BACKGROUND: Mineral iron(III) recognition by bacteria is considered a matter of debate. The peculiar surface chemistry of novel naked magnetic nanoparticles, called SAMNs (surface active maghemite nanoparticles) characterized by solvent exposed Fe(3+) sites on their surface, was exploited for studying mineral iron sensing in Pseudomonas fluorescens. METHODS: SAMNs were applied for mimicking Fe(3+) ions in solution, acting as magnetically drivable probes to evaluate putative Fe(3+) recognition sites on the microorganism surface. Culture broths and nano-bio-conjugates were characterized by UV-Vis spectroscopy and mass spectrometry. RESULTS: The whole heritage of a membrane porin (OprF) of P. fluorescens Ps_22 cells was recognized and firmly bound by SAMNs. The binding of nanoparticles to OprF porin was correlated to a drastic inhibition of a siderophore (pyoverdine) biosynthesis and to the stimulation of the production and rate of formation of a secondary siderophore. The analysis of metabolic pathways, based on P. fluorescens Ps_22 genomic information, evidenced that this putative secondary siderophore does not belong to a selection of the most common siderophores. CONCLUSIONS: In the scenario of an adhesion mechanism, it is plausible to consider OprF as the biological component deputed to the mineral iron sensing in P. fluorescens Ps_22, as well as one key of siderophore regulation. GENERAL SIGNIFICANCE: The present work sheds light on mineral iron sensing in microorganisms. Peculiar colloidal naked iron oxide nanoparticles offer a useful approach for probing the adhesion of bacterial surface on mineral iron for the identification of the specific recognition site for this iron uptake regulation in microorganisms.

• Klíčová slova
• Bacteria, Iron sensing, Maghemite nanoparticles, Membrane proteins, Oprf porin, Siderophores,
• MeSH
• bakteriální adheze genetika   MeSH
• magnetické nanočástice chemie   MeSH
• minerály chemie   metabolismus   MeSH
• poriny chemie   genetika   metabolismus   MeSH
• povrchově aktivní látky chemie   MeSH
• proteiny vnější bakteriální membrány chemie   genetika   metabolismus   MeSH
• Pseudomonas fluorescens chemie   metabolismus   MeSH
• železité sloučeniny chemie   MeSH
• železo chemie   MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• ferric oxide MeSH Prohlížeč
• magnetické nanočástice MeSH
• minerály MeSH
• poriny MeSH
• povrchově aktivní látky MeSH
• proteiny vnější bakteriální membrány MeSH
• železité sloučeniny MeSH
• železo MeSH

Pseudomonas fluorescens is a well-known food spoiler, able to cause serious economic losses in the food industry due to its ability to produce many extracellular, and often thermostable, compounds. The most outstanding spoilage events involving P. fluorescens were blue discoloration of several food stuffs, mainly dairy products. The bacteria involved in such high-profile cases have been identified as belonging to a clearly distinct phylogenetic cluster of the P. fluorescens group. Although the blue pigment has recently been investigated in several studies, the biosynthetic pathway leading to the pigment formation, as well as its chemical nature, remain challenging and unsolved points. In the present paper, genomic and transcriptomic data of 4 P. fluorescens strains (2 blue-pigmenting strains and 2 non-pigmenting strains) were analyzed to evaluate the presence and the expression of blue strain-specific genes. In particular, the pangenome analysis showed the presence in the blue-pigmenting strains of two copies of genes involved in the tryptophan biosynthesis pathway (including trpABCDF). The global expression profiling of blue-pigmenting strains versus non-pigmenting strains showed a general up-regulation of genes involved in iron uptake and a down-regulation of genes involved in primary metabolism. Chromogenic reaction of the blue-pigmenting bacterial cells with Kovac's reagent indicated an indole-derivative as the precursor of the blue pigment. Finally, solubility tests and MALDI-TOF mass spectrometry analysis of the isolated pigment suggested that its molecular structure is very probably a hydrophobic indigo analog.

• Klíčová slova
• Blue mozzarella, Comparative genomics and transcriptomics, Pseudomonas fluorescens,
• MeSH
• biologické pigmenty genetika   MeSH
• down regulace MeSH
• energetický metabolismus genetika   MeSH
• fenotyp MeSH
• fylogeneze MeSH
• genomika MeSH
• mléčné výrobky mikrobiologie   MeSH
• oxidoreduktasy genetika   MeSH
• potravinářská mikrobiologie * MeSH
• Pseudomonas fluorescens genetika   metabolismus   MeSH
• spotřeba kyslíku genetika   MeSH
• stanovení celkové genové exprese MeSH
• transkriptom genetika   MeSH
• tryptofan biosyntéza   MeSH
• upregulace MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• biologické pigmenty MeSH
• oxidoreduktasy MeSH
• tryptofan MeSH