Sorbed substrates, uptake

Does Cell Contact with a Substrate Reservoir Allow the Direct Uptake of Sorbed, Liquid, Gaseous, and... 

DOES CELL CONTACT WITH A SUBSTRATE RESERVOIR ALLOW THE DIRECT UPTAKE OF SORBED, LIQUID, GASEOUS, AND SOLID SUBSTRATES ... 

The principal difference between adsorbed and solid substrates is that the latter are adsorbed to molecules of their own kind. With respect to their bioavailability, multilayer-sorbed molecules should behave like a solid substrate. A calculation shows that the direct uptake of truly adsorbed molecules is probably neither advantageous to bacteria nor can it be shown experimentally. Cells of the dibenzofuran-degrading Sphingomonas sp. HH19k consume at maximum 100 000 molecules per second [14], Assuming that an adhered cell touches a sorbent with 1% of its cell surface at a time, as was proposed by van Loosdrecht et al. [60], it would contact about 100000 sorbed molecules at a time, representing substrate for only one second. This does not contradict the possibility of direct uptake of truly adsorbed molecules, but it illustrates that such an uptake-mechanism would be relatively unimportant. 

The example discussed above shows the effect of different solid substrates on the adsorption of a single type of aqueous cation [Co(II)]. The uptake vs. pH curves in Figure 7.6 show the differences in uptake behavior as a function of pH for a variety of aqueous cations and anions on one type of substrate - ferric hydroxide particles [5]. Some of the cations included in Figure 7.6(a), like Pb2+ and Cr3+, sorb at low pH values, whereas others, like Zn2+ and Ni2+, do not sorb until higher pH values are reached. At low pH values, metal oxide and hydroxide surfaces tend to... 

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