Phototaxis Of Algae Research Articles

Effects of TiO2, SiO2, Ag and CdTe/CdS quantum dots nanoparticles on toxicity of cadmium towards Chlamydomonas reinhardtii

Nanoparticles (NPs) are inevitably released into the aquatic environment for being widely used and may affect the toxicity of other contaminants already present in the environment, such as trace metals. However, the effects of NPs on the ecotoxicity of cadmium (Cd), a common environmental trace metal pollutant, are not well explored. In this study, effects of four widely used NPs TiO2 (n-TiO2), SiO2 (n-SiO2), Ag (n-Ag) and CdTe/CdS core/shell quantum dots (QD) on the toxicity of Cd to the freshwater algae Chlamydomonas reinhardtii were assessed respectively. Cd reduced the algae biomass, impaired the photosynthetic activities, and led to intracellular oxidative stress of algae. At non-toxic concentrations, both n-TiO2 (100 mg L−1) and n-SiO2 (400 mg L−1) attenuated the toxicity of Cd towards the algae for reducing the intracellular Cd contents, and the former was more pronounced. QD (0.5 mg L−1) increased the toxicity of Cd to algae, but n-Ag (0.2 mg L−1) had no significant influence on the Cd toxicity to algae. The microscopic observations on the ultrastructure of algae cells presented the same phenomena and n-TiO2, n-SiO2 aggregations were clearly observed outside the cell wall. Furthermore, the regulation of NPs to the Cd toxicity towards algae was related to the intracellular nitric oxide (NO), an important signaling molecule, rather than the phototaxis of algae. Above all, this study provided a basic understanding about the difference in joint toxicity of different kinds of NPs and Cd to aquatic organisms.

Sheared bioconvection in a horizontal tube

The recent interest in using microorganisms for biofuels is motivation enough to study bioconvection and cell dispersion in tubes subject to imposed flow. To optimize light and nutrient uptake, many microorganisms swim in directions biased by environmental cues (e.g. phototaxis in algae and chemotaxis in bacteria). Such taxes inevitably lead to accumulations of cells, which, as many microorganisms have a density different to the fluid, can induce hydrodynamic instabilites. The large-scale fluid flow and spectacular patterns that arise are termed bioconvection. However, the extent to which bioconvection is affected or suppressed by an imposed fluid flow and how bioconvection influences the mean flow profile and cell transport are open questions. This experimental study is the first to address these issues by quantifying the patterns due to suspensions of the gravitactic and gyrotactic green biflagellate alga Chlamydomonas in horizontal tubes subject to an imposed flow. With no flow, the dependence of the dominant pattern wavelength at pattern onset on cell concentration is established for three different tube diameters. For small imposed flows, the vertical plumes of cells are observed merely to bow in the direction of flow. For sufficiently high flow rates, the plumes progressively fragment into piecewise linear diagonal plumes, unexpectedly inclined at constant angles and translating at fixed speeds. The pattern wavelength generally grows with flow rate, with transitions at critical rates that depend on concentration. Even at high imposed flow rates, bioconvection is not wholly suppressed and perturbs the flow field.

A tribute to Per Halldal (1922–1986), a Norwegian photobiologist in Sweden

We present here a tribute to Per Halldal (February 2, 1922-March 26, 1986), a leader, an instrumentalist, an expert on phototaxis in algae, and one whom we remember, even after 20 years of his death, as a person who spread joy, enthusiasm and knowledge wherever he went.

Progress in phototaxis mechanism research and micromanipulation techniques of algae cells

Abstract Phototactic movement is a characteristic of some microorganisms, response to light environment. Most of the algae have dramatically phototactic responses, underlying the complicated biological, physical and photochemical mechanisms are involved. With the development of the micro/nano and sensor techniques, great progress has been made in the research of the algae phototaxis. This review article summarizes the progress made in the research on the functional phototactic structures, the mechanisms of photo-response process and photodynamics of phototaxis in algae, and describes the latest developed micro-tracking technique and micromanipulation technique. Moreover, based on our o research results, the potential correlation between the phototaxis and photosynthesis is discussed, and the directions for future research of the phototactic mechanism are proposed. *Supported by National Natural Science Foundation of China (Grant No. 30570422)

An automated technique for the study of cyclic fluctuations in sexual motivation in an avian species

Diurnal fluctuations in sexual behavior occur in freely interacting pairs of male and female birds. These fluctuations are difficult to interpret because they may reflect fluctuations in the motivation of the male, the motivation of the female, or both. A method was developed to study the sexual motiva­ tion of male Japanese quail in response to a standard stimulus. Sexual behavior was elicited by a taxi­ dermic model of a female quail in a squatting posture. Sensors beneath and in the back of the model served to detect when the male mounted and made cloacal contact with the model. The technique al­ lowed continuous recording of male sexual behavior under standard conditions. When males were maintained on a photoperiod with lights on at 0600 h and off at 2200 h, sexual behavior peaked in the early afternoon, with a secondary peakjust before lights-out. Studies of chronobiology have revealed cyclic fluctu­ ations in a variety of aspects ofphysiology and behavior including phototaxis in algae (Euglena gracilis), oxygen uptake in Microtus arvalis, fur renewal in Lynx canaden­ sis, nest building in rats, and locomotor activity in the fiddler crab (Uca pugnax) (Saunders, 1977). The peri­