Morten Hentzer

Bio: Morten Hentzer is an academic researcher from Technical University of Denmark. The author has contributed to research in topics: Pseudomonas aeruginosa & Biofilm. The author has an hindex of 25, co-authored 28 publications receiving 7886 citations. Previous affiliations of Morten Hentzer include University of Copenhagen.

Quantification of biofilm structures by the novel computer program COMSTAT.

Abstract: The structural organization of four microbial communities was analysed by a novel computer program, COMSTAT, which comprises ten features for quantifying three-dimensional biofilm image stacks. Monospecies biofilms of each of the four bacteria, Pseudomonas putida, P. aureofaciens, P. fluorescens and P. aeruginosa, tagged with the green fluorescent protein (GFP) were grown in flow chambers with a defined minimal medium as substrate. Analysis by the COMSTAT program of four variables describing biofilm structure ‐ mean thickness, roughness, substratum coverage and surface to volume ratio ‐ showed that the four Pseudomonas strains represent different modes of biofilm growth. P. putida had a unique developmental pattern starting with single cells on the substratum growing into micro-colonies, which were eventually succeeded by long filaments and elongated cell clusters. P. aeruginosa colonized the entire substratum, and formed flat, uniform biofilms. P. aureofaciens resembled P. aeruginosa, but had a stronger tendency to form micro-colonies. Finally, the biofilm structures of P. fluorescens had a phenotype intermediate between those of P. putida and P. aureofaciens. Analysis of biofilms of P. aureofaciens growing on 0<03 mM, 0< 1m M or 0< 5m M citrate minimal media showed that mean biofilm thickness increased with increasing citrate concentration. Moreover, biofilm roughness increased with lower citrate concentrations, whereas surface to volume ratio increased with higher citrate concentrations.

Alginate Overproduction Affects Pseudomonas aeruginosa Biofilm Structure and Function

Abstract: During the course of chronic cystic fibrosis (CF) infections, Pseudomonas aeruginosa undergoes a conversion to a mucoid phenotype, which is characterized by overproduction of the exopolysaccharide alginate. Chronic P. aeruginosa infections involve surface-attached, highly antibiotic-resistant communities of microorganisms organized in biofilms. Although biofilm formation and the conversion to mucoidy are both important aspects of CF pathogenesis, the relationship between them is at the present unclear. In this study, we report that the overproduction of alginate affects biofilm development on an abiotic surface. Biofilms formed by an alginate-overproducing strain exhibit a highly structured architecture and are significantly more resistant to the antibiotic tobramycin than a biofilm formed by an isogenic nonmucoid strain. These results suggest that an important consequence of the conversion to mucoidy is an altered biofilm architecture that shows increasing resistance to antimicrobial treatments.

Screening for Quorum-Sensing Inhibitors (QSI) by Use of a Novel Genetic System, the QSI Selector

Abstract: With the widespread appearance of antibiotic-resistant bacteria, there is an increasing demand for novel strategies to control infectious diseases. Furthermore, it has become apparent that the bacterial life style also contributes significantly to this problem. Bacteria living in the biofilm mode of growth tolerate conventional antimicrobial treatments. The discovery that many bacteria use quorum-sensing (QS) systems to coordinate virulence and biofilm development has pointed out a new, promising target for antimicrobial drugs. We constructed a collection of screening systems, QS inhibitor (QSI) selectors, which enabled us to identify a number of novel QSIs among natural and synthetic compound libraries. The two most active were garlic extract and 4-nitro-pyridine-N-oxide (4-NPO). GeneChip-based transcriptome analysis revealed that garlic extract and 4-NPO had specificity for QS-controlled virulence genes in Pseudomonas aeruginosa. These two QSIs also significantly reduced P. aeruginosa biofilm tolerance to tobramycin treatment as well as virulence in a Caenorhabditis elegans pathogenesis model.

Pseudomonas aeruginosa tolerance to tobramycin, hydrogen peroxide and polymorphonuclear leukocytes is quorum-sensing dependent

Abstract: The opportunistic human pathogen Pseudomonas aeruginosa is the predominant micro-organism of chronic lung infections in cystic fibrosis (CF) patients. P. aeruginosa colonizes the CF lungs by forming biofilm structures in the alveoli. In the biofilm mode of growth the bacteria are highly tolerant to otherwise lethal doses of antibiotics and are protected from bactericidal activity of polymorphonuclear leukocytes (PMNs). P. aeruginosa controls the expression of many of its virulence factors by means of a cell-cell communication system termed quorum sensing (QS). In the present report it is demonstrated that biofilm bacteria in which QS is blocked either by mutation or by administration of QS inhibitory drugs are sensitive to treatment with tobramycin and H2O2, and are readily phagocytosed by PMNs, in contrast to bacteria with functional QS systems. In contrast to the wild-type, QS-deficient biofilms led to an immediate respiratory-burst activation of the PMNs in vitro. In vivo QS-deficient mutants provoked a higher degree of inflammation. It is suggested that quorum signals and QS-inhibitory drugs play direct and opposite roles in this process. Consequently, the faster and highly efficient clearance of QS-deficient bacteria in vivo is probably a two-sided phenomenon: down regulation of virulence and activation of the innate immune system. These data also suggest that a combination of the action of PMNs and QS inhibitors along with conventional antibiotics would eliminate the biofilm-forming bacteria before a chronic infection is established.

The cep quorum-sensing system of Burkholderia cepacia H111 controls biofilm formation and swarming motility

Abstract: Burkholderia cepacia and Pseudomonas aeruginosa often co-exist as mixed biofilms in the lungs of patients suffering from cystic fibrosis (CF). Here, the isolation of random mini-Tn5 insertion mutants of B. cepacia H111 defective in biofilm formation on an abiotic surface is reported. It is demonstrated that one of these mutants no longer produces N-acylhomoserine lactones (AHLs) due to an inactivation of the cepR gene. cepR and the cepI AHL synthase gene together constitute the cep quorum-sensing system of B. cepacia. By using a gene replacement method, two defined mutants, H111-I and H111-R, were constructed in which cepI and cepR, respectively, had been inactivated. These mutants were used to demonstrate that biofilm formation by B. cepacia H111 requires a functional cep quorum-sensing system. A detailed quantitative analysis of the biofilm structures formed by wild-type and mutant strains suggested that the quorum-sensing system is not involved in the regulation of initial cell attachment, but rather controls the maturation of the biofilm. Furthermore, it is shown that B. cepacia is capable of swarming motility, a form of surface translocation utilized by various bacteria to rapidly colonize appropriate substrata. Evidence is provided that swarming motility of B. cepacia is quorum-sensing-regulated, possibly through the control of biosurfactant production. Complementation of the cepR mutant H111-R with different biosurfactants restored swarming motility while biofilm formation was not significantly increased. This result suggests that swarming motility per se is not essential for biofilm formation on abiotic surfaces.

Bacterial biofilms: from the natural environment to infectious diseases.

Abstract: Biofilms--matrix-enclosed microbial accretions that adhere to biological or non-biological surfaces--represent a significant and incompletely understood mode of growth for bacteria. Biofilm formation appears early in the fossil record (approximately 3.25 billion years ago) and is common throughout a diverse range of organisms in both the Archaea and Bacteria lineages, including the 'living fossils' in the most deeply dividing branches of the phylogenetic tree. It is evident that biofilm formation is an ancient and integral component of the prokaryotic life cycle, and is a key factor for survival in diverse environments. Recent advances show that biofilms are structurally complex, dynamic systems with attributes of both primordial multicellular organisms and multifaceted ecosystems. Biofilm formation represents a protected mode of growth that allows cells to survive in hostile environments and also disperse to colonize new niches. The implications of these survival and propagative mechanisms in the context of both the natural environment and infectious diseases are discussed in this review.

Biofilms: an emergent form of bacterial life.

Abstract: Bacterial biofilms are formed by communities that are embedded in a self-produced matrix of extracellular polymeric substances (EPS). Importantly, bacteria in biofilms exhibit a set of 'emergent properties' that differ substantially from free-living bacterial cells. In this Review, we consider the fundamental role of the biofilm matrix in establishing the emergent properties of biofilms, describing how the characteristic features of biofilms - such as social cooperation, resource capture and enhanced survival of exposure to antimicrobials - all rely on the structural and functional properties of the matrix. Finally, we highlight the value of an ecological perspective in the study of the emergent properties of biofilms, which enables an appreciation of the ecological success of biofilms as habitat formers and, more generally, as a bacterial lifestyle.

Biofilms as complex differentiated communities.

Abstract: Prokaryotic biofilms that predominate in a diverse range of ecosystems are often composed of highly structured multispecies communities. Within these communities metabolic activities are integrated, and developmental sequences, not unlike those of multicellular organisms, can be detected. These structural adaptations and interrelationships are made possible by the expression of sets of genes that result in phenotypes that differ profoundly from those of planktonically grown cells of the same species. Molecular and microscopic evidence suggest the existence of a succession of de facto biofilm phenotypes. We submit that complex cell-cell interactions within prokaryotic communities are an ancient characteristic, the development of which was facilitated by the localization of cells at surfaces. In addition to spatial localization, surfaces may have provided the protective niche in which attached cells could create a localized homeostatic environment. In a holistic sense both biofilm and planktonic phenotypes may be viewed as integrated components of prokaryote life.

Metagenomics: Application of Genomics to Uncultured Microorganisms

Abstract: Metagenomics (also referred to as environmental and community genomics) is the genomic analysis of microorganisms by direct extraction and cloning of DNA from an assemblage of microorganisms. The development of metagenomics stemmed from the ineluctable evidence that as-yet-uncultured microorganisms represent the vast majority of organisms in most environments on earth. This evidence was derived from analyses of 16S rRNA gene sequences amplified directly from the environment, an approach that avoided the bias imposed by culturing and led to the discovery of vast new lineages of microbial life. Although the portrait of the microbial world was revolutionized by analysis of 16S rRNA genes, such studies yielded only a phylogenetic description of community membership, providing little insight into the genetics, physiology, and biochemistry of the members. Metagenomics provides a second tier of technical innovation that facilitates study of the physiology and ecology of environmental microorganisms. Novel genes and gene products discovered through metagenomics include the first bacteriorhodopsin of bacterial origin; novel small molecules with antimicrobial activity; and new members of families of known proteins, such as an Na+(Li+)/H+ antiporter, RecA, DNA polymerase, and antibiotic resistance determinants. Reassembly of multiple genomes has provided insight into energy and nutrient cycling within the community, genome structure, gene function, population genetics and microheterogeneity, and lateral gene transfer among members of an uncultured community. The application of metagenomic sequence information will facilitate the design of better culturing strategies to link genomic analysis with pure culture studies.