Increase In Cell Concentration Research Articles

Sedimentation of Nodularia spumigena and distribution of nodularin in the food web during transport of a cyanobacterial bloom from the Baltic Sea to the Kattegat

Nodularia spumigena is a toxic cyanobacteria that blooms in the Baltic Sea every year. In the brackish water of the Baltic Sea, its toxin, nodularin, mainly affects the biota in the surface water due to the natural buoyancy of this species. However, the fate of the toxin is unknown, once the cyanobacteria bloom enters the more saline waters of the Kattegat. In order to investigate this knowledge gap, a bloom of N. spumigena was followed during its passage, carried by surface currents, from the Baltic Sea into the Kattegat area, through the Öresund strait. N. spumigena cells showed an increased cell concentration through the water column during the passage of the bloom (up to 130 103 cells ml−1), and cells (4.2 103 cells ml−1) could be found down to 20 m depth, below a pycnocline. Sedimentation trap samples from below the pycnocline (10–12 m depth) also showed an increased sedimentation of N. spumigena filaments during the passage of the bloom. The toxin nodularin was detected both in water samples (0.3–6.0 μg l−1), samples of sedimenting material (a toxin accumulation rate of 20 μg m-2 day−1), zooplankton (up to 0.1 ng ind.−1 in copepods), blue mussels (70–230 μg kg−1 DW), pelagic and benthic fish (herring (1.0–3.4 μg kg−1 DW in herring muscle or liver) and flounder (1.3-6.2 μg kg−1 DW in muscle, and 11.7-26.3 μg kg−1 DW in liver). A laboratory experiment showed that N. spumigena filaments developed a decreased buoyancy at increased salinities and that they were even sinking with a rate of up to 1,7 m day−1 at the highest salinity (32 PSU). This has implications for the fate of brackish water cyanobacterial blooms, when these reach more saline waters. It can be speculated that a significant part of the blooms content of nodularin will reach benthic organisms in this situation, compared to blooms decaying in brackish water, where most of the bloom is considered to be decomposed in the surface waters.

Significantly improved oxidation of bio-based furans into furan carboxylic acids using substrate-adapted whole cells

Abstract Furan carboxylic acids are important building blocks in polymer and fine chemical industries. In this work, a simple substrate adaptation strategy was applied to improve the catalytic performances of Comamonas testosteroni SC1588 cells for the synthesis of various furan carboxylic acids. It was found that biocatalytic synthesis of 5-hydroxymethyl-2-furancarboxylic acid (HMFCA) was substantially promoted by adding histidine and increasing cell concentrations. HMFCA was produced in a quantitative yield from 200 mM HMF in 24 h. Besides, the HMFCA yields of 71%–81% were achieved with the substrate concentrations up to 250–300 mM. It was firstly found that 4-tert-butylcatechol (TBC), as the stabilizer present in HMF, exerted a significantly detrimental effect on whole-cell catalytic synthesis of HMFCA at high substrate concentrations (more than 130 mM). In addition, a variety of furan carboxylic acids such as 2-furoic acid, 5-methyl-2-furancarboxylic acid and 5-methoxymethyl-2-furancarboxylic acid were synthesized with the yields up to 98%.

Influence of Media Heat Sterilization Process on Growth Performance of Representative Strains of the Genus Lactobacillus

Lactic acid bacteria (LAB) are widely applied microorganisms in food, feed, and beverage applications, where they can provide essential functionality for product modification, increase product shelf life, or act as beneficial organisms after consumption. Among these, strains of the genus Lactobacillus are often used as starters, probiotics, or biopreservatives. For all these types of bacterial preparations, a transportable shelf-stable form of concentrated bacteria, preserving their intrinsic properties, is essential for commercial distribution. Former studies revealed a relationship between the culture medium, cellular morphology, and the robustness of Lactobacillus acidophilus NCFM (name derived from North Carolina Food Microbiology) cultures. Due to these insights, a multitude of Lactobacillus strains representative of the genus were screened regarding their sensitivity to thermal medium pretreatment possibly accompanied by the alteration of their chemical composition, such as the formation of Maillard reaction products (MRPs). This study reveals a quite diverse and different growth behavior of those strains in the form of altered or non-altered cell concentrations and the size distributions of the populations, whereby five strains of the L. delbrueckii group in particular showed increased cell concentrations combined with decreased mean cell volumes. The results are of both scientific and industrial relevance, as they highlight the necessity to consider and understand the effects of media sterilization for the applied production strain.

Scalable Culture Strategies for the Expansion of Patient-Derived Cancer Stem Cell Lines.

Cancer stem cells (CSCs) have recently raised great interest as a promising biological system for designing effective cancer therapies. The scarcity of CSCs in vivo and the consequent low numbers obtained from biopsies represent a major hurdle to the development of such strategies. It is therefore necessary to design robust scalable methods to enable efficient expansion of bona fide CSCs in vitro. Here, we evaluated the applicability of computer-controlled bioreactors combined with 3D aggregate culture and microcarrier technology, widely used in stem cell bioprocessing, for the expansion and enrichment of CSCs isolated from different types of solid tumors—colorectal cancer (CRC) and non-small-cell lung cancer (NSCLC) from two patients. Results show that these culture strategies improved cell expansion and CSC enrichment. Both patient-derived CSC lines were able to grow on microcarriers, the best results being achieved for PPlus 102-L, Pro-F 102-L, Fact 102-L, and CGEN 102-L beads (5-fold and 40-fold increase in total cell concentration for CRC and NSCLC cells, respectively, in 6 days). As for 3D aggregate culture strategy, the cell proliferation profile was donor dependent. NSCLC cells were the only cells able to form aggregates and proliferate, and the flat-bottom bioreactor vessel equipped with a trapezoid-shaped paddle impeller was the most efficient configuration for cell growth (21-fold increase in cell concentration achieved in 8 days). Serum-free medium promotes CSC enrichment in both 3D aggregate and microcarrier cultures. The protocols developed herein for CSC expansion have the potential to be transferred to clinical and industrial settings, providing key insights to guide bioprocess design towards the production of enriched CSC cultures in higher quantity and improved quality.

Bactericidal Activity of Superhydrophobic and Superhydrophilic Copper in Bacterial Dispersions.

A method based on nanosecond laser processing was used to design superhydrophilic and superhydrophobic copper substrates. Three different protocols were used to analyze the evolution of the bactericidal activity of the copper substrates with different wettability. Scanning electron microscopy was used to study the variation of cell morphology after the attachment to superhydrophilic and superhydrophobic surfaces. The dispersions of Escherichia coli K12 C600 and Klebsiella pneumoniae 811 in Luria Bertani broth in contact with the superhydrophilic copper surface showed enhanced bacterial inactivation, associated with toxic action of both hierarchically textured copper surface and high content of Cu2+ ions in the dispersion medium. In contrast, the bacterial dispersions in contact with the superhydrophobic copper substrates demonstrated an increase in cell concentration with time until the development of corrosion processes. The resistance of bacterial cells to contact the copper substrates is discussed on the basis of surface forces, determining the primary adhesion and of the protective action of a superhydrophobic state of the surface against electrochemical and biological corrosion.

Development and quantitative characterization of the precursor rheology of hyaluronic acid hydrogels for bioprinting

Bioprinting technologies have tremendous potential for advancing regenerative medicine due to the precise spatial control over depositing a printable biomaterial, or bioink. Despite the growing interest in bioprinting, the field is challenged with developing biomaterials for extrusion-based bioprinting. The paradigm of contemporary bioink studies relies on trial-and-error methods for discovering printable biomaterials, which has little practical use for others who endeavor to develop bioinks. There is pressing need to follow the precedent set by a few pioneering studies that have attempted to standardize bioink characterizations for determining the properties that define printability. Here, we developed a pentenoate-functionalized hyaluronic acid hydrogel (PHA) into a printable bioink and used three recommended, quantitative rheological assessments to characterize the printability: 1) yield stress, 2) viscosity, and 3) storage modulus recovery. The most important characteristic is the yield stress; we found a yield stress upper limit of ∼1000 Pa for PHA. Measuring the viscosity was advantageous for determining shear-thinning behavior, which aided in extruding highly viscous PHA through a nozzle. Post-printing recovery is required to maintain shape fidelity and we found storage modulus recoveries above ∼85% were sufficient for PHA. Two formulations had superior printability (i.e., 1.5 MDa PHA − 4 wt%, and 1 MDa PHA − 8 wt%), and increasing cell concentrations in PHA up to 9 × 106 cells/mL had minimal effects on the printability. Even so, other factors such as sterilization and peptide modifications to enhance bioactivity may influence printability, highlighting the need for investigators to consider such factors when developing new bioinks. Statement of significanceBioprinting has potential for regenerating damaged tissues; however, there are a limited number of printable biomaterials, and developing new bioinks is challenging because the required material physical properties for extrusion-based printing are not yet known. Most new bioinks are developed by trial-and-error, which is neither efficient nor comparable across materials. There is a need for the field to begin utilizing standard methods proposed by a few pioneering studies to characterize new bioinks. Therefore, we have developed the printability of a hyaluronic acid based-hydrogel and characterized the material with three quantitative rheological tests. The current work impacts the bioprinting field by demonstrating and encouraging the use of universal bioink characterizations and by providing printability windows to advance new bioink development.

Membrane stripping enables effective electrochemical ammonia recovery from urine while retaining microorganisms and micropollutants

Ammonia recovery from urine avoids the need for nitrogen removal through nitrification/denitrification and re-synthesis of ammonia (NH3) via the Haber-Bosch process. Previously, we coupled an alkalifying electrochemical cell to a stripping column, and achieved competitive nitrogen removal and energy efficiencies using only electricity as input, compared to other technologies such as conventional column stripping with air. Direct liquid-liquid extraction with a hydrophobic gas membrane could be an alternative to increase nitrogen recovery from urine into the absorbent while minimizing energy requirements, as well as ensuring microbial and micropollutant retention. Here we compared a column with a membrane stripping reactor, each coupled to an electrochemical cell, fed with source-separated urine and operated at 20 A m−2. Both systems achieved similar nitrogen removal rates, 0.34 ± 0.21 and 0.35 ± 0.08 mol N L−1 d−1, and removal efficiencies, 45.1 ± 18.4 and 49.0 ± 9.3%, for the column and membrane reactor, respectively. The membrane reactor improved nitrogen recovery to 0.27 ± 0.09 mol N L−1 d−1 (38.7 ± 13.5%) while lowering the operational (electrochemical and pumping) energy to 6.5 kWhe kg N−1 recovered, compared to the column reactor, which reached 0.15 ± 0.06 mol N L−1 d−1 (17.2 ± 8.1%) at 13.8 kWhe kg N−1.Increased cell concentrations of an autofluorescent E. coli MG1655 + prpsM spiked in the urine influent were observed in the absorbent of the column stripping reactor after 24 h, but not for the membrane stripping reactor. None of six selected micropollutants spiked in the urine were found in the absorbent of both technologies.Overall, the membrane stripping reactor is preferred as it improved nitrogen recovery with less energy input and generated an E. coli- and micropollutant-free product for potential safe reuse. Nitrogen removal rate and efficiency can be further optimized by increasing the NH3 vapor pressure gradient and/or membrane surface area.

Increasing cell concentration does not affect specific ferrous iron oxidation rate in a continuously stirred tank bioreactor

Microbial oxidation of ferrous to ferric iron allows efficient oxidative processing of sulfide minerals under ambient conditions. This study determined the effect of cell concentration of a mixed mesophilic microbial culture on iron oxidation rate, and evaluated if there was a cell concentration threshold that dictates a maximal volumetric iron oxidation rate. A bioreactor with feedback-loading of ferrous media was operated at 30 °C to maintain a redox potential of +480 mV vs. Ag/AgCl at pH of 1.3. A positive and linear correlation (R2 = 0.955) between the cell concentration (6.8 × 107–7.1 × 109 cells mL−1) and volumetric biological iron oxidation (up to 6.9 g L−1 h−1) was observed. The specific iron oxidation was not affected by cell concentration, and no biocatalytic threshold was observed. This indicated that a high cell concentration can be used to achieve a high volumetric iron oxidation rate, enabling the use of a compact reactor size.

Inertial Microfluidic Syringe Cell Concentrator.

Low-cost, easy-to-use cell concentration tools are in urgent demand for biomedical diagnosis in resource-poor settings. Herein, we propose a novel inertial microfluidic syringe cell (IMSC) concentrator that employs inertial focusing to increase cell concentration through ordering the cell and removing the cell-free fluid. A three-part structure, consisting of a cap-shaped upper housing, a circular gasket, and a lower housing with a spiral channel, is adopted for simple fabricating and assembling, which enables the seamless translation of our IMSC concentrator into commercial outcomes without additional redesigning. The performance characterization indicates that our IMSC concentrator is capable of processing samples with different initial concentrations over a broad flow rate range. The satisfactory concentration performances over a broad driving flow rate range make it possible for our IMSC concentrator to be driven by pushing the syringe with single hand. Finally, pollen particles and MCF-7 cells are successfully concentrated at a high throughput of 3.0 mL/min (up to 4.2 × 107 counts/mL) under the hand-powered drive. We envision wide applications of our IMSC concentrator as "centrifugation on a syringe tip" to various cell concentration pretreatments in resource-poor settings.

Analysis of red blood cell partitioning at bifurcations in simulated microvascular networks

Partitioning of red blood cells (RBCs) at vascular bifurcations has been studied over many decades using in vivo, in vitro, and theoretical models. These studies have shown that RBCs usually do not distribute to the daughter vessels with the same proportion as the blood flow. Such disproportionality occurs, whereby the cell distribution fractions are either higher or lower than the flow fractions and have been referred to as classical partitioning and reverse partitioning, respectively. The current work presents a study of RBC partitioning based on, for the first time, a direct numerical simulation (DNS) of a flowing cell suspension through modeled vascular networks that are comprised of multiple bifurcations and have topological similarity to microvasculature in vivo. The flow of deformable RBCs at physiological hematocrits is considered through the networks, and the 3D dynamics of each individual cell are accurately resolved. The focus is on the detailed analysis of the partitioning, based on the DNS data, as it develops naturally in successive bifurcations, and the underlying mechanisms. We find that while the time-averaged partitioning at a bifurcation manifests in one of two ways, namely, the classical or reverse partitioning, the time-dependent behavior can cycle between these two types. We identify and analyze four different cellular-scale mechanisms underlying the time-dependent partitioning. These mechanisms arise, in general, either due to an asymmetry in the RBC distribution in the feeding vessels caused by the events at an upstream bifurcation or due to a temporary increase in cell concentration near capillary bifurcations. Using the DNS results, we show that a positive skewness in the hematocrit profile in the feeding vessel is associated with the classical partitioning, while a negative skewness is associated with the reverse one. We then present a detailed analysis of the two components of disproportionate partitioning as identified in prior studies, namely, plasma skimming and cell screening. The plasma skimming component is shown to under-predict the disproportionality, leaving the cell screening component to make up for the difference. The crossing of the separation surface by the cells is observed to be a dominant mechanism underlying the cell screening, which is shown to mitigate extreme heterogeneity in RBC distribution across the networks.

The influence of cell concentration at cryopreservation on neutrophil engraftment after autologous peripheral blood stem cell transplantation

BackgroundPeripheral blood stem cell concentrations are traditionally adjusted to 20–40×106leukocytes/mL prior to freezing. This low cell concentration at cryopreservation implies larger volumes with more dimethyl sulfoxide being used, and higher cost and toxicity at the time of transplant. Higher cell concentrations have been reported but this is not widely accepted. Moreover, the influence of cell concentration on engraftment has not been well documented. Therefore, this study retrospectively analyzed the influence of peripheral blood stem cell concentration at freezing on engraftment after autologous hematopoietic stem cell transplantation. MethodLeukapheresis products were plasma-depleted and cryopreserved with 5% dimethyl sulfoxide, 6% hydroxyethylamide solution and 4% albumin in a −80°C freezer. Individual patient data from hospital records were reviewed. ResultsFifty consecutive patients with oncological diseases underwent 88 leukaphereses. Median age was six years (range: 1–32 years) and median weight was 19kg (range: 8–94kg). Median leukocyte concentration was 109×106/mL at collection and 359×106 (range: 58–676×106) at freezing with 78% viability (range: 53–95%); leukocyte recovery after thawing was 95% (range: 70–100%). In multivariate analysis, cell concentration (p-value=0.001) had a negative impact on engraftment. Patients infused with bags frozen with <200×106leukocytes/mL engrafted after a median of nine days (range: 8–12 days), 200–400×106leukocytes/mL after 11 days (range: 9–20 days); 400–600×106leukocytes/mL after 12 days (range: 8–19 days) and with cell concentrations >600×106leukocytes/mL, engraftment was after 14 days (range: 13–22 days). ConclusionIn patients with adequate CD34 cell collections, total leukocyte concentrations of 282×106/mL, freezing with 5% dimethyl sulfoxide and 6% hydroxyethylamide solution without a controlled-rate freezer, and storing cells at −80°C yielded excellent engraftment. Further increases in cell concentration may delay engraftment, without affecting safety.

Microfluidics: A New Layer of Control for Extrusion-Based 3D Printing.

Advances in 3D printing have enabled the use of this technology in a growing number of fields, and have started to spark the interest of biologists. Having the particularity of being cell friendly and allowing multimaterial deposition, extrusion-based 3D printing has been shown to be the method of choice for bioprinting. However as biologically relevant constructs often need to be of high resolution and high complexity, new methods are needed, to provide an improved level of control on the deposited biomaterials. In this paper, we demonstrate how microfluidics can be used to add functions to extrusion 3D printers, which widens their field of application. Micromixers can be added to print heads to perform the last-second mixing of multiple components just before resin dispensing, which can be used for the deposition of new polymeric or composite materials, as well as for bioprinting new materials with tailored properties. The integration of micro-concentrators in the print heads allows a significant increase in cell concentration in bioprinting. The addition of rapid microfluidic switching as well as resolution increase through flow focusing are also demonstrated. Those elementary implementations of microfluidic functions for 3D printing pave the way for more complex applications enabling new prospects in 3D printing.

Improving the ecological relevance of aquatic bacterial communities in biodegradability screening assessments

Concentrating cells from aqueous samples is a common requirement for the enumeration of biomass, investigations of microbial diversity and detection of relatively rare organisms in the environment. Accurately representing the initial sampled environments in the concentrated cells is of particular importance when the subsequent analyses have tangible environmental, economic and societal consequences, as is the case with environmental exposure and risk assessment of chemicals. This study investigated the potential use of four different cell concentration methods: centrifugation, membrane filtration, tangential flow filtration and column colonisation. These methods were assessed against a series of scientific and practical criteria, including: similarity of concentrated community to initial environmental sample; cell concentration achieved; biodegradation test outcome; sample throughput; and capital and maintenance costs. All methods increased cell concentration by as little as 10-fold to as much as 1000-fold. DGGE and 454 pyrosequencing analysis showed concentrated communities to have >60% similarity to each other, and the initial sample. There was a general trend for a more reliable assessment of 4-nitrophenol biodegradation in 96-well plate biodegradation assays, with increasing cell concentration. Based on the selection criteria, it is recommended that there is not one concentration method fit for all purposes, rather, the appropriate method should be selected on a case-by-case basis. Membrane filtration would be the most suitable method for low sample volumes; the increased throughput capacity of tangential flow filtration renders it most suitable for large volumes; and centrifugation is most suitable for samples with high initial biomass concentrations. The poor similarity in microbial community composition of the column colonised samples compared to the initial samples, suggested a concentration basis; this combined with its low sample throughput precluded this approach for future concentration studies of planktonic bacterial samples.

An integrated growth kinetics and computational fluid dynamics model for the analysis of algal productivity in open raceway ponds

An integrated growth kinetic, light transfer and computational fluid dynamics (CFD) model was developed to simulate the algal growth in open raceway ponds (ORP). C. vulgaris was used as a model algal strain. The coefficients of the growth kinetics were experimentally determined for the prediction of the growth of C. vulgaris as a function of environmental factors of light intensity, temperature and pH value. Experiments were conducted to grow C. vulgaris in lab-scale ORPs with medium depths of 0.20, 0.25 and 0.30 m to validate the mathematical model. The final measured biomass concentration after the 3-week growth were 0.48, 0.41, and 0.35 g/L for the ORPs with the medium depths of 0.20, 0.25, and 0.30 m, respectively. The predicted algal productivities for a 3-week cultivation were 7.3, 7.4, and 7.5 g/m2/day for depths of 0.20, 0.25, and 0.30 m, respectively, which well agreed with the measured values of 6.8, 7.2 and 7.4 g/m2/day, respectively. The biomass productivity decreased with the increase of growth time due to the increase of cell concentration. The model was further used to analyze the effects of different harvesting strategies on the algal productivity in ORPs. The algal productivity for the 3-week cultivation in the ORP with a 0.2 m depth by harvesting 50% algae at the target 0.2 g/L cell density was 10.5 g/m2/day, which was 43.8% higher than 7.3 g/m2/day for the 3-week cultivation under the same condition without harvesting at a final cell density of 0.48 g/L. The average algal productivity decreased with the increase of harvesting cell density.

Biofilms in Full-Scale Drinking Water Ozone Contactors Contribute Viable Bacteria to Ozonated Water.

Concentrations of viable microbial cells were monitored using culture-based and culture-independent methods across multichamber ozone contactors in a full-scale drinking water treatment plant. Membrane-intact and culturable cell concentrations in ozone contactor effluents ranged from 1200 to 3750 cells/mL and from 200 to 3850 colony forming units/mL, respectively. Viable cell concentrations decreased significantly in the first ozone contact chamber, but rose, even as ozone exposure increased, in subsequent chambers. Our results implicate microbial detachment from biofilms on contactor surfaces, and from biomass present within lime softening sediments in a hydraulic dead zone, as a possible reason for increasing cell concentrations in water samples from sequential ozone chambers. Biofilm community structures on baffle walls upstream and downstream from the dead zone were significantly different from each other ( p = 0.017). The biofilms downstream of the dead zone contained a significantly ( p = 0.036) higher relative abundance of bacteria of the genera Mycobacterium and Legionella than the upstream biofilms. These results have important implications as the effluent from ozone contactors is often treated further in biologically active filters and bacteria in ozonated water continuously seed filter microbial communities.

Phytoplankton Concentration Measurements Base On Arduino Microcontroller

In this research is designing and manufacture Phytoplankton concentration measurements in liquid medium based on arduino microcontroller. The design works with by exploiting fluorescence phenomenon, by using Purple Light Emitting Diode (λ = 405 nm, P = 10 mW, frequency modulation 625 Hz) as a light source absorbed by phytoplankton, mesuring vessel, optical filters, and photodiodes. Data obtained of the photodiode sensor is then conducted data acquisition by arduino, the quantitiy of phytoplankton concentration will be displayed on the lcd. From testing to Phytopathton for the concentration range it was found that for the concentration range 102 - 106 cells / ml obtained a consistent relationship the intensity of fluorescence with the increase in cell concentration. Gradients obtained for high range concentration with R2 = 0.9632 lower than the low range concentration with R2 = 0.9642.

Petroleum Product as Substrate for the Production of Biosurfactive Amphiphlies by &lt;i&gt;Pseudomonas Aeruginosa&lt;/i&gt;

Biosurfactant production by Pseudomonas aeruginosa by utilizing diesel as the source of energy and carbon was studied in this research. Biosurfactant-producing strain of the organism was isolated from hydrocarbon-contaminated water and grown in a mineral medium supplemented with diesel. Production of biosurfactant was assayed by monitoring the increase in cell concentration, biosurfactant concentration, emulsification index and decrease in surface tension. Highest level of cell concentration and biosurfactant concentration (3.3^10 8 CFU/ml and 0.0108mg/ml respectively) were obtained at 132hrs. Emulsification index reached its maximum with 33.3% at 108hrs. Surface tension reached its minimum at 120hrs with a value of 1.1^10 -6 N/m. The results showed that diesel can be utilized by P. aeruginosa to produce biosurfactant and early stationary phase isolates can be used to obtain higher yield. It also revealed the increasing potentiality of microorganisms in the aspect of oil spill cleanup and rapid reclamation of contaminated lands and water bodies. Keywords : Biosurfactant, diesel, surface tension, emulsification index, cell biomass, Pseudomonas aeruginosa .

Comparative Studies on the Biosurfactant Production Capacity of &lt;i&gt;Bacillus Subtilis&lt;/i&gt; and &lt;i&gt;Pseudomonas Aeruginosa&lt;/i&gt; Using Engine Oil and Diesel Respectively as Substrate

The study was carried out to compare the the production capabilities and the biosurfactant activity of the bacteria, Bacillus subtilis and Pseudomonas aeruginosa using engine oil and diesel as the substrates respectively. The test organisms were isolated from engine oil contaminated soil as in the case of the Bacillus subtilis, which was collected from an automobile workshop in Samaru, Zaria and hydrocarboncontaminated water in the case of the Pseudomonas aeruginosa. The medium used for the experiment was a mineral medium supplemented with 2% engine oil and 2% diesel as the sole source of carbon and energy for Bacillus subtilis and Pseudomonas aeruginosa respectively. Production of biosurfactant was assayed by monitoring the increase in cell concentration, biosurfactant concentration, emulsification index and decrease in surface tension. Highest level of cell concentration and biosurfactant concentration (3.3 x 108 CFU/ml and 0.0106mg/ml respectively) were obtained at 144 h for the Pseudomonas aeruginosa using diesel as source of carbon and energy while the highest level of cell concentration and biosurfactant concentration (3.2 x 108 CFU/ml and 0.0096mg/ml respectively) were obtained at 120hrs for the Bacillus subtilis using engine oil as source of carbon and energy. The research show that Pseudomonas aeruginosa using diesel as the sole source of carbon and energy is better for the production of biosurfactant than Bacillus subtilis using engine oil as the sole source of carbon and energy.Key words: Biosurfactant, engine oil, diesel, Pseudomonas aeruginosa, Bacillus subtilis.

The Influence of Short Values of Hydraulic and Sludge Retention Time on Performance of a Membrane Bioreactor Treating Sunflower Oil Refinery Wastewater

In this work, the performance of organic pollutant removal, membrane fouling and sludge morphology in a submerged membrane bioreactor (MBR) treating sunflower oil refinery wastewater (SORW) containing high oleic content was studied during 52 days’ operation at short values of 18 h and 10 days for hydraulic retention time and sludge retention time, respectively. The removal efficiencies of chemical oxygen demand (COD), oil and grease (OG p-value=0.034 and rP=0.920; p-value=0.003, respectively). Additionally, increase in MLVSS concentration which was due to an increase in cell concentration and was not related to accumulation of OG p-value=0.037 and rP=0.773; p-value=0.024, respectively). The results of SVI, ST, EPS, particle size distribution and microscopic observation showed change in sludge morphology to flocs of smaller size (unimodal, with mode of 20 μm) with high compressibility (SVI=44.0 mL g–1 MLSS) and bioflocculating ability (ST=20.4±3.3 NTU). The results of the present study were indicative of a very good potential of the MBR for treatment of SORWs.

Local Heterogeneities Improve Matrix Connectivity in Degradable and Photoclickable Poly(ethylene glycol) Hydrogels for Applications in Tissue Engineering.

Hydrolytically degradable poly(ethylene glycol) (PEG) hydrogels are promising platforms for cell encapsulation and tissue engineering. However, hydrolysis leads to bulk degradation and a decrease in hydrogel mechanical integrity. Despite these challenges, hydrolytically degradable hydrogels have supported macroscopic neotissue growth. The goal of this study was to combine experimental methods with a multiscale mathematical model to analyze hydrogel degradation concomitant with neocartilage growth in PEG hydrogels. Primary bovine chondrocytes were encapsulated at increasing densities (50, 100, and 150 million cells/mL of precursor solution) in a radical-mediated photoclickable hydrogel formed from 8-arm PEG-co-caprolactone end-capped with norbornene and cross-linked with PEG dithiol. Two observations were made in the experimental system: (1) the cell distribution was not uniform and cell clustering was evident, which increased with increasing cell density and (2) a significant decrease in the initial hydrogel compressive modulus was observed with increasing cell concentration. By introducing heterogeneities in the form of cell clusters and spatial variations in the network structure around cells, the mathematical model explained the drop in initial modulus and captured the experimentally observed spatial evolution of ECM and the construct modulus as a function of cell density and culture time. Overall, increasing cell density led to improved ECM formation, ECM connectivity, and overall modulus. This study strongly points to the importance of heterogeneities within a cell-laden hydrogel in retaining mechanical integrity as the construct transitions from hydrogel to neotissue.