Project description:Climate change is one of the main factors shaping the distributions and biodiversity of organisms, among others by greatly altering water availability, thus exposing species and ecosystems to harsh desiccation conditions. Insects are specially threatened by these challenging dry environments, thanks to their small size and thus large surface area to volume ratio. Drosophila melanogaster is a great model to study the response of populations to rapidly changing conditions, because of its southern African origin and recent and fast worldwide spreading. Desiccation stress response is a complex and extensively studied trait, however the natural variation and underlying molecular and physiological mechanisms responsible for the tolerance in natural European D. melanogaster populations has never been studied. Here we subjected to desiccation stress 74 natural D. melanogaster European strains, belonging to five different climate zones. We found that the strains belonging to the cold semi-arid climates are more tolerant compared to the others, and that this tolerance can be explained by the combination of altitude and evaporation. The tolerant strains had a lower level of initial water content and lost less water during desiccation stress. We found that the reduction in the water loss happens through a decrease in the respiration rate in desiccation stress conditions, and by having a less permeable cuticle prior the stress exposure. The decreased rate of respiration in the tolerant strains is a consequence of the down-regulation of genes related to diverse metabolic processes. Moreover, we found that the genes related to response to stimulus and environmental sensing are up-regulated only in the tolerant strains. We also identified four transposable element insertions, which might be responsible for changes in gene expression. Overall, our study for the first time described the physiological and transcriptomic changes underlying the desiccation tolerance of natural European D. melanogaster strains, and generated a list of putative mutations shaping desiccation stress response.

Project description:Climate change is one of the main factors shaping the distribution and biodiversity of organisms, among others by greatly altering water availability, thus exposing species and ecosystems to harsh desiccation conditions. Insects are especially threatened by these challenging dry environments, because of their small size and thus large surface area to volume ratio. Drosophila melanogaster is a great model to study the response of populations to rapidly changing conditions, because of its southern-central African origin and recent worldwide colonization. Desiccation stress response is a complex and extensively studied trait, however the natural variation in tolerance, and the underlying transcriptomic and physiological mechanisms are still not clear. Here we subjected to desiccation stress 74 natural D. melanogaster European strains, belonging to five different climate zones. We found that the strains from cold semi-arid climates are more tolerant compared with the ones from hot summer mediterranean climate zones. Moreover, the variance in the tolerance of the strains correlates with the interaction of altitude and evaporation. We found that the tolerant strains had a lower level of initial water content and lose less water during desiccation stress. The reduction in the water loss is probably due to the decrease in the respiration rate in desiccation stress conditions, and to the cuticular hydrocarbon composition found in tolerant strains. Moreover, we found that the genes related to response to stimulus and environmental sensing are up-regulated only in the tolerant strains. Furthermore, we identified several desiccation candidate genes unique for the tolerant strains that can be targeted by tRNA derived fragments, known to be important in post-transcriptional gene regulation in several stress responses. We also looked for transposable element insertions possibly affecting the expression of genes relevant in desiccation tolerance, however, except for four insertions, there is no clear association between the presence of the TE insertions and the tolerance level of the strains. Overall, our study for the first time described the physiological and transcriptomic changes underlying the desiccation tolerance of natural European D. melanogaster strains and puts tRFs in the scope of desiccation related studies as possible regulators of desiccation tolerance.

Project description:Nitrite-oxidizing bacteria are vital players in the global nitrogen cycle that convert nitrite to nitrate during the 2nd step of nitrification. Within this functional guild, the genus Nitrospira is among the most widespread and phylogenetically and physiologically diverse nitrite oxidizers and its members drive nitrite oxidation in many natural and biotechnological ecosystems. Despite their ecological and biotechnological importance, our understanding of Nitrospira’s energy metabolism is still limited. The main bottleneck for a detailed biochemical characterization of Nitrospira is biomass production, since they are slow-growing organisms and fastidious to culture. In this study, we cultured Nitrospira moscoviensis in a continuous stirred tank reactor system (CSTR) allowing constant biomass harvesting. Additionally, this cultivation setup enabled accurate control of physicochemical parameters and thus avoided fluctuating levels of nitrite and accumulation of nitrate. We performed transcriptome analysis and confirmed constant gene expression profiles in the chemostat culture over a period of two weeks. The transcriptomic data supports the predicted core metabolism of N. moscoviensis, including the reductive TCA cycle as a CO2 fixation pathway, the novel bd-like oxidase as terminal oxidase and the octaheme nitrite reductase involved in nitrogen assimilation. Additionally, the expression of multiple copies of respiratory complexes suggests functional differentiation of these copies within the respiratory chain. Transcriptome analysis also suggests a soluble and a membrane-bound gamma subunit as part of the nitrite oxidoreductase (NXR), the enzyme catalyzing nitrite oxidation. Overall, the transcriptome data provided novel insights into the metabolism of Nitrospira supporting the genome-based prediction of key pathways. Moreover, the application of a CSTR to cultivate Nitrospira is an important foundation for future proteomic and biochemical characterizations, which are crucial for a better understanding of canonical and complete nitrifying microorganisms.

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