Metallophilic, Metal-Resistant, and Metal-Tolerant Microorganisms

Abstract

AbstractMetals are found in high concentration around metal processing industries or in dumping sites. The microorganisms present in such metal-rich environments resist high concentration of metals and are termed as metallophiles and metal-resistant microorganisms. Metal-tolerant microorganisms can survive at high concentrations of metals. Metals essential for bacterial life include copper, cobalt, nickel, chromium, molybdenum, and zinc. while cadmium, silver, mercury, and lead ions are toxic to living things. The natural habitats for metallophiles are deep-sea or terrestrial hydrothermal sources but they are found mostly in man-made metal-rich environments. Metal-resistant bacteria include Thiobacillus ferrooxidans, Bacillus, Pseudomonas, Staphylococcus, Micrococcus, and Coryneforms. In many microorganisms, the genes controlling metal resistance are carried on plasmids. The heavy metals cause environmental pollution and metallophiles work as their bioremediators by removing the metals through different mechanisms such as biosorption, bioreduction, and biooxidation.In India, metal-rich environments exist mainly in mining areas, groundwater and aquifers, and metallophilic, metal-resistant microorganisms have been reported from such areas. These include Acinetobacter, Pseudomonas, Citrobacter, Microbacterium, Thiobacillus, and Bacillus. Applications of metallophiles have been described for recovery of metals. Five novel species of metallophilic microorganisms, new to Science, have been reported from India.KeywordsMetallophilicMetal resistantMetal tolerantMetal processing industriesMetal resistance genes on plasmidsBiosorptionChromate reductionArsenic contaminated groundwater