Sapwood and heartwood affect differentially bacterial and fungal community structure and successional dynamics during Quercus petraea decomposition

In forests, bacteria and fungi are key players in wood degradation. Still, studies focusing on bacterial and fungal successions during the decomposition process depending on the wood types (i.e. sapwood and heartwood) remain scarce. This study aimed to understand the effect of wood type on the dynamics of microbial ecological guilds in wood decomposition. Using Illumina metabarcoding, bacterial and fungal communities were monitored every 3 months for 3 years from Quercus petraea wood discs placed on forest soil. Wood density and microbial enzymes involved in biopolymer degradation were measured. We observed rapid changes in the bacterial and fungal communities and microbial ecological guilds associated with wood decomposition throughout the experiment. Bacterial and fungal succession dynamics were very contrasted between sapwood and heartwood. The initial microbial communities were quickly replaced by new bacterial and fungal assemblages in the sapwood. Conversely, some initial functional guilds (i.e. endophytes and yeasts) persisted all along the experiment in heartwood and finally became dominant, possibly limiting the development of saprotrophic fungi. Our data also suggested a significant role of bacteria in nitrogen cycle during wood decomposition.     

Detecting the footprint of changing atmospheric nitrogen deposition loads on acid grasslands in the context of climate change

Although atmospheric nitrogen (N) deposition and climate changes are both recognized as major components of global change, their interaction at ecosystem level is less well understood. A stratified resampling approach was used to investigate the potential impact of changing levels of atmospheric nitrogen deposition and climate change on species composition of nutrient‐poor acid grasslands within the French Atlantic Domain (FAD). The study was based on a comparison, over a period of 25 years, of 162 past and present vegetation records assigned to the species‐rich Nardus grasslands and distributed in regional community types (CTs). Similarly, the characterization of N deposition and climate was stratified according to (i) past (1980–1990) and present (1995–2005) periods, and (ii) FAD and CT scales. Despite the relatively short time span between sampling periods, significant N deposition and climate changes were detected as well as vegetation changes. Correspondence analysis showed that the relative importance of N deposition and climate in explaining vegetation changes depended on the spatial scale of investigation (FAD vs. local CTs) and the CT. At the FAD scale, the increase of annual mean temperature and decrease of water availability were clearly related to the changes in floristic composition. At the local scale, the most stable CT experienced no significant climate change and a stable load of N deposition, whereas the CTs characterized by the largest floristic changes were associated with dramatic climate changes and moderate loads in both oxidized and reduced N deposition. Despite the narrow gradient of deposition investigated, N deposition was related to significant grassland community changes, depending on the region, i.e. climate context, and on whether N deposition was in the oxidized or reduced form. Our results suggest that N deposition drives grassland composition at the local scale, in interaction with climate, whereas climate changes remain the predominant driver at the FAD scale.     

Optimization of a Droplet-Based Millifluidic Device to Investigate the Phase Behavior of Biopolymers,Including Viscous Conditions

Food Biophysics - Phase diagrams are widely used to map and control the assembly states of biopolymers. However, these studies are highly time and material consuming. Here, we present the...     

Specific recognition of reproductive parasite workers by nest-entrance guards in the bumble bee <Emphasis Type="Italic">Bombus terrestris</Emphasis>

Background

The impact of social parasites on their hosts’ fitness is a strong selective pressure that can lead to the evolution of adapted defence strategies. Guarding the nest to prevent the intrusion of parasites is a widespread response of host species. If absolute rejection of strangers provides the best protection against parasites, more fine-tuned strategies can prove more adaptive. Guarding is indeed costly and not all strangers constitute a real threat. That is particularly true for worker reproductive parasitism in social insects since only a fraction of non-nestmate visitors, the fertile ones, can readily engage in parasitic reproduction. Guards should thus be more restrictive towards fertile than sterile non-nestmate workers. We here tested this hypothesis by examining the reaction of nest-entrance guards towards nestmate and non-nestmate workers with varying fertility levels in the bumble bee Bombus terrestris. Because social recognition in social insects mainly relies on cuticular lipids (CLs), chemical analysis was also conducted to examine whether workers’ CLs could convey the relevant information upon which guards could base their decision. We thus aimed to determine whether an adapted defensive strategy to worker reproductive parasitism has evolved in B. terrestris colonies.

Results

Chemical analysis revealed that the cuticular chemical profiles of workers encode information about both their colony membership and their current fertility, therefore providing potential recognition cues for a suitable adjustment of the guards’ defensive decisions. We found that guards were similarly tolerant towards sterile non-nestmate workers than towards nestmate workers. However, as predicted, guards responded more aggressively towards fertile non-nestmates.

Conclusion

Our results show that B. terrestris guards discriminate non-nestmates that differ in their reproductive potential and respond more strongly to the individuals that are a greatest threat for the colony. Cuticular hydrocarbons are the probable cues underlying the specific recognition of reproductive parasites, with the specific profile of highly fertile bees eliciting the agonistic response when combined with non-colony membership information. Our study therefore provides a first piece of empirical evidence supporting the hypothesis that an adapted defensive strategy against worker reproductive parasitism exists in B. terrestris colonies.

     

Genomics and genetics of Sulfolobus islandicus LAL14/1, a model hyperthermophilic archaeon

The 2 465 177 bp genome of Sulfolobus islandicus LAL14/1, host of the model rudivirus SIRV2, was sequenced. Exhaustive comparative genomic analysis of S. islandicus LAL14/1 and the nine other completely sequenced S. islandicus strains isolated from Iceland, Russia and USA revealed a highly syntenic common core genome of approximately 2 Mb and a long hyperplastic region containing most of the strain-specific genes. In LAL14/1, the latter region is enriched in insertion sequences, CRISPR (clustered regularly interspaced short palindromic repeats), glycosyl transferase genes, toxin–antitoxin genes and MITE (miniature inverted-repeat transposable elements). The tRNA genes of LAL14/1 are preferential targets for the integration of mobile elements but clusters of atypical genes (CAG) are also integrated elsewhere in the genome. LAL14/1 carries five CRISPR loci with 10 per cent of spacers matching perfectly or imperfectly the genomes of archaeal viruses and plasmids found in the Icelandic hot springs. Strikingly, the CRISPR_2 region of LAL14/1 carries an unusually long 1.9 kb spacer interspersed between two repeat regions and displays a high similarity to pING1-like conjugative plasmids. Finally, we have developed a genetic system for S. islandicus LAL14/1 and created ΔpyrEF and ΔCRISPR_1 mutants using double cross-over and pop-in/pop-out approaches, respectively. Thus, LAL14/1 is a promising model to study virus–host interactions and the CRISPR/Cas defence mechanism in Archaea.