Jaromír Hradecký

The geomagnetic field is a persistent environmental condition under which biological systems have evolved. Its absence creates hypomagnetic conditions, potentially disrupting this equilibrium. This study examined the effects of hypomagnetic fields on Saccharomyces cerevisiae growth and metabolism across three culture volumes (10, 75, and 250 mL). Growth inhibition was most pronounced in the smallest volume, with up to 42% reduction in 10-mL cultures, decreasing to 24% in 75 mL, and none in 250-mL cultures. Budding analysis showed significant early inhibition in 10-mL cultures at 2, 4, and 6 h, and in 75-mL cultures at 6 h, whereas no significant budding inhibition was detected in 250-mL cultures. These results suggest that smaller volumes amplify the impact of hypomagnetic exposure, whereas larger volumes may buffer it. These shifts indicate that hypomagnetic exposure affects growth kinetics and extracellular volatile profiles without causing visible cell-surface damage detectable by scanning electron microscopy (SEM), although the underlying molecular mechanism remains unresolved. Our findings identify cultivation volume as an important modifier of microbial sensitivity to magnetic-field deprivation and have implications for interpreting microbial responses in magnetically altered environments, including space-biology models, shielded structures, and fermentation-based systems. IMPORTANCE: Microorganisms are commonly studied under controlled temperature, medium, and aeration conditions, but the magnetic field environment is rarely considered as an experimental variable. This study shows that short-term hypomagnetic exposure alters growth kinetics and volatile metabolic output in Saccharomyces cerevisiae . Importantly, the magnitude of the response depended on cultivation volume: growth inhibition was strongest in small static batch cultures and was not statistically detectable in the largest volume tested. These findings identify cultivation volume as an important modifier of microbial sensitivity to magnetic field deprivation, probably through its influence on culture physiology, gas exchange, metabolite accumulation, and growth phase. The study therefore has implications for the design and interpretation of microbial magnetic-field experiments, including work performed in shielded environments, space biology models, and fermentation-related systems.

Key message: Pine weevil feeding on bark reduced root carbohydrate concentrations in Scots pine seedlings, while no changes were detected in needle phenolics or non-volatile metabolomic profiles after seven days. Context: The large pine weevil ( Hylobius abietis L.) is a major bark-feeding pest of conifer seedlings in Europe. Pine weevil feeding has been shown to induce systemic volatile emissions from undamaged shoots, raising the question of whether bark feeding also affects whole-plant carbon allocation and systemic chemical responses. Aims: We investigated how pine weevil feeding affects organ-specific compounds from primary and secondary metabolism in Scots pine ( Pinus sylvestris L.) seedlings and whether these responses differed between two local provenances. Methods: Soluble sugars were quantified in roots and needles to assess organ-specific changes in carbohydrate status. Phenolic compounds and non-volatile metabolomic profiles were analyzed in needles to evaluate systemic chemical responses after seven days of pine weevil feeding. Stem damage was quantified, and treatment and provenance effects were evaluated using linear mixed-effects models. Results: Pine weevil feeding significantly reduced soluble carbohydrate concentrations in roots but not in needles. No treatment effect was detected for total needle phenolic concentrations, although ferulic acid decreased following pine weevil feeding. Non-volatile metabolomic profiles showed no clear separation between damaged and control seedlings. Conclusion: Pine weevil feeding decreased carbohydrate levels in roots but did not induce detectable changes in secondary metabolites in the two tested provenances.

Key message: Nemozoma  elongatum (Linnaeus, 1761) shows a positive response to artificially produced lures targeting its two main prey species, Pityogenes chalcographus (Linnaeus, 1761) and Taphrorychus bicolor (Herbst, 1793), with a preference for P. chalcographus. We do not recommend using these lures in traps because they could unintentionally capture N. elongatum. However, these lures could potentially aid in controlling target pests by leveraging allochthonous kairomones to attract predators to areas with higher pest densities. Context: Nemozoma  elongatum in Central Europe primarily preys on P. chalcographus and T. bicolor, but it can target nearly 40 species of bark beetles. While it responds well to the aggregation pheromone of P. chalcographus, its response to artificial lures for T. bicolor is unknown. Aims: The study aimed to confirm if N. elongatum beetles react in the same way to a lure containing bicolorin and Chalcoprax® and if their response to the prey abundance of P. chalcographus parallels the response observed in T. bicolor. Methods: During 2022, three Theysohn® pheromone traps were set with Beech Bark Beetle Lure®, containing bicolorin, and one trap with Chalcoprax® in mature beech stands at 11 study sites across the Czech Republic. To study the dependence of the numbers of N. elongatum captured, GLMMs were used to analyze the following variables: both lures, abundance of prey species, abundance of beech, age of beech, altitude, presence of adjacent non-forest areas (such as a freshly exposed edge of a beech forest), and the distances to the nearest spruce forest and the nearest clear-cut area. Results: N. elongatum prefers P. chalcographus as its primary prey, as indicated by its response to the tested lures. Its abundance is dependent on the presence of T. bicolor and P. chalcographus. Conclusion: N. elongatum is a prey opportunist that responds to bark beetle aggregation pheromones, as confirmed for several species. It is frequently caught in traps with Chalcoprax® and bicolorin, the pheromone of T. bicolor. Although more commonly attracted to Chalcoprax®, indicating a preference for P. chalcographus, N. elongatum may consume other species given its attraction to volatile compounds from host trees.

Plants and insects coevolved as an evolutionarily successful and enduring association. The molecular arms race led to evolutionary novelties regarding unique mechanisms of defence and detoxification in plants and insects. While insects adopt mechanisms to conquer host defence, trees develop well-orchestrated and species-specific defence strategies against insect herbivory. However, current knowledge on the molecular underpinnings of fine-tuned tree defence responses against different herbivore insects is still restricted. In the current study, using a multi-omics approach, we unveiled the defence response of Populus tremula against aphids (Chaitophorus populialbae) and spongy moths (Lymantria dispar) herbivory. Comparative differential gene expression (DGE) analyses revealed that around 272 and 1203 transcripts were differentially regulated in P. tremula after moth and aphid herbivory compared to uninfested controls. Interestingly, 5716 transcripts were differentially regulated in P. tremula between aphids and moth infestation. Further investigation showed that defence-related stress hormones and their lipid precursors, transcription factors, and signalling molecules were over-expressed, whereas the growth-related counterparts were suppressed in P. tremula after aphid and moth herbivory. Metabolomics analysis documented that around 37% of all significantly abundant metabolites were associated with biochemical pathways related to tree growth and defence. However, the metabolic profiles of aphid and moth-fed trees were quite distinct, indicating species-specific response optimization. After identifying the suitable reference genes in P. tremula, the omics data were further validated using RT-qPCR. Nevertheless, our findings documented species-specific fine-tuning of the defence response of P. tremula, showing conservation on resource allocation for defence overgrowth under aphid and moth herbivory. Such findings can be exploited to enhance our current understanding of molecular orchestration of tree responses against herbivory and aid in developing insect pest resistance P. tremula varieties.

The main biochemical traits were estimated in poplar leaves under biotic attack (aphids and spongy moth infestation). Changes in the abundance of bioactive compounds in genetically uniform individuals of European aspen (Populus tremula), such as proline, polyphenolic compounds, chlorophylls a and b, and volatile compounds, were determined between leaves damaged by sucking insects (aphid—Chaitophorus nassonowi) and chewing insects (spongy moth—Lymantria dispar) compared to uninfected leaves. Among the nine analyzed phenolic compounds, only catechin and procyanidin showed significant differences between the control leaves and leaves affected by spongy moths or aphids. GC-TOF-MS volatile metabolome analysis showed the clear separation of the control versus aphids-infested and moth-infested leaves. In total, the compounds that proved to have the highest explanatory power for aphid-infested leaves were 3-hexenal and 5-methyl-2-furanone, and for moth-infested leaves, trans-α-farnesene and 4-cyanocyclohexane. The aphid-infested leaves contained around half the amount of chlorophylls and twice the amount of proline compared to uninfected leaves, and these results evidenced that aphids influence plant physiology more than chewing insects.

Termites can feed on wood thanks to their association with their gut microbes. However, the current understanding of termites as holobiont is limited.

Fecal microbiota transfer may serve as a therapeutic tool for treating obesity and related disorders but currently, there is no consensus regarding the optimal donor characteristics. We studied how microbiota from vegan donors, who exhibit a low incidence of non-communicable diseases, impact on metabolic effects of an obesogenic diet and the potential role of dietary inulin in mediating these effects. Ex-germ-free animals were colonized with human vegan microbiota and fed a standard or Western-type diet (WD) with or without inulin supplementation. Despite the colonization with vegan microbiota, WD induced excessive weight gain, impaired glucose metabolism, insulin resistance, and liver steatosis. However, supplementation with inulin reversed steatosis and improved glucose homeostasis. In contrast, inulin did not affect WD-induced metabolic changes in non-humanized conventional mice. In vegan microbiota-colonized mice, inulin supplementation resulted in a significant change in gut microbiota composition and its metabolic performance, inducing the shift from proteolytic towards saccharolytic fermentation (decrease of sulfur-containing compounds, increase of SCFA). We found that (i) vegan microbiota alone does not protect against adverse effects of WD; and (ii) supplementation with inulin reversed steatosis and normalized glucose metabolism. This phenomenon is associated with the shift in microbiota composition and accentuation of saccharolytic fermentation at the expense of proteolytic fermentation.

Termites represent one of the most important insect groups worldwide due to their key role as plant decomposers and proxy of carbon recycling in the tropical rainforest ecosystems. Besides, high relevance in research has been given to these social insects due to a prominent role as urban pests. However, one of the most fascinating aspects of termites are their defence strategies that prevent the growth of detrimental microbiological strains on their nests. One success factor is the key role of the nest allied microbiome. Understanding how beneficial microbial strains aid termites in pathogen biocontrol strategies could provide us with an enhanced repertoire for fighting antimicrobial resistant strains or mine for genes for bioremediation purposes. We carried out a multiomics approach for dissecting the nest microbiome in a wide range of termite species, covering several feeding habits and three geographical locations at two tropical sides of the Atlantic Ocean, and an African savanna. Our experimental approach included untargeted volatile metabolomics, targeted evaluation of volatile naphthalene, taxonomical profile for bacteria and fungi through amplicon sequencing, and further dive into the genetic repertoire through a metagenomic sequencing approach. Volatile naphthalene was present in species belonging to the genera Nasutitermes and Cubitermes . We further assessed the apparent differences in terms of bacterial community structure, having found a stronger influence from feeding habits and genera, rather than the geographical location. Lastly, our metagenomic analysis revealed that the gene content provides both soil feeding genera with similar functional profiles, while the wood feeding genus shows a different one. These results seem to be independent of the geographical location, indicating that the nest functional profile is heavily influenced by the diet of the termite inhabiting, building, and maintaining the nest.

Ips duplicatus (Coleoptera: Curculionidae) is a bark beetle that recently invaded southern Europe. It produces intense outbreaks in the spruce stands installed outside their natural area. Pheromone dispensers with different designs are used for monitoring this species. Compounds are released either by wick (ID Ecolure) or polyethene foil (ID RO and Pheagr IDU). We performed a series of laboratory and field experiments to compare the efficiency and sustainability of these dispensers in terms of pheromone release. The first experiment compared the Ips duplicatus capture dynamics between the ID Ecolure and ID RO in pheromones traps in three localities for 60 days. Release rates of used dispensers were evaluated in the same period. The second experiment analyzed headspace chemical composition in three dispensers (ID Ecolure, ID RO, Pheagr IDU) and tested their activity in pheromone traps. Active compounds content released by tested dispensers varied. The wick dispensers’ release rates (ID Ecolure) were strongly reduced from 365 to 50 mg/day within two weeks and then steadily to 16 mg/day after 60 days. Release rates of the polyethene dispensers (ID RO) remained constant over 60 days (20–24 mg/day). The highest initial emission was in the ID Ecolure. The ratio of pheromone components (ipsdienol/E-myrcenol) was lower for ID Ecolure (5) and ID RO (10) and higher for Pheagr IDU (565). In the field experiments, significantly more Ips duplicatus were caught with ID Ecolure than ID RO and Pheagr IDU in the first two weeks. Later, the attractivity of ID RO remained high, but captures by ID Ecolure were significantly reduced. The captures of Ips typograhus were also considered. We propose that the wick-type dispensers are a promising tool for controlling the hibernating beetle generation. The foil release dispensers can be used to monitor Ips duplicatus flight activity.