C. Rouland

Use of soil enzyme activities to monitor soil quality in natural and improved fallows in semi-arid tropical regions

Soil enzyme activities (β-glucosidase, amylase, chitinase, xylanase) were investigated in natural and improved fallows of the semi-arid zone of Senegal. The effect of age (4-, 11-, and 21-year-old), management (fenced versus grazed), and vegetation (natural, Acacia holocericea, Andropogon gayanus) were compared. Principal component analysis revealed a relationship between enzyme activities and the age and the management of fallows. β-Glucosidase and amylase activities were significantly higher in the oldest natural fallows. The highest xylanase activity was recorded for the A. gayanus improved fallows. This fallow also showed highest chitinase activity, similar to that of the 21-year-old natural fenced fallow. Amongst the different types of fallow management studied, the introduction of A. holocericea depleted all the tested activities. No relationships between enzymes activities and soil organic content, and total microbial biomass were evident. The reasons for the observed variations are discussed.

Purification and properties of cellulases from the termite Macrotermes mülleri (Termitidae, Macrotermitinae) and its symbiotic fungus Termitomyces sp.

Abstract 1. 1. From termite Macrotermes mulleri , two cellulases (celluases I T and II), respectively, a 1,4-β-glucan glucanohydrolase (EC 3.2.1.4) and a 1,4-β-glucan cellobiohydrolase (EC 3.2.1.91) were purified by procedures including hydroxyapatite adsorption chromatography, ion exchange chromatographies on DEAE Sepharose and Mono Q ® , and molecular sieving column Superose ® 12. 2. 2. The 1,4-β-glucan glucanohydrolase (cellulase I F isolated from mycotetes of termite symbiotic fungus Termitomyces sp.) was also purified. The comparison of kinetic data and physical properties suggested that cellulases I T and I F were identical. 3. 3. The apparent molecular weights of cellulases I and II as determined by SDS-PAGE were respectively 34,000 and 52,000. 4. 4. The pH optimum of both enzymes was 4.4 and K m values determined with CMC as substrate were 0.75% for cellulase I and 10% for cellulase II. 5. 5. These enzymes differed also by their thermal stability, their optimal activity temperature and the effect of cations on their activity.

Nutritional factors affecting methane emission from termites

Abstract Because of their numbers and diet, termites are important potential producers of atmospheric methane. This methane production is due to the anaerobic degradation of plant material by a symbiotic microflora localized in the termites hindgut. The bacterial population and the methane production are correlated to the termites nutrition mode. The xylophageous termites possess primarily acetogenic bacteria and thus are low methane producers; on the other hand, the soil-feeding and some of the fungus-growing termites have numerous methanogenic bacteria in their guts and produce high quantities of methane but no acetate. It is, therefore, essential to take into account the distribution of the different termite alimentary groups before assessing their global annual methane production.

Activities of the digestive enzymes in the gut and in tissue culture of a tropical geophagous earthworm, Polypheretima elongata ( Megascolecidae )

Abstract Endogeic geophagous earthworms from tropical areas seem to digest soil organic matter through a mutualist earthworm microflora-digestion system and the intestinal mucus produced by earthworms was supposed to play a central role in the process of digestion. A large range of glucosidic substrates characteristic of plant material was used to reveal the activities of digestive enzymes in the gut (wall and contents) of Polypheretima elongata. This worm consumes some plant substrates tested and is able mainly to degrade root and fungal substrates. It corroborates that tropical endogeic earthworms feed on litter debris and soils poor in organic matter. These glucosidic activities were higher than those found previously in Pontoscolex corethrurus. The in vitro tissue culture of gut wall allowed us to infer that P. elongata can synthesize by itself all its extra and intracellular enzymes, contrary to P. corethrurus which requires the microflora of the soil ingested in order to hydrolyse some substrates such as cellulose and mannan. It should be interesting to compare cellulases and mannanases of both earthworms after extraction and purification and to study the mechanisms by which P. corethrurus may enhance microbial activities.

PURIFICATION AND PROPERTIES OF THE XYLANASES FROM THE TERMITE MACROTERMES BELLICOSUS AND ITS SYMBIOTIC FUNGUS TERMITOMYCES SP.

Four xylanases were purified, two from the termite Macrotermes bellicosus workers (XIT and X2T) and two from its symbiotic fungus Termitomyces sp. (X1Mc and X2Mc). The analysis of the step required for the purification of X1T and X1Mc and the comparison of their different properties suggested that xylanases X1T and X1Mc were the same enzyme, X1. The determination of the reducing sugars by TLC revealed that X1 was an endoxylanase (EC 3.2.1.8) and X2T and X2Mc were endoxylanases (EC 3.2.1.37). The apparent molecular weights of the three xylanases, determined by SDS-polyacrylamide gel electrophoresis, were 36 kDa for X1, 56 kDa for X2T and 22.5 kDa for X2Mc. The optimal pH of the three xylanases was approximately 5.5, and Km values determined with birchwood xylan as substrate were 0.2% for X1, 0.1% for X2T and 0.3% for X2Mc, showing a high affinity for this substrate. The three enzymes differed also by their thermal stability.

Digestive capacities of leaf-cutting ants and the contribution of their fungal cultivar to the degradation of plant material

Leaf-cutting ants (tribe Attini) are a unique group of ants that cultivate a fungus that serves as a main source of their food. The fungus is grown on fresh leaves that are harvested by workers. We examine the respective contribution of ants and their symbiotic fungus in the degradation of plant material by examining the digestive capacities of seven Attini species in the genera Atta and Acromyrmex. The results show that both, the ants and their mutualistic fungi, have complementary enzymatic activities. Ants are specialized in the degradation of low molecular weight substrates (oligosaccharides and heterosides) whereas the fungus displays high polysaccharidase activity. The two genera Atta and Acromyrmex are not distinguished by a specific enzymatic activity. The seven different mutualistic associations examined display a similar enzymatic profile but have quantitative differences in substrate degradation activities. The respective contribution of ants and the fungus garden in plant degradation are discussed.

Synergistic activities of the enzymes involved in cellulose degradation, purified from Macrotermes mülleri and from its symbiotic fungus Termitomyces sp.

Abstract 1. 1. Enzymes involved in cellulose degradation purified from the forest fungus-growing termite Macrotermes mulleri and from the mycotetes of its symbiotic fungus Termitomyces sp. have been studied. 2. 2. Synergism was observed especially between cellulase I (fungus), cellulase II (termite) and β-glucosidase A (termite). 3. 3. The importance of this synergistic enzymatic activity in the digestive metabolism of M. mulleri is discussed.

The role of the symbiotic fungus in the digestive metabolism of two species of fungus-growing ants

Abstract. Leaf-cutting ants live in an obligatory symbiosis with a fungus which they grow on fresh leaves harvested by workers. This study attempts to clarify the respective role of ants and fungus in the degradation of plant material, in order to highlight the evolutionary basis of this mutualistic association. The symbiotic system of two ant species, Acromyrmex subterraneus subterraneus and Acromyrmex crassispinus, was investigated. To identify the digestive carbohydrases, a total of 19 specific and synthetic plant material substrates were tested on workers from different castes (major and minor), larvae and fungus. Extracts of A. subterraneus and A. crassispinus workers showed high enzymatic activity particularly on starch, maltose, sucrose and α-1,4 glucoside. Larvae degraded starch, sucrose, maltose but also laminarin, and all the detected activities were higher than those found for workers. The symbiotic fungus of A. subterraneus was mostly active on laminarin, xylan and cellulose, while the symbiotic fungus of A. crassispinus was mostly active on laminarin, starch, maltose and sucrose. The enzymatic activities of ants and fungus belonging to the same symbiotic system tended not to overlap, suggesting that the association is highly evolved and of an ancient origin.

Experimental manipulation of termites (Isoptera, Macrotermitinae) foraging patterns in a Sahelo-Sudanese savanna: effect of litter quality

SummaryThe foraging pattern of four sympatric fungus-growing termite species was followed for five months of the dry season in a semi-arid savanna (Senegal). Experimental plots were established with and without termites (exclusion with insecticide) and amended with different litter quality: Acacia leaves, millet canes, ground millet (<500 µm), Combretum wood and cattle manure. Results showed different foraging patterns between the fungus-growing species. Odontotermes nilensis, for example, rapidly developed its foraging activity on the litter. In contrast, Macrotermes subhyalinus delayed its foraging activity but, extensively collected the food after its discovery. Differences in food preference were evident between the termite species: Odonto-termes nilensis foraged preferentially on millet, canes and Acacia leaves, Macrotermes subhyalinus preferred cane and ground millet. Ancistrotermes guineensis selected the millet, and Microtermes sp. was mostly recorded foraging on pieces of dead wood. Relationships between different foraging parameters were established to assess the relative intensity of this activity over the dry season. The comparison between untreated plots and plots treated with Fipronil® (Aventis) clearly demonstrated that the exclusion of termites from part of the savanna is possible and that this possibility can be used to study their role on the soil and organic matter cycle in situ.

The termites of the Mayombe Forest Reserve, Congo (Brazzaville): transect sampling reveals an extremely high diversity of ground-nesting soil feeders

Sampling using a replicated standard transect method in an extensive undisturbed primary hill rain forest in Congo (Brazzaville) revealed a very high species richness of termites, especially soil-feeding soldierless termites (Apicotermitinae). The assemblage, as estimated by the transects, resembled that previously characterized in comparable forest in southern Cameroon, but with some species turnover reflecting the gamma diversity of the Guinean-Congolese block as a whole. Species richness was three or four times that shown by a previous study addressed to mound populations alone, emphasizing the importance of sampling soil-feeding termites neither building nor living in mounds.