Anne Pando

Effect of earthworms on plant Lantana camara Pb-uptake and on bacterial communities in root-adhering soil.

The present study aimed to assess the potential abilities of Lantana camara, an invasive plant species for phytoremediation in the presence of earthworm Pontoscolex corethrurus. Effects of earthworm on growth and lead (Pb) uptake by L. camara plant were studied in soil artificially contaminated at 500 or 1000mg of Pb kg(-1) soil. This species has a promising value for phytoremediation because it can uptake as much as 10% of 1000mgkg(-1) of Pb per year. Moreover, the presence of earthworms enhanced plant biomass by about 1.5-2 times and increased the uptake of lead by about 2-3 times. In the presence of earthworm, L. camara was thus able to uptake up 20% of Pb presence in the soil, corresponding to remediation time of 5 years if all organs are removed. As soil microorganisms are known to mediate many interactions between earthworms and plants, we documented the effect of earthworms on the bacterial community of root-adhering soil of L. camara. Cultivable bacterial biomass of root-adhering soil increased in the presence of earthworms. Similar trend was observed on bacterial metabolic activities. The increase of lead concentrations from 500 to 1000mgkg(-1) did not have any significant effect either on plant growth or on bacterial biomass and global activities but affected the structure and functional diversity of the bacterial community. These results showed that we should broaden the ecological context of phytoremediation by considering plant/microbial community/earthworm interactions that influence the absorption of heavy metals.

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.

Molecular diversity and host specificity of termite-associated Xylaria

Studies have revealed that some Xylaria species were closely associated with fungus-growing termite nests. However this relationship rarely had been investigated and the host specificity of termite-associated Xylaria was not yet clearly established. Eighteen Xylaria rDNA-ITS sequences were obtained from fungus combs belonging to 11 Macrotermitinae species from eight regions. Low diversity was found between isolates, and nine sequences were retrieved. Termite-associated Xylaria were shown to be monophyletic, with three main clades, all including strains from various termite hosts and geographical localities. This new molecular study shows no species specificity with respect to fungus-growing termites, which suggests that there might be substrate specialization.

Occurrence of fungi in combs of fungus-growing termites (Isoptera: Termitidae, Macrotermitinae).

Fungus-growing termites cultivate their mutualistic basidiomycete Termitomyces species on a substrate called a fungal comb. Here, the Suicide Polymerase Endonuclease Restriction (SuPER) method was adapted for the first time to a fungal study to determine the entire fungal community of fungal combs and to test whether fungi other than the symbiotic cultivar interact with termite hosts. Our molecular analyses show that although active combs are dominated by Termitomyces fungi isolated with direct Polymerase Endonuclease Restriction - Denaturing Gradient Gel Electrophoresis (PCR-DGGE), they can also harbor some filamentous fungi and yeasts only revealed by SuPER PCR-DGGE. This is the first molecular evidence of the presence of non-Termitomyces species in active combs. However, because there is no evidence for a species-specific relationship between these fungi and termites, they are mere transient guests with no specialization in the symbiosis. It is however surprising to notice that termite-associated Xylaria strains were not isolated from active combs even though they are frequently retrieved when nests are abandoned by termites. This finding highlights the implication of fungus-growing termites in the regulation of fungi occurring within the combs and also suggests that they might not have any particular evolutionary-based association with Xylaria species.

Inter-Population Differences and Seasonal Dynamic of the Bacterial Gut Community in the Endangered Land Snail Helix pomatia (Gastropoda: Helicidae)

ABSTRACT Among the multifaceted environmental factors, the bacterial community ingested with soil and food might play an important role in physiological processes of terrestrial gastropods, with consequences on population dynamics and species distribution patterns. Therefore, we investigated the bacterial gut community structure and seasonal dynamic in three populations of the protected endangered land snail Helix pomatia. The PCR-DGGE fingerprinting analysis followed by Nonmetric Multidimensional Scaling (NMDS) showed that Gamma-and Alphaproteobacteria were common to all populations, while Mollicutes and Betaproteobacteria were population specific. Allochthonous strains might be transiently abundant in the gut of foraging snails with respect to habitat conditions. Autochthonous strains were permanently present in the gut, even after expulsion of the gut content at hibernation beginning. Some of these permanent strains are known to have ice-nucleating activity, which is consistent with the limited cold hardiness in this species. Snails that did not enter hibernation despite being exposed to winter conditions had a poor bacterial community. In conclusion, the bacterial community structure differed between habitats and physiological states, and might be important for physiological processes and survival. Further studies should focus on the individual variation in bacterial community and investigate how it is affected by environmental changes.

Systematic variability enhances the reproducibility of an ecological study

Many scientific disciplines currently are experiencing a “reproducibility crisis” because numerous scientific findings cannot be repeated consistently1–4. A new but controversial hypothesis postulates that stringent levels of environmental and biotic standardization in experimental studies reduces reproducibility by amplifying impacts of lab-specific environmental factors not accounted for in study designs5–8. A corollary to this hypothesis is that the deliberate introduction of controlled systematic variability (CSV) in experimental designs can increase reproducibility. We tested this hypothesis using a multi-laboratory microcosm study in which the same ecological experiment was repeated in 14 laboratories. Each laboratory introduced environmental and genotypic CSV within and among treatments in replicated microcosms established in either growth chambers (with stringent control of environmental conditions) or glasshouses (with more variable environmental conditions). The introduction of genotypic CSV increased reproducibility of results in growth chambers but had no significant effect in glasshouses where reproducibility also was lower. Environmental CSV had little effect on reproducibility. This first deliberate attempt at reproducing an ecological experiment with added CSV reveals that introducing genotypic CSV in experiments carried out under controlled environmental conditions with stringent standardization can increase reproducibility by buffering against unaccounted lab-specific environmental and biotic factors that may otherwise strongly bias experimental outcomes.