Formation of bacterial streamers during filtration in microfluidic systems

Bacterial behavior during filtration is complex and is influenced by numerous factors. The aim of this paper is to report on experiments designed to make progress in the understanding of bacterial transfer in filters and membranes. Polydimethylsiloxane (PDMS) microsystems were built to allow direct dynamic observation of bacterial transfer across different microchannel geometries mimicking filtration processes. When filtering Escherichia coli suspensions in such devices, the bacteria accumulated in the downstream zone of the filter forming long streamers undulating in the flow. Confocal microscopy and 3D reconstruction of streamers showed how the streamers are connected to the filter and how they form in the stream. Streamer development was found to be influenced by the flow configuration and the presence of connections or tortuosity between channels. Experiments showed that streamer formation was greatest in a filtration system composed of staggered arrays of squares 10?μm apart.     

Investigation of virus retention by size exclusion membranes under different flow regimes

Virus removal by filter membranes is regarded as a robust and efficient unit operation, which is frequently applied in the downstream processing of biopharmaceuticals. The retention of viruses by virus filtration membranes is predominantly based on size exclusion. However, recent results using model membranes and bacteriophage PP7 point to the fact that virus retention can also significantly be influenced by adsorptive interactions between virus, product molecules, and membranes. Furthermore, the impact of flow rate and flow interruptions on virus retention have been studied and responsible mechanisms discussed. The aim of this investigation was to gain a holistic understanding of the underlying mechanisms for virus retention in size exclusion membranes as a function of membrane structure and membrane surface properties, as well as flow and solution conditions. The results of this study contribute to the differentiation between size exclusion and adsorptive effects during virus filtration and broaden the current understanding of mechanisms related to virus breakthroughs after temporary flow interruptions. Within the frame of a Design of Experiments approach it was found that the level of retention of virus filtration membranes was mostly influenced by the membrane structure during typical process-related flow conditions. The retention performance after a flow interruption was also significantly influenced by membrane surface properties and solution conditions. While size exclusion was confirmed as main retention mechanism, the analysis of all results suggests that especially after a flow interruption virus retention can be influenced by adsorptive effects between the virus and the membrane surface. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2747, 2019.     

In situ filtration of Anchusa officinalis culture in a cell-retention stirred tank bioreactor

Summary The effect of agitation and aeration on filtration of Anchusa officinalis culture in a stirred tank bioreactor integrated with an internal filter unit was investigated. Increases in suction head of the pump that drove the filtration process were measured at impeller speeds of 100 and 200 rpm. Surprisingly, suction head attained at 200 rpm was about 40% higher than at 100 rpm. Direct observation of the cake deposition process in the reactor using a dilute cell suspension revealed that the filter cake formed at 100 rpm was thicker, but less compact. Aeration at 0.4 vvm was shown to have little effect on the filtration rate, since the bulk fluid flow was dominated by the impeller hydrodynamics. The initial flux can be recovered by filter backwashing with compressed air at a flow rate of 0.6 vvm for a duration of 5 minutes.     

Selective isolation of bacteria for metagenomic analysis: Impact of membrane characteristics on bacterial filterability

For indirect DNA extraction for metagenomics studies, bacterial cells can be effectively separated from sample debris by using a simple size exclusion technique, such as filtration, and thereafter lysed. The requirement for the optimal recovery of cells in filtrates is critical to achieve sufficient DNA yield and a representative population. Particles smaller than the filter pore size are expected to be found in the filtrate, whereas particles larger than the filter pore sizes are excluded. However, this is not always the case. It is established that the membrane pore size influences filtration efficiency to some degree. In addition the physicochemical characteristics of the filter suspension and characteristics of the microbial cells being filtered influence the exclusion property of a membrane. This review provides an overview of membrane filtration techniques and the factors that affect filterability of bacteria cells through a filter membrane. © 2015 American Institute of Chemical Engineers Biotechnol. Prog., 31:853–866, 2015     

Capture of bacteria from fermentation broth by body feed filtration: a solved problem?

The direct capture of bacteria produced in high cell density fermentation by filtration is not possible once the milliliter-scale has been surpassed. Filtration in the presence of a filter aid (body feed filtration) constitutes a putative and scalable alternative, but only if conditions proposed by industry for large-scale filtration processes, namely, flow rates (for aqueous solutions) in the range of 500-1,500 L/(m(2) x h) and a filter aid concentration of 相似文献   

Computational Fluid Dynamics of Fish Gill Rakers During Crossflow Filtration

We study crossflow filtration mechanisms in suspension-feeding fishes using computational fluid dynamics to model fluid flow and food particle movement in the vicinity of the gill rakers. During industrial and biological crossflow filtration, particles are retained when they remain suspended in the mainstream flow traveling across the filter surface rather than traveling perpendicularly to the filter. Here we identify physical parameters and hydrodynamic processes that determine food particle movement and retention inside the fish oral cavity. We demonstrate how five variables affect flow patterns and particle trajectories: (1) flow speed inside the fish oral cavity, (2) incident angle of the flow approaching the filter, (3) dimensions of filter structures, (4) particle size, and (5) particle density. Our study indicates that empirical experiments are needed to quantify flow parameters inside the oral cavity, and morphological research is needed to quantify dimensions of the filter apparatus such as gill rakers, the gaps between rakers, and downstream barriers. Ecological studies on suspension-feeding fishes are also needed to quantify food particle size and density, as these variables can affect particle retention due to hydrodynamic processes during crossflow filtration.     

Macroscopic Streamer Growths in Acidic, Metal-Rich Mine Waters in North Wales Consist of Novel and Remarkably Simple Bacterial Communities

The microbial composition of acid streamers (macroscopic biofilms) in acidic, metal-rich waters in two locations (an abandoned copper mine and a chalybeate spa) in north Wales was studied using cultivation-based and biomolecular techniques. Known chemolithotrophic and heterotrophic acidophiles were readily isolated from disrupted streamers, but they accounted for only <1 to 7% of the total microorganisms present. Fluorescent in situ hybridization (FISH) revealed that 80 to 90% of the microbes in both types of streamers were β-Proteobacteria. Terminal restriction fragment length polymorphism analysis of the streamers suggested that a single bacterial species was dominant in the copper mine streamers, while two distinct bacteria (one of which was identical to the bacterium found in the copper mine streamers) accounted for about 90% of the streamers in the spa water. 16S rRNA gene clone libraries showed that the β-proteobacterium found in both locations was closely related to a clone detected previously in acid mine drainage in California and that its closest characterized relatives were neutrophilic ammonium oxidizers. Using a modified isolation technique, this bacterium was isolated from the copper mine streamers and shown to be a novel acidophilic autotrophic iron oxidizer. The β-proteobacterium found only in the spa streamers was closely related to the neutrophilic iron oxidizer Gallionella ferruginea. FISH analysis using oligonucleotide probes that targeted the two β-proteobacteria confirmed that the biodiversity of the streamers in both locations was very limited. The microbial compositions of the acid streamers found at the two north Wales sites are very different from the microbial compositions of the previously described acid streamers found at Iron Mountain, California, and the Rio Tinto, Spain.     

Efficacy of iodine-treated biocidal filter media against bacterial spore aerosols

Aims: To assess the effectiveness of iodine-treated biocidal filter media against bacterial spore aerosols. Methods and Results: Bacillus subtilis spores were aerosolized and introduced into a filtration system. Both treated and untreated filters exhibited high viable removal efficiency (>99·996%) with negligible variation in pressure drop during the entire experiment. The viability of collected spores on the filter was investigated by enumeration of spores extracted from the filter by vortexing. At room temperature and low relative humidity (RH), the survival fraction of the treated filter was significantly lower than that of the untreated filter (P-value < 0·05). Meanwhile, at room temperature and high RH and at high temperature and high RH, the survival fractions on the treated medium were statistically the same as the untreated control at room temperature and low RH. Conclusions: Both treated and untreated filters achieved excellent viable removal efficiency for spores. The pressure drop of the treated filter was not affected by the iodine treatment. The viability of collected bacterial spores was decreased because of the exertion of iodine disinfectant. Significance and Impact of the Study: The evaluation demonstrates that the iodine-treated filter is a viable medium for respiratory protection against infectious spore aerosols. The results warrant further evaluation of smaller biological agents, which exhibit higher penetration.     

LOSS OF NUTRIENTS FROM WATER SAMPLES BY FILTRATION AND ITS AFFECT ON ALGAL BIOASSAY PROCEDURES

SUMMARY

Water samples were collected from fourteen sampling points along the Hunyani River system and subjected to various filtration treatments involving glass fibre filters and 1,2 and 0,45 pm membrane filters. Chemical analyses of the filtered waters showed that nitrogen, phosphorus and iron were lost by different filtration treatments. Filtration by membrane filters led to a reduction of algal growth potential as demonstrated by algal bioassays using Selanastrwn capricornutum Printz as the test alga.

Algal bioassays showed that biologically available phosphorus was primarily removed by the 1,2 μm membrane filter while biologically available nitrogen and iron was principally lost by filtration through the 0,25 μm membrane filter. A refined algal bioassay designed to determine the identity of limiting micronutrients found that all essential micronutrients were affected by membrane filtration.     

Macroscopic streamer growths in acidic, metal-rich mine waters in north wales consist of novel and remarkably simple bacterial communities

The microbial composition of acid streamers (macroscopic biofilms) in acidic, metal-rich waters in two locations (an abandoned copper mine and a chalybeate spa) in north Wales was studied using cultivation-based and biomolecular techniques. Known chemolithotrophic and heterotrophic acidophiles were readily isolated from disrupted streamers, but they accounted for only <1 to 7% of the total microorganisms present. Fluorescent in situ hybridization (FISH) revealed that 80 to 90% of the microbes in both types of streamers were beta-Proteobacteria. Terminal restriction fragment length polymorphism analysis of the streamers suggested that a single bacterial species was dominant in the copper mine streamers, while two distinct bacteria (one of which was identical to the bacterium found in the copper mine streamers) accounted for about 90% of the streamers in the spa water. 16S rRNA gene clone libraries showed that the beta-proteobacterium found in both locations was closely related to a clone detected previously in acid mine drainage in California and that its closest characterized relatives were neutrophilic ammonium oxidizers. Using a modified isolation technique, this bacterium was isolated from the copper mine streamers and shown to be a novel acidophilic autotrophic iron oxidizer. The beta-proteobacterium found only in the spa streamers was closely related to the neutrophilic iron oxidizer Gallionella ferruginea. FISH analysis using oligonucleotide probes that targeted the two beta-proteobacteria confirmed that the biodiversity of the streamers in both locations was very limited. The microbial compositions of the acid streamers found at the two north Wales sites are very different from the microbial compositions of the previously described acid streamers found at Iron Mountain, California, and the Rio Tinto, Spain.     

Secondary flow as a mechanism for the formation of biofilm streamers

In most environments, such as natural aquatic systems, bacteria are found predominantly in self-organized sessile communities known as biofilms. In the presence of a significant flow, mature multispecies biofilms often develop into long filamentous structures called streamers, which can greatly influence ecosystem processes by increasing transient storage and cycling of nutrients. However, the interplay between hydrodynamic stresses and streamer formation is still unclear. Here, we show that suspended thread-like biofilms steadily develop in zigzag microchannels with different radii of curvature. Numerical simulations of a low-Reynolds-number flow around these corners indicate the presence of a secondary vortical motion whose intensity is related to the bending angle of the turn. We demonstrate that the formation of streamers is directly proportional to the intensity of the secondary flow around the corners. In addition, we show that a model of an elastic filament in a two-dimensional corner flow is able to explain how the streamers can cross fluid streamlines and connect corners located at the opposite sides of the channel.     

Monitoring of the toxic dinoflagellate Karenia brevis using gyroxanthin-based detection methods

The threat to human health and fisheries resources due to blooms of the toxic dinoflagellate Karenia brevis has lead to widespread public concern and calls for continuous monitoring of coastal waters for this organism. Here, a rapid and sensitive photopigment-based monitoring approach is described that incorporates refinements to standard filtration and analytical methods. This method uses the biomarker pigment gyroxanthin-diester contained in cells of some gymnodiniod species including K. brevis. Investigations of the retention efficiencies of five filter types for gyroxanthin from natural blooms of K. brevis showed no significant differences between GF/F, GF/C, 934-AH, GF/A or GF/D filters. Retention efficiencies were generally greater than 98% of cells added, indicating that the larger nominal pore size filters may be used safely for sample collection, reducing overall filtration times for large volumes of water. Simulated bloom experiments using cultures of K. brevis added to unfiltered water from Galveston Bay showed that retention of gyroxanthin on GF/D filters was significantly lower than on other filter types. There were significant interactions (p < 0.01) between filter type and cell density for the variables gyroxanthin, gyroxanthin chl a^–1 and gyroxanthin cell^–1, suggesting that the performance of the different filter types was dependent on cell density. Retention efficiencies for the simulated blooms ranged between >99% of cells retained and <30% of cells retained (greatest losses were for the GF/D filters). Combined results of natural and simulated blooms indicated that GF/C, 934-AH or GF/A filters gave the best retention efficiency with the fastest filtration times. Sample processing times were also improved by modifying the flow gradients in an existing HPLC protocol allowing the analysis of 106 samples in 24 h. The resulting protocol is suitable for incorporation into routine water quality monitoring programs, and would greatly facilitate the early detection and tracking of K. brevis blooms in coastal waters.     

Automated fast filtration and on‐filter quenching improve the intracellular metabolite analysis of microorganisms

To reliably determine intracellular metabolite concentrations in microorganisms, accurate sampling and sample inactivation strategies are crucial. Here, we present a method for automated fast filtration and on‐filter quenching of microbial samples to overcome metabolite leakage induced by cold shock and significantly reduce the sampling and treatment time compared to manual filtration methods. The whole process of sampling, sample filtration, filter wash, and quenching of the filter with liquid nitrogen was finished in less than 6–15 s, depending on the experimental setup. By integration into an automated fast sampling device, we compared our method to the conventional methanol quenching method and showed that intracellular amino acid contents in Escherichia coli were significantly increased (≥75%) with our fast filtration and on‐filter quenching method. Furthermore, we investigated different filter types for the fast filtration and the efficiency of metabolite extraction from cells held on filters. Additionally, we found that the fast filtration behaves considerably different during exponential and nonexponential growth, probably due to variations of cell morphologies. Overall, we demonstrated that the automation of the fast filtration method significantly reduces the time for filtration and quenching and hence enlarge the number of metabolites that can be quantified with this leakage‐free sampling method.     

Bioprocessing of polluted suspended matter from the water column by the zebra mussel (Dreissena polymorpha Pallas)

Measurements of pseudofaeces production of Dreissena polymorpha were carried out with the aim of developing a biological filter at the freshwater inlet of Lake Volkerak-Zoommeer, the Netherlands. Bioprocessing of polluted suspended matter by suspended cultures of D. polymorpha occurs by filtration and sedimentation of the suspended matter as pseudofaeces. The measurements were conducted under semi-natural conditions.Pseudofaeces production was mainly determined by the dry matter content of the water; the relation is linear. Temperature was of much less importance. This agrees with earlier investigations of the filtration rate of D. polymorpha. Even at the lowest temperature measured during the experiments (6.4 °C) no large decrease in activity was observed. The relation of pseudofaeces production with shell length was sigmoid in shape, in accordance with measurements of the filtration rate.The pseudofaeces produced was slightly more polluted than suspended matter, partly due to a finer grainsize. D. polymorpha from Lake IJsselmeer exposed for 217 days at the intended location of the filter showed bioaccumulation of toxicants, especially organic pollutants and Polycyclic Aromatic Hydrocarbons (up to 10-fold accumulation). The required number of D. polymorpha in the biological filter to treat the waterflow of 14 m³ s^–1 entering Lake Volkerak-Zoommeer is 1.24 * 10⁹. The purification efficiency of the filter, the reduction of the amount of toxicants, partly depends on the binding properties of the toxicants and is highest for those strongly bound to suspended matter.     

Robust scale-up of dead end filtration: impact of filter fouling mechanisms and flow distribution

Robust design of a dead end filtration step and the resulting performance at manufacturing scale relies on laboratory data collected with small filter units. During process development it is important to characterize and understand the filter fouling mechanisms of the process streams so that an accurate assessment can be made of the filter area required at manufacturing scale. Successful scale-up also requires integration of the lab-scale filtration data with an understanding of flow characteristics in the full-scale filtration equipment. A case study is presented on the development and scale-up of a depth filtration step used in a 2nd generation polysaccharide vaccine manufacturing process. The effect of operating parameters on filter performance was experimentally characterized for a diverse set of process streams. Filter capacity was significantly reduced when operating at low fluxes, caused by both low filtration pressure and high stream viscosity. The effect of flux on filter capacity could be explained for a variety of diverse streams by a single mechanistic model of filter fouling. To complement the laboratory filtration data, the fluid flow and distribution characteristics in manufacturing-scale filtration equipment were carefully evaluated. This analysis identified the need for additional scale-up factors to account for non-uniform filter area usage in large-scale filter housings. This understanding proved critical to the final equipment design and depth filtration step definition, resulting in robust process performance at manufacturing scale.     

Filtration of bacteria and yeast by ultrasound-enhanced sedimentation

Continuous flow filtration of suspensions of eukaryotic cells by ultrasonic standing wave enhanced sedimentation has recently been reported. The filtration efficiency for Escherichia coli in such a filter has been characterized at frequencies of 1 and 3 MHz in the present work and compared with results for Saccharomyces cerevisiae. The yeast can be filtered at greater than 99% efficiency at a flow rate of 5 ml min^-1 at either frequency. The filtration efficiency of the smaller E. coli at 3 MHz is in excess of 80% at concentrations in the region of 10¹⁰ mI^-1 but decreased at lower concentrations. However, E. coli in a mixed suspension with yeast were, because of inter-particle interactions, removed with the filtrate at an efficiency ranging from 80 to 50% over the eight orders of bacterial concentrations tested (down to 10³ mI^-1) at 3 MHz. Quantitative considerations show that poor filtration of pure suspensions of the smaller cells at the lower frequency arises because, at reasonable flow rates, the residence time is not sufficient for the cells to reach the pressure nodal cell concentration regions. The filtration efficiencies of both cell types are comparable at 3 MHz. It is suggested that the more comparable efficiencies arise because concentration regions are narrower at the high frequency and Stokes drag by the filter bulk flow inhibits sedimentation of the concentrated cells.     

The filter pads and filtration mechanisms of the devil rays: Variation at macro and microscopic scales

Three lineages of cartilaginous fishes have independently evolved filter feeding (Lamniformes: Megachasma and Cetorhinus, Orectolobiformes: Rhincodon, and Mobulidae: Manta and Mobula); and the structure of the branchial filters is different in each group. The filter in Rhincodon typus has been described; species within the Lamniformes have simple filamentous filters, but the anatomy and ultrastructure of the branchial filter in the mobulid rays varies and is of functional interest. In most fishes, branchial gill rakers are elongated structures located along the anterior ceratobranchial and/or epibranchial arches; however, mobulid gill rakers are highly modified, flattened, lobe‐like structures located on the anterior and posterior epibranchial elements as well as the ceratobranchials. The ultrastructure of the filter lobes can be smooth or covered by a layer of microcilia, and some are denticulated along the dorsal and ventral lobe surface. Flow through the mobulid oropharyngeal cavity differs from other filter‐feeding fishes in that water must rapidly deviate from the free stream direction. There is an abrupt 90° turn from the initial inflowing path to move through the laterally directed branchial filter pores, over the gill tissue, and out the ventrally located gill slits. The deviation in the flow must result in tangential shearing stress across the filter surface. This implies that mobulids can use cross‐flow filtration in which this shearing force serves as a mechanism to resuspend food particles initially caught by sieving or another capture mode. These particles will be transported by the cross filter flow toward the esophagus. We propose that species with cilia on the rakers augment the shear mediated movement of particles along the filter with ciliary transport. J. Morphol. 274:1026–1043, 2013. © 2013 Wiley Periodicals, Inc.     

Diversity of Bacterial Communities that Colonize the Filter Units Used for Controlling Plant Pathogens in Soilless Cultures

In recent years, increasing the level of suppressiveness by the addition of antagonistic bacteria in slow filters has become a promising strategy to control plant pathogens in the recycled solutions used in soilless cultures. However, knowledge about the microflora that colonize the filtering columns is still limited. In order to get information on this issue, the present study was carried out over a 4-year period and includes filters inoculated or not with suppressive bacteria at the start of the filtering process (two or three filters were used each year). After 9 months of filtration, polymerase chain reaction (PCR)–single strand conformation polymorphism analyses point out that, for the same year of experiment, the bacterial communities from control filters were relatively similar but that they were significantly different between the bacteria-amended and control filters. To characterize the changes in bacterial communities within the filters, this microflora was studied by quantitative PCR, community-level physiological profiles, and sequencing 16SrRNA clone libraries (filters used in year 1). Quantitative PCR evidenced a denser bacterial colonization of the P-filter (amended with Pseudomonas putida strains) than control and B-filter (amended with Bacillus cereus strains). Functional analysis focused on the cultivable bacterial communities pointed out that bacteria from the control filter metabolized more carbohydrates than those from the amended filters whose trophic behaviors were more targeted towards carboxylic acids and amino acids. The bacterial communities in P- and B-filters both exhibited significantly more phylotype diversity and markedly distinct phylogenetic compositions than those in the C-filter. Although there were far fewer Proteobacteria in B- and P-filters than in the C-filter (22% and 22% rather than 69% of sequences, respectively), the percentages of Firmicutes was much higher (44% and 55% against 9%, respectively). Many Pseudomonas species were also found in the bacterial communities of the control filter. The persistence of the amended suppressive-bacteria in the filters is discussed with regards to the management of suppressive microflora in soilless culture.     

Dewatering of algal suspension using microfiltration with cross flow in the presence of magnetite as a filter aid

Dewatering algal suspensions is an important step in the extraction of oil and other useful substances from algae. In this study, spherical Nannochloropsis sp. and ellipsoidal Monoraphidium sp. suspensions were dewatered in the presence of different amounts of 350-nm magnetite particles using a microfiltration membrane with 360-nm pores in cross-flow mode. Magnetite functions as a filter aid by reducing the deformation of the cake of filtered algae on the membrane and providing paths for water to flow through the filtration cake of algae. In the case of Nannochloropsis sp., the highest dewatering rate was obtained when the number ratio, defined based on the size and ideal density, between Nannochloropsis sp. and magnetite was 1:12.5, but the addition of magnetite had no observable effect on the filtration of ellipsoidal Monoraphidium sp. suspensions through the membrane. After dewatering, magnetite was effectively separated from the concentrated algal suspension by the application of a magnetic field in an open flow system. Magnetite has the potential to enhance dewatering performance using a cross-flow membrane system.     

The contribution of bacteria to the total adenosine triphosphate extracted from the microbiota in the water of a salt-marsh creek

The contribution of bacteria to the total adenosine 5-triphosphate (ATP) measured in estuarine samples was investigated. A portion of the bacterial population present in samples was separated from other biological materials by filtration through a 1.0-μm filter (Nucleopore). The quantification of ATP and the enumeration of bacteria (by epifluorescence microscopy) was performed on filtered and unfiltered portions of each sample as well as on cultured organisms. The values of ATP per cell averaged 1.48 × 10⁻¹⁵ g/cell from laboratory cultures and generally two orders-of-magnitude lower in bacteria from the natural system with values ranging from 0.24 to 28.8 × 10⁻¹⁷ g/cell. In bacteria collected from the marsh waters, the higher values of ATP per cell were observed in samples collected during the warmer months. When samples were obtained from areas of the marsh influenced by oceanic waters, the highest values of ATP per cell were observed at low tide. The nucleotide levels in bacterial cells in the high marsh were not markedly influenced by the tides. Bacterial ATP contributed from < 1–83% of the ATP measured in the total microbiota; the average content was 25% of the total. Generally, waters from the high marsh i.e., water influenced strongly by sediment microbes, contained a greater percentage of bacterial ATP.