**5.3. Metal accumulation**

In order to have the physiological effect on the growth of cells, heavy metals must enter the cell [19, 59, 60]. Metal uptake system in bacteria is grouped in two types; one is fast and unspecific, constitutively expressed and does not require ATP. They are usually driven only by the chemiosmotic gradient across the cytoplasmic membrane of bacteria. The second type of uptake system is highly specific, slow, inducible and dependent on ATP, in addition to the chemiosmotic gradient. They are only induced in times of need, starvation or a special metabolic situation [61].

As cell surface encounter metal ion, formation of a complex takes place, which is a pre-requisite for uptake of metals by the organism [59, 60]. Once surface sorption takes place, the metal is transported into the periplasmic space of Gram-negative cells and transported further into the cytoplasm [60]. When cell encounters high concentration of any heavy metal, the heavy metal ion is transported into the cytoplasm, accumulated inside the cell due to one type of metal uptake which is fast, unspecific, constitutively expressed and does not require ATP [61]. The cations of heavy metals interact with physiological ions Cd2+ with Zn2+ or Ca2+, Ni2+ and Co2+ with Fe2+, Zn2+ with Mg2+ thus inhibit the function of respective physiological cations. This result in oxidative stress in the cell [1].

*6.1.1.1. Bacterial biosorption*

given in **Table 2**.

**Metals Bacteria Temperature** 

*Cupriavidus metallidurans*

CH34

*Geobacillus thermodenitrificans*

6. Gold *Cupriavidus metallidurans* CH34

**Sr. No.**

Bacterial cell wall encountering the metal ion is the first component of biosorption. The metal ions get attached to the functional groups (amine, carboxyl, hydroxyl, phosphate, sulfate, amine) present on the cell wall [49, 67]. The general metal uptake process involves binding of metal ions to reactive groups present on bacterial cell wall followed by internalization of metal ions inside cell [48]. More metal is uptaken by Gram positive bacteria due to presence of glycoproteins. Less metal uptake by Gram negative bacteria is observed due to phospholipids and LPS [68, 69]. Biosorption of various metals by different bacteria is

**pH Agitation Time Wt** 

— — — — — — [111–114]

25 5 100 12 — 51 [122]

**— — — — — —** [125]

**(g/L)**

**q(mg/g) or % removal**

Biosorption of Heavy Metals

27

http://dx.doi.org/10.5772/intechopen.72099

**References**

**(°C)**

1. Arsenic *Bacillus* sp. KM02 — — — — — — [108]

2. Cadmium *Pseudomonas putida* mt2 — — — — — — [111–114]

3. Chromium *Micrococcus* sp. 35 5 120 24 — 92% [117]

4. Cobalt *Rhodopseudomonas palustris* — — — — — — [120] 5. Copper *Stenotrophomonas maltophilia* 25 5 140 2 20 0.57 [116]

*Kocuria* sp. — — — — — — [109] *Bacillus* sp. — — — — — — [110]

*Enterobacter cloacae* 25 5 240 2 0.1 58.9% [115] *Stenotrophomonas maltophilia* 28 5 140 2 20 0.12 [116] *Actinomycetes* sp. 30 6 150 24 5 32.63 [116]

*Bacillus licheniformis* 28 3.5 120 48 — 95% [116] *Staphylococcus saprophyticus* 27 2 150 3 0.2 24.1 [118] *Enterobacter cloacae* 25 4 240 2 0.1 55.8 [115] *Pseudomonas aeruginosa* 25 — — — — 1.07 [119] *Micrococcus* sp. 35 5 120 24 — 92% [117]

*Bacillus licheniformis* 28 2.5 120 48 — 32% [121]

*Bacillus cereus* 25 5.5 — 24 1.0 50.32 [119] *Pseudomonas aeruginosa* 25 — — — — 0.67 [119] *Thiobacillus thiooxidans* 30 5 786 2 0.25 39.84 [123] *Enterobacter cloacae* 25 5 240 2 0.1 78.9 [115] *Staphylococcus saprophyticus* 27 3.5 150 2 0.2 14.5 [118]
