Metatranscriptomic profiles of Eastern subterranean termites, Reticulitermes flavipes (Kollar), fed on second generation feedstocks

Second generation lignocellulosic feedstocks are being considered as an alternative to the first generation biofuels that are derived from grain starches and sugars. However, the current pre-treatment methods of second generation biofuel production are inefficient and expensive due to the recalcitrant nature of lignocellulose. In this study we used the lower termite Reticulitermes flavipes (Kollar), a wood feeding specialist, to identify potential lignocellulose pretreatment genes/enzymes. Metatranscriptomic profiling was performed on worker termite guts after feeding on corn stover (CS), soybean residue (SR) or paper to identify microbial community, pathway and gene level responses. Community profiles after CS and SR feeding were different from the paper feeding profile. Functional profiles after CS feeding were similar to paper and SR; whereas paper and SR showed different profiles. At the community level, protist symbiont abundance decreased significantly in termites feeding on SR relative to paper and CS. At the functional level, amino acid and carbohydrate metabolism pathways were downregulated in termites feeding on SR. Gene expression analyses showed significant downregulation of genes after SR feeding relative to paper and CS. However, stereotypical lignocellulase genes/enzymes were not differentially expressed, but rather were among the most abundant/ constitutively expressed genes. These results suggest that the effect of second generation feedstocks on termite lignocellulose metabolism is minimal and thus, the most abundantly expressed genes appear as the best candidate catalysts for use in corn stover and soybean residue pretreatment and saccharification.