Asian Journal of Microbiology and Biotechnology

Heavy-metal contamination can alter cyanobacterial physiology and pigment composition, making carotenoid responses potentially useful for environmental monitoring. This study evaluated time-dependent carotenoid responses in Calothrix sp., C. brevissima CCCNO:65, and C. maechica 19 following exposure to lead (Pb) and arsenic (As). Cultures were maintained in BG-11 medium under controlled light, temperature, and aeration conditions and exposed independently to 0, 2, or 5 ppm of each metal for six days. Carotenoid content was quantified spectrophotometrically at 450 nm, with measurements taken on Days 0, 3, and 6. The three cultures showed distinct temporal responses. In Calothrix sp., carotenoid content declined by Day 3 and partially recovered by Day 6, with Pb at 2 ppm approaching the control value. C. brevissima CCCNO:65 showed increases under both arsenic treatments by Day 3, and by Day 6 the As-treated values were higher than the control; Pb at 5 ppm also showed recovery after an earlier decrease. C. maechica 19 exhibited a different pattern, with Pb at 5 ppm increasing by Day 6 while As at 5 ppm declined to the lowest recorded Day 6 value. These findings show that carotenoid responses to Pb and As were culture-, dose-, and time-dependent. Carotenoid measurements may therefore provide a useful stress-responsive endpoint, although their interpretation for bioremediation or bioindicator applications requires additional physiological and metal-uptake measurements.