Metabolites, exocellular

Solubility of Exocellular Nickel Complexes in the Soil. To evaluate the effect of microbial metabolites on Ni solubility in soil, the soluble exocellular solution, separated after growth of the 20 selected bacterial isolates and all fungal isolates, was eluted through a column of soil. The concentrations and forms of Ni in the eluates were compared to the concentrations and forms of Ni in water and in the growth medium before and after microbial growth. A column (0.8 x 4 cm) was packed (1.5 g/cc) with sieved (<2 mm), air-dry Ritzville silt loam (1.0 g) and an aliquot of the filtered (<0.4 M<) exocellular medium (2 ml) was eluted through the soil. After 1 ml of eluant was collected, the Ni concentration was determined from the concentration of radio-tracer. Metal form was characterized in soil eluates by TLC and TLE as previously described. 

Figure 1. Thin-layer chromatographic behavior of nickel complexes with exocellular fungal metabolites (a) before and (b) after elution through soil. Nickel was visualized by autoradiography intensity is directly related to nickel concentration.

Other self-produced compounds for exocellular electron transfer. In addition to electron transfer by nanowires and endogenous mediators like pyocyanin, electron transfer can also occur through interspecies hydrogen transfer, the production of intermediate metabolites such as formate and acetate and other chemicals. An overall review of this subject is provided by Stams et al. (2006). However, here the focus is on direct electron transfer and thus these other routes of interspecies chemical transfer will not be addressed. 

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