48. 1:54and the other on the other side and
49. 1:56typically what they'll tell you to do is
50. 1:57take some kind of marker on the backside
51. 2:00of the plate and draw a line just so you
52. 2:02know where you're plating but the point
53. 2:04is on either side of that line on the
54. 2:06plate you have a different species of
55. 2:07bacteria and presumably in your course
56. 2:10one of these species will
57. 2:13produce amylase and the other will not
58. 2:15so how do you know
59. 2:17well you plate them on there and you
60. 2:18incubate them right and the bacteria
61. 2:21perform their metabolism as normal and
62. 2:23one of them is going to be breaking down
63. 2:25starch and the other is not so how do
64. 2:27you tell well what you do is after the
65. 2:30incubation period we use an iodide type
66. 2:33of reagent okay and they have special
67. 2:35names you pour some iodide on here and
68. 2:38it can cause a color change so let's
69. 2:41think about this logically for a second
70. 2:43if you have a species of bacteria that
71. 2:46does produce amylase the starch that's
72. 2:50present on the plate would be broken
73. 2:53down right there wouldn't be starch
74. 2:54there anymore right but if the bacteria
75. 2:57does not produce amylase then it's not
76. 3:00going to be breaking down the starch and
77. 3:02so that starch will remain on the plate
78. 3:04so with the iodide does is it reacts
79. 3:07with the starch and causes it to turn
80. 3:10dark purple okay so if there's starch
81. 3:13remaining on one side of the plate the
82. 3:15iodide causes it to change to a dark
83. 3:18purple color well on which side here a
84. 3:21on the right or B on the Left which side
85. 3:23has starch remaining well clearly over
86. 3:26here on the left side B this is the site
87. 3:28where starch is remaining because all of
88. 3:30it turns this dark purple color so
89. 3:33starch remains here on the left side so
90. 3:36that means that the bacteria on this
91. 3:38left side B do not produce amylase
92. 3:41because if they did they'd be breaking
93. 3:43the starch down but they don't produce
94. 3:45this enzyme amylase so the starch
95. 3:47remains there and it turns this dark
96. 3:50purple color so therefore over here on
97. 3:51the left side B because of this purple
98. 3:54color change we would say these bacteria
99. 3:56are amylase negative they do not
100. 3:58manufacture this enzyme amylase but over
101. 4:02here on the right side we see there's a
102. 4:04clearing mainly in the center of this
103. 4:07right side of the of the dish okay but
104. 4:10you can see here there's a large
105. 4:11clearing where there's no purple color
106. 4:13that's because over here on the right
107. 4:15side the a bacteria they did produce
108. 4:18amylase they did produce it and so they
109. 4:22cleared this whole area here in white
110. 4:25of starch they cleared it they
111. 4:28metabolized it and broke it down to
112. 4:29glucose and disaccharides so there's no
113. 4:32starch here because they produced this
114. 4:34enzyme therefore if you see a clearing a
115. 4:38significant clearing on any side of the
116. 4:39petri dish that means they do produce
117. 4:42amylase and would therefore be amylase
118. 4:44positive all right so the starch
119. 4:47hydrolysis test is really a simple test
120. 4:49with an enzyme that many of you have
121. 4:51probably seen in the context of anatomy
122. 4:54and physiology and gives a pretty
123. 4:56straightforward and simple result if you
124. 4:58see a clearing after you add the iodide
125. 5:01you have an amylase positive species
126. 5:04whereas if the whole side of the petri
127. 5:06dish is purple you do not produce
128. 5:08amylase or the bacteria I should say do
129. 5:10not produce amylase and therefore you
130. 5:12have an amylase and negative species all
131. 5:14right so hopefully this video gave you a
132. 5:16little intuition on the starch
133. 5:17hydrolysis test please make sure to LIKE
134. 5:19this video and subscribe to the channel
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136. 5:23thank you very much