RETRACTED: A Self-Produced Trigger for Biofilm Disassembly that Targets Exopolysaccharide

This article has been retracted: please see Elsevier Policy on Article Withdrawal (http://www.elsevier.com/locate/withdrawalpolicy).This article has been retracted at the request of the authors. In this article, we reported that norspermidine is produced in aged biofilm cultures of Bacillus subtilis and that norspermidine could disassemble and inhibit B. subtilis biofilms. Both claims have been challenged by Hobley et al. (2014, Cell 156, 844–854). We have subsequently repeated the experiments and have found that the new results can no longer support our original conclusions. Therefore, the most appropriate course of action is to retract the article. We offer our apologies for these errors and for any inconvenience that they may have caused

In vitro models for studying implant-associated biofilms - A review from the perspective of bioengineering 3D microenvironments

Biofilm research has grown exponentially over the last decades, arguably due to their contribution to hospital acquired infections when they form on foreign body surfaces such as catheters and implants. Yet, translation of the knowledge acquired in the laboratory to the clinic has been slow and/or often it is not attempted by research teams to walk the talk of what is defined as 'bench to bedside'. We therefore reviewed the biofilm literature to better understand this gap. Our search revealed substantial development with respect to adapting surfaces and media used in models to mimic the clinical settings, however many of the in vitro models were too simplistic, often discounting the composition and properties of the host microenvironment and overlooking the biofilm-implant-host interactions. Failure to capture the physiological growth conditions of biofilms in vivo results in major differences between lab-grown- and clinically-relevant biofilms, particularly with respect to phenotypic profiles, virulence, and antimicrobial resistance, and they essentially impede bench-to-bedside translatability. In this review, we describe the complexity of the biological processes at the biofilm-implant-host interfaces, discuss the prerequisite for the development and characterization of biofilm models that better mimic the clinical scenario, and propose an interdisciplinary outlook of how to bioengineer biofilms in vitro by converging tissue engineering concepts and tools.</p

A Bacterial Biofilm Polysaccharide Affects the Morphology and Structure of Calcium Oxalate Crystals

Biomineralization describes the process of mineral precipitation from soluble precursors by living organisms. It is sometimes associated with single bacterial cells, for example, the formation of magnetosomes by magnetotactic bacteria, as well as with groups of bacterial cells that form biofilms and precipitate calcium carbonate (CaCO3). Recently, there has been growing evidence connecting isolated bacteria and bacterial biofilms with calcium oxalate (CaOx) formation in kidney stones. Therefore, in this study, we examined the effect of a principal exopolysaccharide bacterial biofilm component on the crystallization of CaOx. We observed that the exopolysaccharide, identified as levan, induced the formation of both octahedral CaOx dihydrate (COD, Weddellite) and pancake-like CaOx monohydrate crystals (COM, Whewellite) in a concentration-dependent manner. A combined analysis of the CaOx crystals that formed in the presence of levan, using scanning electron microscopy, Raman spectroscopy, and X-ray diffraction, indicated that levan affects both the nucleation and the growth of CaOx and that its interaction with CaOx is stereospecific. Given the emerging relation between bacterial biofilms and kidney stones, which are prevalent within approximately 12% of the worldwide population, it is important to decipher the effect of biofilm extracellular polymers on the formation of CaOx crystals as it may assist in the development of future treatments to interfere with kidney stone formation

Bacterial Model Membranes Reshape Fibrillation of a Functional Amyloid Protein

Biofilms are aggregates of cells that form surface-associated communities. The cells in biofilms are interconnected with an extracellular matrix, a network that is made mostly of polysaccharides, proteins, and sometimes nucleic acids. Some extracellular matrix proteins form fibers, termed functional amyloid or amyloid-like, to differentiate their constructive function from disease-related amyloid fibers. Recent functional amyloid assembly studies have neglected their interaction with membranes, despite their native formation in a cellular environment. Here, we use TasA, a major matrix protein in biofilms of the soil bacterium <i>Bacillus subtilis</i>, as a model functional amyloid protein and ask whether the bacterial functional amyloid interacts with membranes. Using biochemical, spectroscopic, and microscopic tools, we show that TasA interacts distinctively with bacterial model membranes and that this interaction mutually influences the morphology and structure of the protein and the membranes. At the protein level, fibers of similar structure and morphology are formed in the absence of membranes and in the presence of eukaryotic model membranes. However, in the presence of bacterial model membranes, TasA forms disordered aggregates with a different β sheet signature. At the membrane level, fluorescence microscopy and anisotropy measurements indicate that bacterial membranes deform more considerably than eukaryotic membranes upon interaction with TasA. Our findings suggest that TasA penetrates bacterial more than eukaryotic model membranes and that this leads to membrane disruption and to reshaping the TasA fiber formation pathway. Considering the important role of TasA in providing integrity to biofilms, our study may direct the design of antibiofilm drugs to the protein–membrane interface

Donor-strand exchange drives assembly of the TasA scaffold in Bacillus subtilis biofilms.

Many bacteria in nature exist in multicellular communities termed biofilms, where cells are embedded in an extracellular matrix that provides rigidity to the biofilm and protects cells from chemical and mechanical stresses. In the Gram-positive model bacterium Bacillus subtilis, TasA is the major protein component of the biofilm matrix, where it has been reported to form functional amyloid fibres contributing to biofilm structure and stability. Here, we present electron cryomicroscopy structures of TasA fibres, which show that, rather than forming amyloid fibrils, TasA monomers assemble into fibres through donor-strand exchange, with each subunit donating a β-strand to complete the fold of the next subunit along the fibre. Combining electron cryotomography, atomic force microscopy, and mutational studies, we show how TasA fibres congregate in three dimensions to form abundant fibre bundles that are essential for B. subtilis biofilm formation. Our study explains the previously observed biochemical properties of TasA and shows how a bacterial extracellular globular protein can assemble from monomers into β-sheet-rich fibres, and how such fibres assemble into bundles in biofilms

Dynamic metabolic exchange governs a marine algal-bacterial interaction

Emiliania huxleyi is a model coccolithophore micro-alga that generates vast blooms in the ocean. Bacteria are not considered among the major factors influencing coccolithophore physiology. Here we show through a laboratory model system that the bacterium Phaeobacter inhibens, a well-studied member of the Roseobacter group, intimately interacts with E. huxleyi. While attached to the algal cell, bacteria initially promote algal growth but ultimately kill their algal host. Both algal growth enhancement and algal death are driven by the bacterially-produced phytohormone indole-3-acetic acid. Bacterial production of indole-3-acetic acid and attachment to algae are significantly increased by tryptophan, which is exuded from the algal cell. Algal death triggered by bacteria involves activation of pathways unique to oxidative stress response and programmed cell death. Our observations suggest that bacteria greatly influence the physiology and metabolism of E. huxleyi. Coccolithophore-bacteria interactions should be further studied in the environment to determine whether they impact micro-algal population dynamics on a global scale. DOI: http://dx.doi.org/10.7554/eLife.17473.00