Concentration Of Suspended Cells Research Articles

Cleaner utilization of electroplating sludge by bioleaching with a moderately thermophilic consortium: A pilot study

The semi-pilot scale bioleaching of electroplating sludge by the moderately thermophilic acidophilic consortium was carried out for the first time. During the microbial cultivation, Leptospirillum ferriphilum CS13, Acidithiobacillus caldus S2, and Sulfobacillus acidophilus CS5 could grow rapidly in a 300 L aeration packed reactor, in which the total suspended cell concentration could fluctuate around 3 × 108 cells/mL and the community structure remained relatively stable. During the bioleaching process, the microbial stock solution could effectively leach heavy metals from electroplating sludge in a stirred reactor within a few hours. Meanwhile, the effects of pH, temperature, the quantity of active culture, and liquid-solid ratio on the bioleaching behavior were also investigated. The optimal conditions for electroplating sludge bioleaching were pH 1.5, temperature 45 °C, bacterial liquid ratio 40%, liquid-solid ratio 4:1 L kg−1, and leaching time 5 h. The total removal rate of various heavy metals in electroplating sludge was over 99%. The bioleaching residue was successfully passed the TCLP test, and the total contents of heavy metals in the residue were also well below the regulatory criteria. In addition, the XRD analysis of the bioleaching residue was also confirmed that the moderately thermophilic consortium bioleaching provided a cleaner process than chemical leaching on the removal of the residual fraction metals, which was feasible and attractive for industrial treatment of electroplating sludge.

Effect of intermittent 222 nm krypton-chlorine excilamp irradiation on microbial inactivation in water

In order to assure the microbial safety of drinking water, krypton-chlorine (KrCl) excilamp treatment has emerged as a possible technology to replace the use of conventional 254-nm low-pressure mercury UVC lamps. The aim of this study was to evaluate the disinfection efficiency of the KrCl excilamp emitting power narrow-band UVC radiation at 222-nm against a spectrum of bacteria at different initial populations in model contaminated water and to develop a strategy to effectively sterilize water contaminated with high concentrations of microorganisms. Different inoculum levels (104−5, 105−6, and 106−7 CFU/ml) of Escherichia coli O157:H7, Salmonella enterica serovar Typhimurium, and Listeria monocytogenes suspended in sterile distilled water were irradiated with a KrCl excilamp. In water of high inoculum density (106−7 CFU/ml), higher resistance to UVC was observed than in samples of medium and low cell density, as a high concentration of suspended cells lowered the transmittance of UVC rays. However, intermittent application of 222-nm UV irradiation in water containing a high inoculum level showed higher inactivation capacity against all three pathogens than continuous irradiation at the same dose. The results of this study provide an interesting insight into the use of an intermittent 222-nm UVC treatment system in batch-type water reservoir facilities to reduce the risk of waterborne disease.

Continuous Flow Microfluidic Bioparticle Concentrator

Innovative microfluidic technology has enabled massively parallelized and extremely efficient biological and clinical assays. Many biological applications developed and executed with traditional bulk processing techniques have been translated and streamlined through microfluidic processing with the notable exception of sample volume reduction or centrifugation, one of the most widely utilized processes in the biological sciences. We utilize the high-speed phenomenon known as inertial focusing combined with hydraulic resistance controlled multiplexed micro-siphoning allowing for the continuous concentration of suspended cells into pre-determined volumes up to more than 400 times smaller than the input with a yield routinely above 95% at a throughput of 240 ml/hour. Highlighted applications are presented for how the technology can be successfully used for live animal imaging studies, in a system to increase the efficient use of small clinical samples, and finally, as a means of macro-to-micro interfacing allowing large samples to be directly coupled to a variety of powerful microfluidic technologies.

The effect of light direction and suspended cell concentrations on algal biofilm growth rates.

Algae biofilms were grown in a semicontinuous flat plate biofilm photobioreactor to study the effects of light direction and suspended algal cell populations on algal biofilm growth. It was determined that, under the growth conditions and biofilm thicknesses studied, light direction had no effect on long-term algal biofilm growth (26 days); however, light direction did affect the concentration of suspended algal cells by influencing the photon flux density in the growth medium in the photobioreactors. This suspended algal cell population affected short-term (7 days) algae cell recruitment and algal biofilm growth, but additional studies showed that enhanced suspended algal cell populations did not affect biofilm growth rates over the long term (26 days). Studying profiles of light transmittance through biofilms as they grew showed that most of the light became attenuated by the biomass after just a few days of growth (88 % after 3 days). The estimated biofilm thicknesses after these few days of growth were approximately 150 μm. The light attenuation data suggests that, although the biofilms grew to 700-900 μm, under these light intensities, only the first few hundred micrometers of the biofilm is receiving enough light to be photosynthetically active. We postulate that this photosynthetically active layer of the biofilm grows adjacent to the light source, while the rest of the biofilm is in a stationary growth phase. The results of this study have implications for algal biofilm photobioreactor design and operation.

Exposure of Escherichia coli ATCC 12806 to Sublethal Concentrations of Food-Grade Biocides Influences Its Ability To Form Biofilm, Resistance to Antimicrobials, and Ultrastructure

Escherichia coli ATCC 12806 was exposed to increasing subinhibitory concentrations of three biocides widely used in food industry facilities: trisodium phosphate (TSP), sodium nitrite (SNI), and sodium hypochlorite (SHY). The cultures exhibited an acquired tolerance to biocides (especially to SNI and SHY) after exposure to such compounds. E. coli produced biofilms (as observed by confocal laser scanning microscopy) on polystyrene microtiter plates. Previous adaptation to SNI or SHY enhanced the formation of biofilms (with an increase in biovolume and surface coverage) both in the absence and in the presence (MIC/2) of such compounds. TSP reduced the ability of E. coli to produce biofilms. The concentration of suspended cells in the culture broth in contact with the polystyrene surfaces did not influence the biofilm structure. The increase in cell surface hydrophobicity (assessed by a test of microbial adhesion to solvents) after contact with SNI or SHY appeared to be associated with a strong capacity to form biofilms. Cultures exposed to biocides displayed a stable reduced susceptibility to a range of antibiotics (mainly aminoglycosides, cephalosporins, and quinolones) compared with cultures that were not exposed. SNI caused the greatest increase in resistances (14 antibiotics [48.3% of the total tested]) compared with TSP (1 antibiotic [3.4%]) and SHY (3 antibiotics [10.3%]). Adaptation to SHY involved changes in cell morphology (as observed by scanning electron microscopy) and ultrastructure (as observed by transmission electron microscopy) which allowed this bacterium to persist in the presence of severe SHY challenges. The findings of the present study suggest that the use of biocides at subinhibitory concentrations could represent a public health risk.

Tsukamurella sp. E105 as a new biocatalyst for highly enantioselective hydrolysis of ethyl 2-(2-oxopyrrolidin-1-yl) butyrate

A new bacterial strain, E105, has been introduced as a biocatalyst for the enantioselective hydrolysis of ethyl (R,S)-2-(2-oxopyrrolidin-1-yl) butyrate, (R,S)-1, to (S)-2-(2-oxopyrrolidin-1-yl) butyric acid, (S)-2. This strain was isolated from 60 soil samples using (R,S)-1 as the sole carbon source. The isolate was identified as Tsukamurella tyrosinosolvens E105, based on its morphological characteristics, physiological tests, and 16S rDNA sequence analysis. The process of cell growth and hydrolase production for this strain was then investigated. The hydrolase activity reached its maximum after cultivation at 200rpm and 30°C for 36h. Furthermore, the performance of the enantioselective hydrolysis of (R,S)-1 was studied. The optimal reaction temperature, initial pH, substrate concentration, and concentration of suspended cells were 30°C, 6.8, 10 and 30g/l (DCW), respectively. Under these conditions, a high conversion (>45%) of the product (S)-2 with an excellent enantiomeric excess (ee) (>99%), and a satisfied enantiomeric ratio (E) (>600) as well were obtained. This study showed that the bacterial isolate T. tyrosinosolvens E105 displayed a high enantioselectivity towards the hydrolysis of racemic ethyl 2-(2-oxopyrrolidin-1-yl) butyrate.

Continuous ethanol production using immobilized yeast cells entrapped in loofa-reinforced alginate carriers

A culture of Saccharomyces cerevisiae M30 entrapped in loofa-reinforced alginate was used for continuous ethanol fermentation in a packed-bed reactor with initial sugar concentrations of 200-248 g/L. Maximum ethanol productivity of 11.5 g/(L·h) was obtained at an ethanol concentration of 57.4 g/L, an initial sugar concentration of 220 g/L and a dilution rate (D) of 0.2 h-1. However, a maximum ethanol concentration of 82.1 g/L (productivity of 9.0 g/(L·h)) was obtained at a D of 0.11 h-1. Ethanol productivity in the continuous culture was 6-8-fold higher than that in the batch culture. Due to the developed carrier's high biocompatibility, high porosity, and good mechanical strength, advantages such as cell regeneration, reusability, altered mechanical strength, and high capacity to trap active cells in the reactor were achieved in this study. The immobilized cell reactor was successfully operated for 30 days without any loss in ethanol productivity. The average conversion yield was 0.43-0.45 throughout the entire operation, with an immobilization yield of 47.5%. The final total cell concentration in the reactor was 37.3 g/L (17.7 g/L immobilized cells and 19.6 g/L suspended cells). The concentration of suspended cells in the effluent was 0.8 g/L.

Continuous ethanol production using immobilized yeast cells entrapped in loofa-reinforced alginate carriers.

A culture of Saccharomyces cerevisiae M30 entrapped in loofa-reinforced alginate was used for continuous ethanol fermentation in a packed-bed reactor with initial sugar concentrations of 200-248 g/L. Maximum ethanol productivity of 11.5 g/(L·h) was obtained at an ethanol concentration of 57.4 g/L, an initial sugar concentration of 220 g/L and a dilution rate (D) of 0.2 h-1. However, a maximum ethanol concentration of 82.1 g/L (productivity of 9.0 g/(L·h)) was obtained at a D of 0.11 h-1. Ethanol productivity in the continuous culture was 6-8-fold higher than that in the batch culture. Due to the developed carrier’s high biocompatibility, high porosity, and good mechanical strength, advantages such as cell regeneration, reusability, altered mechanical strength, and high capacity to trap active cells in the reactor were achieved in this study. The immobilized cell reactor was successfully operated for 30 days without any loss in ethanol productivity. The average conversion yield was 0.43-0.45 throughout the entire operation, with an immobilization yield of 47.5%. The final total cell concentration in the reactor was 37.3 g/L (17.7 g/L immobilized cells and 19.6 g/L suspended cells). The concentration of suspended cells in the effluent was 0.8 g/L.

Bacterial immobilization by adhesion onto agave-fiber/polymer foamed composites

Adhesion of Pseudomonas putida F1 onto agave-fiber/recycled-polyethylene foamed composites was studied under different controlled conditions. The adhesion process was analyzed in batch experiments controlling factors such as pH, contact time, temperature, initial biomass concentration and ionic strength; and was verified by scanning electron microscopy (SEM). The number of adhered bacteria after the experimental time was determined by difference between concentration of suspended cells in NaCl solution contained in two different Erlenmeyer flasks, one of the flasks with composite pellets and the other one without them. The concentration of cells in each flask was obtained using the serial dilution technique. Experimental data analysis showed that adsorption follows first-order kinetics. And it was further corroborated to be an irreversible process. For the first time, an equation is proposed here to predict the correlation between adhered bacteria and aqueous pH. In addition to the obvious reuse of waste material, these results suggested that agave-fiber/polymer foamed composites could be used as support for bacterial immobilization to be applied, among others in environmental processes such as bioremediation and biofiltration of gases with almost limitless possibilities.

Effect of hot trub and particle addition on fermentation performance of Saccharomyces cerevisiae

In this investigation, the effect of hot trub (a precipitation product of the wort boiling process in beer manufacturing) addition on fermentation performance was observed under variation of yeast vitality, and origin and the amount of hot trub. Its addition improved suspended cell concentrations for all yeast vitalities tested, and the more trub was added, the greater the effect. Further, pilot-scale fermentations showed significantly lower pH values and an accelerated extract degradation, thus, advancing fermentation by roughly 1 day for hot trub addition versus the fermentation of extremely bright wort. Since the positive effect of trub has often been associated with its particulate characteristics, fermentations with fractionated model particles, such as poly(vinylpyrrolidones) and kieselguhr, of different particle sizes were carried out under variation of yeast vitality and particle amounts. The addition of both particle types also improved fermentation performance, however, the effect was not as great as that of hot trub. Particulate material may improve the development of CO 2 from the fermenting medium, thus reducing its concentration and inhibitory effect on yeast metabolism. The most effective fraction of kieselguhr had a 40 μm peak which also occurred in particle size distributions of all hot trubs investigated. This could be of particular interest when discussing particle effects.

Dynamics of drinking water biofilm in flow/non-flow conditions

Drinking water biofilm formation on polyvinyl chloride (PVC), cross-linked polyethylene (PEX), high density polyethylene (HDPE) and polypropylene (PP) was followed in three different reactors operating under stagnant or continuous flow regimes. After one week, a quasi-steady state was achieved where biofilm total cell numbers per unit surface area were not affected by fluctuations in the concentration of suspended cells. Metabolically active cells in biofilms were around 17–35% of the total cells and 6–18% were able to form colony units in R 2A medium. Microbiological analysis showed that the adhesion material and reactor design did not affect significantly the biofilm growth. However, operating under continuous flow (0.8–1.9 Pa) or stagnant water had a significant effect on biofilm formation: in stagnant waters, biofilm grew to a less extent. By applying mass balances and an asymptotic biofilm formation model to data from biofilms grown on PVC and HDPE surfaces under turbulent flow, specific growth rates of bacteria in the biofilm were found to be similar for both materials (around 0.15 day −1) and much lower than the specific growth rates of suspended bacteria (around 1.8 day −1).

Effects of operating conditions on the adhesive strength of Pseudomonas fluorescens biofilms in tubes

Understanding the mechanical properties of biofilms, especially the force required to disrupt them and remove them from substrata is very important to development of antibiofouling strategies. In this work, a novel micromanipulation technique with a specially designed T-shaped probe has been developed to serve as an experimental means to measure directly the adhesive strength of biofouling deposits on the surface of a glass test stud. The basic principle of this novel technique is to pull away a whole biofilm accumulated on the surface of a glass test stud with T-shaped probe, and to measure simultaneously the force imposed on the biofilm. The adhesive strength between the biofilms and the surface to which they are attached, is defined as the work per unit area required to remove the biofilms from the surface. The biofouling experiments were performed on an elaborate design of a simulated heat exchanger system. A monoculture of Pseudomonas fluorescens was chosen as the fouling microorganism for the laboratory studies. Results indicate that the adhesive strength of the biofilm was affected by the conditions of operation, such as biofilm age, nutrient concentration, suspended cell concentration, pH, surface roughness of the substratum and fluid velocity. As noted, the effect of fluid velocity on the biofilm adhesive strength seemed to overwhelm other factors. At the same operating conditions, the biofilm adhesive strength increased as the fluid velocity increased within the range of 0.6–1.6 m/s. In addition, the flow-related biofilm structures were observed that biofilms generally grew as a more compact pattern at the higher fluid velocity. Apparently, the fluid velocity can affect the biofilm structure, which in turn determines the biofilm adhesive strength. The knowledge of the biofilm adhesive strength with associated influences of the operating conditions may be used to define better cleaning procedures.

Mathematical modeling of granular activated carbon (GAC) biofiltration system

In this study, a mathematical model of a fixed bed Granular Activated Carbon (GAC) biofiltration system was developed to predict the organic removal efficiency of the filter. The model consists of bulk transportation, adsorption, utilization, and biodegradation of organics. The variation of the specific surface area due to biofilm growth and the effect of filter backwash were also included in the model. The intrapellet diffusion and the diffusion of substrate in the biofilm were described by linear driving force approximation (LDFA) method. Biodegradation of organics was described by Monod kinetics. Sips adsorption isotherm was used to analyze the initial adsorption equilibrium of the system. The model showed that the organic removal efficiency of the biofilter greatly depends on the parameters related to the biological activities such as the maximum rate of substrate utilization (k max) and biomass yield (Y) coefficients. Parameters such as suspended cell concentration (X s) and decay constant (K d) had little effects on the model simulation results. The filter backwash also had no significant impact on the performance of the biofilter.

Biooxidation of a gold concentrate in a continuous stirred tank reactor: mathematical model and optimal configuration

A model was developed to represent the biooxidation by Acidithiobacillus ferrooxidans of a refractory gold concentrate in a continuous stirred tank reactor (CSTR). The model accounts for the growth of attached and planktonic cells, their role in mineral solubilisation, and the contribution of ferric ions to the process. Predicted solubilisation rates increase with increasing solids dilution rates until a maximum, in agreement with the experimental results. Concentration of suspended cells was more affected by changes in solids dilution rates than attached cells did, behaviour well represented by the model. The model was also able to predict the observed increase in cell growth and mineral solubilisation due to the decrease in particle size and the enrichment of the air with CO 2. Finally, the model was used to predict the optimal configuration of a continuous biooxidation system that minimises the residence time required to attain a defined degree of mineral solubilisation. This configuration was found to be a two-stage system consisting of a CSTR followed by a plug flow reactor. The latter can be replaced by a series of smaller equal-size CSTRs.

Light Attenuation in Suspension of the Purple Bacterium Rhodobacter capsulatus and the Green Alga Chlamydomonas reinhardtii.

A simple and rapid calculation method, which is based on the Beer-Lambert law and Rose and Lloyd’s hypothesis, was proposed for the determination of light attenuation profiles in suspensions of photosynthetic microorganisms. In this method, extinction coefficients measured spectrophotometrically at a single concentration of suspended cells over the whole range of wavelengths emitted from different light sources were used for reflecting the physical and biological characteristics of cells, which may change during a course of cultivation. The validity of this approach was confirmed by use of suspensions of two kinds of photosynthetic cells, the purple bacterium Rhodobacter capsulatus and the green alga Chlamydomonas reinhardtii, illuminated by three light sources with different irradiation spectra. This approach can estimate well the profiles of the light attenuation in these systems, irrespective of the spectra of the light sources, until the transmitted light intensity falls to one tenth of the incident intensity.

Biogenic production of cyanide and its application to gold recovery.

Chromobacterium violaceum is a cyanogenic (cyanide-producing) microorganism. Cyanide is used on an industrial scale to complex and recover gold from ores or concentrates of ores bearing the precious metal. A potentially useful approach in gold mining operations could be to produce cyanide biologically in relatively small quantities at the ore surface. In this study, C. violaceum grown in nutrient broth formed a biofilm and could complex and solubilize 100% of the gold on glass test slides within 4-7 days. Approximately 50% of the cyanide- recoverable gold could be mobilized from a biooxidized sulfidic-ore concentrate. Complexation of cyanide in solution by gold appeared to have a beneficial effect on cell growth--viable cell counts were nearly two orders of magnitude greater in the presence of gold-coated slides or biooxidized ore substrates than in their absence. C. violaceum was cyanogenic when grown in alternative feedstocks. When grown in a mineral salt solution supplemented with 13.3% v/v swine fecal material (SFM), cells exhibited pigmentation and suspended cell concentrations comparable to cultures grown in nutrient broth. Glycine supplements stimulated production of cyanide in 13.3% v/v SFM. In contrast, glycine was inhibitory when added at the time of inoculation in the more concentrated SFM, decreasing cell numbers and reducing ultimate bulk-solution cyanide concentrations. However, aeration and addition of glycine to stationary phase cells grown on 13.3% v/v SFM anaerobically resulted in rapid production and high concentrations (up to 38 mg l(-1)) of cyanide. This indicates that biogenesis of cyanide may be supported in remote areas using locally produced and inexpensive agricultural feedstocks in place of commercial media.

Efficacy of silver-coated fabric to prevent bacterial colonization and subsequent device-based biofilm formation.

Efficacy of silver-coated poly(ethylene terephthalate) to prevent bacterial attachment and subsequent infection was quantified in vitro, in both batch- and flowing-fluid experiments. Kinetic analysis of batch suspended cell cultures of Staphylococcus epidermidis (SE), at various growth-limiting nutrient concentrations, in the absence of any fabric, indicated a maximum culture growth rate constant micro(max) = 0.78 +/- 0.02 h(-1). Batch experiments for Control fabric samples indicated that SE cultures exhibited about the same suspended cell growth rate (0.72 +/- 0.02 h(-1)) as observed in batch suspended cultures without fabric. Suspended SE cultures in the presence of silver-coated fabric grew at a considerably lower rate, 0.15 +/- 0.01 h(-1), indicating the inhibitory effect of Ag(+2) ion released from the fabric. Growth rates of suspended SE cultures were 5-6 times higher in the fluid phase in contact with the Control fabric compared to cultures exposed to silver-coated fabric. Maximum suspended cell concentrations attained at time = 24 h were 1-2 orders of magnitude higher for Control fabrics vs. silver-coated fabric. In all batch colonization experiments, both live and dead SE bacterial cells accumulate on the surfaces of both silver-coated and Control fabrics. Adherent viable SE cells accumulated to 1-2 orders of magnitude more ( approximately 5 x 10(+8) cells/cm(2)) on Control fabric than SE cells on the silver-coated fabric ( approximately 1.1 x 10(+6) cells/cm(2)), respectively. Between 70-95% SE cells on the Control fabric were viable, while on the silver-coated fabric samples, at 24 h, viable cells were less than 10% of the adherent community (i.e., greater than 90% nonviable cells). In flow cell colonization experiments, SE cells accumulated on Control fabric to a maximum adherent cell concentration of 6 x 10(+7) - 8 x 10(+7) cells/cm(2) by 24 h with the proportion of viable cells remaining relatively constant at 76% throughout an experiment. Both noninvasive microscopic enumeration and destructive assays gave the same results for adherent cell numbers. Using silver-coated fabric, total cells numbers (live + dead) reached a level of approximately 1.1 x 10(+7) - 3.0 x 10(+7) cells/cm(2) after about 6 h and remained constant. However, while the proportion of viable cells initially on the surface was 63-75%, this fraction dropped continuously during each experiment to less than 6% viable cells at 24 h. Regardless of the criteria, the number of viable or nonviable cells attached to silver-coated fabric were significantly lower than on Control fabric.

Effects of Shock Waves on Living Tissue Cells and its Deformation Process Using a Mathematical Model.

In this study, damage of living tissue cells (red blood cells and cancer cells) and experimental cell models (microcapsules) by plane shock waves is carried out experimentally. In addition, the effects of physical condition on the degree of damage are evaluated by constructing an appropriate mathematical model. To explain these phenomena, the red blood cells and the microcapsules are modeled mathematically as two spherical elastic shells filled with liquid. The fundamental equations express the oscillation of the spherical elastic shell in response to the incident pressure wave in the surrounding fluid. Frequency responses of the elastic shell model of two living tissue cells with mutual interaction in water are analyzed. From the results of this analysis, the effects of (1) the rise time of shock waves, (2) the distance between cells on shock-induced damage, (3) the concentration of suspended cells and (4) the incideuce angle of shock waves are discussed. It is found that effects of these parameters are large in certain cases.

Characterization of absorption and scattering properties for various yeast strains by time-resolved spectroscopy.

An understanding of the optical properties of biological media and cells is essential to the development of noninvasive optical studies of tissues. Unicellular organisms offer a unique opportunity to investigate the factors affecting light propagation, since they can be manipulated in ways impossible for more complex biological samples. In this study, we examined optical absorption and scattering properties of strongly multiple scattering yeast suspensions by means of near-infrared (NIR) time-resolved spectroscopy (TRS) and a sample substitution method. We determined the critical parameters for photon migration by varying the cell organelle content, the cell ploidy, the cell size, and the concentration of suspended cells. The results indicate that the photon absorption is insensitive to cell differentiation and that the cell volume is the primary factor determining light-scattering property.

A statistical analysis of the effect of substrate utilization and shear stress on the kinetics of biofilm detachment

One of the least understood processes affecting biofilm accumulation is detachment. Detachment is the removal of cells and cell products from an established biofilm and subsequent entrainment in the bulk liquid. The goal of this research was to determine the effects of shear stress and substrate loading rate on the rate of biofilm detachment. Monopopulation Pseudomonas aeruginosa and undefined mixed population biofilms were grown on glucose in a RotoTorque biofilm reactor. Three levels of shear stress and substrate loading rate were used to determine their effects on the rate of detachment. Suspended cell concentrations were monitored to determine detachment rates, while other variables were measured to determine their influence on the detachment rate. Results indicate that detachment rate is directly related to biofilm growth rate and that factors which limit growth rate will also limit detachment rate. No significant influence of shear on detachment rate was observed.A new kinetic expression that incorporates substrate utilization rate, yield, and biofilm thickness was compared to published detachment expressions and gives a better correlation of data obtained both in this research and from previous research projects, for both mono- and mixed-population biofilms.