No abstract

Iridescent color appearances are widespread in nature. They arise from the interaction of light with micron- and submicron-sized physical structures spatially arranged with periodic geometry and are usually associated with bright angle-dependent hues. Iridescence has been reported for many animals and marine organisms. However, iridescence has not been well studied in bacteria. Recently, we reported a brilliant “pointillistic” iridescence in colony biofilms of marine Flavobacteria that exhibit gliding motility. The mechanism of their iridescence is unknown. Here, using a multi-disciplinary approach, we show that the cause of iridescence is a unique periodicity of the cell population in the colony biofilm. Cells are arranged together to form hexagonal photonic crystals. Our model highlights a novel pattern of self-organization in a bacterial biofilm. ”Pointillistic” bacterial iridescence can be considered a new light-dependent phenomenon for the field of microbiology.

The activity of a reference preparation of rainbow trout circulating interferon (IFN), induced by experimental infection of fish with viral haemorrhagic septicaemia virus, was detected on the basis of its non-specific protective effect for RTG-2 cells, grown in microplates and challenged with infectious pancreatic necrosis virus. The IFN was titrated by spectrophotometric assessment of the absorbancy (wavelength 595 nm) of dried cell monolayers, stained with crystal violet after virus challenge. By definition, the reciprocal of the IFN sample dilution giving a cell layer with 50 % of the dye absorbancy of the uninfected control cell layer represented the IFN titre. This spectrophotometric method of determining IFN titre appeared as sensitive as the plaque assay normally used for this purpose, but was better suited to the processing of large numbers of IFN samples, required by investigations on the pathogenes~s of fish viroses. The method proved effective at detecting IFN in homogenates of whole rainbow trout fry, thus allowing individual screening for IFN of small fish which are the usual targets of systemic viroses.

Can. Enr. 108: 1037Enr. 108: -1040Enr. 108: (1976 The intensive use of sex pheromone traps in an insecticide-free apple orchard from 1972 to 1974 reduced the codling moth population and level of fruit damage. The sex ratio of bait-trapped adults indicated that the male population was being reduced by the pheromone traps. In commercial orchards pheromone trapping of males suppressed codling moth damage to fruit but the amount of damage was above acceptable economic levels: