Transformation and mineralization of C-14-labeled cellulose, peptidoglycan, and protein by the soil-feeding termite Cubitermes orthognathus

We performed feeding trials with the soil-feeding termite Cubitermes orthog nathus using soil spiked by uniformly C-14-labeled preparations of cellulos e, peptidoglycan, protein, and bacterial cells (Bacillus megaterium and Esc herichia coli). When incubated in soil for 8 days in the absence of termite s, cellulose and peptidoglycan showed low mineralization rates (0.5% and 0. 2%, respectively). However, when termites were present, their mineralizatio n rates strongly increased (21.6% and 30.6%, respectively). The mineralizat ion rate of protein was 12.4% in the control soils and increased to 36.2% i n the presence of termites. Mineralization of bacterial cells in control so ils occurred in two phases (rapid mineralization during the first 4-5 days and stabilization thereafter). When termites were present, the rates of min eralization of bacterial cells increased and the stabilization phase was ab olished. In all cases, radiolabel accumulated in the termites and the solub ility of the labeled compounds located in the gut increased strongly. Miner alization was accompanied by transformation of residual carbon from the hum ic acid fraction to the fulvic acid fraction during gut passage. High-perfo rmance gel permeation chromatography demonstrated a strong shift in the siz e distribution of the residual carbon from high-molecular-weight towards lo w-molecular-weight molecules in the gut of termites and an accumulation of small molecules in the termite bodies. The present study provides strong ev idence that structural polysaccharides of plants and bacteria and microbial biomass are carbon and energy sources for soil-feeding termites.