The last piece in the cellulase puzzle: the characterisation of  -glucosidase from the herbivorous gecarcinid land crab Gecarcoidea natalis

ABSTRACTField experiments comparing leaf-fall in the presence and absence of the red land crab, Gecarcoidea natalis, in rain forest on Christmas Island, Indian Ocean showed that, by eating and returning leaves to their burrows, they significantly reduced accumulation of leaf-fall on the forest floor. Red crabs removed 30–50% of the leaf-fall at the experimental sites during the study. Differences in leaf-fall mass between crab-access and exclusion quadrats were positively correlated with the density of foraging red crabs. Red crabs also generated spatial heterogeneity in the distribution of litter on the forest floor by returning litter to their burrows. Leaves lined chambers of 64% of excavated burrows and litter biomass around the entrances was significantly greater than that on off-burrow locations. This was reflected in the significantly higher concentrations of organic matter and nutrients (N, P, K, Ca, Na, and Mg) associated with soils near burrow entrances. These results suggest that a single species, G. natalis, is the major processor of leaf-fall in rain forest on Christmas Island and may affect (1) the temporal and spatial patterns of nutrient availability and (2) the diversity and biomass of the litter fauna.

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Urate deposits in the gecarcinid land crab Gecarcoidea natalis are synthesised de novo from excess dietary nitrogen

Journal of Experimental Biology ◽

10.1242/jeb.200.17.2347 ◽

1997 ◽

Vol 200 (17) ◽

pp. 2347-2354 ◽

Cited By ~ 2

Author(s):

S Linton ◽

P Greenaway

Keyword(s):

Direct Evidence ◽

De Novo ◽

Heavy Isotope ◽

High Nitrogen ◽

Land Crab ◽

Dietary Nitrogen ◽

Dietary Period ◽

Ad Libitum ◽

Gecarcoidea Natalis ◽

Low Nitrogen

The urate content of the gecarcinid land crab Gecarcoidea natalis was correlated to the amount of nitrogen assimilated. Crabs fed a high-nitrogen diet (ad libitum amounts of soy beans and fig leaves, Ficus macrophylla) for 6 weeks assimilated approximately 23 times more nitrogen (33.9±5.6mmolkg-1day-1) than animals fed a diet low in nitrogen (fig leaves alone) (1.5±0.7mmolkg-1day-1). Animals maintained on a high-nitrogen diet accumulated urate (67.1±29.4mmolkg-1drymass), while animals fed the low-nitrogen diet did not accumulate significant amounts of urate compared with the control animals killed at the beginning of the dietary period. The urate deposits clearly originate from the excess dietary nitrogen ingested on the high-nitrogen diet. The intake of preformed dietary purine was low (0.028±0.005mmolkg-1drymass) and at most could only account for 0.04% of the urate accumulated by crabs fed the high-nitrogen diet. This indicates that the urate was synthesised de novo. When crabs were fed a high-nitrogen diet supplemented with [15N]glycine, the 15N heavy isotope was incorporated into urate. This provided direct evidence that the urate was synthesised de novo.

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Synergistic interaction of an endo-β-1,4-glucanase and a β-glucohydrolase leads to more efficient hydrolysis of cellulose-like polymers in the gecarcinid land crab, Gecarcoidea natalis

Australian Journal of Zoology ◽

10.1071/zo12074 ◽

2012 ◽

Vol 60 (5) ◽

pp. 299 ◽

Cited By ~ 2

Author(s):

Benjamin J. Allardyce ◽

Stuart M. Linton

Keyword(s):

Carboxymethyl Cellulose ◽

Cellulose Hydrolysis ◽

Competitive Inhibitor ◽

Synergistic Interaction ◽

Land Crab ◽

Hydrolysis Of Cellulose ◽

Complementary Nature ◽

Gecarcoidea Natalis ◽

Hydrolysis Of

This study investigated synergism between endo-β-1,4-glucanase and β-glucohydrolase enzymes from Gecarcoidea natalis. Together, these enzymes efficiently hydrolyse the cellulose-like polymer, carboxymethyl cellulose, to glucose. Endo-β-1,4-glucanase and β-glucohydrolase, isolated previously from G. natalis, were incubated in vitro using a ratio of the measured activities that matches that found in their digestive juice (5.4 : 1). Their combined activity, measured as the release of glucose from carboxymethyl cellulose, was greater than the sum of their separate activities. Hence they synergistically released glucose from carboxymethyl cellulose (degree of synergy: 1.27). This may be due to the complementary nature of the products of endo-β-1,4-glucanase activity and the preferred substrates of the β-glucohydrolase. β-glucohydrolase may also enhance cellulose hydrolysis by removing cellobiose, a potential competitive inhibitor of endo-β-1,4-glucanase. The synergistic interaction of these two enzymes further supports the previous suggestion that this species possesses a novel two-enzyme cellulase system that differs from the traditional three-enzyme fungal model.

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