(spirr-you-line-a) a spiral bacterium, motile, moves by cork-screw motion. A blue-green alga. If the cells are irradiated with ultraviolet light, the pigment absorbs some radiant energy and re-emits at with lower energy - with the colour shifted to the red end of the spectrum. Fluorescence microscopy removes the irradiating ultraviolet light, leaving the red colour of the fluorescing pigments. Fluorescence microscopy.