New insights from NMR, FTIR, X-ray diffraction and physical chemistry into digestive processes in the wood-boring marine crustacean Limnoria quadripunctata
G P Malyon, S LaBarre, N Kervarec, P Carey, J McGeehan, X Xie, A Klüppel, S M Cragg
This paper summarises preliminary findings of a multi-technique exploration of the degradation of lignocellulose in the marine isopod Limnoria quadripunctata. Scanning electron microscopy revealed connections between the digestive gland and the hindgut that would permit the exchange of fluids between the two organs while the food mass is retained in place within the hindgut. This enables enzymes to be delivered to the substrate and breakdown products to be absorbed. FTIR and X-ray diffraction were used to show changes in wood chemistry during digestion. Cellulose crystallinity appears reduced after digestion, but lignin structure appeared little changed. NMR spectroscopy of animals under various feeding regimes measured the generation of breakdown products and levels of metabolites. Glucose was detected as a direct result of the animals feeding on 13C-labelled straw. This is the first direct evidence of total cellulose breakdown to the monomer. The importance of oxygen levels during digestion was shown by direct measurement with microelectrodes and indirectly by observing feeding on substrates impregnated with anti-oxidants. The hindgut lumen was found to be relatively anoxic. The antioxidant BHT significantly reduces feeding rates under laboratory conditions. These findings taken together give a picture of the effects of the activity of the recently described suite of digestive enzymes on their substrate.