Heavy Metals Bioremediation: Cd2+, Pb2+ and Zn2+ bioremoval by Serratia marcescens CCMA1010 in aqueous solution

Abstract

Microorganisms offer cost-effective and sustainable solutions for the bioremediation of toxic metals. S. mar- cescens CCMA1010 was investigated for its growth and metal removal potential in aqueous solution with Cd²⁺, Pb²⁺, and Zn²⁺. The bacterium tolerated all three metals, with a minimum inhibitory concentration (MIC) ranking of Zn²⁺ > Pb²⁺ > Cd²⁺. Remarkably, Pb²⁺ had minimal impact on growth compared to the control. A brown coloration in Pb²⁺ treatments suggested the bioprecipitation. FTIR analysis confirmed spectral changes linked to sulphate and phosphate groups, supporting the probability of this mechanism. No similar evidence was found for Cd²⁺ or Zn²⁺. The bioremoval experiment was designed to construct a predictive model and identify the optimal conditions for maximum metal uptake (q), using a Rotatable Central Composite Design (RCCD) with 27 exper- imental runs, including factorial points, axial points, and three central points. The statistical modeling (P-value) showed that quadratic models for Cd²⁺ and Pb²⁺ uptake were significant (p < 0.05), with initial metal concen- tration as the main influencing factor. The p-value for Zn²⁺ (q) was not significant (p > 0.05). The F-values indicate that both models (Cd²⁺ and Pb²⁺) were statistically significant, with only a 0.01% and 0.46% probability, respectively, that such high F-values could have occurred due to random noise. Variables such as pH and in- teractions between multiple metals were not statistically significant under the tested conditions. These results highlight S. marcescens CCMA1010 as a promising candidate for heavy metal bioremediation, particularly for lead removal through bioprecipitation pathways.