A comparative study on heavy metal (cadmium) tolerance and biosorption capacity of locally isolated lactic acid bacteria

Heavy metals (HM) have less biological role but show extreme toxicity in living systems. Lactic acid bacteria (LAB) are beneficial microorganisms, some of which have the ability to chelate HM and may be used to treat heavy metals poisoning. The aim of the current study was to select and identify Cd-removing probiotic LAB strains, for future pharmaceutical application. Seventeen LAB strains, from human excretions and animal fecal matter, were initially verified for their probiotic properties. The strains which could survive in the presence of Cd (≥100 ppm) were selected. The metal removal efficiency of isolates was compared, through atomic absorption spectrophotometry (AAS), by measuring the reduction in Cd contents of CdCl2 5 mg/L (3.05 ppm of Cd) supplemented broth following 24 h culturing of the strains. The Cd reduction of 38–75% was recorded in culture broth. The Cd removal ability significantly varied (p < 0.05) with microbial surface charge, incubation period, temperature and pH of media. Levilactobacillus brevis MW362790 and Pediococcus pentosaceus MT323062, identified through 16S rRNA gene sequencing, were recognized as strong Cd chelators. These strains may have application in pharmaceutical or agriculture (farm animals) for protection against cadmium toxicity. Further studies are suggested on in vivo metal detoxification potential.