Biology subjects

Poulsen, M.

Publications and source records attributed to Poulsen, M..

6 recordsLinked to original sources

bioRxiv2018

Gating modules of the AMPA receptor pore domain revealed by unnatural amino acid mutagenesis

Ionotropic glutamate receptors (iGluRs) are responsible for fast synaptic transmission throughout the nervous system. Conformational changes of the transmembrane domain (TMD) underlying ion channel activation and desensitization remain poorly understood. Here, we explored the dynamics of the TMD of AMPA-type iGluRs using genetically-encoded unnatural amino acid (UAA) photo-crosslinkers, p-benzoyl-L-phenylalanine (BzF) and p-azido-L-phenylalanine (AzF). We introduced UAAs at sites throughout the TMD of the GluA2 receptor and characterized these mutants in patch-clamp recordings, exposing them to glutamate and UV light. This approach revealed a range of optical effects on the activity of mutant receptors. We found evidence that an interaction between the Pre-M1 and the M4 TMD helix was essential for normal activation and desensitization. Photoactivation at F579AzF, a residue behind the selectivity filter, had extraordinarily broad effects on gating and desensitization. This observation suggests coupling to other parts of the receptor and like in other tetrameric channels, selectivity filter gating.

neuroscience↗

bioRxiv2018

The origin of fungi-culture in termites was associated with a shift to a mycolytic gut bacteria community

Termites forage on a range of substrates, and it has been suggested that diet shapes the composition and function of termite gut bacterial communities. Through comparative analyses of gut metagenomes in nine termite species with distinct diets, we characterise bacterial community compositions and identify biomass-degrading enzymes and the bacterial taxa that encode them. We find that fungus-growing termite guts are enriched in fungal cell wall-degrading and proteolytic enzymes, while wood-feeding termite gut communities are enriched for plant cell wall-degrading enzymes. Interestingly, wood-feeding termite gut bacteria code for abundant chitinolytic enzymes, suggesting that fungal biomass within the decaying wood likely contributes to gut bacteria or termite host nutrition. Across diets, the dominant biomass-degrading enzymes are predominantly coded for by the most abundant bacterial taxa, suggesting tight links between diet and gut community composition, with the most marked shift being the communities coding for the mycolytic capacity of the fungus-growing termite gut.

ecology↗

bioRxiv2018

Gut microbial compositions mirror caste-specific diets in a major lineage of eusocial insects

Eusocial insects owe their ecological success to the division of labour and processes within colonies often rely on the presence of specific microbial symbionts, but associations between microbial community compositions and castes with different tasks and diets within colonies remain largely unexplored. Fungus-growing termites evolved to use fungi to externally degrade plant material, complemented by specific and complex gut microbiotas. Here we explore to which extent division of labour and dietary differences within fungus-growing termite castes are linked to gut bacterial community structure. Using amplicon sequencing, we characterise community compositions in sterile (worker and soldier) and reproductive (queen and king) termites and combine this with gut enzyme, microscopy, and in situ analyses to further elucidate sterile caste-specific microbiota compositions. Gut bacterial communities are structured primarily according to termite caste and genus. In contrast to the observed rich and diverse sterile caste microbiotas, royal pair microbiotas are extremely skewed and dominated by few bacterial taxa, reflecting the specialised dietary intake and unique, reproduction-centred lifestyle of the queen and king.

microbiology↗

bioRxiv2018

The scent of symbiosis: gut bacteria affect social interactions in leafcutting ants

Animal gut microbiota affect host physiology and behaviour. In eusocial Hymenoptera, where colony-level integrity is preserved via a nestmate discrimination system based on cuticular hydrocarbon mixtures, microorganismal effects may influence social dynamics. Although nestmate recognition has undergone a thorough exploration during the last four decades, few studies have investigated the putative role of gut microbes. Here we integrate metagenomic, chemical and behavioural approaches to test whether gut microbes affect nestmate recognition in Acromyrmex echinatior leaf-cutting ants. Treating workers with a sterile diet or with antibiotics resulted in a substantial alteration of their gut microbial communities. In pairwise social interactions, untreated vs. antibiotic-treated nestmates behaved more aggressively than other nestmate and non-nestmate pairs, suggesting that the suppression of microbes indirectly alters chemical social cues and triggers aggressive behaviour. Chemical analyses on treated individuals revealed a decrease in the abundance of two metapleural gland antifungal compounds, and we confirmed the correspondence between aggression levels and chemical profile differences. Feeding microbiota-remodelled ants with conspecific faecal droplets partially restored the original bacterial communities. Furthermore, non-nestmates fed with faecal droplets from different colonies were unusually aggressive compared to pairs fed with faecal droplets from the same colony. This suggests that chemicals derived from microbial strains may shape nestmate recognition, opening novel questions about the role of microorganisms in the evolution of social behaviour.

evolutionary biology↗

bioRxiv2018

Inter- and intra-domain functional redundancy in the rumen microbiome during plant biomass degradation

BackgroundRuminant livestock is a major source of the potent greenhouse gas methane (CH4), produced by the complex rumen microbiome. Using an integrated approach, combining quantitative metatranscriptomics with gas- and volatile fatty acid (VFA) profiling, we gained fundamental insights into temporal dynamics of the cow rumen microbiome during feed degradation.\n\nResultsThe microbiome composition was highly individual and remarkably stable within each cow, despite similar gas emission and VFA profiles between cows. Gene expression profiles revealed a fast microbial growth response to feeding, reflected by drastic increases in microbial biomass, CH4 emissions and VFA concentrations. Microbiome individuality was accompanied by high inter- and intra-domain functional redundancy among pro- and eukaryotic microbiome members in the key steps of anaerobic feed degradation. Methyl-reducing but not CO2-reducing methanogens were correlated with increased CH4 emissions during plant biomass degradation.\n\nConclusionsThe major response of the rumen microbiome to feed intake was a general growth of the whole community. The high functional redundancy of the cow-individual microbiomes was possibly linked to the robust performance of the anaerobic degradation process. Furthermore, the strong response of methylotrophic methanogens is suggesting that they might play a more important role in ruminant CH4 emissions than previously assumed, making them potential targets for CH4 mitigation strategies.

microbiology↗

bioRxiv2017

Hemimetabolous genomes reveal molecular basis of termite eusociality

Around 150 million years ago, eusocial termites evolved from within the cockroaches, 50 million years before eusocial Hymenoptera, such as bees and ants, appeared. Here, we report the first, 2GB genome of a cockroach, Blattella germanica, and the 1.3GB genome of the drywood termite, Cryptotermes secundus. We show evolutionary signatures of termite eusociality by comparing the genomes and transcriptomes of three termites and the cockroach against the background of 16 other eusocial and non-eusocial insects. Dramatic adaptive changes in genes underlying the production and perception of pheromones confirm the importance of chemical communication in the termites. These are accompanied by major changes in gene regulation and the molecular evolution of caste determination. Many of these results parallel molecular mechanisms of eusocial evolution in Hymenoptera. However, the specific solutions are remarkably different, thus revealing a striking case of convergence in one of the major evolutionary transitions in biological complexity.

evolutionary biology↗