Biofilms最新文献

Through their special way of life, biofilms have several advantages over organisms in planktonic growth. By being surface-attached and producing a mass of extracellular polymeric substances (EPS), microorganisms possess inherent self-immobilization, which decreases the expenditure of downstream processing in industrial applications. Furthermore, they are more resilient against environmental stress and toxic substances, such as antibiotics. An important factor here is diffusion, of substrate into the biofilm and metabolites through and out of the biofilm; however, these mechanisms are still poorly understood. By utilizing a specially developed diffusion model and CLSM FRAP microscopy, diffusion constants in the living, fully hydrated biofilm of L. lactis during development can be assessed. With it, heatmaps of diffusional constants and finally a diffusion profile encompassing a true 3D space of the living biofilm in growth can be generated. With those, possible hotspots and changes of diffusion inside the biofilm structure with regard to changing cultivation conditions and the substratum can be identified, thus furthering our understanding of diffusion in biofilms and how they react to their environment.

The project is funded by the DFG (UL 170/14-1) and the collaborative research center (SFB) 926 on “microscale morphology of component surfaces” (MICOS).

Chronic wounds, for instance venous, pressure, arterial and diabetic ulcers, are a major health problem throughout the world. Compared with normal wounds, those that take more than four weeks to heal are defined as chronic. Interestingly, the numbers of patients suffering from chronic wounds and the cost for treatment have been increasing during the past two decades. There is increasing evidence that suggests that bacteria infect those chronic wounds and there exist as a biofilm, which affects wound healing and success of treatment. To study biofilms in infected wounds, both in vitro and in vivo biofilm models are important to be developed.

In this project, a dynamic ex vivo chronic wound biofilm model for Staphylococcus aureus using a 3D printed chamber and porcine skin was developed. This dynamic model then used to determine antibiotic treatment by using poly(ε‐caprolactone) (PCL) electrospun fibrous mats containing different antibiotics, e.g. tetracycline, gentamicin and fusidic acid. Furthermore, electrospun PCL/silk fibroin scaffolds were also used as carrier of gentamicin. The killing effect of mature S. aureus MRSA 252 growing in the wound model was tested by both viable count and qPCR.

The results indicated that this newly designed dynamic model was successful in mimicking single-strain biofilm on infected chronic wounds. Compared with traditional biofilm assays, the flow system generates an air-liquid-solid interface, which more closely approaches to real conditions. Furthermore, results from using electrospun fibrous scaffolds provided strong evidence for their potential in clinical applications to treat infected skin.

Marine fouling biofilms typically have diverse community assemblages in which microalgae are strongly represented.  The visible light absorption properties of microalgal photosynthetic pigments typically drive the overall visible light reflectance spectra of these biofilms.  In some cases diagnostic spectral features can be used to infer algal taxonomy, while in mixed communities the overlapping pigment signatures of the constituent species often blur together.  In this study, we apply methods common in remote sensing approaches to spectral data to extract information from subtle variations in the reflectance spectra of mixed composition marine biofilms.  We demonstrate that marine biofilm community composition, as evidenced by their reflectance spectra, is both spatially heterogenous and spatially structured.

Visible-NIR hyperspectral images (3.3nm x 200 bands) of biofilms grown on 7.5cm x 7.5cm panels (n=9), immersed in a coastal marina at ~1m depth for 13 months, were captured with a benchtop line-scan imager.   The hyperspectral data were smoothed and transformed to consolidate the major aspects of spectral variability.  A novel active learning spectral classification method incorporating iterative spectral library building by k-means clustering and spectral angle mapping, followed by hierarchical clustering by spectral similarity, discovered more than 70 distinct spectral classes present in the biofilms.  Accordingly, the hyperspectral images of the fouling biofilms were converted to spatially explicit spectral class maps, where each class was assumed representative of a distinct community compositional mix.  Hyperspectral indexing calibrated to chl a surface area density was used to map biomass for the same images. 

Cross-tabulating the spectral class and biomass data, it was apparent that for these biofilms, different biomass density levels were consistently associated with specific community compositions (spectral classes.)  Only a small number of the possible classes were represented in the densest areas of biofilm, suggesting that these species composition mixes have a competitive advantage.  In contrast, the full diversity of class types was present in the low biomass areas. 

Our hyperspectral approach does not convey exact species composition, as would pooled metagenomic sampling or in-depth microscopy.  However it does allow for the examination of spatially explicit changes in biofilm composition at relatively large scales (the landscape), and so may be a useful tool in hypothesis generation, long term monitoring, and other environmental biofilm applications.

Feast-famine moving bed biofilm reactors (MBBRs) were found to be removing a number of organic micropollutants effectively from wastewater in previous studies. It was hypothesized that micropollutant-degrading organisms in the biofilm communities were possibly enriched by feast-famine selective pressure. We established a MBBR operated in feast-famine regimes (alternating influent/effluent wastewater) to test the hypothesis. The development of degradation kinetics of 36 micropollutants and the microbial communities in the biofilm were assessed simultaneously for 19 time points during the 70-day adaptation.

During this adaptation, 16S rRNA gene amplicon sequencing showed that the microbial communities shifted greatly from the initial biofilm composition in the first 8 days toward a more steady development afterwards. Ammonia oxidizing bacteria (Nitrosomonas) and nitrite oxidizing bacteria (Nitrospira) were strongly enriched (both > 18 % relative abundance at day 43), which led to high nitrification capability. Notably, the biofilm absorbed and nitrified ammonia during the feast regime, while releasing stored nitrate during the famine regime. Twenty-four out of studied 36 micropollutants showed enhanced reaction rate constants k (especially for propranolol up to 6600 %) during the adaptation. Maximum k values were observed between day 22 and 67 during the adaptation. DNA concentration in the biofilm was used as a proxy for biomass, and normalized reaction rate constants relative to the DNA concentration as k_DNA were used for understanding the degradation reaction rates of MPs per DNA concentration unit. During the adaptation, the DNA concentration continuously increased suggesting growth and accumulation of microorganisms. However, k_DNA of 21 micropollutants showed a decreased removal after day 11, which suggests the relative abundance of the respective degraders decreased while their absolute abundance increased. It suggests that the colonization rates of the MP degraders were slower than the non-degraders under the selective pressure of the feast-famine regime. By mining correlations between the microbial community and k_DNA of micropollutants, 88 operational taxonomic units (OTUs) belonging to different taxonomic groups were found to correlate significantly with removal rates of micropollutants (Pearson correlation coefficients, r > 0.5, p < 0.05). Thus, these identified OTUs are potential candidates as the degraders of the respective micropollutants. In summary, the feast-famine strategy was successful for enhancing the degradation of some compounds, but the feast-famine regime in this study was not successful in selecting microorganisms in biofilm with high removal capability for many micropollutants. Nevertheless, this study contributed to a better understanding of what occurred during the adaptation process of biofilms with potential for micropollutant degradation.

Biofilm development on medical devices is of particular concern and finding new strategies for preventing surface colonization and infection development are urgent. Antimicrobial biosurfactants such as rhamnolipids (RLs), emerge as one possible solution due their lack of resistance development. Using nanoparticles as delivery systems for these compounds may be a promising alternative in the context of biofilm-infections control. As such, the aim of this study was to encapsulate RLs into chitosan nanoparticles (RLs-NPs), test their antimicrobial activity and their biocompatibility profile.

Blank nanoparticles (b-NPs) and RLs-NPs were prepared by ionic gelation. For particles characterization, zeta potential, size distribution and encapsulation efficiency were performed. Minimal inhibitory concentration and biofilm inhibition ability were evaluated towards Staphylococcus aureus (ATCC 25923). To access NPs cytocompatibility the in vitro tetrazolium dye assay (MTT) and morphology observation were performed with a mouse fibroblastic cell line (L929).

RLs-NPs presented an encapsulation efficiency of 74.2±1.3%, a size ranging from 300 to 400 nm and a zeta potential of  37±1 mV. The minimum inhibitory concentration of RLs-NPs was 130 mg/mL and a 99% biofilm inhibition was achieved with these NPs meaning that their antimicrobial activity is also effective towards sessile bacteria. When compared to control, cell cultures grown in the presence of RLs-NPs presented no significant differences regarding the MTT reduction values and morphology analysis, suggesting that NPs up to 500 mg/mL did not significantly interfere with viability and proliferation.

The results revealed that the RLs-NPs were able to inhibit bacterial growth showing adequate cytocompatibility and might become, after additional studies, a possible approach to fight S. aureus biofilm associated infections.

Acknowledgments: Support for this work was provided by FCT through Portuguese government, PTDC/BTM-SAL/29335/2017 and Pest-UID/DTP/04138/2019

The paper presents the biological degradation of different road surfaces. Microorganisms are able to damage the structure and function of synthetic polymers. Some of road pavements, that are still in developing stage are porous and contain high amount of polyurethane (up to 10% by weight) or polymer modified asphalts. The same fungal enzymes can break down the polyurethanes or metabolize the plasticizers in various polymers, resulting in embrittlement and loss of strength. Many sources, indicate that enzymes produced by fungi (so also produced by lichens) have adverse effect on polyurethane resins. According to literature, bacteria and lichens may deteriorate polyurethane resin resulting in loss of bonds between particles (rubber and stone chippings). It may be possible to decrease sensitivity of the road pavements to attack of bacteria and lichens by adding certain substances (inhibitors) to the mix. The paper presents pilot study related to biological interactions with poroelastic road pavements containing rubber and polyurethane resin.

Microbially influenced corrosion (MIC), is acknowledged to be the direct cause of catastrophic corrosion failures, with damages ranging to many billions of US$. In spite of extensive research and numerous publications, fundamental questions still remain unanswered. In 1993, J.F.D. Stott published a review paper in Corrosion Science, entitled “What progress in the understanding of microbially influenced corrosion has been made in the last 25 years?“ He concluded, “The most commonly asked question about MIC is: what will be the expected corrosion rate of material x in an environment where aggressive microorganisms proliferate?... For many materials we can no more answer this question now than we could 25 years ago.” Now, over 50 years later, that question is still open. Current MIC research does not provide data related to detection and verification in the field, diagnosing, modelling or prediction. Laboratory experiments seldom attempt to recreate relevant natural or industrial electrolytes. A sober, solution-oriented contemplation of the state-of-art and acknowledgement of the substantial deficiencies in our understanding may help shift MIC research into a direction which could actually produce useful answers.