Phototaxis Assay of Filamentous Cyanobacteria Using Focused Light Illumination

Abstract

Source: Weber, N. et. al., Natural Transformation, Protein Expression, and Cryoconservation of the Filamentous Cyanobacterium Phormidium lacuna. J. Vis. Exp. (2022)

This video demonstrates a focused LED-based assay for studying phototaxis in filamentous cyanobacteria. The bacteria migrate toward the light source, forming a dense accumulation at the illuminated center, which is visualized and quantified through pixel intensity analysis of the captured image.

Protocol

1. Assay for phototaxis
   1. For phototaxis experiments, prepare light-emitting diode (LED) holders (here, with a 3D printer) in which the selected 5 mm LEDs are mounted to irradiate an area of 20 mm² from below to above (Figure 1). If required, use many LED holders in parallel, connecting each LED electrically through a resistor and potentiometer to an adjustable power supply. Measure and adjust the LED intensities, depending on the experiment. Ensure that the whole setting is in a dark room or a closed, dark container.
   2. Place 8 mL of the medium containing Phormidium lacuna into a 6 cm Petri d....

Results

Figure 1: Phototaxis experiment. Left: LED holder with 4 red LEDs, connected to an adjustable power suppl.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Petri dishes polystyrole, 60 mm x 15 mm	Merck	P5481-500EA
Photometer Nanodrop ND-1000	Peqlab Biotechnologie
Photometer Uvikon XS	Goebel Instrumentelle Analytik GmbH
Pipetman 10-100 µL	Gilson	SKU: FA10004M
software, URL
ImageJ		Software for immage processing (pixel intensities, circle diameter)
Culture media
f/2 -liquid medium	artificial seawater, 0.1 % (v/v) trace element solution, 0.05 % (v/v) vitamin solution, 0.88 mM sodium nitrate, 36 µM monosodium phosphate