Analysis of photoreceptor proteins of microorganisms by gradient gel electrophoresis and other biochemical separation methods

Structure, fluorescent properties and proposed function in phototaxis of the stigma apparatus in the ciliate chlamydodon mnemosyne

Chlamydodon mnemosyne, a brackish-water ciliate which feeds on cyanobacteria, is capable of sensing the direction of light. Cells are negatively phototactic in the well-fed state and tend to swim towards the light source when mildly starved. Severely starved cells normally fail to show phototactic responses. An autofluorescent substance, which is present in all life cycle stages, occurs in, or immediately beneath, the plasma membrane of this ciliate. It is located in the anterior left side of a cell, in the same region where mildly starved cells accumulate small orange globules that form a structure known as the stigma. The diameter of the whole area where the autofluorescent substance is located appears to be smaller than the stigma; typically, it consists of two rows of blue-green fluorescence, each row subdivided into 5–10 squares. Since the blue-green autofluorescence is excited by both blue (450–490 nm) and near-ultraviolet (340–380 nm) light, it possibly originates from flavin- and/or pterin-like molecules. We suggest that the autofluorescent substance located in or beneath the plasma membrane of Chlamydodon mnemosyne acts as a photoreceptor pigment in phototaxis and that photo-orientation of this ciliate is triggered by a combined mechanism involving the photoreceptor and either the stigma or a number of light-absorbing food vacuoles as a shading device.

Behavioral mutants of Euglena gracilis: functional and spectroscopic characterization

Three mutant strains of the phytoflagellate Euglena gracilis Z have been characterized in order to analyze the signal perception and signal transduction pathways involved in photo- and gravitaxis. Using the fluorescence of the chromophoric groups believed to be involved in photoperception (flavins and pterins) a method was developed for an in situ and in vivo detection of the paraxonemal body, the proposed location of the photoreceptor molecules. Two of the mutant strains, 1224-5/9f and 1224-5/1f, do not possess a stigma and also lack a paraxonemal body, as indicated by fluorescence measurements. The third strain, FB, has a small stigma, but only some cells contain a paraxonemal body. In contrast to the present hypothesis on photoorientation of Euglena, all strains were able to orient with respect to the light direction. However, the mutant strains did not show any orientation at low irradiances. At medium and high irradiances the strains 1224-5/9f and 1224-5/1f oriented perpendicular to the light direction (diaphototaxis) while cells of strains of FB showed partly negative phototaxis and partly diaphototaxis. Diaphototaxis was never observed in the wild type strain. Strains 1224-5/9f and 1224-5/1f showed normal graviresponses compared with the wild type. Astasia longa, a nonphtototactic relative of E. gracilis, as well as strain FB were both negative and positive gravitactic at all culture ages tested. This result confirmed the hypothesis that the paraxonemal body is not directly involved in graviperception.