Malays. Appl. Biol. (2017) 46(4): 225–232
RESPONSES OF A FRESHWATER MICROALGA,
Scenedesmus regularis EXPOSED TO 50% INHIBITION
CONCENTRATION OF Pb2+ AND Hg2+
WAN BAYANI WAN OMAR1,3, HAZLINA AHAMAD ZAKERI2*, NAKISAH MAT AMIN2
and NUR HIDAYAH KAMILIA RASSMAN1
1School of Marine and Environmental Sciences, Universiti Malaysia Terengganu,
21030 Kuala Nerus, Terengganu, Malaysia
2School of Fundamental Science, Universiti Malaysia Terengganu,
21030 Kuala Nerus, Terengganu, Malaysia
3Institute of Marine Biotechnology, Universiti Malaysia Terengganu,
21030 Kuala Nerus, Terengganu, Malaysia
*Email: This e-mail address is being protected from spambots. You need JavaScript enabled to view it
Accepted 22 November 2017, Published online 31 December 2017
ABSTRACT
High concentrations of heavy metals such as lead (Pb2+) and mercury (Hg2+) can have negative effects on the aquatic organisms. Some organisms may even accumulate the metals into their cells. Since the metals are persistent and difficult to be removed, it is important to understand their toxicity mechanisms and effects on the organisms. In this study, Scenedesmus regularis a widely used microalgae in bioremediation was used as a model organism. The toxicity effects of 50% inhibition concentration (IC50) of Pb2+ and Hg2+ on S. regularis total soluble protein (TSP) concentration, caspase-3/7-like enzyme activity and morphology were assessed. About 7.2 mg/L of Pb2+and 0.42 mg/L of Hg2+ were required to inhibit half of S. regularis population. At these concentrations, Pb2+ significantly reduced TSP concentration of the alga by 81% while the reduction was 53% with Hg2+. Presence of Pb2+ and Hg2+ also induced the production of caspase-3/7-like enzyme in the alga, Fluorescence images showed an increase in the intensity of green signals indicating high activity of caspase-3/7-like enzyme in the algal cells after treatment. Late apoptotic stage and necrotic activity were also evident in metal-treated algal cells. Specific activity of caspase-3 was significantly increased to 4-fold in treated cells. Scanning electron microscope images were clearly shown ruptured cells and holes formed on the membrane in Hg2+ treated cells. Further analysis on the mechanism of defence triggered within the alga to tolerate the metal’s toxicity at 50% population would allowed us to elicit the pathways involved in metal’s detoxification.
Key words: Scenedesmus regularis, heavy metals, caspase-3/7-like activity, lead, mercury
