Shrimp aquaculture ponds are an established technology that helps answer the demand for high-protein food while reducing the impact of fishing on the oceans.

However, as a closed system, high in organic matter, aquaculture ponds in general and those used for shrimp in particular tend to develop anoxic sediments and favour sulfate reduction to H2S. The development of hydrogen sulphide, in return, is toxic to the shrimp and can lead to lower yields.

A standard solution to the problem is to inject air into the sediments. However, this solution requires additional infrastructure, is costly to operate, and can also disturb other essential life forms in the pond, such as benthic plants. 

In this work by Torun et al. (2024), the authors used a carefully designed lab model of shrimp ponds to show that the addition of molybdate at concentrations as low as 5 mg/l delayed the accumulation of H2S and pushed the zone rich in sulphide deeper into the sediment.

The postulated mechanism for the inhibition in H2S production is that molybdate binds to the ATP sulfurylase in sulphate-reducing bacteria (SRB), and together with ATP, they generate adenosine 5′-phosphosulfate (APS) that cannot be used as an electron acceptor.

Surprisingly, however, the growth of SRB was stimulated rather than inhibited in this experiment. While the exact cause remains unknown, the authors postulate that SRB resorted to alternative metabolic pathways such as fermentation.

Overall, while this work was done on a model system in the lab, adding molybdate to shrimp aquaculture ponds is a promising technique and should be tested on a larger scale.

Reference

Torun F, Hostins B, Schryver PD, Boon N, Vrieze JD. (2024). Molybdate delays sulphide formation in the sediment and transfer to the bulk liquid in a model shrimp pond. bioRxiv, ver.3, peer-reviewed and recommended by Peer Community In Microbiology. https://doi.org/10.1101/2023.11.16.567380

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

The paper "Diversity of bacterial symbionts associated with the tropical plant bug Monalonion velezangeli (Hemiptera: Miridae) revealed by high-throughput 16S rRNA sequencing" by Navarro-Escalante et al. (2023) is a valuable contribution to entomological research, particularly in the context of pest management. This descriptive study, while not delving into the functional characterization of the associated bacterial strains, lays an essential groundwork for understanding the bacterial components of the microbiota of this agricultural pest. This study is interesting because it provides new information on insect microbiota, especially in a family for which the knowledge of the diversity of bacterial symbionts is very limited.

One of the study's core strengths lies in its exploration and definition of the core microbiota of M. velezangeli, which could serve as a foundation for future research aimed at pest control strategies. The use of 16S rRNA sequencing, despite its known limitations, has enabled the profiling of these bacterial communities. The paper highlights the absence of differences in the bacterial communities associated with the nymph and adult stages of the pest, indicating a stable association of these microbes throughout the insect's life cycle.

A standout point in the study is the overwhelming presence of the symbiont Wolbachia, accounting for approximately 92% of the bacterial composition. However, intriguingly, the authors also note the absence of Wolbachia in some individuals, suggesting a more complex dynamic that warrants further investigation. This finding is particularly noteworthy, as it opens up questions about the role of Wolbachia and its impact on the biology and ecology of M. velezangeli.

The researchers have carefully addressed all the reviewers’ comments and suggestions. They also addressed a potential bias in their study - the overwhelming presence of Wolbachia - by analyzing the bacterial community after the removal of Wolbachia sequences. This careful approach enriches the study's credibility and ensures a more accurate representation of the pest's microbiota.

The identification of potentially culturable strains within the core microbiome represents an interesting perspective of this research. This information could be used in future efforts to develop pest control strategies, particularly those employing paratransgenic approaches. The possibility of manipulating these culturable strains to combat M. velezangeli presents an exciting avenue for sustainable pest management.

While the study does not investigate the localization of these associated bacteria, whether in the gut or elsewhere, including potentially in dedicated symbiotic organs, it nevertheless offers a valuable descriptive account. This baseline knowledge will be useful for any subsequent functional or localization studies, which could further unravel the complex interactions between M. velezangeli and its microbial partners.

In conclusion, the work of Navarro-Escalante et al. is a notable effort to set the stage for future research into the biology of M. velezangeli and its associated microbiota. The findings from this study provide a good reference point for further investigations aimed at pest's biology and exploring innovative pest control strategies. It also represents a valuable contribution to understanding the basic biology of insect-bacteria interactions. 

Reference

Navarro-Escalante​ L., Benavides​ P. and Acevedo​, F.E. (2023) Diversity of bacterial symbionts associated with the tropical plant bug Monalonion velezangeli (Hemiptera: Miridae) revealed by high-throughput 16S-rRNA sequencing. Research Square​, ver. 7 peer-reviewed and recommended by PCI Microbiology. https://doi.org/10.21203/rs.3.rs-2022560/v7​

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