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

Abstract

 We performed feeding trials with the soil-feeding termite Cubitermes orthognathus using soil spiked by uniformly ¹⁴C-labeled preparations of cellulose, peptidoglycan, protein, and bacterial cells (Bacillus megaterium and Escherichia coli). When incubated in soil for 8 days in the absence of termites, cellulose and peptidoglycan showed low mineralization rates (0.5% and 0.2%, respectively). However, when termites were present, their mineralization rates strongly increased (21.6% and 30.6%, respectively). The mineralization rate of protein was 12.4% in the control soils and increased to 36.2% in the presence of termites. Mineralization of bacterial cells in control soils occurred in two phases (rapid mineralization during the first 4–5 days and stabilization thereafter). When termites were present, the rates of mineralization of bacterial cells increased and the stabilization phase was abolished. In all cases, radiolabel accumulated in the termites and the solubility of the labeled compounds located in the gut increased strongly. Mineralization was accompanied by transformation of residual carbon from the humic acid fraction to the fulvic acid fraction during gut passage. High-performance gel permeation chromatography demonstrated a strong shift in the size distribution of the residual carbon from high-molecular-weight towards low-molecular-weight molecules in the gut of termites and an accumulation of small molecules in the termite bodies. The present study provides strong evidence that structural polysaccharides of plants and bacteria and microbial biomass are carbon and energy sources for soil-feeding termites.