ORCID Profile
0000-0002-9751-474X
Current Organisations
IT University of Copenhagen
,
Københavns Universitet
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Publisher: Wiley
Date: 22-11-2017
DOI: 10.1002/MBO3.552
Publisher: Wiley
Date: 04-02-2005
Publisher: Cold Spring Harbor Laboratory
Date: 08-11-2016
DOI: 10.1101/086413
Abstract: Animals have evolved to maintain homeostasis in a changing external environment by adapting their internal metabolism and feeding behaviour. Metabolism and behaviour are coordinated by neuromodulation a number of the implicated neuromodulatory systems are homologous between mammals and the vinegar fly, an important neurogenetic model. We investigated whether silencing fly neuromodulatory networks would elicit coordinated changes in feeding, behavioural activity and metabolism. We employed transgenic lines that allowed us to inhibit broad cellular sets of the dopaminergic, serotonergic, octopaminergic, tyraminergic and neuropeptide F systems. The genetically-manipulated animals were assessed for changes in their overt behavioural responses and metabolism by monitoring eleven parameters: activity climbing ability in idual feeding group feeding food discovery both fed and starved respiration fed and starved lipid content and fed/starved body weight. The results from these 55 experiments indicate that in idual neuromodulatory system effects on feeding behaviour, motor activity and metabolism are dissociated.
Publisher: Frontiers Media SA
Date: 17-10-2017
Publisher: Springer Science and Business Media LLC
Date: 20-05-2015
DOI: 10.1038/SREP10052
Abstract: Stress response plays an important role on microbial adaptation under hostile environmental conditions. It is generally unclear how the signaling transduction pathway mediates a stress response in planktonic and biofilm modes of microbial communities simultaneously. Here, we showed that metalloid tellurite (TeO 3 2– ) exposure induced the intracellular content of the secondary messenger cyclic di-GMP (c-di-GMP) of Pseudomonas aeruginosa . Two diguanylate cyclases (DGCs), SadC and SiaD, were responsible for the increased intracellular content of c-di-GMP. Enhanced c-di-GMP levels by TeO 3 2– further increased P. aeruginosa biofilm formation and resistance to TeO 3 2– . P. aeruginosa Δ sadC Δ siaD and PAO1 lac - yhjH mutants with low intracellular c-di-GMP content were more sensitive to TeO 3 2– exposure and had low relative fitness compared to the wild-type PAO1 planktonic and biofilm cultures exposed to TeO 3 2– . Our study provided evidence that c-di-GMP level can play an important role in mediating stress response in microbial communities during both planktonic and biofilm modes of growth.
Publisher: American Society for Microbiology
Date: 18-08-2022
DOI: 10.1128/IAI.00061-22
Abstract: Pseudomonas aeruginosa is generally believed to establish biofilm-associated infections under the regulation of the secondary messenger c-di-GMP. To evaluate P. aeruginosa biofilm physiology during ocular infections, comparative transcriptomic analysis was performed on wild-type P. aeruginosa PAO1, a Δ wspF mutant strain (high c-di-GMP levels), and a p lac - yhjH -containing strain (low c-di-GMP levels) from mouse corneal infection, as well as in vitro biofilm and planktonic cultures. The c-di-GMP content in P. aeruginosa during corneal infection was monitored using a fluorescent c-di-GMP reporter strain. Biofilm-related genes were induced in in vivo PAO1 compared to in vitro planktonic bacteria. Several diguanylate cyclases and phosphodiesterases were commonly regulated in in vivo PAO1 and in vitro biofilm compared to in vitro planktonic bacteria.
Publisher: Springer Science and Business Media LLC
Date: 21-07-2014
DOI: 10.1038/NCOMMS5462
Abstract: Bacteria assume distinct lifestyles during the planktonic and biofilm modes of growth. Increased levels of the intracellular messenger c-di-GMP determine the transition from planktonic to biofilm growth, while a reduction causes biofilm dispersal. It is generally assumed that cells dispersed from biofilms immediately go into the planktonic growth phase. Here we use single-nucleotide resolution transcriptomic analysis to show that the physiology of dispersed cells from Pseudomonas aeruginosa biofilms is highly different from those of planktonic and biofilm cells. In dispersed cells, the expression of the small regulatory RNAs RsmY and RsmZ is downregulated, whereas secretion genes are induced. Dispersed cells are highly virulent against macrophages and Caenorhabditis elegans compared with planktonic cells. In addition, they are highly sensitive towards iron stress, and the combination of a biofilm-dispersing agent, an iron chelator and tobramycin efficiently reduces the survival of the dispersed cells.
Publisher: Wiley
Date: 12-12-2005
DOI: 10.1111/J.1365-2958.2005.05008.X
Abstract: Pseudomonas aeruginosa produces extracellular DNA which functions as a cell-to-cell interconnecting matrix component in biofilms. Comparison of extracellular DNA and chromosomal DNA by the use of polymerase chain reaction and Southern analysis suggested that the extracellular DNA is similar to whole-genome DNA. Evidence that the extracellular DNA in P. aeruginosa biofilms and cultures is generated via lysis of a subpopulation of the bacteria was obtained through experiments where extracellular beta-galactosidase released from lacZ-containing P. aeruginosa strains was assessed. Experiments with the wild type and lasIrhlI, pqsA, pqsL and fliMpilA mutants indicated that the extracellular DNA is generated via a mechanism which is dependent on acyl homoserine lactone and Pseudomonas quinolone signalling, as well as on flagella and type IV pili. Microscopic investigation of flow chamber-grown wild-type P. aeruginosa biofilms stained with different DNA stains suggested that the extracellular DNA is located primarily in the stalks of mushroom-shaped multicellular structures, with a high concentration especially in the outer part of the stalks forming a border between the stalk-forming bacteria and the cap-forming bacteria. Biofilms formed by lasIrhlI, pqsA and fliMpilA mutants contained less extracellular DNA than biofilms formed by the wild type, and the mutant biofilms were more susceptible to treatment with sodium dodecyl sulphate than the wild-type biofilm.
Publisher: Frontiers Media SA
Date: 07-10-2015
Publisher: Cold Spring Harbor Laboratory
Date: 06-01-2017
DOI: 10.1101/098749
Abstract: Biofilms are extremely tolerant toward antimicrobial treatment and host immune clearance due to their distinct physiology and protection by extracellular polymeric substances. Bis-(3´-5´)-cyclic dimeric guanosine monophosphate (c-di-GMP) is an essential messenger that regulates biofilm formation by a wide range of bacteria. However, there is a lack of physiological characterization of biofilms in vivo as well as the roles of c-di-GMP signaling in mediating host-biofilm interactions. Here, we employed dual RNA-Seq to characterize the host and pathogen transcriptomes during Pseudomonas aeruginosa infection using a mouse keratitis model. In vivo P. aeruginosa biofilms maintained a distinct physiology compared with in vitro P. aeruginosa biofilms, with enhanced virulence and iron uptake capacity. C-di-GMP synthesis was enhanced in P. aeruginosa cells in vivo, potentially due to down-regulation of the expression of several phosphodiesterases (e.g., DipA, NbdA). Increased intracellular c-di-GMP levels were required for long-term ocular colonization of P. aeruginosa and impaired host innate immunity.
Publisher: American Society for Microbiology
Date: 05-2013
DOI: 10.1128/AAC.02499-12
Abstract: Bis-(3′-5′)-cyclic dimeric GMP (c-di-GMP) is an intracellular second messenger that controls the lifestyles of many bacteria. A high intracellular level of c-di-GMP induces a biofilm lifestyle, whereas a low intracellular level of c-di-GMP stimulates dispersal of biofilms and promotes a planktonic lifestyle. Here, we used the expression of different reporters to show that planktonic cells, biofilm cells, and cells dispersed from biofilms (DCells) had distinct intracellular c-di-GMP levels. Proteomics analysis showed that the low intracellular c-di-GMP level of DCells induced the expression of proteins required for the virulence and development of antimicrobial peptide resistance in Pseudomonas aeruginosa . In accordance with this, P. aeruginosa cells with low c-di-GMP levels were found to be more resistant to colistin than P. aeruginosa cells with high c-di-GMP levels. This finding contradicts the current dogma stating that dispersed cells are inevitably more susceptible to antibiotics than their sessile counterparts.
Publisher: Springer Science and Business Media LLC
Date: 22-09-2021
DOI: 10.1186/S12866-021-02318-8
Abstract: Biofilms disperse in response to specific environmental cues, such as reduced oxygen concentration, changes in nutrient concentration and exposure to nitric oxide. Interestingly, biofilms do not completely disperse under these conditions, which is generally attributed to physiological heterogeneity of the biofilm. However, our results suggest that genetic heterogeneity also plays an important role in the non-dispersing population of P. aeruginosa in biofilms after nutrient starvation. In this study, 12.2% of the biofilm failed to disperse after 4 d of continuous starvation-induced dispersal. Cells were recovered from the dispersal phase as well as the remaining biofilm. For 96 h starved biofilms, rugose small colony variants (RSCV) were found to be present in the biofilm, but were not observed in the dispersal effluent. In contrast, wild type and small colony variants (SCV) were found in high numbers in the dispersal phase. Genome sequencing of these variants showed that most had single nucleotide mutations in genes associated with biofilm formation, e.g. in wspF, pilT , fha1 and aguR . Complementation of those mutations restored starvation-induced dispersal from the biofilms. Because c-di-GMP is linked to biofilm formation and dispersal, we introduced a c-di-GMP reporter into the wild-type P. aeruginosa and monitored green fluorescent protein (GFP) expression before and after starvation-induced dispersal. Post dispersal, the microcolonies were smaller and significantly brighter in GFP intensity, suggesting the relative concentration of c-di-GMP per cell within the microcolonies was also increased. Furthermore, only the RSCV showed increased c-di-GMP, while wild type and SCV were no different from the parental strain. This suggests that while starvation can induce dispersal from the biofilm, it also results in strong selection for mutants that overproduce c-di-GMP and that fail to disperse in response to the dispersal cue, starvation.
Publisher: Wiley
Date: 26-03-2008
Publisher: Springer Science and Business Media LLC
Date: 29-08-2017
DOI: 10.1038/S41598-017-09886-8
Abstract: For the last decade, chemical control of bacterial virulence has received considerable attention. Ajoene, a sulfur-rich molecule from garlic has been shown to reduce expression of key quorum sensing regulated virulence factors in the opportunistic pathogen Pseudomonas aeruginosa . Here we show that the repressing effect of ajoene on quorum sensing occurs by inhibition of small regulatory RNAs (sRNA) in P . aeruginosa as well as in Staphylococcus aureus , another important human pathogen that employs quorum sensing to control virulence gene expression. Using various reporter constructs, we found that ajoene lowered expression of the sRNAs RsmY and RsmZ in P . aeruginosa and the small dual-function regulatory RNA, RNAIII in S . aureus , that controls expression of key virulence factors. We confirmed the modulation of RNAIII by RNA sequencing and found that the expression of many QS regulated genes encoding virulence factors such as hemolysins and proteases were lowered in the presence of ajoene in S . aureus . Importantly, our findings show that sRNAs across bacterial species potentially may qualify as targets of anti-virulence therapy and that ajoene could be a lead structure in search of broad-spectrum compounds transcending the Gram negative-positive borderline.
Publisher: American Society for Microbiology
Date: 08-2003
DOI: 10.1128/JB.185.15.4585-4592.2003
Abstract: Bacteria growing in biofilms often develop multicellular, three-dimensional structures known as microcolonies. Complex differentiation within biofilms of Pseudomonas aeruginosa occurs, leading to the creation of voids inside microcolonies and to the dispersal of cells from within these voids. However, key developmental processes regulating these events are poorly understood. A normal component of multicellular development is cell death. Here we report that a repeatable pattern of cell death and lysis occurs in biofilms of P. aeruginosa during the normal course of development. Cell death occurred with temporal and spatial organization within biofilms, inside microcolonies, when the biofilms were allowed to develop in continuous-culture flow cells. A subpopulation of viable cells was always observed in these regions. During the onset of biofilm killing and during biofilm development thereafter, a bacteriophage capable of superinfecting and lysing the P. aeruginosa parent strain was detected in the fluid effluent from the biofilm. The bacteriophage implicated in biofilm killing was closely related to the filamentous phage Pf1 and existed as a prophage within the genome of P. aeruginosa . We propose that prophage-mediated cell death is an important mechanism of differentiation inside microcolonies that facilitates dispersal of a subpopulation of surviving cells.
Location: United Kingdom of Great Britain and Northern Ireland
No related grants have been discovered for Tim Tolker-Nielsen.