Physiological and Biochemical Response of a Hot-Spring Cyanobacterium Nostoc Sp. Strain HKAR-2 to Aluminum Toxicity

Aluminum is an undesirable water pollutant released by water treatment plants and metal processing industries that exhibit enormous toxic effects on water bodies. In the present study, we have investigated the effects of aluminum toxicity on the physiological and biochemical behavior of a hot-spring cyanobacterium Nostoc sp. strain HKAR-2. The growth of cyanobacterium was declined up to 33% by increasing aluminum concentration from 0.2 to 0.6 mM at pH 7.5 as compared to control (non-treated). However, the growth had further declined up to 87 and 92% by decreasing the pH to 6.0 and 5.0, respectively, as compared to control (pH 7.5) after 12 days of treatment. The amount of protein, chlorophyll, mycosporine-like amino acids, phycobiliproteins, extracellular and intracellular macronutrients such as phosphate and nitrate contents, and nitrate reductase activity was also declined at pH 7.5 as compared to non-treated control. In addition, aluminum also altered the sodium and potassium ions in both extracellular and intracellular environments. There was an increase in the activity of antioxidative enzymes such as catalase (CAT), superoxide dismutase (SOD), and ascorbic peroxidase (APX) ranging from 58, 79, and 40%, respectively, at 0.6 mM aluminum. The increase in intracellular concentration of aluminum was directly proportional to the inhibition of cyanobacterial growth at pH 7.5. In conclusion, aluminum showed acute toxicity on the hot-spring cyanobacterium Nostoc sp. strain HKAR-2, which indicates that aluminum may adversely affect the microbiota of hot-spring habitats.