Root cap is an important determinant of rhizosphere microbiome assembly

Plants impact the development of their rhizosphere microbial communities. It is yet unclear to what extent the root cap and specific root zones contribute to microbial community assembly. To test the roles of root caps and root hairs in the establishment of microbiomes along maize roots (Zea mays), we compared the composition of prokaryote (archaea and bacteria) and protist (Cercozoa and Endomyxa) microbiomes of intact or decapped primary roots of maize inbred line B73 with its isogenic root hairless (rth3) mutant. In addition, we tracked gene expression along the root axis to identify molecular control points for an active microbiome assembly by roots. Absence of root caps had stronger effects on microbiome composition than the absence of root hairs and affected microbial community composition also at older root zones and at higher trophic levels (protists). Specific bacterial and cercozoan taxa correlated with root genes involved in immune response. Our results indicate a central role of root caps in microbiome assembly with ripple-on effects affecting higher trophic levels and microbiome composition on older root zones

Extreme summers impact cropland and grassland soil microbiomes

The increasing frequency of extreme weather events highlights the need to understand how soil microbiomes respond to such disturbances. Here, metagenomics was used to investigate the effects of future climate scenarios (+0.6 °C warming and altered precipitation) on soil microbiomes during the summers of 2014-2019. Unexpectedly, Central Europe experienced extreme heatwaves and droughts during 2018-2019, causing significant impacts on the structure, assembly, and function of soil microbiomes. Specifically, the relative abundance of Actinobacteria (bacteria), Eurotiales (fungi), and Vilmaviridae (viruses) was significantly increased in both cropland and grassland. The contribution of homogeneous selection to bacterial community assembly increased significantly from 40.0% in normal summers to 51.9% in extreme summers. Moreover, genes associated with microbial antioxidant (Ni-SOD), cell wall biosynthesis (glmSMU, murABCDEF), heat shock proteins (GroES/GroEL, Hsp40), and sporulation (spoIID, spoVK) were identified as potential contributors to drought-enriched taxa, and their expressions were confirmed by metatranscriptomics in 2022. The impact of extreme summers was further evident in the taxonomic profiles of 721 recovered metagenome-assembled genomes (MAGs). Annotation of contigs and MAGs suggested that Actinobacteria may have a competitive advantage in extreme summers due to the biosynthesis of geosmin and 2-methylisoborneol. Future climate scenarios caused a similar pattern of changes in microbial communities as extreme summers, but to a much lesser extent. Soil microbiomes in grassland showed greater resilience to climate change than those in cropland. Overall, this study provides a comprehensive framework for understanding the response of soil microbiomes to extreme summers

Sample preservation and storage significantly impact taxonomic and functional profiles in metaproteomics studies of the human gut microbiome

With the technological advances of the last decade, it is now feasible to analyze microbiome samples, such as human stool specimens, using multi-omic techniques. Given the inherent sample complexity, there exists a need for sample methods which preserve as much information as possible about the biological system at the time of sampling. Here, we analyzed human stool samples preserved and stored using different methods, applying metagenomics as well as metaproteomics. Our results demonstrate that sample preservation and storage have a significant effect on the taxonomic composition of identified proteins. The overall identification rates, as well as the proportion of proteins from were much higher when samples were flash frozen. Preservation in RNAlater overall led to fewer protein identifications and a considerable increase in the share of , as well as . Additionally, a decrease in the share of metabolism-related proteins and an increase of the relative amount of proteins involved in the processing of genetic information was observed for RNAlater-stored samples. This suggests that great care should be taken in choosing methods for the preservation and storage of microbiome samples, as well as in comparing the results of analyses using different sampling and storage methods. Flash freezing and subsequent storage at -80 °C should be chosen wherever possible

Water Deficit History Selects Plant Beneficial Soil Bacteria Differently Under Conventional and Organic Farming

Water deficit tolerance is critical for plant fitness and survival, especially when successive drought events happen. Specific soil microorganisms are however able to improve plant tolerance to stresses, such as those displaying a 1-aminocyclopropane-1-carboxylate (ACC) deaminase activity. Microorganisms adapted to dry conditions can be selected by plants over time because of properties such as sporulation, substrate preference, or cell-wall thickness. However, the complexity and interconnection between abiotic factors, like drought or soil management, and biotic factors, like plant species identity, make it difficult to elucidate the general selection processes of such microorganisms. Using a pot experiment in which wheat and barley were grown on conventional and organic farming soils, we determined the effect of water deficit history on soil microorganisms by comparing single and successive events of water limitation. The analysis showed that water deficit strongly impacts the composition of both the total microbial community (16S rRNA genes) and one of ACC deaminase-positive (acdS(+)) microorganisms in the rhizosphere. In contrast, successive dry conditions moderately influence the abundance and diversity of both communities compared to a single dry event. We revealed interactive effects of the farming soil type and the water deficit conditioning treatment. Indeed, possibly due to better nutrient status, plants grown on soils from conventional farming showed higher growth and were able to select more adapted microbial taxa. Some of them are already known for their plant-beneficial properties like the Actinobacteria Streptomyces, but interestingly, some Proteobacteria were also enriched after a water deficit history under conventional farming. Our approach allowed us to identify key microbial taxa promoting drought adaptation of cereals, thus improving our understanding of drought effects on plant-microbe interactions

Sample Preservation and Storage Significantly Impact Taxonomic and Functional Profiles in Metaproteomics Studies of the Human Gut Microbiome

With the technological advances of the last decade, it is now feasible to analyze microbiome samples, such as human stool specimens, using multi-omic techniques. Given the inherent sample complexity, there exists a need for sample methods which preserve as much information as possible about the biological system at the time of sampling. Here, we analyzed human stool samples preserved and stored using different methods, applying metagenomics as well as metaproteomics. Our results demonstrate that sample preservation and storage have a significant effect on the taxonomic composition of identified proteins. The overall identification rates, as well as the proportion of proteins from Actinobacteria were much higher when samples were flash frozen. Preservation in RNAlater overall led to fewer protein identifications and a considerable increase in the share of Bacteroidetes, as well as Proteobacteria. Additionally, a decrease in the share of metabolism-related proteins and an increase of the relative amount of proteins involved in the processing of genetic information was observed for RNAlater-stored samples. This suggests that great care should be taken in choosing methods for the preservation and storage of microbiome samples, as well as in comparing the results of analyses using different sampling and storage methods. Flash freezing and subsequent storage at −80 °C should be chosen wherever possible