Microbial utilization of amino acids and a peptide bound on homoionic montmorillonite and kaolinite

The ability of microorganisms to utilize amino acids and a peptide bound on montmorillonite (M) and kaolinite (K) homoionic to different cations as a sole source of carbon (C) or nitrogen (N) was studied. Proline bound on M homoionic to hydrogen or calcium was used by Agrobacterium radiobacter as a source of N only when the medium was supplemented with glucose, but it was not utilized as a C source even when NH4NO3 was added to the medium. Arginine bound on M homoionic to hydrogen was used as a source of both C and N in the absence of exogenous glucose or NH4NO3, whereas when complexed on M homoionic to aluminum, it was used only as a source of N or C in the presence of glucose or NH4NO3, respectively. Glycylglycine bound on K homoionic to sodium was used as a source of N in the presence of glucose. Aspartic acid and cysteine were not used by A. radiobacter, other bacteria, or fungi when bound on the homoionic clays. These differences in utilization of the bound amino acids and peptide may have been related to their relative affinity for the clays and microbial permeases, their location on the clays and the yield of energy from their intracellular metabolism as compared to the energy necessary for their transport from the clays into the cell.