What mechanisms do microorganisms use to remediate heavy metal contamination?

Microorganisms employ multiple mechanisms for heavy metal bioremediation: 1) Biosorption - passive binding of metals to cell walls/surfaces through functional groups (carboxyl, phosphoryl, amino); rapid, can use dead biomass; not specific. 2) Bioaccumulation - active uptake and intracellular accumulation; requires living cells with metal transport systems. 3) Biotransformation - enzymatic conversion to less toxic or mobile forms; Cr(VI) reduction to Cr(III), Hg(II) volatilization to Hg(0) by mercury reductase, selenate/selenite reduction to elemental selenium. 4) Bioprecipitation - metabolic products precipitate metals; sulfate-reducing bacteria produce sulfide that precipitates metal sulfides; phosphate release precipitates metal phosphates. 5) Biomineralization - formation of stable mineral phases incorporating metals. Selection depends on metal type, concentration, and site conditions. Bacteria (Pseudomonas, Bacillus), fungi (Aspergillus, Penicillium), and algae all used for metal bioremediation.