无介体微生物燃料电池阳极生物膜传质分析

针对无介体微生物燃料电池阳极侧生物膜内的传递过程建立了一维稳态扩散传输模型,模型认为底物氧化产生的电子以直接方式传递至阳极,并考虑了生物膜内电势及pH的变化,计算获得了微生物燃料电池生物膜内的底物浓度、电势、电流密度以及pH值分布,讨论了生物膜的电导率、阳极电势和缓冲液浓度对生物膜内传质特性及产电性能的影响。计算结果表明随着生物膜电导率和阳极电势的增大,生物膜内底物浓度及pH值均降低,电池电流密度升高;进口缓冲液浓度越大,生物膜内pH值越高,有利于维持阳极生物膜内微生物的活性。     

氢基质生物膜反应器在饮用水处理中的研究进展

该文对氢基质生物膜反应器(MBf R)的作用机理、特性以及对饮用水中氧化性污染物的去除可行性进行了论述,并对国内外利用该技术去除饮用水中常见氧化性污染物(如:重金属离子:重铬酸盐、砷酸盐、硒酸盐等;无机阴离子:硝酸盐、溴酸盐、高氯酸盐;卤代有机化合物:对氯硝基苯、三氯乙烷、三氯乙烯、氯仿)的研究现状进行了总结。最后指出了MBf R研究中存在的问题以及在工程应用上的现状和发展前景。     

阳极双电层电容对微生物燃料电池性能的影响

采用3种活性炭粉制备具有不同电容的阳极,研究了双电层电容阳极对单室空气阴极微生物燃料电池启动、运行、性能、阳极生物膜附着的影响。结果表明:当电极表面积相近的情况下,阳极双电层电容从0.0012 F增加到22.72 F时,微生物燃料电池启动时间缩短了68.0%,电池的最大功率密度增加了16.8倍,达到546.1 m W·m-2。扫描电子显微镜的结果表明高电容的阳极表面附着的微生物量比低电容电极的高1倍。因此,微生物燃料电池性能受阳极双电层电容的影响,而与阳极表面积的相关性小。     

生物膜厚度对膜曝气生物膜反应器硝化性能的影响

在设定的膜内压力下(2 k Pa)启动并运行膜曝气生物膜反应器(MABR),对生物膜生长过程中的硝化性能及生物膜组成变化进行了分析。实验结果表明,在生物膜厚度增长到(293.3±5.8)μm的过程中,生物膜内的总氧通量先增加后减少,最高可达21.3 g O2?m?2?d?1,证实了生物膜的存在可增强MABR的氧传质能力。在生物膜厚度增长的过程中,氨氮表面去除负荷也是先增加后减少,最高可达4.91 g N?m?2?d?1,表明在MABR硝化过程中存在最佳的生物膜厚度,根据所研究最佳生物膜厚度为(119.0±3.0)μm,此时MABR具有最高的氧通量和氨氮表面去除负荷,硝化性能最好。生物膜内胞外聚合物(EPS)成分分析结果表明,随着生物膜厚度的增加,生物膜内层紧密型EPS的含量增加,导致氧传质阻力增加,这是生物膜内氧通量及氨氮去除负荷随生物膜厚度先增加后下降的内在原因。     

Introducing a Semi-Coated Model to Investigate Antibacterial Effects of Biocompatible Polymers on Titanium Surfaces

Peri-implant infections from bacterial biofilms on artificial surfaces are a common threat to all medical implants. They are a handicap for the patient and can lead to implant failure or even life-threatening complications. New implant surfaces have to be developed to reduce biofilm formation and to improve the long-term prognosis of medical implants. The aim of this study was (1) to develop a new method to test the antibacterial efficacy of implant surfaces by direct surface contact and (2) to elucidate whether an innovative antimicrobial copolymer coating of 4-vinyl-N-hexylpyridinium bromide and dimethyl(2-methacryloyloxyethyl) phosphonate (VP:DMMEP 30:70) on titanium is able to reduce the attachment of bacteria prevalent in peri-implant infections. With a new in vitro model with semi-coated titanium discs, we were able to show a dramatic reduction in the adhesion of various pathogenic bacteria (Streptococcus sanguinis, Escherichia coli, Staphylococcus aureus, Staphylococcus epidermidis), completely independently of effects caused by soluble materials. In contrast, soft tissue cells (human gingival or dermis fibroblasts) were less affected by the same coating, despite a moderate reduction in initial adhesion of gingival fibroblasts. These data confirm the hypothesis that VP:DMMEP 30:70 is a promising antibacterial copolymer that may be of use in several clinical applications.     

Identification of Pathogenicity-Related Genes in Biofilm-Defective Acidovorax citrulli by Transposon Tn5 Mutagenesis

Biofilm formation is important for virulence of a large number of plant pathogenic bacteria. Indeed, some virulence genes have been found to be involved in the formation of biofilm in bacterial fruit blotch pathogen Acidovorax citrulli. However, some virulent strains of A. citrulli were unable to format biofilm, indicating the complexity between biofilm formation and virulence. In this study, virulence-related genes were identified in the biofilm-defective strain A1 of A. citrulli by using Tn5 insertion, pathogenicity test, and high-efficiency thermal asymmetric interlaced PCR (hiTAIL-PCR). Results from this study indicated that 22 out of the obtained 301 mutants significantly decreased the virulence of strain A1 compared to the wild-type. Furthermore, sequence analysis indicated that the obtained 22 mutants were due to the insertion of Tn5 into eight genes, including Aave 4244 (cation diffusion facilitator family transporter), Aave 4286 (hypothetical protein), Aave 4189 (alpha/beta hydrolase fold), Aave 1911 (IMP dehydrogenase/GMP reductase domain), Aave 4383 (bacterial export proteins, family 1), Aave 4256 (Hsp70 protein), Aave 0003 (histidine kinase, DNA gyrase B, and HSP90-like ATPase), and Aave 2428 (pyridoxal-phosphate dependent enzyme). Furthermore, the growth of mutant Aave 2428 was unaffected and even increased by the change in incubation temperature, NaCl concentration and the pH of the LB broth, indicating that this gene may be directly involved in the bacterial virulence. Overall, the determination of the eight pathogenicity-related genes in strain A1 will be helpful to elucidate the pathogenesis of biofilm-defective A. citrulli.     

A Phytochemical–Halogenated Quinoline Combination Therapy Strategy for the Treatment of Pathogenic Bacteria

With the continued rise of drug‐resistant bacterial infections coupled with the current discouraging state of the antibiotic pipeline, the need for new antibacterial agents that operate through unique mechanisms compared with conventional antibiotics and work in synergy with other agents is at an all‐time high. We have discovered that gallic acid, a plant‐derived phytochemical, dramatically potentiates the antibacterial activities of several halogenated quinolines (up to 11 800‐fold potentiation against Staphylococcus aureus) against pathogenic bacteria, including drug‐resistant clinical isolates. S. aureus demonstrated the highest sensitivity towards gallic acid–halogenated quinoline combinations, including one halogenated quinoline that demonstrated potentiation of biofilm eradication activity against a methicillin‐resistant S. aureus (MRSA) clinical isolate. During our studies, we also demonstrated that these halogenated quionlines operate through an interesting metal(II) cation‐dependent mechanism and display promising mammalian cytotoxicity.     

Evaluation of alginate and zein films as a carrier of natamycin to increase the shelf life of kashar cheese

The aim of this study was to develop alginate and zein films containing natamycin, a natural antifungal agent, in order to limit/prevent the mould growth on the surface of kashar cheeses. The films were prepared by casting, and characterized in terms of antimicrobial and mechanical properties (tensile strength, elongation-at-break, and elastic modulus), and their morphology was examined by scanning electron microscopy (SEM). Mechanical properties of the zein films were found to be weaker than the alginate films. SEM analysis indicated that alginate films have a more regular structure than zein films, and a more homogenous distribution was observed at lower concentrations of natamycin. The antifungal activities of both films increased as the natamycin concentration (100, 200, 500, 1000, 2000, and 4000 ppm) increased; however, alginate films exhibited relatively high antifungal activity. The effects of films on the shelf life of kashar cheeses inoculated with Aspergillus niger and Penicillium camemberti were investigated during their storage under refrigerator conditions for 45 days. At high-natamycin concentrations, zein films showed higher antifungal activity against both fungi at the end of the storage period.     

Pore-scale modeling of competition and cooperation of multispecies biofilms for nutrients in changing environments

In this article, we developed a pore-scale model of integrated lattice Boltzmann method and cellular automata to investigate competitive growth of aerobic nitrite and ammonium oxidizers in a bioreactor. The results showed that inlet nutrient concentrations have significant effects on maximum biofilm concentration, ratio of microorganisms' concentrations, growth pattern, and time. The local availability of oxygen could control the competition, resulting in different growth patterns. The coexistence of ammonium and nitrite in same inlet zone increased not only the biofilm concentration (7%) but also the ratio of microorganisms' concentrations (36%). Although this coexistence decreased the total biofilm concentration in some cases, it increased the growth rate about 25%. Changes of the maximum biomass concentration could change biofilm concentration of about 40% and microorganisms' concentrations ratio of about 30%. This framework provides a powerful tool to improve our understanding of dynamic interdependency of many complex microbial consortia systems with environments.