Response of heat-shock protein (HSP) genes to temperature and salinity stress in the antarctic psychrotrophic bacterium Psychrobacter sp. G

Comparative Proteomic Analysis of Psychrophilic vs. Mesophilic Bacterial Species Reveals Different Strategies to Achieve Temperature Adaptation

The old debate of nature (genes) vs. nurture (environmental variables) is once again topical concerning the effect of climate change on environmental microorganisms. Specifically, the Polar Regions are experiencing a drastic increase in temperature caused by the rise in greenhouse gas emissions. This study, in an attempt to mimic the molecular adaptation of polar microorganisms, combines proteomic approaches with a classical microbiological analysis in three bacterial species Shewanella oneidensis, Shewanella frigidimarina, and Psychrobacter frigidicola. Both shewanellas are members of the same genus but they live in different environments. On the other hand, Shewanella frigidimarina and Psychrobacter frigidicola share the same natural environment but belong to a different genus. The comparison of the strategies employed by each bacterial species estimates the contribution of genome vs. environmental variables in the adaptation to temperature. The results show a greater versatility of acclimatization for the genus Shewanella with respect to Psychrobacter. Besides, S. frigidimarina was the best-adapted species to thermal variations in the temperature range 4–30°C and displayed several adaptation mechanisms common with the other two species. Regarding the molecular machinery used by these bacteria to face the consequences of temperature changes, chaperones have a pivoting role. They form complexes with other proteins in the response to the environment, establishing cooperation with transmembrane proteins, elongation factors, and proteins for protection against oxidative damage.

Gene expression responses to thermal shifts in the endangered lichen Lobaria pulmonaria

Anthropogenic climate change has led to unprecedented shifts in temperature across many ecosystems. In a context of rapid environmental changes, acclimation is an important process as it may influence the capacity of organisms to survive under novel thermal conditions. Mechanisms of acclimation could involve upregulation of stress response genes involved in protein folding, DNA damage repair and the regulation of signal transduction genes, along with a simultaneous downregulation of genes involved in growth or the cell cycle, in order to maintain cellular functions and equilibria. We transplanted Lobaria pulmonaria lichens originating from different forests to determine the relative effects of long-term acclimation and genetic factors on the variability in expression of mycobiont and photobiont genes. We found a strong response of the mycobiont and photobiont to high temperatures, regardless of sample origin. The green-algal photobiont had an overall lower response than the mycobiont. Gene expression of both symbionts was also influenced by acclimation to transplantation sites and by genetic factors. L. pulmonaria seems to have evolved powerful molecular pathways to deal with environmental fluctuations and stress and can acclimate to new habitats by transcriptomic convergence. Although L. pulmonaria has the molecular machinery to counteract short-term thermal stress, survival of lichens such as L. pulmonaria depends mostly on their long-term positive carbon balance, which can be compromised by higher temperatures and reduced precipitation, and both these outcomes have been predicted for Central Europe in connection with global climate change.

Hydrogen sulfide, a novel small molecule signalling agent, participates in the regulation of ganoderic acids biosynthesis induced by heat stress in Ganoderma lucidum

Hydrogen sulfide (H₂S), an emerging small-molecule signalling agent, was recently shown to play a significant role in many physiological processes, but relatively few studies have been conducted on microorganisms compared with mammals and plants. By studying the pretreatment of H₂S donor sodium hydrosulfide (NaHS) and the scavenger hypotaurine (HT) and Cystathionine β-synthase silenced strains, we found that H₂S could alleviate the HS-induced ganoderic acids (GAs) biosynthesis. Our transcriptome results also showed that many signaling pathways and metabolic pathways, such as the glycolysis, TCA, oxidative phosphorylation and pentose phosphate pathway, are influenced by H₂S. Further experimental results indicated that H₂S could affect the physiological process of Ganoderma lucidum by interacting with multiple signals, including ROS, NO, AMPK, sphingolipid, mTOR, phospholipase D and MAPK, and physiological and pharmacological analyses showed that H₂S might alleviate the biosynthesis of GAs by inhibiting the intracellular calcium in G. lucidum.

Transcriptomic response to thermal and salinity stress in introduced and native sympatric Palaemon caridean shrimps

Organisms develop local adaptations to cope with spatially and temporally variable environments such as estuarine habitats, where abiotic parameters such as salinity and temperature fluctuate continuously. Studying the regulation of gene expression in a variable environment allows us to understand the underlying molecular mechanisms of these adaptations and the relative roles of the genetic and plastic response. The transcriptomes of the European native Palaemon longirostris (PL) and the introduced P. macrodactylus (PM) shrimps are described and compared after an experiment simulating summer conditions in the Guadalquivir Estuary, Spain. Specimens, collected in the Guadalquivir Estuary, were maintained at a temperature and salinity of 20 °C and 5 ppt for the control, and 30 °C and 15 ppt for the stress treatment. A large amount of differential gene expression was observed: 16,013 and 2,594 for PL and PM respectively. Functionally annotated unigenes revealed some differences, with PL seemingly having to face stronger physiological stress than PM. Thus, PM seems to have greater resistance than PL under conditions of high temperature and salinity. These results constitute a step forward in the understanding of the underlying molecular mechanisms of genetic adaptation of native invertebrates, and alien taxa that have successfully invaded estuaries in temperate regions around the world.

Fungal and cyanobacterial gene expression in a lichen symbiosis: Effect of temperature and location

Organisms have evolved different cellular mechanisms to deal with environmental stress, primarily through complex molecular mechanisms including protein refolding and DNA repair. As mutualistic symbioses, lichens offer the possibility of analyzing molecular stress responses in a particularly tight interspecific relationship. We study the widespread cyanolichen Peltigera membranacea, a key player in carbon and nitrogen cycling in terrestrial ecosystems at northern latitudes. We ask whether increased temperature is reflected in mRNA levels of selected damage control genes, and do the response patterns show geographical associations? Using real-time PCR quantification of 38 transcripts, differential expression was demonstrated for nine cyanobacterial and nine fungal stress response genes (plus the fungal symbiosis-related lec2 gene) when the temperature was increased from 5 °C to 15 °C and 25 °C. Principle component analysis (PCA) revealed two gene groups with different response patterns. Whereas a set of cyanobacterial DNA repair genes and the fungal lec2 (PC1 group) showed an expression drop at 15 °C vs. 5 °C, most fungal candidates (PC2 group) showed increased expression at 25 °C vs. 5 °C. PC1 responses also correlated with elevation. The correlated downregulation of lec2 and cyanobacterial DNA repair genes suggests a possible interplay between the symbionts warranting further studies.