Pb2+ biosorption by Serratia marcescens CCMA 1010 and its relation with zntR gene expression and ZntA efflux pump regulation

Global concerns about the preservation and restoration of aquatic environments are rising and pollution related to heavy metals is one of the main worries. Indeed, this issue has been a challenge for the metallurgical industry and other activities associated with metal contamination. Thus, over time, several physical and chemical methods have been developed and applied to remove metals from water. However, these methods can be associated with high costs, and bioremediation using plants, fungi, and bacteria is considered a viable alternative. This paper reports experiments on lead removal from an aqueous medium using active and inactive Serratia marcescens CCMA 1010 and a study on the effect of lead in this bacterial strain regarding the expression of the zntR gene, which produces the zntR protein known to have a role as a regulator of the ZntA efflux pump of metals (Pb2+, Cd2+, Zn2+). The amount of removed Pb2+ by active biomass remained below ∼25 mg/L for the initial concentrations tested up to 120 mg/L but increased to removals of ∼70 and ∼167 mg/L for the tested concentrations of 220 and 300 mg/L, respectively. On the other hand, the removal of Pb2+ by inactive biomass increased in direct relation to the initial tested concentration, with removed percentages around 25 %. Interestingly, in cultures with 15 and 60 mg/L Pb2+ the expression of zntR was 27 to 74 and 87 to 177 times lower (respectively) than in cultures without Pb2+, while in cultures with 120 mg/L Pb2+, the zntR expression was just 1.3 to 9.3 times lower than in the absence of Pb2+. The results confirm the potential of S. marcescens CCMA 1010 for Pb2+ biosorption, the presence of Pb2+ resistance mechanisms in this strain, and contribute to a better understanding of the ZntA transmembrane protein regulation.