Browsing publications of the research group microbial communication (KOM) by Title
Now showing items 86-89 of 89
A unique mechanism for methyl ester formation via an amide intermediate found in myxobacteria.Secondary metabolism involves a broad diversity of biochemical reactions that result in a wide variety of biologically active compounds. Terminal amide formation during the biosynthesis of the myxobacterial electron-transport inhibitor, myxothiazol, was analyzed by heterologous expression of the unique nonribosomal-peptide synthetase, MtaG, and incubation with a synthesized substrate mimic. These experiments provide evidence that the terminal amide is formed from a carrier protein-bound myxothiazol acid that is thioesterified to MtaF. This intermediate is transformed to an amide by extension with glycine and subsequent oxidative cleavage by MtaG. The final steps of melithiazol assembly involve a highly similar protein-bound intermediate (attached to MelF, a homologue of MtaF), which is transformed to an amide by MelG (homologue of MtaG). In this study, we also show that the amide moiety of myxothiazol A can be hydrolyzed in vivo to the formerly unknown free myxothiazol acid by heterologous expression of melJ in the myxothiazol producer Stigmatella aurantiaca DW4/3-1. The methyltransferase MelK can finally methylate the acid to give rise to the methyl ester, which is produced as the final product in the melithiazol A biosynthetic pathway. These experiments clarify the role of MelJ and MelK during melithiazol assembly.
An Unprecedented Medium-Chain Diunsaturated -acylhomoserine Lactone from Marine Group Bacteria.N-acylhomoserine lactones (AHLs), bacterial signaling compounds involved in quorum-sensing, are a structurally diverse group of compounds. We describe here the identification, synthesis, occurrence and biological activity of a new AHL, N-((2E,5Z)-2,5-dodecadienoyl)homoserine lactone (11) and its isomer N-((3E,5Z)-3,5-dodecadienoyl)homoserine lactone (13), occurring in several Roseobacter group bacteria (Rhodobacteraceae). The analysis of 26 strains revealed the presence of 11 and 13 in six of them originating from the surface of the macroalgae Fucus spiralis or sediments from the North Sea. In addition, 18 other AHLs were detected in 12 strains. Compound identification was performed by GC/MS. Mass spectral analysis revealed a diunsaturated C12 homoserine lactone as structural element of the new AHL. Synthesis of three likely candidate compounds, 11, 13 and N-((2E,4E)-2,4-dodecadienoyl)homoserine lactone (5), revealed the former to be the natural AHLs. Bioactivity test with quorum-sensing reporter strains showed high activity of all three compounds. Therefore, the configuration and stereochemistry of the double bonds in the acyl chain seemed to be unimportant for the activity, although the chains have largely different shapes, solely the chain length determining activity. In combination with previous results with other Roseobacter group bacteria, we could show that there is wide variance between AHL composition within the strains. Furthermore, no association of certain AHLs with different habitats like macroalgal surfaces or sediment could be detected. View Full-Text
The urinary microbiota of men and women and its changes in women during bacterial vaginosis and antibiotic treatment.The urinary microbiota is similarly complex as the vaginal and penile microbiota, yet its role as a reservoir for pathogens and for recurrent polymicrobial biofilm diseases like bacterial vaginosis (BV) is not clear.
Use of Single-Frequency Impedance Spectroscopy to Characterize the Growth Dynamics of Biofilm Formation in Pseudomonas aeruginosa.Impedance spectroscopy has been applied in prokaryotic and eukaryotic cytometry as a label-free method for the investigation of adherent cells. In this paper, its use for characterizing the growth dynamics of P. aeruginosa biofilms is described and compared to crystal violet staining and confocal microscopy. The method allows monitoring the growth of biofilm-forming P. aeruginosa in a continuous and label-free manner over a period of 72 h in a 96 well plate format. Impedance curves obtained for P. aeruginosa PA14 wild type and mutant strains with a transposon insertion in pqsA and pelA genes exhibited distinct phases. We propose that the slope of the declining curve following a maximum at ca. 35-40 h is a measure of biofilm formation. Transplant experiments with P. aeruginosa biofilms and paraffin suggest that the impedance also reflects pellicle formation at the liquid-air interface, a barely considered contributor to impedance. Finally, the impairment of biofilm formation upon treatment of cultures with L-arginine and with ciprofloxacin, tobramycin and meropenem was studied by single frequency impedance spectroscopy. We suggest that these findings qualify impedance spectroscopy as an additional technique to characterize biofilm formation and its modulation by small molecule drugs.