Physiological and Photosynthetic ToxiCity of Thallium in Synechocystis sp. PCC6803
The physiological and photosynthetic toxiCity mechanism of monovalent thallium, Tl(I), in a cyanobacteria, Synechocystis sp. PCC6803, was examined based on a series of batch culture experiments, determination of the pigments content and measurements of photosynthetic activities under the metal exposure conditions. Results showed that micro-molar level of Tl(I) drastically inhibit its growth, then 50% inhibitory concentration (IC50) was approximately 1 μM. An acclimating incubation with 0.5 μM Tl(I) for 72 h bring no significant changes in IC50 of thallium for growth. Chlorophyll a and phycobiliproteins content per cell basis decreased by 71% and 94% during 72 h incubation with 2.5 μM Tl(I), respectively. Results from pigments determination suggested that metabolic defect was rose by thallium exposure in Synechocystis sp. PCC6803. Then, to investigate the effect of thallium on energy generation process, acute dose-response of Tl(I) on photosynthetic O2 evolution activities were measured. No effect on net photosynthetic O2 evolution activity per chlorophyll basis was observed in 1 mM and below Tl(I) exposure, while 20 mM Tl(I) decrease the activity by 60%. Furthermore, 20 mM thallium did not affect 1,4-benzoquinone dependent PSII activity. These photosynthetic 50% inhibitory doses of thallium were approximately 2,000-fold higher than IC50 of growth. Thus, photosynthetic energy metabolism did not constitute a limiting factor of growth under the thallium exposure. These results suggested that substance metabolic defect and/or NADP reducing processes could be the main process involved in thallium toxiCity in Synechocystis sp. PCC6803.
KeywordsThallium heavy metal toxiCity photosynthesis cyanobacteria
Unable to display preview. Download preview PDF.
- Asami T et al. (2002) Contamination of the sediments and soil with thallium and related harmful metals discharged from the Hosokawa mine and smelter, Miyagi Prefecture, Japan J Field Sci 2:13–22.Google Scholar
- Kunze M (1972) Der Einfluss von Thalliumazetate auf das Wach-stum von Acholeplasmataceae, Mycoplasmataceae und einigen Bakterien-spezies. Zbl Bakt I Abt Orig A 222:535–539.Google Scholar
- Porra RJ et al. (1989) Determination of accurate extinction coefficients and simultaneous equations for assaying chlorophylls a and b extracted with four different solvents: Verification of the concentration of chlorophyll standards by atomic absorption spectroscopy. Biochim Biophys Acta 975:384–394.CrossRefGoogle Scholar
- Sholl W (1980) Bestimmung von thallium in verschiedenn anorgnischen und organischen Matrices. Ein einfaches photometrisches Routineverfahren mit Brillantgrün. Landwirtsch Forsch 37:275–286.Google Scholar
- Zhou D, Liu D (1985) Chronic thallium poisoning in a rural area of Guizhou Province, China. J Environ Health 48:14–18.Google Scholar