Effect Of Initial Cell Concentration Research Articles

Effect of Initial Cell Concentration on Bio-Oxidation of Pyrite before Gold Cyanidation

Bio-oxidation of refractory sulfidic gold minerals has been applied at the commercial scale as a pre-treatment to improve gold yields and reduce chemical consumption during gold cyanidation. In this study, the effect of initial cell concentration on the oxidation of pyritic gold ore was evaluated with four aerated bioreactors at 30 °C with 10% pulp density and pH maintained at 1.4 with NaOH. Results of NaOH consumption and changes in soluble Fe and S concentrations indicated that increasing the initial cell concentration from 2.3 × 107 to 2.3 × 1010 cells mL−1 enhanced pyrite oxidation during the first week. However, by day 18 the reactor with the lowest initial cell concentration showed profound performance enhancement based on soluble Fe and S concentrations, sulfide-S and pyrite contents in the residues, and subsequent gold leaching of the bio-oxidation residues by cyanidation. Overall, the results showed that the cell concentration was clearly beneficial during the initial stages of oxidation (first 7–8 days).

Modeling the effect of initial cell concentration and soluble solids on the plasma inactivation of yeast in apple juices

Atmospheric cold plasma is a powerful and profitable microbial decontamination technology in the food industry. The microbial load and food matrix have a great influence on the plasma inactivation effect. This study aimed to quantify the effects of initial cell concentration and soluble solids on the inactivation of yeast in apple juice by gas-phase surface discharge plasma. A computer simulation model was developed to predict the inactivation process using commercial finite element software, COMSOL Multiphysics, and the model was verified by experiments. Studies have shown that the inactivation of yeast was affected by the initial cell concentration and soluble solids. These effects were quantified by fitting equations and used as model inputs. The simulation model predicted the D-value of plasma inactivation of yeast under different discharge voltages and apple juice volume, which was verified in experiments. Therefore, the established model can be used for plasma development to predict how the food matrix affects the inactivation process, thereby providing useful and practical tools for amplifying the commercial application of plasma.

Effects of initial cell concentration, growth phase, and process parameters on the viability of Lactobacillus rhamnosus GG after spray drying

During spray drying, probiotics encounter several stresses which can reduce their viability. To obtain powder with a sufficient amount of viable probiotics, we evaluated the effects of different process parameters, such as initial cell concentration and the bacterial growth phase, on the viability of the model probiotic Lactobacillus rhamnosus GG. Increasing the initial biomass did not positively impact bacterial viability after spray drying. For growth, we found that stationary grown bacterial cells were more resistant to the spray-drying process than mid-log grown cells, probably owing to an initiated stress response. Furthermore, a full factorial 3³ design was used to assess the influence of three different conditions of inlet temperature, feed rate, and atomizing air flow on the outlet temperature and bacterial viability after spray drying. As expected, inlet temperature had the largest influence on both outlet temperature and log-reduction in bacterial viability. An interaction effect was also observed between feed rate and inlet temperature. Considering the viability of L. rhamnosus GG, the optimal outlet temperature ranged between 50 and 60 °C for obtaining powders with the lowest log-reductions in viability.

Effect of culture age and initial inoculum size on lipid accumulation and productivity in a hybrid cultivation system of Chlorella vulgaris

Chlorella vulgaris was cultivated in a hybrid (two-stage) system. The effect of the transferring time from nutrient-replete phase with a low light intensity (photobioreactor) to the nutrient deprivation phase (open pond) with a higher light intensity, as well as the effect of initial cell concentration in the deprivation phase, on the growth rate and lipid content of the microalgae was investigated. The microalgae were transferred to the nutrient deprived medium at different intervals with various initial cell concentrations. Transferring the cultivated medium of the 4th day with the initial cell concentration of 66mgL−1 into the deprivation phase resulted in a highest lipid productivity of 9.21±0.64mgL−1d−1 and lipid content of 53.97±4.30%. In a single-stage cultivation where a medium with nitrogen deficiency was used, despite a low lipid content (maximum 30%), a lipid productivity of 9.95±0.46mgL−1d−1 was observed that was slightly higher than that for the hybrid system.

Model‐based analysis of the role of biological, hydrological and geochemical factors affecting uranium bioremediation

Uranium contamination is a serious concern at several sites motivating the development of novel treatment strategies such as the Geobacter-mediated reductive immobilization of uranium. However, this bioremediation strategy has not yet been optimized for the sustained uranium removal. While several reactive-transport models have been developed to represent Geobacter-mediated bioremediation of uranium, these models often lack the detailed quantitative description of the microbial process (e.g., biomass build-up in both groundwater and sediments, electron transport system, etc.) and the interaction between biogeochemical and hydrological process. In this study, a novel multi-scale model was developed by integrating our recent model on electron capacitance of Geobacter (Zhao et al., 2010) with a comprehensive simulator of coupled fluid flow, hydrologic transport, heat transfer, and biogeochemical reactions. This mechanistic reactive-transport model accurately reproduces the experimental data for the bioremediation of uranium with acetate amendment. We subsequently performed global sensitivity analysis with the reactive-transport model in order to identify the main sources of prediction uncertainty caused by synergistic effects of biological, geochemical, and hydrological processes. The proposed approach successfully captured significant contributing factors across time and space, thereby improving the structure and parameterization of the comprehensive reactive-transport model. The global sensitivity analysis also provides a potentially useful tool to evaluate uranium bioremediation strategy. The simulations suggest that under difficult environments (e.g., highly contaminated with U(VI) at a high migration rate of solutes), the efficiency of uranium removal can be improved by adding Geobacter species to the contaminated site (bioaugmentation) in conjunction with the addition of electron donor (biostimulation). The simulations also highlight the interactive effect of initial cell concentration and flow rate on U(VI) reduction.

Effect of Initial Cell Concentration on Ethanol Production by Flocculent Saccharomyces cerevisiae with Xylose-Fermenting Ability

Different initial cell concentrations of a recombinant flocculent Saccharomyces cerevisiae MA-R4 were evaluated for their effects on xylose fermentation and glucose-xylose cofermentation. A high initial cell concentration greatly increased both the substrate utilization and ethanol production rates. During xylose fermentation, the highest rates of xylose consumption (2.58 g/L h) and ethanol production (0.83 g/L h) were obtained at an initial cell concentration of 13.1 g/L. During cofermentation, the highest rates of glucose consumption (14.4 g/L h), xylose consumption (2.79 g/L h), and ethanol production (6.68 g/L h) were obtained at an initial cell concentration of 12.7 g/L. However, a high initial cell density had no positive effect on the maximum ethanol concentration and ethanol yield mainly due to the increased amount of by-products including xylitol. The ethanol yield remained almost constant (0.34 g/g) throughout xylose fermentation (initial cell concentration range, 1.81-13.1 g/L), while it was slightly lower at high initial cell concentrations (9.87 and 12.7 g/L) during cofermentation. The determination of the appropriate initial cell concentration is necessary for the improvement of substrate utilization and ethanol yield.

Adhesion behavior and removability of Escherichia coli on stainless steel surface

Adhesion behavior of Escherichia coli from its suspension onto stainless steel (type 304) surface was studied, focusing on the effects of initial cell concentration of suspension, suspending medium, and roughness of stainless steel surface. The results demonstrated that the adhesion of E. coli was significantly enhanced by the cell concentration of contaminants. The adhesion was observed even in short contact periods of time, but it increased and reached a plateau within 3–4 h. The plateau value of surface cell density was roughly proportional to the cell concentration of the suspension. Rinsing experiments indicated that a relatively high percentage of cells were found to be irreversibly attached on the surface when peptone saline was used as a suspending medium. The adherent cells were however shown to be quite vulnerable to removal with water as a rinsing medium. Moreover surface roughness was found to affect the removability of adherent cells.

Production of Hard-Type Cheese Using Free or Immobilized Freeze-Dried Kefir Cells as a Starter Culture

This study provides a contribution to hard-type cheese starter culture production through the use of a freeze-dried culture in the ripening of hard-type cheeses. The effect of initial cell concentration, ripening temperature, and cell immobilization of kefir on the degree of openness, mold spoilage, microbial associations, physicochemical characteristics, and aroma-related compounds was studied. Use of kefir starter cultures resulted in cheese with an increased shelf life and resistance to spoilage as compared to control cheeses without kefir inoculants. Furthermore, the freeze-dried kefir culture improved aroma, taste, and texture characteristics while increasing the degree of openness in comparison to traditional hard-type cheese products. The kefir culture resulted in an increase in counts of total aerobic bacteria, yeasts and molds, lactococci, and lactobacilli until the 15th day of ripening. From then on, only lactobacilli counts increased, reaching levels up to 9.17 log CFU/g in cheeses ripened at 5 degrees C using freeze-dried kefir cells immobilized on casein. SPME-GC/MS analysis revealed major differences in volatile composition, especially with regard to alcohols (up to 75%), carbonyl compounds (up to 75%), and esters (up to 64%) between cheeses made with kefir cells and cheeses made without kefir inoculants.

The effect of initial cell concentration on xylose fermentation by Pichia stipitis

Xylose was fermented using Pichia stipitis CBS 6054 at different initial cell concentrations. A high initial cell concentration increased the rate of xylose utilization, ethanol formation, and the ethanol yield. The highest ethanol concentration of 41.0 g/L and a yield of 0.38 g/g was obtained using an initial cell concentration of 6.5 g/L. Even though more xylitol was produced when the initial cell concentrations were high, cell density had no effect on the final ethanol yield. A two-parameter mathematical model was used to predict the cell population dynamics at the different initial cell concentrations. The model parameters, a and b correlate with the initial cell concentrations used with an R(2) of 0.99.

Disinfection of Legionella pneumophila by ultrasonic treatment with TiO 2

An ultrasonic treatment system, using a TiO 2 photocatalyst, was used to disinfect Legionella pneumophila. A kinetic study of the process indicates that TiO 2 significantly improves the disinfection process. The concentrations of viable cells were reduced to 6% of the initial concentrations in the presence of 0.2 g/ml TiO 2 after a 30 min of treatment period, while only an 18% reduction was observed in the absence of TiO 2. The potency of the disinfection could be enhanced, to some extent, by increasing the amount of TiO 2 used. Cell concentrations were decreased by an order of 3 within 30 min of treatment in the presence of 1.0 g/ml TiO 2. The disinfection power in the presence of TiO 2 versus Al 2O 3 was also compared and the findings showed that TiO 2 induced a higher cell killing. No significant effect of initial cell concentration on the disinfection was found in the range of 10 2–10 7 CFU/ml after a 30 min of treatment period. The mechanism of cell killing was investigated by examining the effects of OH radical scavengers such as ascorbic acid, histidine and glutathione. The disinfection power was reduced in samples that contained these radical scavengers, thus indicating the importance of OH radicals.

Response surface analysis on the effect of cell concentration and light intensity on hydrogen production by Rhodopseudomonas capsulata

Abstract A mixture of acetate, propionate and butyrate was used as a carbon source to produce H 2 by Rhodopseudomonas capsulata . The specific H 2 production rate, H 2 yield and light efficiency were evaluated at various levels of initial cell concentration and light intensity by applying response surface methodology. The mixture of 1.8 g/l acetate, 0.2 g/l propionate and 1.0 g/l butyrate could be readily utilized by R. capsulata for H 2 production. Their consumption rate followed the order of acetate > propionate > butyrate. The response surface methodology results demonstrated the effects of initial cell concentration and light intensity as well as their interactive effects on H 2 production. The optimum R H 2 was achieved at an initial cell concentration of 0.77 g/l and a light intensity of 4170 lux. Initial cell concentrations of 0.6–1.2 g/l and light intensities of 3000 lux or higher were suitable for H 2 yield and light efficiency.

Optimisation of initial cell concentration enhances freeze-drying tolerance of Pseudomonas chlororaphis

The freeze-drying tolerance of Pseudomonas chlororaphis, an antifungal bacterium used as biocontrol agent was investigated. P. chlororaphis is freeze-drying sensitive and the viability drops more than 3 log units in the absence of protective freeze-drying medium. Of the freeze-drying media tested, lactose, sucrose, trehalose, glutamate, sucrose with glutamate, skimmed milk, and skimmed milk with trehalose, skimmed milk gave the lowest survival (0.6 ± 0.2%) and sucrose the highest (6.4 ± 1.2%). Cellular accumulation of sucrose from the freeze-drying medium and the protective effect of sucrose were dependent on sucrose concentration. The effect of initial cell concentration, from 1 × 10 7 to 5 × 10 10 CFU/ml, on survival after freeze-drying was studied for carbon starved cells with sucrose as freeze-drying medium. The highest freeze-drying survival values, 15–25%, were obtained for initial cell concentrations between 1 × 10 9 and 1 × 10 10 CFU/ml. For cell concentrations outside this window more than 10 times lower survival values were observed. P. chlororaphis was cultivated to induce stress response that could confer protection against freeze-drying inactivation. Carbon starvation and, to a lesser extent, heat treatment enhanced freeze-drying tolerance. By combining optimal cell concentration, optimal sucrose concentration and carbon starvation the survival after freeze-drying was 26 ± 6%.

Disinfection kinetics of Legionella pneumophila by ultraviolet irradiation

Disinfection kinetics of Legionella pneumophila by ultraviolet irradiation was investigated. The change in viable cell concentration with exposure time could be divided into three steps: lag step in which little change in viable cell concentration was observed, fast disinfection step and slow disinfection step. The slow disinfection step was not observed at the initial cell concentrations below about 10(6) cfu/mL. The disinfection kinetics were well described with two parameters; lag time and disinfection rate constant of the fast disinfection step. The effects of UV intensity, temperature and initial cell concentration in the kinetic parameters were investigated. With increasing initial cell concentration, the lag time decreased and the disinfection rate constant increased. The effects of initial cell concentration on the kinetic parameters were considered to be attributed to the decrease in the effective UV irradiation intensity due to the partial shield of UV light by the disinfected cells. The empirical correlations were presented for predicting the lag time and disinfection rate constant. Furthermore, UV disinfection of L. pneuophila in a model hot-tub connected with external irradiation chamber was also discussed.

Inactivation and injury of Escherichia coli O157:H7 and Staphylococcus aureus by pulsed electric fields

Two pathogenic microorganisms Escherichia coli O157:H7 and Staphylococcus aureus, suspended in peptone solution (0.1% w/v) were treated with 12, 14, 16 and 20 kV/cm electric field strengths with different pulse numbers up to 60 pulses. Pulsed electric field (PEF) treatment at 20 kV/cm with 60 pulses provided nearly 2 log reduction in viable cell counts of E. coli O157:H7 and S. aureus. S. aureus cells were slightly more resistant than E.coli O157:H7 cells. The results related to the effect of initial cell concentration of E. coli O157:H7 on the PEF inactivation showed that more inactivation was obtained by decreasing initial cell concentration. Any possible injury by PEF was also investigated after applying 20 kV/cm electric field to the microorganisms. As a result, it was determined that there was 35.92 to 43.36% injury in E. coli O157:H7 cells, and 17.26 to 30.86% injury in S. aureus cells depending on pulse number. The inactivation results were also described by a kinetic model.

Effect of biotreatment with Thiobacillus ferrooxidans on the floatability of sphalerite and galena

The bacterium Thiobacillus ferrooxidans triggers the surface modification of sulfide minerals to provide hydrophilicity or hydrophobicity for the flotation of sphalerite and galena. The effects of initial cell concentration, period of biotreatment and pulp density on the floatability of the minerals are discussed. With galena, flotation enhancement obtained through sulfuric acid treatment was retarded by biotreatment at all cell concentrations due to chemical effects. Such a decrease occurred for sphalerite only at cell concentrations sufficiently high for bacterial attachment to the mineral surface. The variables affecting surface modification (and, thus, flotation response of the minerals) include the cell concentration used for bacterial conditioning, the period of biotreatment and the pulp density. Although bacterial growth during biotreatment was observed even in the absence of nutrients, such growth was more common in the sphalerite suspension than in the galena suspension. Cell protein estimations suggest that more cells are attached on galena than on sphalerite. Probable reaction mechanisms associated with bacterial modification are discussed.

Mechanism of freezing injury to erythrocytes: Effect of initial cell concentration on the post-thaw hemolysis

It has been previously reported that the post-thaw hemolysis of erythrocytes, frozen under various conditions, depends upon the initial cell concentration; increasing the cell concentration decreases the proportion of intact cells after freeze-thawing. In the present study, the effect of cell concentration upon post-thaw hemolysis, examined mainly by the morphological observation of freezing patterns in specimens with or without cryoprotectant glycerol, was most marked in concentrated cell suspensions in which the cells had become shrunken as a result of extracellular freezing. The addition of glycerol lessened the packing effect progressively as the concentration was increased. The results thus obtained may be explained by assuming that cells, deformed in the freezing process, and rigid at low temperatures, might undergo mechanical damage when subjected to compression and abnormal contact.

Effect of initial cell concentration of the postthaw hemolysis of frozen erythrocytes

Effect of initial cell concentration of the postthaw hemolysis of frozen erythrocytes

The effect of the initial cell concentration upon survival of bacteria at -22 C.

The effect of the initial cell concentration upon survival of bacteria at -22 C.