Biology subjects

Urajova, P.

Publications and source records attributed to Urajova, P..

4 recordsLinked to original sources

bioRxiv2026

Cyanochelin uptake reveals an exclusively cyanobacterial class of AMIN-domain TonB-dependent transporters

Siderophore transport is central to microbial competition, because it determines access to iron, frequently a limiting nutrient. While siderophore-mediated iron uptake via TonB-dependent transporters (TBDTs) has been extensively studied in heterotrophic bacteria, little is known about the functionality and specificity of TBDTs in cyanobacteria. In the present study we functionally characterise the import system of cyanochelin B, a photolytic {beta}-hydroxy aspartate siderophore produced by several filamentous cyanobacteria, including Leptolyngbya sp. NIES-3755. We have identified a cyanochelin B putative transport cassete localized in the vicinity of the cyanochelin biosynthetic gene cluster in Leptolyngbya genome. By expressing the import genes heterologously in a model unicellular cyanobacterium Synechocystis sp. PCC 6803, we established that the transport cassette reconstitutes cyanochelin B-dependent growth, consistent with cyanochelin-mediated iron acquisition. Systematic gene dissection showed that the TBDT (CctA) and the substrate-binding protein (CctB), responsible for binding the siderophore in the periplasm, are alone sufficient for cyanochelin import into Synechocystis cells, with the permeases, ATPase and a cassette-associated ferredoxin supplied in trans by the host. CctA carries an N-terminal AMIN domain, a fusion found only in cyanobacterial TBDTs. The cassette accepts the structurally similar cyanochelin A but not cyanochelin C, enterobactin or pyoverdine, indicating limited promiscuity. The phylogenetic placement of cyanochelin receptors within a broader clade containing citrate-hydroxamate-type siderophore receptors suggests an evolutionary link between transport systems for chemically distinct cyanobacterial siderophores. Our study reports the first functional heterologous expression of a cyanobacterial TonB-dependent transporter and establishes Synechocystis as a promising platform for cyanobacterial xenosiderophore-uptake studies.

microbiology↗

bioRxiv2026

Structural and Stereochemical Elucidation of Cyanochelin C, a Siderophore Associated with Novel Class of Cyanobacterial Acyl Hydrolases

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 {beta}-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.

microbiology↗

bioRxiv2025

Cyanochelin B: A siderophore produced by cyanobacterium Leptolyngbya sp. NIES-3755 with photolytic properties that negate iron monopolization in the UV-light

Siderophores are low-molecular-weight compounds excreted by microorganisms to facilitate iron uptake in times of its unavailability. Microbes may produce siderophores to monopolize iron and achieve competitive exclusion of other strains. Alternatively, siderophores may be exchanged for other substrates in mutualistic relationships. Siderophores that employ {beta}-hydroxy-aspartate ({beta}-OH-Asp) for iron chelation were shown to undergo UV-mediated photolytic cleavage with simultaneous reduction of Fe3+ to Fe2+. Photolytic siderophores can mediate algal-bacterial mutualism, where the bacteria provide iron in exchange for dissolved organic carbon. We use an interdisciplinary strategy to provide a complex characterization of cyanochelin B, a photolytic {beta}-OH-Asp-containing siderophore produced by filamentous cyanobacterium Leptolyngbya sp. NIES-3755. A combination of nuclear magnetic resonance, high resolution mass spectrometry and bioinformatic analyses complemented with Marfeys and Muratas methods yielded the structure of cyanochelin B with the configuration of its stereocenters. Cyanochelin B-iron complexes exposed to UV- light photolyze within minutes (t1/2 = 8.9 min; [~]3.5 uE UV-A) and release reduced Fe2+. We have co-cultured Leptolyngbya together with Synechocystis PCC6803 as a reporter strain lacking siderophore production. The cultivation setup was based on membrane-separated compartments accommodating individual strains and employed alginate-embedded FeCl3 to simulate poorly accessible precipitated iron. Our results demonstrate that in the absence of UV-light cyanochelin B can monopolize iron in favor of Leptolyngbya. However, UV-light eliminates any monopolization of iron and makes it available to competing organisms. Finally, we report the isolation of novel cyanochelin B-producing strains of Phormidesmis from field material and discuss the phenomenon of photolytic siderophores in a broader context. ImportanceIron is an essential micronutrient that is required by all living organisms as a cofactor of indispensable enzymes. Due to its specific properties it is mostly precipitated and biologically unavailable. To facilitate iron uptake, microbes produce siderophores - low-molecular-weight compounds that bind iron. Siderophores are mediators of microbial interactions and facilitate competitive exclusion of non-compatible strains or foster mutualistic partners and cheater strains. We report a full structural elucidation of cyanochelin B, a photolytic cyanobacterial siderophore that contains {beta}-OH-Asp. Our co-culture experiments show that cyanochelin B may monopolize iron to its producer or make it accessible to other strains depending on the presence of UV light. Moreover, our data suggest that the benefits from production of photolytic siderophores are not restricted to symbiotic partners of the producer but rather available to the whole irradiated community. Of known siderophores, 17.5% contain the photoreactive {beta}-OH-Asp and can function in a similar way.

microbiology↗

bioRxiv2021

Quorum sensing signals from epibiont mediate the induction of bioactive peptides in mat-forming cyanobacteria Nostoc

The regulation of oligopeptides production is essential in understanding their ecological role in complex microbial communities including harmful cyanobacterial blooms. The role of chemical communication between the cyanobacterium and the microbial community harboured as epibionts within its phycosphere is at an initial stage of research and little is understood about its specificity. Herein, we present insight into the role of a bacterial epibiont in regulating production of cyanobacterial oligopeptides microviridins, well-known elastase inhibitors with presumed anti-grazing effects, in an ecologically important cyanobacterial genus Nostoc. Heterologous expression and identification of specific signal molecules from the epibiont suggest the role of a quorum sensing-based interaction. Further, physiological experiments show an increase in microviridin production without affecting cyanobacterial growth and photosynthetic activity. Simultaneously, oligopeptides presenting a selective inhibition pattern provide support for their specific function in response to the presence of cohabitant epibionts. Thus, the chemical interaction revealed in our study provides an example of an interspecies signalling pathway monitoring the bacterial flora around the cyanobacterial filaments and induction of intrinsic species-specific metabolic responses. IMPORTANCEThe regulation of cyanopeptide production beyond microcystin is essential to understand their ecological role in complex microbial communities, e.g. harmful cyanobacterial blooms. The role of chemical communication between the cyanobacterium and the epibionts within its phycosphere is at an initial stage of research and little is understood about its specificity. The frequency of cyanopeptide occurrence also demonstrates the need to understand the contribution of cyanobacterial peptides to the overall biological impact of cyanopeptides on aquatic organisms and vertebrates including humans. Our results shed light on the epibiont control of cyanopeptide production via quorum sensing mechanisms and we posit that such mechanisms may be widespread in natural cyanobacterial bloom community regulation.

microbiology↗