The results indicate that CychB supports a specific subset of co-habiting heterotrophic bacteria during iron starvation, further emphasizing the role of cyanobacteria as key drivers of nutrient flows within globally important microbial soil crust ecosystems, supporting microbial life in nutrient-limited environments.
Abstract
Cyanobacteria are key prokaryotic primary producers in diverse ecosystems, yet the role of cyanobacterial siderophores in shaping their associated microbiomes remains unexplored. Our study demonstrates the benefits provided to the heterotrophic co-habitants of filamentous cyanobacteria in terrestrial microbial biofilms, focusing on the recently discovered widespread siderophores cyanochelins. To address the acceptance of cyanochelin B (CychB) across multiple bacterial classes, we first investigated its role in providing iron to a model siderophore producer P. aeruginosa PAO1 and selected Pseudomonas natural isolates, which were found to utilize CychB under iron limiting conditions while downregulating endogenous siderophore production. In response to CychB, PAO1 expresses a siderophore internalization cluster, which is localized in multiple Pseudomonas natural isolates. Using metagenome analysis, we characterized the bacterial community recruited along with CychB producing Phormidesmis cyanobacteria under long-term iron starvation. Potential CychB acceptor bacteria associated with the CychB producer were predominantly lacking endogenous siderophore machineries. Using siderophore selective pressure, we isolated a genuine CychB acceptor, gram-negative bacterium Methyloversatilis sp. S146 and demonstrated that its genome hosts an iron processing cluster overexpressed after CychB feeding, recognizing Methyloversatilis as a candidate for further mechanistic investigation of iron acquisition–driven microbial interactions. Our results indicate that CychB supports a specific subset of co-habiting heterotrophic bacteria during iron starvation, further emphasizing the role of cyanobacteria as key drivers of nutrient flows within globally important microbial soil crust ecosystems, supporting microbial life in nutrient-limited environments. These findings provide a mechanistic foundation to elucidate the role of cyanochelins as a public good in these communities.
This study functionally characterise the import system of cyanochelin B, a photolytic β-hydroxy aspartate siderophore produced by several filamentous cyanobacteria, and reports the first functional heterologous expression of a cyanobacterial TonB-dependent transporter and establishes Synechocystis as a promising platform for cyanobacterial xenosiderophore-uptake studies.
Jan Mašek, B. P. Falcao, Lucie Kajan Grodecká et al.· bioRxiv· 0 citations
This study demonstrates that Bacillus velezensis SPE2, a low-abundance isolate from the phycosphere of dinoflagellate, exhibits a wide degree of antagonistic activity against multiple marine Flavobacteriaceae strains, a dominant taxonomic group across the phycosphere of diverse phytoplankton species.
Runlin Cai, Hao Feng, Yang Liu et al.· Environmental Microbiome· 0 citations
Iron is a key micronutrient that constrains microbial growth and productivity in many aquatic and terrestrial environments due to its limited bioavailability. Microorganisms evolved sophisticated acquisition strategies, including the production of siderophores, high-affinity iron-chelating molecules that facilitate iron solubilisation and uptake. Cyanobacteria, photosynthetic prokaryotes and major contributors to global primary production, also depend on iron as a cofactor to their core metabolic enzymes. However, very few cyanobacterial siderophores were described so far, and cyanobacteria remain an underxplored source of possibly novel siderophores. Here we report a novel cyanobacterial siderophore, cyanochelin C, that employs two β-hydroxyaspartate residues for iron chelation. We provide extensive nuclear magnetic resonance (NMR) and mass spectrometry (MS) evidence on the molecular structure and identify the corresponding biosynthetic gene cluster (BGC). Bioinformatic analysis of the BGC further revealed the presence of an acylase CcsQ clustering with a broader cyanobacteria-specific family of acylases associated with predicted siderophore-encoding BGCs. Discovery of cyanochelin C and its deacylation by CcsQ expands the known structural diversity of cyanobacterial siderophores and improves the understanding of important enzymatic reactions.
Viviana Di Matteo, L. Štenclová, B. P. Falcao et al.· bioRxiv· 0 citations
Summary Ecological niche partitioning shapes microbial communities in terrestrial mosses, yet its underlying mechanisms and associated viral diversity remain poorly understood. Here, we characterized prokaryotic and viral communities in the rhizosphere soil (Rs) and endophytic niche (Pc) of Pogonatum cirratum using amplicon and metagenomic sequencing. Rs exhibited higher species richness, co-dominated by Pseudomonadota, Acidobacteriota, and Actinomycetota, whereas Pc was dominated by Pseudomonadota (81.13%) but showed greater functional diversity. Source tracking revealed that 10.57% of Pc taxa originated from Rs, suggesting host-mediated filtration of beneficial microbes. Deterministic processes predominantly governed prokaryotic assembly, with iron cycling accounting for ∼14% of total metabolic potential in both niches. Rs contained more biosynthetic gene clusters, while viral communities diverged in taxonomy and auxiliary metabolic genes profiles. These findings demonstrate that P. cirratum maintains compartmentalized prokaryotic and viral communities through niche-specific abiotic filtering and biotic selection, promoting nutrient acquisition and stress resilience in bryophyte-dominated ecosystems.
Chao-Jian Hu, Muhammad Asif, Jin-Hui Liu et al.· iScience· 0 citations
These findings deepen the understanding of Microcystis’ phycosphere functioning and demonstrate the value of multi-omics systems biology approaches, while suggesting that metabolic complementarity between species and across phycospheres could play a role in bloom-associated microbiome structure.
Juliette Audemard, Nicolas Creusot, Julie Leloup et al.· ISME Communications· 0 citations
Eukaryote-associated microbes are ubiquitous, but their essential roles in the development and ecology of their host is yet to be fully understood, partly because complex associations cannot be reconstituted and, in many instances, the genetic tools to elucidate those roles are not available. Here, we report the conjugative transfer of DNA into Nostoc azollae within three Azolla fern hosts. N. azollae is a filamentous, N2-fixing, heterocyst-forming cyanobacterium which is the predominant obligate endosymbiont of the complex microbial community associated with the floating ferns of the genus Azolla. The cyanobiont provides fixed nitrogen to its host, supporting maximum growth rates without any N-fertilizer and making Azolla symbioses both ecologically and agriculturally important. Triparental mating protocols and fluorescent reporter detection were optimized for the cyanobiont isolated from the fern, allowing the further demonstration of heterologous gene expression in N. azollae driven by several promoters, including some of a CRISPR-associated transposon (CAST) system. Azolla was then treated with a cytokinin hormone to render fern shoot apexes amenable to in planta conjugation, permitting DNA transfer to, and gene expression in two distinct developmental stages of N. azollae within Azolla. These included (i) cells of filaments from the Shoot Apical Nostoc colony, the only cyanobacterial stem-cell population vertically transmitted across fern generations, and (ii) cells from differentiated filaments in early formed Azolla leaf cavities. Our approach represents a technically groundbreaking advance for the genetic engineering of cyanobacterial endosymbioses that may be useful for other symbiotic systems, opening a way to investigate these important biological entities.
Cristina Sarasa-Buisán, E. Güngör, Enrique Flores et al.· ISME Communications· 0 citations
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