English: Observations under direct epi-illumination of Cellulophaga lytica CECT 8139’s colonies grown on several agar media. C. lytica was aerobically grown for 24  h at 25  °C on (a)' Marine Agar (MA), (b) MA supplemented with black ink, (c) Cytophaga agar (CYT) or (d) Low Nutrient (LN) medium. In (1,2), macroscopic pictures were taken under oblique epi-illumination with a light angle of 67.5°. (1), standard isolation procedure. (2), streaking procedure using a thin 5 cm-linear streak for inoculation. In (3), optical digital microscopy was used and pictures were taken at ×50 (a), ×100 (b,c) or ×200 (d) magnifications. To avoid specular reflections, the camera was oriented at a 60° angle from the Petri dish. In macroscopic pictures (1,2), the green iridescence appearance is dominant but blue and other colors (such as red and violet at the colony edges) are also observed. In (b), a little ink (1% v/v) was added to the culture medium in order to limit reflections of incident light into the agar at the time of observation. Gliding motility can be identified as the spreading zone from the colony center (for instance, see 2(a–c),). Bacterial agarolysis corresponds to the dark halo visible on colony edges. In the particular LN condition, C. lytica forms transparent colonies which appear green iridescent when moving the Petri dish and/or changing the illumination-observation angles. In microscopic pictures, the iridescent “speckles” are well visible. Green speckles are dominant but yellow, orange, red and violet “pointillistic” iridescences are easily observed at the colony edges.