Nitrous oxide (N2O) emissions by termites : does the feeding guild matter ?

In the tropics, termites are major players in the mineralization of organic matter leading to the production of greenhouse gases including nitrous oxide (N2O). Termites have a wide trophic diversity and their N-metabolism depends on the feeding guild. This study assessed the extent to which N2O emission levels were determined by termite feeding guild and tested the hypothesis that termite species feeding on a diet rich in N emit higher levels of N2O than those feeding on a diet low in N. An in-vitro incubation approach was used to determine the levels of N2O production in 14 termite species belonging to different feeding guilds, collected from a wide range of biomes. Fungus-growing and soil-feeding termites emit N2O. The N2O production levels varied considerably, ranging from 13.14 to 117.62 ng N2O-N d(-1) (g dry wt.)(-1) for soil-feeding species, with Cubitermes spp. having the highest production levels, and from 39.61 to 65.61 ng N2O-N d(-1) (g dry wt.)(-1) for fungus-growing species. Wood-feeding termites were net N2O consumers rather than N2O producers with a consumption ranging from 16.09 to 45.22 ng N2O-N d(-1) (g dry wt.)(-1). Incubating live termites together with their mound increased the levels of N2O production by between 6 and 13 fold for soil-feeders, with the highest increase in Capritermes capricornis, and between 14 and 34 fold for fungus-growers, with the highest increase in Macrotermes muelleri. Ammoniaoxidizing (amoA-AOB and amoA-AOA) and denitrifying (nirK, nirS, nosZ) gene markers were detected in the guts of all termite species studied. No correlation was found between the abundance of these marker genes and the levels of N2O production from different feeding guilds. Overall, these results support the hypothesis that N2O production rates were higher in termites feeding on substrates with higher N content, such as soil and fungi, compared to those feeding on N-poor wood

Agricultural use of household compost in Brazzaville market gardening belt

After the finalization of the household filth processing through aerobic fermentation or compostage, which allowed us to get an organic tool, so important in the plant production, the following communication studies the fertilising values of compost from household filth and raw wastes. Conducted in the fields, the study has revelead being successful with positive effects of the burying of compost upon the output of gardenmarket cultivation (in the Brazzaville poor soil). More over, the direct burying of household filth go along with depressive effects mainly on short-cycle vegetative cultivation

Microbiological and Biochemical Characterization of Cassava Retting, a Traditional Lactic Acid Fermentation for Foo-Foo (Cassava Flour) Production

The overall kinetics of retting, a spontaneous fermentation of cassava roots performed in central Africa, was investigated in terms of microbial-population evolution and biochemical and physicochemical parameters. During the traditional process, endogenous cyanogens were almost totally degraded, plant cell walls were lysed by the simultaneous action of pectin methylesterase and pectate lyase, and organic acids (C(inf2) to C(inf4)) were produced. Most microorganisms identified were found to be facultative anaerobes which used the sugars (sucrose, glucose, and fructose) present in the roots as carbon sources. After 24 h of retting, the fermentation reached an equilibrium that was reproducible in all the spontaneous fermentations studied. Lactic acid bacteria were largely predominant (over 99% of the total flora after 48 h) and governed the fermentation. The epiphytic flora was first replaced by Lactococcus lactis, then by Leuconostoc mesenteroides, and finally, at the end of the process, by Lactobacillus plantarum. These organisms produced ethanol and high concentrations of lactate, which strongly acidified the retting juice. In addition, the rapid decrease in partial oxygen pressure rendered the process anaerobic. Strict anaerobes, such as Clostridium spp., developed and produced the volatile fatty acids (mainly butyrate) responsible, together with lactate, for the typical flavor of retted cassava. Yeasts (mostly Candida spp.) did not seem to play a significant role in the process, but their increasing numbers in the last stage of the process might influence the flavor and the preservation of the end products

Characterization of N2O emission and associated bacterial communities from the gut of wood-feeding termite Nasutitermes voeltzkowi

Xylophagous termites rely on nitrogen deficient foodstuff with a low C/N ratio. Most research work has focused on nitrogen fixation in termites highlighting important inflow and assimilation of atmospheric nitrogen into their bodies fundamentally geared up by their intestinal microbial symbionts. Most of termite body nitrogen is of atmospheric origin, and microbially aided nitrification is the principal source of this nitrogen acquisition, but contrarily, the information regarding potent denitrification process is very scarce and poorly known, although the termite gut is considered to carry all favorable criteria necessary for microbial denitrification. Therefore, in this study, it is hypothesized that whether nitrification and denitrification processes coexist in intestinal milieu of xylophagous termites or not, and if yes, then is there any link between the denitrification product, i.e., N2O and nitrogen content of the food substrate, and moreover where these bacterial communities are found along the length of termite gut. To answer these questions, we measured in vivo N2O emission by Nasutitermes voeltzkowi (Nasutitermitinae) maintained on different substrates with varying C/N ratio, and also, molecular techniques were applied to study the diversity (DGGE) and density (qPCR) of bacterial communities in anterior and posterior gut portions. Rersults revealed that xylophagous termites emit feeble amount of N2O and molecular studies confirmed this finding by illustrating the presence of an ample density of N2O-reductase (nosZ) gene in the intestinal tract of these termites. Furthermore, intestinal bacterial communities of these termites were found more dense and diverse in posterior than anterior portion of the gut

Gut-specific actinobacterial community structure and diversity associated with the wood-feeding termite species, Nasutitermes corniger (Motschulsky) described by nested PCR-DGGE analysis

This comprehensive survey studied the actinobacterial community structure and putative representative members associated with the gut of the wood-feeding termite, Nasutitermes corniger (Motschulsky), using nested PCR-DGGE and 16S rDNA sequences analyses. The closest relatives of the actinobacteria inhabiting the gut of Nasutitermes corniger were in five families, regardless of the geographical origin of the termite colony: Propionibacteriaceae, Streptomycetaceae, Cellulomonodaceae, Corynebacteriaceae and Rubrobacteraceae. Feeding termites on beech wood did not result in substantial changes in the actinobacterial community structure as revealed by DGGE banding patterns. Most of the 16S rDNA sequences obtained after excision and sequencing of DGGE bands clustered with those previously retrieved in termite guts. These results confirm the presence of gut-specific actinobacteria. Except for the 16S rDNA sequences affiliated to Streptomycetaceae and Cellulomonodaceae, no sequence had more than 97% similarity with the closest isolated strains, indicating the presence of microorganisms that have not yet been cultivated. These results suggest that members of the Actinomycetales order account for the largest proportion of the Actinobacteria phylum inhabiting the gut of the termite N. corniger

Xylophagous termites : a potential sink for atmospheric nitrous oxide

To provide a better understanding of soil-atmosphere gas exchange processes, this study describes the atmospheric nitrous oxide (N2O) uptake by xylophagous termites and the biological process involved. The N2O consumption rates of three xylophagous termite species (Hodotermes mossambicus, Nasutitermes voeltzkowi and Hodotermopsis sjoestedti) were determined in incubation vials with ambient, artificially enhanced N2O concentrations in the headspace. Live individuals of the three termite species significantly decreased N2O concentrations (88%) in the headspace of the vials after 24 h incubation in the dark. The acetylene reduction assay method applied to N. voeltzkowi, a xylophagous termite species, showed a decrease in N2O uptake in acetylene-treated individuals, indicating the potential involvement of termite gut denitrifying microbes. The N-2 formed is potentially subjected to assimilation via nitrogenase reductase into termite biomass through biological fixation as demonstrated by the reduction of acetylene to ethylene at an average rate of 18.21 +/- 1.34 nmol C2H4 g(-1) dw d(-1). Further studies should focus on measurements of N2O-reductase (nosZ) gene activity in termite guts to gain a better understanding of the N2O reduction process in xylophagous termite species

Characterization of N2O emissions and associated microbial communities from the ant mounds in soils of a humid tropical rainforest

Tropical rainforest soils harbor a considerable diversity of soil fauna that contributes to emissions of N2O. Despite their ecological dominance, there is limited information available about the contribution of epigeal ant mounds to N2O emissions in these tropical soils. This study aimed to determine whether ant mounds contribute to local soil N emissions in the tropical humid rainforest. N2O emission was determined in vitro from individual live ants, ant-processed mound soils, and surrounding reference soils for two trophically distinct and abundant ant species: the leaf-cutting Atta mexicana and omnivorous Solenopsis geminata. The abundance of total bacteria, nitrifiers (AOA and AOB), and denitrifiers (nirK, nirS, and nosZ) was estimated in these soils using quantitative PCR, and their respective mineral N contents determined. There was negligible N2O emission detected from live ant individuals. However, the mound soils of both species emitted significantly greater (3-fold) amount of N2O than their respective surrounding reference soils. This emission increased significantly up to 6-fold in the presence of acetylene, indicating that, in addition to N2O, dinitrogen (N-2) is also produced from these mound soils at an equivalent rate (N2O/N-2 = 0.57). Functional gene abundance (nitrifiers and denitrifiers) and mineral N pools (ammonium and nitrate) were significantly greater in mound soils than in their respective reference soils. Furthermore, in the light of the measured parameters and their correlation trends, nitrification and denitrification appeared to represent the major N2O-producing microbial processes in ant mound soils. The ant mounds were estimated to contribute from 0.1 to 3.7% of the total N2O emissions of tropical rainforest soils