Heavy metals remediation through lactic acid bacteria: Current status and future prospects

With the development of industrialization and urbanization, heavy metal (HM) pollution has become an urgent problem in many countries. The use of microorganisms to control HM pollution has attracted the attention of many scholars due to its advantages of mild conditions, low process cost, and no secondary pollution. In this context, this review aimed to compile recent advances on the potential of lactic acid bacteria (LAB) as HMs biosorbents. As a food-safe class of probiotic, LAB can not only be used for HM remediation in soil and wastewater, but most importantly, can be used for metal removal in food. The extracellular adsorption and intracellular accumulation are the main mechanisms of HM removal by LAB. Lactic acid (LA) fermentation is also one of the removal mechanisms, especially in the food industry. The pH, temperature, biomass, ion concentration and adsorption time are the essential parameters to be considered during the bioremediation. Although the LAB remediation is feasible in theory and lab-scale experiments, it is limited in practical applications due to its low efficiency. Therefore, the commonly used methods to improve the adsorption efficiency of LAB, including pretreatment and mixed-cultivation, are also summarized in this review. Finally, based on the review of literature, this paper presents the emerging strategies to overcome the low adsorption capacity of LAB. This review proposes the future investigations required for this field, and provides theoretical support for the practical application of LAB bioremediation of HMs.