Prediction of the impact induced by Cd in binary interactions with other divalent metals on wild-type and Cd-resistant strains of Dictyosphaerium chlorelloides

The metals present in freshwater have a toxic profile with bioaccumulation and are biomagnified along the aquatic food chain. The metals induce high sensitivity in most aquatic organisms, while others, such as some microalgae species, evolve towards resistance. Therefore, this research predicted through the Combination Index method the binary interaction exposed to divalent metals by inhibiting population growth in a Cd-resistant strain (Dc RCd100 ) compared to the wild-type strain (Dc1M wt ) of Dictyosphaerium chlorelloides and evaluate the specific resistance level obtained by Dc RCd100 to Cd relative to other divalent metals.The results showed that Dc RCd100 presents resistance compared to Dc1M wt in individual exposure in the order of Fe 2+ > Ni 2+ > Cd 2+ > Co 2+ > Zn 2+ > Cu 2+ > Hg 2+ with 50% inhibitory concentration at 72 h of exposure ( IC 50(72) ) values 1253, 644.4, 423, 162.7, 141.3, 35.1, and 9.9 µM, respectively. It induces cross-resistance with high antagonistic rates (Combination Index ( CI ); CI > > 1) in the Cd/Zn and Cd/Cu. Cd/Ni, its initial response, is antagonistic, and it ends in an additive ( CI = 1). Dc RCd100 showed a lower resistance in Co, and Cd/Fe resistance was reduced individually. The interaction with Hg increased its resistance ten times more than individually.This research highlights the use of the CI as a highly efficient prediction method of the binary metal interactions in wild-type and Cd-resistant strains of D. chlorelloides . It may have the potential for metal accumulation, allowing the development of new methods of bioremediation of metals in effluents, and to monitor the concentration of metals in wastewater, its relative availability, transport, and mechanisms on resistant strains of microalgae. Graphical abstract