Abstract
BackgroundSecond generation lignocellulosic feedstocks are being considered as an alternative to first generation biofuels that are derived from grain starches and sugars. However, the current pre-treatment methods for 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), as a model to identify potential pretreatment genes/enzymes specifically adapted for use against agricultural feedstocks.ResultsMetatranscriptomic profiling was performed on worker termite guts after feeding on corn stover (CS), soybean residue (SR), or 98% pure cellulose (paper) to identify (i) microbial community, (ii) pathway level and (iii) gene-level responses. Microbial community profiles after CS and SR feeding were different from the paper feeding profile, and protist symbiont abundance decreased significantly in termites feeding on SR and CS relative to paper. Functional profiles after CS feeding were similar to paper and SR; whereas paper and SR showed different profiles. Amino acid and carbohydrate metabolism pathways were downregulated in termites feeding on SR relative to paper and CS. Gene expression analyses showed more significant down regulation of genes after SR feeding relative to paper and CS. Stereotypical lignocellulase genes/enzymes were not differentially expressed, but rather were among the most abundant/constitutively-expressed genes.ConclusionsThese results suggest that the effect of CS and SR feeding on termite gut lignocellulase composition is minimal and thus, the most abundantly expressed enzymes appear to encode the best candidate catalysts for use in saccharification of these and related second-generation feedstocks. Further, based on these findings we hypothesize that the most abundantly expressed lignocellulases, rather than those that are differentially expressed have the best potential as pretreatment enzymes for CS and SR feedstocks.Electronic supplementary materialThe online version of this article (doi:10.1186/s12864-015-1502-8) contains supplementary material, which is available to authorized users.
Highlights
Second generation lignocellulosic feedstocks are being considered as an alternative to first generation biofuels that are derived from grain starches and sugars
Our findings show a clear ability of R. flavipes to feed and survive on two very different plant feedstocks (CS and Soybean Residue (SR)); transcripts encoding wood-associated lignocellulases identified through previous work were not affected by the diets
Feeding observations Worker termites feeding on diets of paper, corn stover (CS) and soybean residue (SR) had 100% survivorship across all replicates after 7 days of feeding bioassays
Summary
Second generation lignocellulosic feedstocks are being considered as an alternative to first generation biofuels that are derived from grain starches and sugars. We used the lower termite Reticulitermes flavipes (Kollar), as a model to identify potential pretreatment genes/enzymes adapted for use against agricultural feedstocks. Second generation biofuels are produced from various kinds of plant biomass including agricultural/forest by-products, organic wastes and other dedicated feedstocks [1]. The lower termite, Reticulitermes flavipes (Kollar), is used as a model in this study to investigate potential mechanisms of lignocellulose feedstock digestion. A recombinant enzyme cocktail of R. flavipes enzymes was shown to result in the release of free sugars from wood substrate in vitro [16]. This evidence supports the further investigation and application of R. flavipes digestion mechanism(s) in biofuel production from lignocellulose biomasses
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