The effects of copper and zinc on Spirulina platensis growth and heavy metal accumulation in its cells

Abstract

The effects of copper and zinc on Spirulina platensis (Nordst.) Geitl. growth and the capability of this cyanobacterium for accumulation of these heavy metals (HMs) were studied. S. platensis tolerance to HMs was shown to depend on the culture growth phase. When copper was added during the lag phase, its lethal concentration was 5 mg/l, whereas 4 mg/l were lethal during the linear growth phase. Zinc concentration of 8.8 mg/l was lethal during the linear but not lag phase of growth. HM-treated S. platensis cells were capable for accumulation of tenfold more copper and zinc than control cells. Independently of Cu 2+ content in the medium and of the growth phase, cell cultures accumulated the highest amount of this metal as soon as after 1 h, which may be partially determined by its primary sorption by cell-wall polysaccharides. A subsequent substantial decrease in the intracellular copper content occurred due to it secretion, which was evident from the increased metal concentration in the culturing medium. When zinc was added during the linear growth phase, similar pattern of its accumulation was observed: the highest content after 1 h and its subsequent decrease to the initial level. When the initial density of the culture was low and the cells had much time to adapt to HM, zinc accumulated during the entire linear growth phase, and thereafter the metal was secreted to the medium. The mechanisms of S. platensis tolerance to HM related to both their sorption by the cell walls and secretion of metal excess into the culturing medium and its conversion into the form inaccessible for the cells are discussed.

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“…Zinc toxic effects are shown to be related to metal binding to SH-groups of proteins, in the plasma membranes in particular (Nalimova et al, 2005;Tripathi and Gaur, 2006). Zinc effects practically all physiological processes: cell division, membrane functioning, photosynthesis, and respiration (Nalimova et al, 2005). Inhibition of algal cell division by zinc was not related to the intracellular zinc concentration.…”

“…In literature, many data on the effects of zinc on the growth of these species belonging to the family, Scenedesmaceae (Chlorophyta) are reported (Abd-El-Monem et al, 1998;Tripathi and Gaur, 2006). Zinc toxic effects are shown to be related to metal binding to SH-groups of proteins, in the plasma membranes in particular (Nalimova et al, 2005;Tripathi and Gaur, 2006). Zinc effects practically all physiological processes: cell division, membrane functioning, photosynthesis, and respiration (Nalimova et al, 2005).…”

“…Zinc is an essential micronutrient in all biota owing to its involvement in many physiological processes. It is essential in the maintenance of plasma membrane stability, in the activation of more than 300 enzymes (WHO, 2001), DNA and ribonucleic acid (RNA) synthesis and cell proliferation (U.S. EPA, 2005); however, it becomes toxic when available in higher concentrations (Nalimova et al, 2005) since it decreases cell division, mobility, total chlorophyll content, ATPase activity and carotenoid/chlorophyll ratio in microalgae (Omar, 2002). The toxicity of zinc depends on the external concentration, the zinc speciation, and the pH and hardness of the water (WHO, 2001).…”

“…Disadvantages of these methods are their high cost prize, low economic efficiency, especially during removing small amounts of heavy metals, and a necessity of slag burial. Biological methods of metal detoxication and removal from aqueous solutions lack these disadvantages (Nalimova et al, 2005). Microalgae have been found to be very effective in removing heavy metals from wastewater because of their large surface area and high binding affinity (Chong et al, 2000).…”

Modelling growth of, and removal of Zn and Hg by a wild microalgal consortium

“…Stringent environmental regulations have been enforced in attempts to keep the levels of Hg 2+ and Zn 2+ below the maximum allowable thresholds, so the demand has increased for new technologies focused on metal removal from wastewaters; this constitutes a classical remediation approach, before the (much more effective) strategy of cleaner industrial technologies is put to work. Removal of excessive levels of heavy metals from industrial wastewaters has traditionally been effected by chemical precipitation, chemical oxidation or reduction, ion exchange, evaporation, electrolysis or membrane-mediated processes; however, such physicochemical approaches are either inefficient or extremely expensive, especially in the presence of very low concentrations of heavy metals-say within the range 1-100 mg/L (Cruz et al 2004;Gupta and Rastogi 2008b;Nalimova et al 2005). Biological methods of metal detoxification and removal from aqueous solutions have meanwhile emerged as promising alternatives, and microbial biomass (either viable or inactivated) can indeed uptake and concentrate heavy metals from wastewaters; it is indeed about to become an economically feasible alternative because of its high specific metal binding capacity (even from dilute media) (Gupta and Rastogi 2008a), coupled with the possibility of metal recovery from said biomass afterwards (Bayramoğlu and Arıca 2008;Cruz et al 2004).…”