Plant pathogens can cause devastating damage to crop (Strange and Scott 2005) greatly affecting a food resource in growing need on our planet. A significant proportion of global crops require irrigation, and with this, bare the risk of being affected by irrigation-borne pathogens (Lamichhane and Bartoli, 2015). Detection of plant pathogens in irrigation water can effectively be used to minimize this risk. River water makes up a major irrigation water source. Morris et al., (2023), propose monitoring whole river catchments to understand plant pathogen population dynamics and generate models to prevent outbreaks, similar to practices regarding water-borne human pathogens.

Monitoring 270 km of the river Durance, Morris et al., (2023) reveal that two groups of bacteria known to host pathogenic strains, Pseudomonas syringae and the Soft Rot Pectobacteriaceae are present in relatively high numbers across the entire catchment or significant parts of it, respectively, with their abundance mostly correlated to water temperature. Nevertheless, despite their presence no major outbreaks have been reported in recent years. The authors suggest that the current environmental conditions in the lower, agriculture-dominated part of the catchment may not generate the necessary environment for an outbreak. Alternatively, as also suggested, though some potentially pathogenic variants were detected in the study, they may not match the crops currently grown in the area (Morris et al., 2023).

The authors thus bring up the need for large scale monitoring and call for observations on potential land-use changes in the area that may alter the sensitive and seemingly stable conditions in such a way that outbreaks will be triggered. Change of land use, specifically from rural to agricultural use, has been repeatedly recognized to influence biodiversity (e.g., Ionescu et al., 2022). Furthermore, agricultural environments, with a dense network of irrigation channels, natural and man-made ponds, and larger reservoirs, will accelerate the spread of organisms through multiple biotic and abiotic vectors (Karnatak and Wollrab, 2020), and with this likely plant- (and other) pathogens. Overall, the work by Morris et al., (2023) highlights that studying the presence and distribution of plant pathogens in water used for irrigation across large areas, is bound to identify which potential pathogens are omnipresent, awaiting for the right condition for an outbreak; and which are rather spread from, isolated, local sources and thus can be effectively mitigated.

References

Strange, R. N., and Scott, P. R. (2005). Plant disease: a threat to global food security. Annu. Rev. Phytopathol. 43, 83–116. https://doi.org/10.1146/annurev.phyto.43.113004.133839

Lamichhane, J.R. and Bartoli, C. (2015), Plant pathogenic bacteria in open irrigation systems: what risk for crop health? Plant Pathol, 64: 757-766. https://doi.org/10.1111/ppa.12371

C.E. Morris, C. Lacroix, C. Chandeysson, C. Guilbaud, C. Monteil, S. Piry, Rochelle Newall E., S. Fiorini, F. Van Gijsegem, M.A. Barny, O. Berge (2023) Comparative abundance and diversity of populations of the Pseudomonas syringae and Soft Rot Pectobacteriaceae species complexes throughout the Durance River catchment from its French Alps sources to its delta. bioRxiv, 2022.09.06.506731, ver. 3 peer-reviewed and recommended by Peer Community in Microbiology. https://doi.org/10.1101/2022.09.06.506731 

Ionescu, D., Bizic, M., Karnatak, R., Musseau, C. L., Onandia, G., Kasada, M., Berger, S. A., et al. (2022). From Microbes to Mammals: Pond Biodiversity Homogenization across Different Land-Use Types in an Agricultural Landscape. Ecological Monographs 92(3): e1523. https://doi.org/10.1002/ecm.1523

The human vaginal microbiota plays a key role in urogenital health. Enhancing our understanding of the dynamics of the vaginal microbiota can provide valuable insights for maintaining health and design strategies to prevent urogenital diseases. Health status evolves over time. The work by Kamiya et al. (2024) addressed the dynamic interplay between vaginal microbiota and health using a robust, high-resolution longitudinal cohort of 125 reproductive-aged women, followed for a median duration of 8.6 months in Montpellier, France. The participants were recruited within the PAPCLEAR study, which aimed to better understand the course and natural history of human papillomaviruses infections in healthy, young women (Murall et al. 2019). Each participant contributed at least three vaginal samples, from which microbiota barcoding was performed.

The vaginal microbiota was clustered using the approach developed by Ravel et al. (2011) which categorizes microbial communities in 5 community state types with varying health implications. Transitions between community states were estimated using a hierarchical Bayesian Markov model. These transitions were associated with 16 covariates covering lifestyle, sexual practices and medication. This hierarchical approach allowed for the quantification of individual differences among women. The study characterized the stability of vaginal microbial communities and identified alcohol consumption as the strongest covariate driving community transitions. The results indicated that alcohol consumption promotes non-optimal communities. 

The modelling approach, however, indicated that individual variability among the women was not fully accounted for by the selected 16 covariates, suggesting the need to explore additional key factors, including dynamic covariates. The authors clearly identified several  potential limitations of the study, including the variability associated to home sampling,  the resolution of the microbial categories, and the impact of the clustering method on the analysis.    

My decision to recommend this manuscript is supported by the solid and rigorous analysis of the study, strengthened by the clear presentation of methods, data and analysis. While applying advanced computational techniques, the authors provide a solid biological interpretation of their results. This work makes a substantial contribution by expanding the understanding of vaginal microbiota dynamics and its interplay with health. It sets a framework for further evaluation of strategies aimed at promoting vaginal health. Moreover, it presents a generic methodology that could be applied to other microbial ecosystems.   

References

Kamiya T, Tessandier N, Elie B, Bernat C, Boué V, Grasset S, Groc S, Rahmoun M, Selinger C, Humphrys MS, Bonneau M, Graf C, Foulongne V, Reynes J, Tribout V, Segondy M, Boulle N, Ravel J, Murall CL, Alizon S (2024) Factors shaping vaginal microbiota long-term community dynamics in young adult women. medRxiv, 2024.04.08.24305448, ver.3 peer-reviewed and recommended by PCI Microbiol. https://doi.org/10.1101/2024.04.08.24305448

Murall CL, Rahmoun M, Selinger C, Baldellou M, Bernat C, Bonneau M, Boué V, Buisson M, Christophe G, D’Auria G, Taroni F De, Foulongne V, Froissart R, Graf C, Grasset S, Groc S, Hirtz C, Jaussent A, Lajoie J, Lorcy F, Picot E, Picot MC, Ravel J, Reynes J, Rousset T, Seddiki A, Teirlinck M, Tribout V, Tuaillon É, Waterboer T, Jacobs N, Bravo IG, Segondy M, Boulle N, Alizon S (2019) Natural history, dynamics, and ecology of human papillomaviruses in genital infections of young women: protocol of the PAPCLEAR cohort study. BMJ Open, 9, e025129. https://doi.org/10.1136/BMJOPEN-2018-025129

Ravel J, Gajer P, Abdo Z, Schneider GM, Koenig SSK, McCulle SL, Karlebach S, Gorle R, Russell J, Tacket CO, Brotman RM, Davis CC, Ault K, Peralta L, Forney LJ (2011) Vaginal microbiome of reproductive-age women. Proceedings of the National Academy of Sciences of the United States of America, 108. https://doi.org/10.1073/pnas.1002611107

The Burkholderia sensu lato group is predominant in the rhizosphere of rice. It includes both plant growth promoting rhizobacteria (typically members of the Paraburkholderia genus) and phytopathogens (typically members of the Burkholderia genus). Better understanding the interaction between Burkholderia sensu lato and their host plant is therefore crucial to advance our knowledge of the ecology of rice, a plant that feeds more than half of the humans on the planet.

The perception of root exudates from their host is key for rhizobacteria. Is the response to root exudates more related to the phylogeny of the bacteria, i.e. genus-dependent, or is it strain-specific? This question is not trivial for the Burkholderia sensu lato group, which has experienced shifting outlines over the last twenty years. During the early stages of rice root colonization, Wallner et al. [1] investigated the transcriptomic regulation of three strains of each Burkholderia and Paraburkholderia genera, in addition to a genomic comparison, in order to better understand their early colonization strategies. 

While these six strains possess a large proportion of gene homologues, their experiment shows their response to root exudates to be strain-specific. In the study, rice root exudates affected several metabolic pathways of interest in most strains, noticeably including i) the Entner-Doudoroff pathway, which had never been reported to be activated in relation to root colonization and ii) the putrescine pathway, which may reflect signaling controlling root colonization. 

The work by Wallner et al. provides new insights on the strain-level response of the transcriptomic regulation of Burkholderia sensu lato in response to root exudates in the early stages of root colonization. Beyond this, the next steps will hopefully shed light on what happens in more complex environments, within a complex bacterial community and during later colonization stages.

Reference

Wallner A, Klonowska A, Guigard L, King E, Rimbault I, Ngonkeu E, Nguyen P, Béna G, Moulin L (2022) Comparative genomics and transcriptomic response to root exudates of six rice root-associated Burkholderia sensu lato species. BioRxiv, 2022.10.04.510755, version 2 peer-reviewed and recommended by PCI Microbiol. https://doi.org/10.1101/2022.10.04.510755

Engineering plant microbiota can improve plant health and growth sustainably. Emergent approaches include rational Synthetic Communities (SynCom) design or soil amendments and specific agricultural practices to shift resident microbiota and to understand its impact (Moreira et al. 2023). 

In this context, the impact of seed microbiota on the early stages of plant development is becoming an essential topic in the study of plant–microbiota interactions. Behind the well-studied seed-borne pathogens, the seed microbiota can host many other commensal and beneficial organisms that have been neglected in the past. 

The study of Simonin et al. (2023) applies single isolates and synthetic communities (SynCom)  on radish seeds to answer two key questions: what is the role of seed microbiota during the early stages of plant development? How can SynCom influence the seedling health and its microbiota? The study describes an elegant approach to cope with the variability of natural microbiota using SynCom following a gradient of complexity. 

Overall, the study highlighted a contrasted impact of the bacterial strains when applied in isolation or SynCom. The composition and complexity of the SynCom had also an impact on plant seedlings. Importantly, contrasting evolution from seeds to seedlings was observed for 3 strains of Pseudomonas fluorescens within the SynComs, underlining the importance of intra-species level diversity and precluding any generalization of results at species level.  

References 

Moreira, Z. P. M., Chen, M. Y., Ortuno, D. L. Y., & Haney, C. H. (2023). Engineering plant microbiomes by integrating eco-evolutionary principles into current strategies. Current Opinion in Plant Biology, 71, 102316. https://doi.org/10.1016/j.pbi.2022.102316

Simonin, M., Préveaux, A., Marais, C., Garin, T., Arnault, G., Sarniguet, A., & Barret, M. (2023). Transmission of synthetic seed bacterial communities to radish seedlings: impact on microbiota assembly and plant phenotype. bioRxiv, 2023-02. ver. 3 peer-reviewed and recommended by Peer Community in Microbiology. https://doi.org/10.1101/2023.02.14.527860