Biofilms as living catalysts in continuous chemical syntheses

Biofilms are resilient to a wide variety of environmental stresses. This inherited robustness has been exploited mainly for bioremediation. With a better understanding of their physiology, the application of these living catalysts has been extended to the production of bulk and fine chemicals as well as towards biofuels, biohydrogen, and electricity production in microbial fuel cells. Numerous challenges call for novel solutions and concepts of analytics, biofilm reactor design, product recovery, and scale-up strategies. In this review, we highlight recent advancements in spatiotemporal biofilm characterization and new biofilm reactor developments for the production of value-added fine chemicals as well as current challenges and future scenarios.     

Experimental and theoretical investigations of rotating algae biofilm reactors (RABRs): Areal productivity,nutrient recovery,and energy efficiency

Microalgae biofilms have been demonstrated to recover nutrients from wastewater and serve as biomass feedstock for bioproducts. However, there is a need to develop a platform to quantitatively describe microalgae biofilm production, which can provide guidance and insights for improving biomass areal productivity and nutrient uptake efficiency. This paper proposes a unified experimental and theoretical framework to investigate algae biofilm growth on a rotating algae biofilm reactor (RABR). Experimental laboratory setups are used to conduct controlled experiments on testing environmental and operational factors for RABRs. We propose a differential–integral equation-based mathematical model for microalgae biofilm cultivation guided by laboratory experimental findings. The predictive mathematical model development is coordinated with laboratory experiments of biofilm areal productivity associated with ammonia and inorganic phosphorus uptake by RABRs. The unified experimental and theoretical tool is used to investigate the effects of RABR rotating velocity, duty cycle (DC), and light intensity on algae biofilm growth, areal productivity, nutrient uptake efficiency, and energy efficiency in wastewater treatment. Our framework indicates that maintaining a reasonable light intensity range improves biomass areal productivity and nutrient uptake efficiency. Our framework also indicates that faster RABR rotation benefits biomass areal productivity. However, maximizing the nutrient uptake efficiency requires a reasonably low RABR rotating speed. Energy efficiency is strongly correlated with RABR rotating speed and DC.     

Recent developments in sex ratio studies

The allocation of resources to male and female progeny is a major component of the reproductive strategies of all sexual plants and animals. Over the past 30 years there has been intensive theoretical and experimental investigation of how natural selection moulds the sex ratio. Here, we discuss recent exciting developments and new applications of sex allocation theory and highlight some unresolved issues.     

Linearized kinetic model of<Emphasis Type="Italic"> Listeria monocytogenes</Emphasis> biofilm growth

In this study the dynamics of biofilm formation on aluminum has been investigated. The process of cell growth has been observed using fluorescence microscopy. It has been confirmed that the process of biofilm formation can be represented as a sum of two separate processes: cell adhesion and colony proliferation. The derived set of equations describes kinetics of surface population growth and characteristic times for adsorption and combined growth processes, including characteristic time for the nutrient supply depletion. All equations contain variables based on the fundamental characteristics of bacterial population and can be easily determined from the experimental data or estimated theoretically. The developed theoretical model allows obtaining realistic values for population growth time and characteristic time for nutrient limitation occurrence during the biofilm development. Resulting equations qualitatively describe the biofilm formation process, and allow predicting microbial kinetics in the batch reactor system and determining critical values of the process parameters.     

Volumetric measurements in binary solvents: theory to experiment

Interactions of proteins and protein groups with water-soluble cosolvents have been studied for the last 50 years with a variety of theoretical and experimental methods. The contribution of volumetric techniques to these studies is relatively modest, although volumetric properties of solutes are sensitive to the entire spectrum of solute-solvent and solute-cosolvent interactions. This deficiency is partly related to formidable experimental difficulties related to conducting volumetric measurements at high cosolvent concentrations and partly to the lack of the theoretical framework within which volumetric results can be rationalized in terms of solute-solvent and solute-cosolvent interactions. However, recent years have witnessed a revival of interest in application of the volumetric approach to characterization of solute-solvent interactions in protein solutions in binary mixtures. This review presents an overview of recent advances in the field, focusing on both the theoretical and the experimental developments. While presenting the current state of the art, it also outlines the strategy for future volumetric studies that will result in new insights into the old problem of interactions of proteins with protecting and denaturing osmolytes.     

Role of polysaccharides in Pseudomonas aeruginosa biofilm development

During the past decade, there has been a renewed interest in using Pseudomonas aeruginosa as a model system for biofilm development and pathogenesis. Since the biofilm matrix represents a crucial interface between the bacterium and the host or its environment, considerable effort has been expended to acquire a more complete understanding of the matrix composition. Here, we focus on recent developments regarding the roles of alginate, Psl, and Pel polysaccharides in the biofilm matrix.     

Mini-review: Antimicrobial central venous catheters--recent advances and strategies

Central venous catheters (CVCs) nowadays constitute critical devices used in medical care, namely in intensive care units. However, CVCs also represent one of the indwelling medical devices with enhanced risk of nosocomial device-related infection. Catheter-related infections (CRIs) are a major cause of patient morbidity and mortality, often justifying premature catheter removal and an increase in costs and use of resources. Adhesion and subsequent biofilm formation on the surfaces of indwelling catheters is elemental to the onset of pathogenesis. Seeking the prevention of CVC colonisation and CRI, a variety of approaches have been studied, tested and, in some cases, already applied in clinical practice. This review looks at the current preventive strategies often used to decrease the risk of CRIs due to colonization and biofilm formation on catheter surfaces, as well as at the more recent approaches under investigation.     

Keratan sulfate biosynthesis

Keratan sulfate was originally identified as the major glycosaminoglycan of cornea but is now known to modify at least a dozen different proteins in a wide variety of tissues. Despite a large body of research documenting keratan sulfate structure, and an increasing interest in the biological functions of keratan sulfate, until recently little was known of the specific enzymes involved in keratan sulfate biosynthesis or of the molecular mechanisms that control keratan sulfate expression. In the last 2 years, however, marked progress has been achieved in identification of genes involved in keratan sulfate biosynthesis and in development of experimental conditions to study keratan sulfate secretion and control in vitro. This review summarizes current understanding of keratan sulfate structure and recent developments in understanding keratan sulfate biosynthesis.     

不可分型流感嗜血杆菌致病机制及耐药

作为全球两大高发疾病—儿童中耳炎和成人慢性阻塞性肺疾病的急性加重的主要病原菌,不可分型流感嗜血杆菌(NTHi)日益受到国内外学者的关注,然而目前,NTHi感染致病的相关机制及耐药并未得到全面地阐释,在一定程度上影响了临床对NTHi感染的有效控制。该文综合分析NTHi引起的主要感染,从以黏附作用为基础的定植策略、生物膜的形成、免疫逃逸和细菌耐药4个方面对NTHi感染致病的相关机制及耐药作一综述,以期为研究NTHi疫苗和特异抗感染药物提供理论依据。     

Mini-review: Antimicrobial central venous catheters – recent advances and strategies

Central venous catheters (CVCs) nowadays constitute critical devices used in medical care, namely in intensive care units. However, CVCs also represent one of the indwelling medical devices with enhanced risk of nosocomial device-related infection. Catheter-related infections (CRIs) are a major cause of patient morbidity and mortality, often justifying premature catheter removal and an increase in costs and use of resources. Adhesion and subsequent biofilm formation on the surfaces of indwelling catheters is elemental to the onset of pathogenesis. Seeking the prevention of CVC colonisation and CRI, a variety of approaches have been studied, tested and, in some cases, already applied in clinical practice. This review looks at the current preventive strategies often used to decrease the risk of CRIs due to colonization and biofilm formation on catheter surfaces, as well as at the more recent approaches under investigation.     

SrrAB在葡萄球菌生长代谢及存活中的作用研究进展

双组分信号转导系统SrrAB能够感应外界环境中氧浓度的变化,通过磷酸化水平的改变来调控靶基因的转录,进而影响葡萄球菌的多种生物学特性.研究发现SrrAB与葡萄球菌的毒力、生物膜的形成密切相关,而且有氧及厌氧条件下的调控机制不尽相同.然而,SrrAB与葡萄球菌的生长、代谢及其在病原体-宿主互作中的机制尚不清楚.结合课题组...     

Comparative performance of biofilm reactor types

Development of a unified model of biofilm-reactor kinetics is based on substrate-utilization kinetics, mass transport, biofilm growth, and reactor analysis. The model is applied to steady-state conditions for complete-mix, fixed-bed, and fluidized-bed reactors with and without recycle. The results of modeling experiments demonstrate that simple loading factors and kinetic relationships are insufficient to describe the performance of a variety of biofilm processes. Instead, the interactions among utilization kinetics, biofilm growth, and reactor configuration determine the performance. For example, fluidized-bed reactors can achieve superior performance to complete-mix and fixed-bed reactors because the biofilm is evenly distributed throughout the reactor while the liquid regime has plug-flow characteristics. When it is possible, experimental results which demonstrate key concepts are presented.     

Novel strategies for inhibition of bacterial biofilm in chronic rhinosinusitis

An important role has been recently reported for bacterial biofilm in the pathophysiology of chronic diseases, such as chronic rhinosinusitis (CRS). CRS, affecting sinonasal mucosa, is a persistent inflammatory condition with a high prevalence around the world. Although the exact pathological mechanism of this disease has not been elicited yet, biofilm formation is known to lead to a more significant symptom burden and major objective clinical indicators. The high prevalence of multidrug-resistant bacteria has severely restricted the application of antibiotics in recent years. Furthermore, systemic antibiotic therapy, on top of its insufficient concentration to eradicate bacteria in the sinonasal biofilm, often causes toxicity, antibiotic resistance, and an effect on the natural microbiota, in patients. Thus, coming up with alternative therapeutic options instead of systemic antibiotic therapy is emphasized in the treatment of bacterial biofilm in CRS patients. The use of topical antibiotic therapy and antibiotic eluting sinus stents that induce higher antibiotic concentration, and decrease side effects could be helpful. Besides, recent research recognized that various natural products, nitric oxide, and bacteriophage therapy, in addition to the hindered biofilm formation, could degrade the established bacterial biofilm. However, despite these improvements, new antibacterial agents and CRS biofilm interactions are complicated and need extensive research. Finally, most studies were performed in vitro, and more preclinical animal models and human studies are required to confirm the collected data. The present review is specifically discussing potential therapeutic strategies for the treatment of bacterial biofilm in CRS patients.     

Hypothesis for the role of nutrient starvation in biofilm detachment

A combination of experimental and theoretical approaches was used to investigate the role of nutrient starvation as a potential trigger for biofilm detachment. Experimental observations of detachment in a variety of biofilm systems were made with pure cultures of Pseudomonas aeruginosa. These observations indicated that biofilms grown under continuous-flow conditions detached after flow was stopped, that hollow cell clusters were sometimes observed in biofilms grown in flow cells, and that lysed cells were apparent in the internal strata of colony biofilms. When biofilms were nutrient starved under continuous-flow conditions, detachment still occurred, suggesting that starvation and not the accumulation of a metabolic product was responsible for triggering detachment in this particular system. A cellular automata computer model of biofilm dynamics was used to explore the starvation-dependent detachment mechanism. The model predicted biofilm structures and dynamics that were qualitatively similar to those observed experimentally. The predicted features included centrally located voids appearing in sufficiently large cell clusters, gradients in growth rate within these clusters, and the release of most of the biofilm with simulated stopped-flow conditions. The model was also able to predict biofilm sloughing resulting solely from this detachment mechanism. These results support the conjecture that nutrient starvation is an environmental cue for the release of microbes from a biofilm.     

Mitochondrial DNA and ageing

The accumulation of mitochondrial DNA mutations has been proposed as a potential mechanism in the physiological processes of ageing and age-related disease. Although mitochondria have long been anticipated as a perpetrator of ageing, there was little experimental evidence to link these changes directly with the cellular pathology of ageing. Recently, considerable progress in understanding basic mitochondrial genetics and in identifying acquired mtDNA mutations in ageing has been made. Furthermore, the creation of mtDNA-mutator mice has provided the first direct evidence that accelerating the mtDNA mutation rate can result in premature ageing, consistent with the view that loss of mitochondrial function is a major causal factor in ageing. This review will, therefore, focus on recent developments in ageing research related to the role played by mtDNA.     

Mitochondrial DNA and ageing

The accumulation of mitochondrial DNA mutations has been proposed as a potential mechanism in the physiological processes of ageing and age-related disease. Although mitochondria have long been anticipated as a perpetrator of ageing, there was little experimental evidence to link these changes directly with the cellular pathology of ageing. Recently, considerable progress in understanding basic mitochondrial genetics and in identifying acquired mtDNA mutations in ageing has been made. Furthermore, the creation of mtDNA-mutator mice has provided the first direct evidence that accelerating the mtDNA mutation rate can result in premature ageing, consistent with the view that loss of mitochondrial function is a major causal factor in ageing. This review will, therefore, focus on recent developments in ageing research related to the role played by mtDNA.     

Optical Spectra of High-Temperature Superconductors

This paper complements our recent survey [1] of experimental and theoretical work on the optical spectra of high-temperature superconductors. The emphasis is laid on experiments involving single crystals and good textured ceramic samples. Data have been collected on chemically doped samples, as well as on samples in which carriers are created by photodoping. One of the most remarkable consequences is the observation of a photoinduced superconductivity and a phase separation of photoexcited carriers. The theory has offered a few main suggestions but they have all failed to produce the magic formula for understanding the optical response. Nevertheless, bipolaron models seem somewhat closer to reality. Future experimental, theoretical, and practical developments are considered.     

Genome-wide mRNA profiling: impact on compound evaluation and target identification in anti-bacterial research

Array-based mRNA profiling offers a variety of opportunities to address different issues relevant to anti-bacterial research. The technique can be used to investigate the mode of action of antibiotics, bacterial resistance mechanisms and virulence factors, and to identify novel targets. This review discusses recent developments of this highly innovative field of technology with respect to technical requirements and experimental design. Several applications are described in which bacterial mRNA profiling has already been successfully performed, illustrating how the generation of large numbers of diverse datasets can be used as a powerful tool for evaluating anti-bacterial compounds and consequent counteracting mechanisms in the cell.     

Hypothesis for the Role of Nutrient Starvation in Biofilm Detachment

A combination of experimental and theoretical approaches was used to investigate the role of nutrient starvation as a potential trigger for biofilm detachment. Experimental observations of detachment in a variety of biofilm systems were made with pure cultures of Pseudomonas aeruginosa. These observations indicated that biofilms grown under continuous-flow conditions detached after flow was stopped, that hollow cell clusters were sometimes observed in biofilms grown in flow cells, and that lysed cells were apparent in the internal strata of colony biofilms. When biofilms were nutrient starved under continuous-flow conditions, detachment still occurred, suggesting that starvation and not the accumulation of a metabolic product was responsible for triggering detachment in this particular system. A cellular automata computer model of biofilm dynamics was used to explore the starvation-dependent detachment mechanism. The model predicted biofilm structures and dynamics that were qualitatively similar to those observed experimentally. The predicted features included centrally located voids appearing in sufficiently large cell clusters, gradients in growth rate within these clusters, and the release of most of the biofilm with simulated stopped-flow conditions. The model was also able to predict biofilm sloughing resulting solely from this detachment mechanism. These results support the conjecture that nutrient starvation is an environmental cue for the release of microbes from a biofilm.