Exposure of Dunaliella tertiolecta to Lead and Aluminum: Toxicity and Effects on Ultrastructure

Abstract

The growth response of the marine alga Dunaliella tertiolecta to different concentrations of lead and aluminum was investigated. Both metals had a stimulatory effect at low concentration and an inhibitory effect at high concentration (hormesis). The IC25 values of lead are 8.43, 7.29, and 6.74 mg L-1 for 24, 48, and 72 h, respectively. The corresponding values for aluminum are 30.54, 22.42, and 18.16 mg L-1. Although it seems that the two metals are not directly toxic to the alga at the concentrations found in the environment, as implied by the IC25 values and the environmental concentrations of the metals, low concentrations of both metals, alone and in combination, affected the ultrastructure. The growth of batch-grown cells exposed to 0.5 mg L-1 lead and aluminum, alone and combined, during the 24-h exponential phase was investigated. The same cells were also examined under an electron microscope to determine the biological effects of the two metals on the ultrastructure. The most obvious effects of lead were disrupted thylakoidal membranes, accumulated polyphosphate bodies and vacuoles, and lead precipitates on the cell surface. These ultrastructural alterations were partially present in aluminum-treated and lead-aluminum-treated cells. In joint exposure, the most important change was the lysis of the cell membrane. Aluminum and lead seem to act synergistically on the cell membrane leading to cell membrane lysis.

Intracellular Metal Compartmentalization in the Green Algal Model System Micrasterias Denticulata (Streptophyta) Measured by Transmission Electron Microscopy-Coupled Electron Energy Loss Spectroscopy1

“…Like in other algae (Nassiri et al. 1997a,b, Sacan et al. 2007), Al‐ and Cu‐treated Micrasterias cells featured an increased number of vacuoles with electron‐dense precipitations.…”

“…Thus, the uncommonly thick primary wall and its bloated appearance induced in young semicells by Al and also by Cu may be a result of a loss of the Ca 2+ bonds of pectins. Al‐treated cells also showed a wavy plasma membrane, which was also observed in Dunaliella tertiolecta after Al exposure (Sacan et al. 2007).…”

Evaluation of the potential of microalgae Microcystis novacekii in the removal of Pb2+ from an aqueous medium

“…Cordero et al [41] reported a Pb 2+ DE 50 (dose that inhibits in 50% the growth of the species) of 0.4 mg L −1 for the microalgae Tetraselmis chuii. Pb 2+ concentrations over 0.5 mg L −1 affected the Dunaliella tertiolecta cell ultrastructure, leading to the rupture of the tilacoid membrane, the build-up of polyphosphate bodies, and the precipitation of Pb 2+ on the cell wall [42]. However, this species resists high concentrations of Pb 2+ , presenting a DE 25 (dose that inhibits in 25% the growth of the species) of 8.43 mg L −1 after 24 h.…”

The increasing aluminum content affects the growth, cellular chlorophyll a and oxidation stress of cyanobacteria Synechococcus sp. WH7803

“…Aluminum (Al) plays an important role in marine ecosystems due to its inhibition or promotion effects on phytoplankton (Vrieling et al 1999, Saçan et al 2007, although its concentration is very low as it is a particle-reactive element, easily removed from seawater (Minakawa & Watanabe 1998, Koshikawa et al 2002. Naturally, marine dissolved Al is mainly derived from atmospheric precipitations and river run-offs, and its concentration is thus increasing as a result of increasing severe sandstorms and acidic precipitations caused by atmospheric pollution (Han et al 2008, Ren et al 2011.…”

“…The effects of Al on marine organisms were also observed to be species-specific, e.g. Vrieling et al (1999) found that the increased Al positively affected the growth and final cell density of pennate Navicula salinarum, but not of centric species Thalassiosira weissflogii; while Saçan (2007) found that Al negatively affected the growth of diatom Minutocellus polymorphus and green alga Dunaliella tertiolecta. However, a limited Al effect was observed for the growth of diatom Skeletonema costatum (Stoffyn 1979); and no significant effects were detected on the brown macroalga Hormosira banksii, sea urchin embryo Heliocidaris tuberculata and 2 juvenile fish species of Lates calcarifer and Acanthochromis polyacanthus, even at an extremely high Al level (37 μmol l -1 ) (Golding 2014).…”