This study investigates the phototactic behavior of filamentous cyanobacteria using a controlled light environment. The methodology involves measuring the migration of cyanobacteria towards an illuminated area, providing insights into their phototactic response.
Begin with a dish containing a filamentous cyanobacteria culture positioned over a small window fitted with an LED-mounted holder in a dark room.
The LED illuminates the dish from below, creating a small light zone.
During incubation, the filamentous cyanobacteria migrate toward the illuminated center, demonstrating phototaxis.
Over time, the cyanobacteria migrate and accumulate at the illuminated center, forming a visibly dense bacterial zone.
After incubation, place a white paper beneath the dish to enhance contrast.
Capture an image of the illuminated area and analyze it using software.
Draw a line across the dish that passes through the center of the bacterial zone to generate a pixel intensity profile.
Compare the average pixel intensity outside and inside the bacterial zone.
Next, draw a line at the maximum intensity within the central region to determine the diameter of the bacterial zone, which represents cyanobacterial phototaxis.
Prepare LED holders where the five millimeter LEDs are mounted to irradiate an area of 20-millimeters square from below to above. Measure and adjust the LED intensities. Ensure that the whole setting is in a dark room or a closed, dark container.
Place eight milliliters of the medium containing P. lacuna into a six-centimeter Petri dish, close the Petri dish with the lid, and place it on an LED holder so that the LED is in the center of the Petri dish. After typically two days, capture an image of the Petri dish with a smartphone camera aimed directly at the position of the light treatment. Use a holder and a white sheet as a background to ensure the same distance and light conditions for every picture.
Open the ImageJ software, click on File, Open, and select the file. Then, click on Enter. Select the straight button and press the left mouse button to draw a line from one end of the Petri dish to the opposite end.
Ensure that the line passes through the center of the circle of filaments. Click on Analyze and Measure to see the length of the Petri dish. Then, click on Analyze and Plot Profile in the ImageJ menu.
Estimate an average value for the pixel intensity outside the circle and another average value for the pixel intensity inside the circle. Point the mouse on the Y position between these values to estimate the X values of both sides of the circle. Note both values and calculate the difference.
Then select the straight button and draw a line at the mid-maximum value of the pixel intensity. Finally, click on Analyze and then Measure to get the length of the inner cell circle.
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