Species of Dominant Bacteria

Some bacteria are more tolerant (or less susceptible) to heavy metal toxicity than other bacteria. There are two basic metal resistance mechanisms or "safe" metal accumulation (bioaccumulation) mechanisms used by metal resistant bacteria (Figure 19.14).

Bacterial reactions with heavy metals can occur extracellularly, pericellularly (surrounding the cell), and intracellularly. Metals may accumulate extracellularly through chelation by extracellular polysaccharides that are secreted by bacteria such as Bacillus and Zoogloea. Chelated metals do not cause toxicity.

Metals may accumulate pericellularly by binding with cell wall components. Here, the chemically bonded metals do not cause toxicity. Metals that accumulate intra-cellularly by transport from bacterial fibrils may cause toxicity, if the metals bind to bacterial enzymes.

FIGURE 19.14 Bioaccumulation of heavy metals. Bacterial can remove or accumulate heavy metals "safe^y" through the adsorption of heavy metals to the polysaccharides surrounding the bacteria or cell wall. The adsorption of heavy metals to bacterial fibrils is "unsafe" due to the absorption to the cytoplasm and "attack" upon enzymes.

FIGURE 19.14 Bioaccumulation of heavy metals. Bacterial can remove or accumulate heavy metals "safe^y" through the adsorption of heavy metals to the polysaccharides surrounding the bacteria or cell wall. The adsorption of heavy metals to bacterial fibrils is "unsafe" due to the absorption to the cytoplasm and "attack" upon enzymes.

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