Bacterial sorption

Bacterial sorption of some metals can be described by the linearized Freundlich adsorption equation log S = log K+n log C, where S is the amount of metal absorbed in pmol g, C is the equilibrium solution concentration in pmol L, and K and n are the Freundlich constants. 

Figure 7.41 Various types of bacterial sorption on solid surfaces (see text).

For major metal analyses, filtration of samples is also necessary, particularly in waters with relatively high particulate and colloidal contents. In these cases filtration prevents both sorption and desorption of metal ions, mainly during long-term storage. In addition, both the filtration as well as the refrigeration at 4°C also reduces bacterial sorption and interferences during analysis. 

Two distinct phases of bacterial sorption on to glass have been observed [78] the first reversible phase may be interpreted in terms of DLVO theory. Reversible sorption of a non-mobile strain (Achromobacter) decreased to zero as the electrolyte concentration of the media was increased, as would be expected. The second irreversible phase is probably the result of polymeric bridging between bacterial cell and the surface in contact with it. It is obviously not easy to apply colloid theory directly but the influence of factors such as ij/o, pH and additives can be predicted and experimentally confirmed. 

Liu S-Y, Z Zheng, R Zhang, J-M Bollag (1989) Sorption and metabolism of metolachlor by a bacterial community. Appl Environ Microbiol 55 733-740. 

Bacterial cell walls contain different types of negatively charged (proton-active) functional groups, such as carboxyl, hydroxyl and phosphoryl that can adsorb metal cations, and retain them by mineral nucleation. Reversed titration studies on live, inactive Shewanella putrefaciens indicate that the pH-buffering properties of these bacteria arise from the equilibrium ionization of three discrete populations of carboxyl (pKa = 5.16 0.04), phosphoryl (oKa = 7.22 0.15), and amine (/ Ka = 10.04 0.67) groups (Haas et al. 2001). These functional groups control the sorption and binding of toxic metals on bacterial cell surfaces. 

Mullen et al. (1989) reported that Bacillus cereus, B. subtilis, E. coli and P. aeruginosa were able to sorb an average of 89% of the total Ag+ and 12-27% of the total Cd2+, Cu2+ and La3+ from a ImM solution. Using polyacrylamide-entrapped cells of Brevibacterium sp strain PBZ, Simine et al. (1998) measured a sorption capacity of 40 mg g-1 and 13 mg g-1 dry biomass for Pb and Cd, respectively. Hall et al. (2001) isolated two bacterial strains of P. syringae that were tolerant to 1000 mg L-1 Cu. Similarly, Amoroso et al. (2001) were able to obtain Streptomyces spp. strains R22 and R25 with a high tolerance to Cr from sediments of the Sail River, Argentina. The cells of R22 and R25 could accumulate 10.0 and 5.6 mg Cr g-1 dry weight, respectively, from a concentration of 50 mg Cr mL 1. Cell fractionation studies with strain R22 showed that most of the chromium... 

Some heavy metal-tolerant bacterial strains and their sorption capacities for Cu and Cd are listed in Table 1. These bacteria show great potential for remediating soils that are contaminated with toxic metals. Our pot culture experiments showed that the growth of tobacco plants in a Cd-polluted Yellow Brown Soil (Alfisol) was significantly promoted by inoculating the soil with P. Putida in comparison with the non-inoculated soil (Fig. 2). 

Table 1. Sorption capacity (mmol kg-1) of some bacterial species for Cu and Cd...

Fowle and Fein (1999) measured the sorption of Cd, Cu, and Pb by B. subtilis and B. licheniformis using the batch technique with single or mixed metals and one or both bacterial species. The sorption parameters estimated from the model were in excellent agreement with those measured experimentally, indicating that chemical equilibrium modeling of aqueous metal sorption by bacterial surfaces could accurately predict the distribution of metals in complex multicomponent systems. Fein and Delea (1999) also tested the applicability of a chemical equilibrium approach to describing aqueous and surface complexation reactions in a Cd-EDTA-Z . subtilis system. The experimental values were consistent with those derived from chemical modeling. 

Fowle et al. (2000) have measured the sorption by a soil bacterium (B. subtilis) of uranyl in 0.1 M NaC104 at 25°C as a function of pH, time, and solid solute ratio, using a batch technique. The stoichiometiy and thermodynamic stability of the important uranyl-surface complexes indicated that uranyl formed two different surface complexes, one involving neutral phosphate functional groups, and another with deprotonated carboxyl functional groups, on the bacterial cell wall ... 

Borrok et al. (2004a) used potentiometric titration to measure Cd sorption by different bacterial consortia, and a surface complexation approach to determine thermodynamic stability constants. When the data were modeled by adopting a single set of stability constants, a similar sorption behavior was shown by a wide range of bacterial species. Further, current models that rely on pure strains of laboratory-cultivated bacterial species appear to overestimate the extent of metal biosorption in natural systems. 

Schlekat, C.E., A.W. Decho, and G.T. Chandler. 1998. Sorption of cadmium to bacterial extracellular polymeric sediment coatings under estuarine conditions. Environ. Toxicol. Chem. 17 1867-1874. 

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