Hexavalent chromium [Cr(VI)] tolerance and reduction activity of Synechococcus sp. and Synechocystis sp. isolated in West and South Bay of Laguna de Bay, Philippines
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Abstract
Abstract. Pujalte ECO, Posadas KDB, Morales TC, Chang ACG. 2024. Hexavalent chromium [Cr(VI)] tolerance and reduction activity of Synechococcus sp. and Synechocystis sp. isolated in West and South Bay of Laguna de Bay, Philippines. Asian J Trop Biotechnol 21: 1-9. Cyanobacteria are prevalent in terrestrial and aquatic ecosystems which can tolerate stress caused by heavy metals. In the Philippines, various anthropogenic activities have contributed to the heavy metal contamination in water systems. Laguna de Bay is the largest inland body of water in the Philippines that functions as a multipurpose lake; however, heavy metal contamination such as hexavalent chromium [Cr(VI)] has progressed through the years due to various anthropogenic activities. This study evaluated the capability of cyanobacterial strains isolated from Laguna de Bay to tolerate and reduce varying concentrations of Cr(VI) using different parameters. Cyanobacterial isolates from Tadlac and Jamboree Lake were subjected to tolerance assay in varying Cr(VI) concentrations, followed by the reduction assay utilizing 1,5-Diphenylcarbazide (1,5-DPCZ) at OD540. Through morphological characterization, two genera were identified: Synechococcus sp. from West Bay and Synechocystis sp. from South Bay. This study revealed that both isolates could tolerate and reduce high Cr(VI) levels within optimum pH of 7 and 8, respectively. The data acquired from the tolerance assay showed that a Cr(VI) concentration of 1000 mg/L still permitted the growth of the two cyanobacteria genera. Percentage reduction of the isolates at their respective optimal pH showed variation wherein Synechococcus sp. at pH 7 exhibited a 58% Cr(VI) average reduction compared to Synechocystis sp. at pH 8, which then exhibited a 66% Cr(VI) average reduction. The present study's findings indicate the potential of the two indigenous cyanobacteria in the bioremediation of Cr(VI) in Laguna de Bay.