NMR studies on lignocellulose deconstructions in the digestive system of the lower termite Coptotermes formosanus Shiraki

Abstract

Termites represent one of the most efficient lignocellulose decomposers on earth. The mechanism by which termites overcome the recalcitrant lignin barrier to gain access to embedded polysaccharides for assimilation and energy remains largely unknown. In the present study, softwood, hardwood, and grass lignocellulose diets were fed to Coptotermes formosanus workers, and structural differences between the original lignocellulose diets and the resulting feces were examined by solution-state multidimensional nuclear magnetic resonance (NMR) techniques as well as by complementary wet-chemical methods. Overall, our data support the view that lignin polymers are partially decomposed during their passage through the termite gut digestive system, although polysaccharide decomposition clearly dominates the overall lignocellulose deconstruction process and the majority of lignin polymers remain intact in the digestive residues. High-resolution NMR structural data suggested preferential removal of syringyl aromatic units in hardwood lignins, but non-acylated guaiacyl units as well as tricin end-units in grass lignins. In addition, our data suggest that termites and/or their gut symbionts may favor degradation of C–C-bonded β–5 and resinol-type β–β lignin inter-monomeric units over degradation of ether-bonded β–O–4 units, which is in contrast to what has been observed in typical lignin biodegradation undertaken by wood-decaying fungi.

A technical soda lignin as sole carbon-diet for a higher termite species, Nasutitermes ephratae: insight into the changes in the gut bacterial community and in the lignin phenolic fraction

“…In agreement with previous studies, the main compounds released by pyrolysis of birch wood and PB1000 were representatives of G and of S compounds [42,43]. The specific release of vinylphenol from PB1000 pyrolysis confirmed the occurrence of p-coumaric units in this sample, as free and/or esterified acid.…”

“…On this basis, the reduction of the pyrolysis S/G ratio induced by gut digestion of birch wood suggests that S lignin units involved in β-O-4 bonds were more degraded than the G analogous structures. In contrast, as reported for lower termites fed with grass lignocellulose [43], the pyrolysis S/G ratio in PB1000-fed termites increased, suggesting that G lignin units might be more degraded than S ones. This preferential degradation of G units in PB1000 might be related to the fact that most G units in grass lignins are terminal units with free phenolic groups [44] which make them more susceptible to oxidative degradations.…”

Fibre‐specific regulation of lignin biosynthesis improves biomass quality in Populus

“…The pretreated cell wall residues were used to determine lignin content using the Klason procedure, as described (Gui et al , ). For thioacidolysis and two‐dimensional (2D) nuclear magnetic resonance (NMR), dried xylem tissue was ground to fine powders by ball milling and extracted sequentially using water and 80% (v/v) ethanol to obtain extractive‐free cell wall residues (CWRs) (Tarmadi et al , ). Analytical thioacidolysis on CWR samples was performed as described previously (Yamamura et al , ) and the released lignin monomers were derivatised with N , O ‐bis(trimethylsilyl)acetamide and quantified using gas chromatography‐mass spectrometry (GC‐MS; QP‐2010 Plus, Shimadzu, Kyoto, Japan) using 4,4′‐ethylenebisphenol as an internal standard (Yue et al , ).…”

“…Adiabatic 2D HSQC experiments were carried out using the standard implementation with parameters described in Mansfield et al (). Data processing and volume integration analysis was conducted using Bruker T op S pin 3.1 software (Bruker Biospin) with procedures described previously (Lam et al , ; Tarmadi et al , ).…”

Downregulation of p‐COUMAROYL ESTER 3‐HYDROXYLASE in rice leads to altered cell wall structures and improves biomass saccharification

“…Adiabatic HSQC NMR experiments were carried out using standard implementation (hsqcetgpsp.3). The detailed NMR methods used were largely as described previously (Kim and Ralph, 2010;Mansfield et al, 2012;Lam et al, 2017;Tarmadi et al, 2018) and as further described in Materials and Methods S1. The relative HSQC NMR contour intensities listed in Figure 5…”