Few studies deal with the understanding of disease ecology, especially in the agricultural domain. Soft rot Pectobacteriaceae are major plant pathogens that frequently co-infect potato tubers. Exploring their ecological relationships can provide valuable insights for effective monitoring and preventing disease. The study of Barny et al (2024) explores the dynamics of synthetic communities of soft rot Pectobacterium species (SRP) following in vitro and in vivo inoculations, focusing on the implications for disease development. To delve into co-infection dynamics, the authors constructed mixed populations comprising six strains, with three strains from each of two species. Through inoculations of both liquid cultures and potatoes, they observed outcomes using amplicon sequencing targeting the gapA gene, along with monitoring bacterial population sizes and symptoms on potato tubers. Results reveal intriguing patterns: competition among strains of the same species, cooperation through trophic interactions, and interference due to toxicity. Thanks to a modelling approach, they suggest that the presence of a cheater strain may be favoured when it is associated with an aggressive strain. This finding is crucial for field sampling strategies, as there is a risk that during an outbreak, only the cheater strain may be detected, potentially overlooking the problematic aggressive strain. 

While the study conducted by Barny et al. (2024) provides valuable insights into strain interactions, it also highlights areas for further exploration to enhance understanding. First, the extent to which different species occupy similar niches in real agricultural scenarios remains unclear. Additionally, comparative genomics analysis on strains and investigating specific gene candidates could offer valuable mechanistic insights into strain dynamics. These areas for future research offer chances to build up our knowledge base in this field and improve how we understand the interactions between bacteria in nature. The implications of the study extend beyond plant pathogens like SRP. Similar scenarios of complex diseases involving closely related species or strains competing within the same niche are observed in human pathogens as well.

Reference

Barny, M.-A., Thieffry, S., Gomes de Faria, C., Thebault, E., Pedron, J. (2024). Bacterial pathogens dynamic during multi-species infections. https://doi.org/10.1101/2023.12.06.570389

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

Improved characterization of food microbial ecosystems, especially those fermented is key to the development of food sustainability. Short-read metabarcoding is one of the most popular ways to study microbial communities. However, this approach remains complex because of the locks and biases it may entail particularly when applied to fungal communities. 

Building and using four mock communities from fermented food (bread, wine, cheese, fermented meat), Rué et al., 2023 demonstrate that combined DADA2 denoising algorithm followed to the FROGS tools gives a more accurate description of fungal communities compared to several commonly used bioinformatic workflows, dealing with all amplicon lengths. Moreover, Rué et al., 2023 provide guidance on which barcode to use (ITS1, ITS2, D1/D2 and RPB2), depending on the fermented food studied.

Practices in metabarcoding of fungi have been recently reviewed by Tedersoo et al., 2022 and their synthesis comes to the same conclusion as Rué et al., 2023.  As the reference databases are far from being complete notably for food ecosystems, the development of specific sequences public databases will enable the scientific community to lift the veil on this whole area of microbial ecology. 

The study conducted by Rué et al. (2023) provides a particularly detailed approach from a technical point of view, which contributes to improving the general practices in the metabarcoding of fungi. The design and the use of mock communities to compare the performances of the different pipelines is a strong point of this study. Another key element is the creation and use of an in-house database of fungal barcode sequences which improved the species-level affiliations

However, the study of fungal communities by metabarcoding is still a promising avenue of research in agri-food sciences. Thus, short-read sequencing, combined with suitable pipelines and databases, should remain of interest to the microbial ecology community (Pauvert et al., 2019; Furneaux et al., 2021). 

References

Furneaux, B., Bahram, M., Rosling, A., Yorou, N. S., & Ryberg, M. (2021). Long‐and short‐read metabarcoding technologies reveal similar spatiotemporal structures in fungal communities. Molecular Ecology Resources, 21(6), 1833-1849. https://doi.org/10.1111/1755-0998.13387

Pauvert, C., Buée, M., Laval, V., Edel-Hermann, V., Fauchery, L., Gautier, A., ... & Vacher, C. (2019). Bioinformatics matters: The accuracy of plant and soil fungal community data is highly dependent on the metabarcoding pipeline. Fungal Ecology, 41, 23-33. https://doi.org/10.1016/j.funeco.2019.03.005

Rué, O., Coton, M., Dugat-Bony, E., Howell, K., Irlinger, F., Legras, J. L., ... & Sicard, D. (2023). Comparison of metabarcoding taxonomic markers to describe fungal communities in fermented foods. BioRxiv,  2023-0113.523754, ver.3 peer-reviewed and recommended by Peer Community in Microbiology. https://doi.org/10.1101/2023.01.13.523754

Tedersoo, L., Bahram, M., Zinger, L., Nilsson, R. H., Kennedy, P. G., Yang, T., ... & Mikryukov, V. (2022). Best practices in metabarcoding of fungi: From experimental design to results. Molecular ecology, 31(10), 2769-2795. https://doi.org/10.1111/mec.16460

In this interesting study by Bruley et al. (2024), the cyanobacterium Microcystis aeruginosa PCC7806 is taken as a model organism for intracellular CaCO3 precipitation in Cyanobacteria, i.e. in the form of intracellular amorphous calcium carbonates (iACC). This phenomenon, which was first described in 2012, is an example of genetically controlled biomineralization in bacteria. Hence, a gene coding for the protein calcyanin (ccyA) has been documented in iACC biomineralizing cyanobacteria. Nevertheless, so far, the functioning of the calcyanin protein remains unknown. As a first step to elucidate its role in iACC biomineralization the authors study the diel variations of ccyA expression. An approximately 2.5-fold variation in abundance of ccyA transcripts has been observed with the highest values of ccyA expression observed during the second half of the dark period. In addition, the authors made a thorough investigation of transcriptomics data, to detect gene-expressions with temporal patterns that positively or negatively correlate with ccyA. A particular focus was made on neighboring genes (both upstream and downstream) to detect a possible operon gathering ccyA with other genes. Very interestingly, the authors discovered that some neighboring genes coding for Ca2+/H+ antiporter systems, showed transcripts with abundances that correlate with that of ccyA. 

This study raises many interesting questions on genetically controlled biomineralization in bacteria and more particularly the function of iACC biomineralization in Cyanobacteria. As the authors write, iACC biomineralization could be involved in carbon-concentrating mechanisms (CCM), intracellular pH buffering, and create “ballast” for buoyancy and floatability regulation. Nevertheless, these roles would require mechanisms for the dissolution of iAAC in concert with its precipitation ; fine-tuning of both resulting in homeostasis or cyclic temporal patterns of iAAC increase/decrease. As a perspective, the response of Microcystis to fluctuations in calcium and/or pCO2 levels could provide valuable insights into the molecular mechanisms underlying the biomineralization of iACC, as well as comparisons with non-iACC biomineralizing strains or with a mutant of PCC 7806 with a deactivated/deleted ccyA gene.

Reference:

Bruley A, Gaëtan J, Gugger M, Pancrace C, Millet M, Gaschignard G, Dezi M, Humbert J-F, Leloup J, Skouri-Panet F, Callebaut I, Benzerara K and Duprat E (2024) Diel changes in the expression of a marker gene and candidate genes for intracellular amorphous CaCO3 biomineralization in Microcystis. bioRxiv, ver.3 peer-reviewed and recommended by PCI Microbiol. https://doi.org/10.1101/2024.07.07.602159

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