Improved mass transfer and biodegradation rates of naphthalene particles using a novel bead mill bioreactor

One of the main challenges in the treatment of polycyclic aromatic hydrocarbons (PAHs) in controlled bioreactors is the hydrophobicity and low solubility of these compounds in the aqueous phase, resulting in appreciable mass transfer limitations within the bioreactor. To address this challenge, we have developed a modified roller bioreactor (Bead Mill Bioreactor) in which inert particles are used to improve mass transfer from the solid phase to the aqueous phase. Experimental results with naphthalene as a model PAH and Pseudomonas putida as a candidate bacterium indicate that both the mass transfer rate from the solid phase to liquid phase and the biodegradation rate in the Bead Mill Bioreactor (BMB) were significantly higher than those in a conventional roller bioreactor (20‐fold and 5.5‐fold, respectively). The enhancement of mass transfer was dependent on the type, size and volumetric loading of the inert particles, as well as concentration of particulate naphthalene. The highest mass transfer coefficient (k_La = 2.1 h^?1) was achieved with 3 mm glass beads at a volumetric loading of 50% (particle volume/working volume) with 10 000 mg dm^?3 particulate naphthalene. The maximum biodegradation rate of naphthalene attained in the bead mill bioreactor (59.2 mg dm^?3 h^?1 based on the working volume and 118.4 mg dm^?3 h^?1 based on the liquid volume) surpasses most other rates published in the literature and is equivalent to values reported for more complex bioreaction systems. The bead mill bioreactor developed in the present work not only enjoys a simple design but shows excellent performance for treatment of PAHs suspended in an aqueous phase. This fundamental information will be of significant value for future studies involving soil‐bound PAHs. Copyright © 2005 Society of Chemical Industry     

Silver nanoparticles enhance Pseudomonas aeruginosa PAO1 biofilm detachment

Objectives: Silver nanoparticles (AgNPs) with a size ranging from 7 to 70?nm were synthesized using the ascorbic acid-citrate seed-mediated growth approach at room temperature.

Methods: The 8?nm silver particles were prepared using gallic acid in alkaline conditions and used as seed to prepare AgNPs.

Results: The presence of ascorbic acid and citrate allows the regulation of size and size distribution of the nanoparticles. The increase in free silver ion-to-seed ratio (Ag⁺/Ag⁰) resulted in changes of particle shape from spherical to pseudo-spherical and minor cylindrical shape. Further, a repetitive seeding approach resulted in the formation of pseudo-spherical particles with higher polydispersity index and minor distributions of tetrahedral particles. Citrate-capped AgNPs were stable and did not agglomerate upon centrifugation. The effect of AgNPs on biofilm reduction was evaluated using static culture on 96-well microtiter plates. Results showed that AgNPs with the smallest average diameter were most effective in the reduction of Pseudomonas aeruginosa biofilm colonies, which accounted for 90% of removal.

Conclusion: The biofilm removal activities of the nanoparticles were found to be concentration-independent particularly for the concentration within the range of 80–200?µg/mL.     

水源水中2-MIB降解菌的筛选

针对特定水处理工艺,研究了投加2-MIB前后水中微生物种群的变化,建立了筛选分离2-MIB降解菌的方法.以生物膜生长成熟的活性炭连续处理含有较高浓度2-MIB水样,然后从活性炭表面取样,用2-MIB为惟一碳源的无机盐培养基筛选和驯养,最后进行划线分离,成功得到2-MIB降解菌种.通过16SrRNA分析,该菌株属于假单胞菌属(Pseudomonas spp.).     

菱角壳黄酮提取物抑菌活性评价及对冷鲜鸭肉中假单胞菌生长特性的影响

为探究菱角壳黄酮提取物的抑菌能力及其对冷鲜鸭肉中假单胞菌生长特性的影响,采用抑菌圈法、MIC值测定和液体中生长曲线来评价其对食品中常见微生物生长的抑制作用,建立假单胞菌经浓度为2.5 mg/mL的黄酮纯化物处理后的鸭肉基质中的一级生长预测模型。结果表明:菱角壳黄酮提取物对假单胞菌、金黄色葡萄球菌有明显的抑制作用,其中黄酮纯化物对假单胞菌和金黄色葡萄球菌的抑菌效果更好,抑菌圈直径分别为(47.01±0.43)、(45.06±0.35) mm;菱角壳黄酮提取物对热杀索丝菌有一定的抑制效果,对大肠杆菌、乳酸菌和酵母菌无抑菌效果。菱角壳黄酮粗提物和纯化物对假单胞菌的MIC值均为3.125 mg/mL,对金黄色葡萄球菌的MIC值分别为12.000和3.125 mg/mL。采用对供试菌抑菌效果最好的菱角壳黄酮纯化物浓度(2.5 mg/mL)处理鸭肉,在不同温度下储藏,发现与10、15和20 ℃相比,0和5 ℃可将冷鲜鸭肉的货架期延长至8 d以上,并且通过建立假单胞菌在经浓度为2.5 mg/mL的菱角壳黄酮纯化物处理后的鸭肉基质中的一级模型可知,在0~15 ℃储藏时,菱角壳黄酮提取物作为保鲜剂的抑菌效果较好,能够有效延长食品保质期,但随温度升高,其抑菌能力逐渐减弱,这为菱角壳开发为天然抑菌剂提供了理论基础。     

桃金娘果实花色苷提取物对两种假单胞菌生物被膜的抑制

为研究桃金娘果实花色苷提取物对隆德假单胞菌(Pseudomonas lundensis)和荧光假单胞菌(Pseudomonas fluorescens)生物被膜的抑制作用,采用肉汤稀释法测定了桃金娘果实花色苷提取物对两种假单胞菌的最小抑菌浓度和最小杀菌浓度,在亚抑菌浓度下采用结晶紫微孔板染色法测定了桃金娘果实花色苷提取物对两种假单胞菌的抑制作用和粘附情况。结果表明,桃金娘果实花色苷提取物对两种假单胞菌均有一定的抑制作用,对隆德假单胞菌和荧光假单胞菌的最小抑菌浓度分别为1500和1000 mg/mL,在500 mg/mL的亚抑菌浓度下,桃金娘果实花色苷提取物对隆德假单胞菌和荧光假单胞菌生物被膜具有显著抑制效果,能够显著降低两种假单胞菌在接触面上的粘附量(p<0.05)。桃金娘果实花色苷提取物具有开发为隆德假单胞菌和荧光假单胞菌生物被膜抑制剂的潜在价值。     

Synthesis of an Anti-CD7 Recombinant Immunotoxin Based on PE24 in CHO and E. coli Cell-Free Systems

Recombinant immunotoxins (RITs) are an effective class of agents for targeted therapy in cancer treatment. In this article, we demonstrate the straight-forward production and testing of an anti-CD7 RIT based on PE24 in a prokaryotic and a eukaryotic cell-free system. The prokaryotic cell-free system was derived from Escherichia coli BL21 Star^TM (DE3) cells transformed with a plasmid encoding the chaperones groEL/groES. The eukaryotic cell-free system was prepared from Chinese hamster ovary (CHO) cells that leave intact endoplasmic reticulum-derived microsomes in the cell-free reaction mix from which the RIT was extracted. The investigated RIT was built by fusing an anti-CD7 single-chain variable fragment (scFv) with the toxin domain PE24, a shortened variant of Pseudomonas Exotoxin A. The RIT was produced in both cell-free systems and tested for antigen binding against CD7 and cell killing on CD7-positive Jurkat, HSB-2, and ALL-SIL cells. CD7-positive cells were effectively killed by the anti-CD7 scFv-PE24 RIT with an IC₅₀ value of 15 pM to 40 pM for CHO and 42 pM to 156 pM for E. coli cell-free-produced RIT. CD7-negative Raji cells were unaffected by the RIT. Toxin and antibody domain alone did not show cytotoxic effects on either CD7-positive or CD7-negative cells. To our knowledge, this report describes the production of an active RIT in E. coli and CHO cell-free systems for the first time. We provide the proof-of-concept that cell-free protein synthesis allows for on-demand testing of antibody–toxin conjugate activity in a time-efficient workflow without cell lysis or purification required.     

eDNA,Amyloid Fibers and Membrane Vesicles Identified in Pseudomonas fluorescens SBW25 Biofilms

Pseudomonas fluorescens SBW25 is a model soil- and plant-associated bacterium capable of forming a variety of air–liquid interface biofilms in experimental microcosms and on plant surfaces. Previous investigations have shown that cellulose is the primary structural matrix component in the robust and well-attached Wrinkly Spreader biofilm, as well as in the fragile Viscous Mass biofilm. Here, we demonstrate that both biofilms include extracellular DNA (eDNA) which can be visualized using confocal laser scanning microscopy (CLSM), quantified by absorbance measurements, and degraded by DNase I treatment. This eDNA plays an important role in cell attachment and biofilm development. However, exogenous high-molecular-weight DNA appears to decrease the strength and attachment levels of mature Wrinkly Spreader biofilms, whereas low-molecular-weight DNA appears to have little effect. Further investigation with CLSM using an amyloid-specific fluorophore suggests that the Wrinkly Spreader biofilm might also include Fap fibers, which might be involved in attachment and contribute to biofilm strength. The robust nature of the Wrinkly Spreader biofilm also allowed us, using MALDI-TOF mass spectrometry, to identify matrix-associated proteins unable to diffuse out of the structure, as well as membrane vesicles which had a different protein profile compared to the matrix-associated proteins. CLSM and DNase I treatment suggest that some vesicles were also associated with eDNA. These findings add to our understanding of the matrix components in this model pseudomonad, and, as found in other biofilms, biofilm-specific products and material from lysed cells contribute to these structures through a range of complex interactions.     

Serratiopeptidase Affects the Physiology of Pseudomonas aeruginosa Isolates from Cystic Fibrosis Patients

Pseudomonas aeruginosa is frequently involved in cystic fibrosis (CF) airway infections. Biofilm, motility, production of toxins and the invasion of host cells are different factors that increase P. aeruginosa’s virulence. The sessile phenotype offers protection to bacterial cells and resistance to antimicrobials and host immune attacks. Motility also contributes to bacterial colonization of surfaces and, consequently, to biofilm formation. Furthermore, the ability to adhere is the prelude for the internalization into lung cells, a common immune evasion mechanism used by most intracellular bacteria, such as P. aeruginosa. In previous studies we evaluated the activity of metalloprotease serratiopeptidase (SPEP) in impairing virulence-related properties in Gram-positive bacteria. This work aimed to investigate SPEP’s effects on different physiological aspects related to the virulence of P. aeruginosa isolated from CF patients, such as biofilm production, pyoverdine and pyocyanin production and invasion in alveolar epithelial cells. Obtained results showed that SPEP was able to impair the attachment to inert surfaces as well as adhesion/invasion of eukaryotic cells. Conversely, SPEP’s effect on pyocyanin and pyoverdine production was strongly strain-dependent, with an increase and/or a decrease of their production. Moreover, SPEP seemed to increase swarming motility and staphylolytic protease production. Our results suggest that a large number of clinical strains should be studied in-depth before drawing definitive conclusions. Why different strains sometimes react in opposing ways to a specific treatment is of great interest and will be the object of future studies. Therefore, SPEP affects P. aeruginosa’s physiology by differently acting on several bacterial factors related to its virulence.     

某市包装饮用水铜绿假单胞菌污染状况分析

目的了解某市生产与流通环节中包装饮用水铜绿假单胞菌的污染状况,为其安全风险控制提供依据。方法采用GB 8538-2016铜绿假单胞菌检验方法,对某市2016~2017年生产与流通环节中的矿泉水(a)、纯净水(b)、其他包装饮用水(c)进行抽样监测与数据分析。结果共抽样228批次,铜绿假单胞菌检出率为12.3%,各类包装饮用水间的检出率差别有统计学意义(P0.05,Fisher’s Exact Test);矿泉水的检出率比纯净水高(P_(a-b)0.0125,Fisher’s Exact Test),矿泉水与其他包装饮用水、以及纯净水与其他包装饮用水检出率无明显差别(P_(a-c)0.0125、P_(b-c)0.0125,Fisher’s Exact Test)。各类包装饮用水铜绿假单胞菌分离株蓝/绿色素表型无明显差异(P0.05,Fisher’s Exact Test)。同时发现分离株对氨苄西林、氨苄西林/舒巴坦、头孢唑啉、头孢替坦、呋喃妥因、复方新诺明耐药(耐药率均为100%)。结论纯净水卫生状况相对矿泉水较好,但各类包装饮用水均发现铜绿假单胞菌污染及出现耐药株,应对包装饮用水产品加强生产管理、改进生产工艺,加强水资源监测与保护。