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The majority of predatory protists are size-limited. Arcellinida (Amoebozoa) exhibit the remarkable ability to prey upon larger rganisms. Here, we examine the co-evolution of their robust shells and predatory behavior. Tracing back to the emergence of eukaryotes, we explore how early amoebozoan predators adapted their cytoskeletons to master phagocytosis. We speculate that the diversity of shell morphology as we see it in extant Arcellinida might be a direct result to their adaptation to prey on large organisms.

Biological nitrogen fixation by free-living bacteria and rhizobial symbiosis with legumes plays a key role in sustainable crop production. Here, we study how different crop combinations influence the interaction between peanut plants and their rhizosphere microbiota via metabolite deposition and functional responses of free-living and symbiotic nitrogen-fixing bacteria. Based on a long-term (8 year) diversified cropping field experiment, we find that peanut co-cultured with maize and oilseed rape lead to specific changes in peanut rhizosphere metabolite profiles and bacterial functions and nodulation. Flavonoids and coumarins accumulate due to the activation of phenylpropanoid biosynthesis pathways in peanuts. These changes enhance the growth and nitrogen fixation activity of free-living bacterial isolates, and root nodulation by symbiotic Bradyrhizobium isolates. Peanut plant root metabolites interact with Bradyrhizobium isolates contributing to initiate nodulation. Our findings demonstrate that tailored intercropping could be used to improve soil nitrogen availability through changes in the rhizosphere microbiome and its functions. Sustainability in agriculture can be improved harnessing biological N 2 fixation in legumes. Here, the authors combine different crops with peanut plants finding that maize and oilseed rape are the most successful combinations which have potential to enhance rhizosphere microbiota N 2 fixation.

Background Unicellular eukaryotes were widely considered to r eproduce without sex. However, recent findings suggest that meiosis, and by extension (sometimes cryptic) sexual reproduction, might be present in almost all eukaryotic lineages. Results Here, we investigate the transcriptomic response underlying starvation-induced fusion in the Rhizaria protist Fisculla terrestris . Investigations of differentially expressed genes (DEGs) with a particular focus on the expression of meiosis-associated genes suggest that some form of meiosis and recombination might occur in these Rhizaria. Conclusions We showed that starvation triggered changes in gene expression of meiosis-associated genes in F. terrestris . However, if these processes are coupled with sexual reproduction remains to be investigated.

Background During wastewater treatment, the wastewater microbiome facilitates the degradation of organic matter, reduction of nutrients, and removal of gut parasites. While the latter function is essential to minimize public health risks, the range of parasites involved and how they are removed is still poorly understood. Results Using shotgun metagenomic (DNA) and metatranscriptomic (RNA) sequencing data from ten wastewater treatment plants in Switzerland, we were able to assess the entire wastewater microbiome, including the often neglected microeukaryotes (protists). In the latter group, we found a surprising richness and relative abundance of active parasites, particularly in the inflow. Using network analysis, we tracked these taxa across the various treatment compartments and linked their removal to trophic interactions. Conclusions Our results indicate that the combination of DNA and RNA data is essential for assessing the full spectrum of taxa present in wastewater. In particular, we shed light on an important but poorly understood function of wastewater treatment – parasite removal. 6ehe_ZkZdE9fr2WhScWVWR Video Abstract

ABSTRACT Plants modulate the soil microbiota by root exudation assembling a complex rhizosphere microbiome with organisms spanning different trophic levels. Here, we assessed the diversity of bacterial, fungal and cercozoan communities in landraces and modern varieties of wheat. The dominant taxa within each group were the bacterial phyla Proteobacteria, Actinobacteria and Acidobacteria; the fungi phyla Ascomycota, Chytridiomycota and Basidiomycota; and the Cercozoa classes Sarcomonadea, Thecofilosea and Imbricatea. We showed that microbial networks of the wheat landraces formed a more intricate network topology than that of modern wheat cultivars, suggesting that breeding selection resulted in a reduced ability to recruit specific microbes in the rhizosphere. The high connectedness of certain cercozoan taxa to bacteria and fungi indicated trophic network hierarchies where certain predators gain predominance over others. Positive correlations between protists and bacteria in landraces were preserved as a subset in cultivars as was the case for the Sarcomonadea class with Actinobacteria. The correlations between the microbiome structure and plant genotype observed in our results suggest the importance of top-down control by organisms of higher trophic levels as a key factor for understanding the drivers of microbiome community assembly in the rhizosphere. Protists as a key factor in rhizosphere microbiome assembly was demonstrated in landraces and modern cultivars of wheat.

Background Antibiotic resistance genes (ARGs) are proliferating in wastewater microbiomes, yet the biotic forces shaping their diversity remain poorly understood. Here, we integrate 14 months of metagenomic and metatranscriptomic data from a wastewater treatment plant to reveal that viruses and microeukaryotes, long-overlooked trophic actors, may play an important role in shaping bacterial and ARG diversity. Results We show that viral and microeukaryotic communities exhibit strong seasonal dynamics that cascade through the microbial food web, significantly structuring prokaryotic communities and subsequently ARG profiles. Crucially, we find that viral and microeukaryotic diversity are positively associated with bacterial diversity, which in turn shapes ARG diversity, underscoring the regulatory potential of ecological interactions. Conclusions Our findings challenge the abiotic-centric paradigm and establish the central role of multi-trophic interactions in shaping ARG dynamics in wastewater ecosystems. 4btXf6bUVLuhYUYiRwpq9T Video Abstract

Background For achieving long-term sustainability of intensive agricultural practices, it is pivotal to understand belowground functional stability as belowground organisms play essential roles in soil biogeochemical cycling. It is commonly believed that resource availability is critical for controlling the soil biodiversity and belowground organism interactions that ultimately lead to the stabilization or collapse of terrestrial ecosystem functions, but evidence to support this belief is still limited. Here, we leveraged field experiments from the Chinese National Ecosystem Research Network (CERN) and two microcosm experiments mimicking high and low resource conditions to explore how resource availability mediates soil biodiversity and potential multi-trophic interactions to control functional trait stability. Results We found that agricultural practice-induced higher resource availability increased potential cross-trophic interactions over 316% in fields, which in turn had a greater effect on functional trait stability, while low resource availability made the stability more dependent on the potential within trophic interactions and soil biodiversity. This large-scale pattern was confirmed by fine-scale microcosm systems, showing that microcosms with sufficient nutrient supply increase the proportion of potential cross-trophic interactions, which were positively associated with functional stability. Resource-driven belowground biodiversity and multi-trophic interactions ultimately feedback to the stability of plant biomass. Conclusions Our results indicated the importance of potential multi-trophic interactions in supporting belowground functional trait stability, especially when nutrients are sufficient, and also suggested the ecological benefits of fertilization programs in modern agricultural intensification. 6BT2faHzT3jQfWsk8Bso8N Video Abstract

Legionellales-infected water is a frequent cause of local outbreaks of Legionnaires’ disease and Pontiac fever. Decontaminations are difficult because Legionellales reproduce in eukaryotic microorganisms (protists). Most often, Legionellales have been isolated from amoebae; however, the culture-based sampling methods are taxonomically biased. Sequencing studies show that amoebae in the cercozoan class Thecofilosea are dominant in soils and wastewater treatment plants, prompting us to screen their capability to serve as potential hosts of endosymbiotic bacteria. Environmental isolates of Thecofilosea contained a surprising richness of endosymbiotic Legionellales, including Legionella . Considering the widespread dispersal of Legionellales in apparently unrelated amoeboid protist taxa, it appears that the morphotype and not the evolutionary origin of amoebae determines their suitability as hosts for Legionellales. We further provide a protocol for gnotobiotic cultivation of Legionellales and their respective hosts, facilitating future genomic and transcriptomic research of host–symbiont relationships.

In this article the affiliation ‘State Key Laboratory of Soil and Sustainable Agriculture, Institute of Soil Science, Chinese Academy of Sciences, Nanjing 210008, China’ for Xinhua Peng was missing. The original article has been corrected.

Background Network analyses are often applied to microbial communities using sequencing survey datasets. However, associations in such networks do not necessarily indicate actual biotic interactions, and even if they do, the nature of the interactions commonly remains unclear. While network analyses are valuable for generating hypotheses, the inferred hypotheses are rarely experimentally confirmed. Results We employed cross-kingdom network analyses, applied trait-based functions to the microorganisms, and subsequently experimentally investigated the found putative predator–prey interactions to evaluate whether, and to what extent, correlations indicate actual predator–prey relationships. For this, we investigated algae and their protistan predators in biocrusts of three distinct polar regions, i.e., Svalbard, the Antarctic Peninsula, and Continental Antarctica. Network analyses using FlashWeave indicated that 89, 138, and 51 correlations occurred between predatory protists and algae, respectively. However, trait assignment revealed that only 4.7–9.3% of said correlations link predators to actually suitable prey. We further confirmed these results with HMSC modeling, which resulted in similar numbers of 7.5% and 4.8% linking predators to suitable prey for full co-occurrence and abundance models, respectively. The combination of network analyses and trait assignment increased confidence in the prediction of predator–prey interactions, as we show that 82% of all experimentally investigated correlations could be verified. Furthermore, we found that more vicious predators, i.e., predators with the highest growth rate in co-culture with their prey, exhibit higher stress and betweenness centrality — giving rise to the future possibility of determining important predators from their network statistics. Conclusions Our results support the idea of using network analyses for inferring predator–prey interactions, but at the same time call for cautionary consideration of the results, by combining them with trait-based approaches to increase confidence in the prediction of biological interactions. FNXjBTWygxbKv-5R-GHg3p Video Abstract