Specific Cell Growth Rate Research Articles

Mathematical modeling of continuous ethanol fermentation in a membrane bioreactor by pervaporation compared to conventional system: Genetic algorithm

In this paper, genetic algorithm was used to investigate mathematical modeling of ethanol fermentation in a continuous conventional bioreactor (CCBR) and a continuous membrane bioreactor (CMBR) by ethanol permselective polydimethylsiloxane (PDMS) membrane. A lab scale CMBR with medium glucose concentration of 100gL−1 and Saccharomyces cerevisiae microorganism was designed and fabricated. At dilution rate of 0.14h−1, maximum specific cell growth rate and productivity of 0.27h−1 and 6.49gL−1h−1 were respectively found in CMBR. However, at very high dilution rate, the performance of CMBR was quite similar to conventional fermentation on account of insufficient incubation time. In both systems, genetic algorithm modeling of cell growth, ethanol production and glucose concentration were conducted based on Monod and Moser kinetic models during each retention time at unsteady condition. The results showed that Moser kinetic model was more satisfactory and desirable than Monod model.

Oxygen transfer as a tool for fine-tuning recombinant protein production by Pichia pastoris under glyceraldehyde-3-phosphate dehydrogenase promoter.

Effects of oxygen transfer on recombinant protein production by Pichia pastoris under glyceraldehyde-3-phosphate dehydrogenase promoter were investigated. Recombinant glucose isomerase was chosen as the model protein. Two groups of oxygen transfer strategies were applied, one of which was based on constant oxygen transfer rate where aeration rate was Q O/V=3 and 10 vvm, and agitation rate was N=900min(-1); while the other one was based on constant dissolved oxygen concentrations, C DO=5, 10, 15, 20 and 40% in the fermentation broth, by using predetermined exponential glucose feeding with μ o=0.15h(-1). The highest cell concentration was obtained as 44gL(-1) at t=9h of the glucose fed-batch phase at C DO=20% operation while the highest volumetric and specific enzyme activities were obtained as 4440UL(-1) and 126Ug(-1) cell, respectively at C DO=15% operation. Investigation of specific enzyme activities revealed that keeping C DO at 15% was more advantageous with an expense of relatively higher by-product formation and lower specific cell growth rate. For this strategy, the highest oxygen transfer coefficient and oxygen uptake rate were K L a=0.045s(-1) and OUR=8.91mmolm(-3)s(-1), respectively.

An Innovative Optical Sensor for the Online Monitoring and Control of Biomass Concentration in a Membrane Bioreactor System for Lactic Acid Production

Accurate real-time process control is necessary to increase process efficiency, and optical sensors offer a competitive solution because they provide diverse system information in a noninvasive manner. We used an innovative scattered light sensor for the online monitoring of biomass during lactic acid production in a membrane bioreactor system because biomass determines productivity in this type of process. The upper limit of the measurement range in fermentation broth containing Bacillus coagulans was ~2.2 g·L−1. The specific cell growth rate (µ) during the exponential phase was calculated using data representing the linear range (cell density ≤ 0.5 g·L−1). The results were consistently and reproducibly more accurate than offline measurements of optical density and cell dry weight, because more data were gathered in real-time over a shorter duration. Furthermore, µmax was measured under different filtration conditions (transmembrane pressure 0.3–1.2 bar, crossflow velocity 0.5–1.5 m·s−1), showing that energy input had no significant impact on cell growth. Cell density was monitored using the sensor during filtration and was maintained at a constant level by feeding with glucose according to the fermentation kinetics. Our novel sensor is therefore suitable for integration into control strategies for continuous fermentation in membrane bioreactor systems.

Advances in recombinant antibody manufacturing.

Since the first use of Chinese hamster ovary (CHO) cells for recombinant protein expression, production processes have steadily improved through numerous advances. In this review, we have highlighted several key milestones that have contributed to the success of CHO cells from the beginning of their use for monoclonal antibody (mAb) expression until today. The main factors influencing the yield of a production process are the time to accumulate a desired amount of biomass, the process duration, and the specific productivity. By comparing maximum cell densities and specific growth rates of various expression systems, we have emphasized the limiting parameters of different cellular systems and comprehensively described scientific approaches and techniques to improve host cell lines. Besides the quantitative evaluation of current systems, the quality-determining properties of a host cell line, namely post-translational modifications, were analyzed and compared to naturally occurring polyclonal immunoglobulin fractions from human plasma. In summary, numerous different expression systems for mAbs are available and also under scientific investigation. However, CHO cells are the most frequently investigated cell lines and remain the workhorse for mAb production until today.

Effects of artificial sweeteners on metal bioconcentration and toxicity on a green algae Scenedesmus obliquus

The ecotoxicity of heavy metals depends much on their speciation, which is influenced by other co-existing substances having chelating capacity. In the present study, the toxic effects of Cd2+ and Cu2+ on a green algae Scenedesmus obliquus were examined in the presence of two artificial sweeteners (ASs), acesulfame (ACE) and sucralose (SUC) by comparing the cell specific growth rate μ and pulse-amplitude-modulated (PAM) parameters (maximal photosystem II photochemical efficiency Fv/Fm, actual photochemical efficiency Yield, and non-photochemical quenching NPQ) of the algae over a 96-h period. Simultaneously, the bioconcentration of the metals by the algal cells in the presence of the ASs was measured. The presence of ACE enhanced the growth of S. obliquus and promoted the bioconcentration of Cd2+ in S. obliquus, while the impacts of SUC were not significant. Meanwhile, EC50 values of Cd2+ on the growth of S. obliquus increased from 0.42 mg/L to 0.54 mg/L and 0.48 mg/L with the addition of 1.0 mg/L ACE and SUC, respectively. As for Cu2+, EC50 values increased from 0.13 mg/L to 0.17 mg/L and 0.15 mg/L with the addition of 1.0 mg/L ACE and SUC, respectively. In summary, the two ASs reduced the toxicity of the metals on the algae, with ACE showing greater effect than SUC. Although not as sensitive as the cell specific growth rate, PAM parameters could disclose the mechanisms involved in metal toxicity at subcellular levels. This study provides the first evidence for the possible impact of ASs on the ecotoxicity of heavy metals.

Enhancement of 5-keto-d-gluconate production by a recombinant Gluconobacter oxydans using a dissolved oxygen control strategy

The rapid and incomplete oxidation of sugars, alcohols, and polyols by the gram-negative bacterium Gluconobacter oxydans facilitates a wide variety of biological applications. For the conversion of glucose to 5-keto-d-gluconate (5-KGA), a promising precursor of the industrial substance L-(+)-tartaric acid, G.oxydans DSM2343 was genetically engineered to strain ZJU2, in which the GOX1231 and GOX1081 genes were knocked out in a markerless fashion. Then, a secondary alcohol dehydrogenase (GCD) from Xanthomonas campestris DSM3586 was heterologously expressed in G.oxydans ZJU2. The 5-KGA production and cell yield were increased by 10% and 24.5%, respectively. The specific activity of GCD towards gluconate was 1.75±0.02U/mg protein, which was 7-fold higher than that of the sldAB in G.oxydans. Based on the analysis of kinetic parameters including specific cell growth rate (μ), specific glucose consumption rate (qs) and specific 5-KGA production rate (qp), a dissolved oxygen (DO) control strategy was proposed. Finally, batch fermentation was carried out in a 15-L bioreactor using an initial agitation speed of 600rpm to obtain a high μ for cell growth. Subsequently, DO was continuously maintained above 20% to achieve a high qp to ensure a high accumulation of 5-KGA. Under these conditions, the maximum concentration of 5-KGA reached 117.75g/L with a productivity of 2.10g/(L·h).

Isolation and growth kinetics of a novel phenol-degrading bacterium Microbacterium oxydans from the sediment of Taihu Lake (China).

Seven phylogenetically diverse phenol-degrading bacterial strains designated as P1 to P7 were isolated from the industry-effluent dump sites of an industrial area near Taihu Lake, China. Through the 16S rDNA sequence analysis, these strains were widely distributed among five different genera: Rhodococcus (P1), Pseudomonas (P2-P4), Acinetobacter (P5), Alcaligenes (P6), and Microbacterium (P7). All seven isolates were capable of growing with phenol as the sole carbon source. Strain P7 was found to be a novel phenol-degrading strain by detailed morphological, physiological and biochemical characteristic analysis as well as the 16S rDNA sequence analyses, and was named Microbacterium oxydans LY1 (M. oxydans LY1 in its short form). Degradation experiments of phenol at various initial concentrations (20-1,000 mg/L) revealed that phenol is an inhibitory substrate to M. oxydans LY1. In a batch culture experiment, more than 95% of the phenol (500 mg/L) was degraded by M. oxydans LY1 at 30°C, pH 7.0 and 120 rpm within 88 h. Phenol concentration higher than 200 mg/L was found to inhibit the bacterial growth. The growth kinetics correlated well with the Haldane model with μmax (maximum specific cell growth rate) = 0.243 h(-1), Ks (saturation constant) = 25.7 mg/L, and Ki (self-inhibition constant) = 156.3 mg/L. This is the first report of the ability of M. oxydans to degrade phenol, and the results could provide important information for bioremediation of phenol-contaminated environments.

Characterization of the growth, chlorophyll content and lipid accumulation in a marine microalgae Dunaliella tertiolecta under different nitrogen to phosphorus ratios

Microalgal lipids are regarded as main future feedstock of biofuels for its higher efficiency of accumulation and sustainable production. In order to investigate the effect of various nitrogen to phosphorus ratios on cells growth, chlorophyll content and accumulation of lipids in Dunaliella tertiolecta, experiments were carried out in modified microalgal medium with inorganic nitrogen (nitrate-nitrogen) or organic nitrogen (urea-nitrogen) as the sole nitrogen source at initial N:P ratios ranging from 1:1 to 32:1. The favorable N:P of 16:1 in the nitrate-N or urea-N medium yielded the maximum cell density and specific growth rate. Decrease in chlorophyll content were observed at the N:P of 4:1 in both nitrate-N and urea-N cultures. It was also observed that the maximum lipids concentration was obtained at the N:P of 4:1 in both nitrate and urea nutrient medium. The lipid productivity and lipid content of cultures in the urea-N medium at the N:P of 4:1were markedly higher than those from cultures with other N:P ratios (p < 0.05). The results of this work illustrate the possibility that higher ratios of nitrogen to phosphorus have enhancing effect on cells growth of D. tertiolecta. Conversely, higher lipid accumulation is associated with a decrease in chlorophyll content under lower ratios of nitrogen to phosphorus. The results confirm the hypothesis of this study that a larger metabolic flux has been channeled to lipid accumulation in D. tertiolecta cells when the ratios of nitrogen to phosphorus drop below a critical level.

Molar ratios of uracil to thymine in algae samples as an indicator of algae growth rate and its application to cyanobacteria-dominated waters

Phytoplankton growth rates are highly dynamic during critical ecological periods, and are of great significance in monitoring programmes as an early warning signal of harmful algal bloom. However, it was still difficult to obtain in situ algal growth rates in a broad spatiotemperal scale. Here we aimed to explore the potential of estimating algal growth rate (AGR) by using a cellular nucleobasederived ratio. AGR in batch cultures of Microcystis aeruginosa (FACHB-905) was calculated by the daily increment of in vivo chlorophyll fluorescence, and culture cells were collected at different growth phase for nucleobase analysis. The specific growth rate of algae cells was found to increase as a logarithmic function of the molar ratio of uracil to thymine in culture cells, and the inflection point of the fitting curve could be a critical value for the exponential phase of algal growth. In a case study conducted in a large reservoir in Yangtze estuary, AGR was estimated from 0.24 to 0.52 day–1 during a Microsystis-dominated period in October 2014 and one site was recognized at high risk of algal blooming. In conclusion, the ratio of uracil to thymine has potential use in estimating of the AGR, and is promising in the analysis on spatiotemporal dynamics of in situ growth rates of dominant algae.

Endoplasmic Reticulum-Associated rht-PA Processing in CHO Cells: Influence of Mild Hypothermia and Specific Growth Rates in Batch and Chemostat Cultures.

BackgroundChinese hamster ovary (CHO) cells are the main host for producing recombinant proteins with human therapeutic applications mainly because of their capability to perform proper folding and glycosylation processes. In addition, mild hypothermia is one of the main strategies for maximising the productivity of these systems. However, little information is available on the effect of culture temperature on the folding and degradation processes of recombinant proteins that takes place in the endoplasmic reticulum.MethodsIn order to evaluate the effect of the mild hypothermia on processing/endoplasmatic reticulum-associated degradation (ERAD) processes, batch cultures of CHO cells producing recombinant human tissue plasminogen activator (rht-PA) were carried out at two temperatures (37°C and 33°C) and treated with specific inhibitors of glycosylation and ERAD I (Ubiquitin/Proteasome system) or ERAD II (Autophagosoma/Lisosomal system) pathways. The effect of mild hypothermia was analysed separately from its indirect effect on specific cell growth rate. To do this, chemostat cultures were carried out at the same incubation conditions as the batch cultures, controlling cell growth at high (0.017 h-1) and low (0.012 h-1) dilution rates. For a better understanding of the investigated phenomenon, cell behaviour was also analysed using principal component analysis (PCA).Results and ConclusionResults suggest that rht-PA is susceptible to degradation by both ERAD pathways studied, revealing that processing and/or ERAD processes are sensitive to temperature cultivation in batch culture. Moreover, by isolating the effect of culture temperature from the effect of cell growth rate verifyed by using chemostat cultures, we have found that processing and/or ERAD processes are more sensitive to reduction in specific growth rate than low temperature, and that temperature reduction may have a positive effect on protein processing. Interestingly, PCA indicated that the integrated performance displayed by CHO cells is modulated predominantly by specific growth rate, indicating that the culture temperature has a lower weighted effect within the range of conditions evaluated in this work.

Effect of malate on docosahexaenoic acid production from Schizochytrium sp. B4D1

Background: Malate involves in the citrate/malate and transhydrogenase cycles to provide precursors for docosahexaenoic acid (DHA) synthesis. The optimal strategy was investigated for increasing DHA production in Schizochytrium species during fermentation. Results: DHA production increased by 47% and reached 5.51 g/L when 4 g malate/L was added during the rapid lipid accumulation stage in shake-flasks culture. Inducing effects of malate was further investigated through the analysis of three kinetic parameters, including specific cell growth rate (μ), specific glucose consumption rate (q Glu ) and DHA formation rate (q DHA ). DHA concentration was enhanced through a novel fed-batch strategy to a maximum value of 30.7 g/L, giving a yield of 0.103 g DHA/g glucose and a productivity of 284 mg L - 1 h - 1 . Conclusion: A novel malate feeding strategy was developed that enhanced DHA yield and productivity of Schizochytrium species which may offer a desirable method for industrial applications. Normal 0 21 false false false EN-US ZH-CN X-NONE /* Style Definitions */ table.MsoNormalTable {mso-style-name:Tabla normal; mso-tstyle-rowband-size:0; mso-tstyle-colband-size:0; mso-style-noshow:yes; mso-style-priority:99; mso-style-parent:; mso-padding-alt:0cm 5.4pt 0cm 5.4pt; mso-para-margin:0cm; mso-para-margin-bottom:.0001pt; mso-pagination:widow-orphan; font-size:10.5pt; mso-bidi-font-size:11.0pt; font-family:Calibri,sans-serif; mso-ascii-font-family:Calibri; mso-ascii-theme-font:minor-latin; mso-hansi-font-family:Calibri; mso-hansi-theme-font:minor-latin; mso-font-kerning:1.0pt; mso-ansi-language:EN-US; mso-fareast-language:ZH-CN;}

The RNA chaperone Hfq enables the environmental stress tolerance super-phenotype of Pseudomonas putida.

The natural physiological regime of the soil bacterium Pseudomonas putida involves incessant exposure to endogenous metabolic conflicts and environmental physicochemical insults. Yet, the role of assisted small RNA-mRNA pairing in the stress tolerance super-phenotype that is the trademark of this bacterium has not been accredited. We have thoroughly explored the physiological consequences -in particular those related to exogenous stress - of deleting the hfq gene of P. putida, which encodes the major RNA chaperone that promotes sRNA-target mRNA interactions. While the overall trend was a general weakening of every robustness descriptor of the Δhfq strain, growth parameters and production of central metabolic enzymes were comparatively less affected than other qualities that depend directly on energy status (e.g. motility, DNA repair). The overall catalytic vigour of the mutant decreased to < 20% than the wild-type strain, as estimated from the specific growth rate of cells carrying the catabolic TOL plasmid pWW0 for m-xylene biodegradation. Several loss-of-function phenotypes could be traced to the effect of the Δhfq deletion on the intracellular contents of the stationary sigma factor RpoS. It thus seems that Hfq, while not indispensable for any essential function, contributes to shape the environmental lifestyle of P. putida.

A Novel Cell Substrate Candidate for Rabies Virus Vaccine Propagation and Production

Rabies is acute and fatal viral encephalitis and is estimated to cause more than 50000 human deaths annually. Several cell cultures have been introduced for rabies vaccine production such as human diploid (HDC), primary hamster kidney, fetal bovine kidney, chick embryo, and continuous line of monkey kidney (VERO) cells. In this study, a novel cell line, derived from dental pulp stem cells (RHDP) was used for rabies virus propagation and was compared to MRC-5 cell line. MRC5 showed a density higher than RHDP. The total cells obtained in a 25ml flask, was 4.2x10 6 ± 1.5x10 5 and 2.1x10 6 ± 2.6x10 5 for MRC-5 and RHDP, respectively. However, RHDP reached its maximum density sooner than MRC. The maximum cell specific growth rate of RHDP was 0.034 μ (h-1) while that of MRC was only 0.010 μ (h-1). The maximum cell division number of RHDP was 1.53 which was achieved three days after culture. Adaptation of the virus to the novel RHDP cell line was achieved after six passages of sub-culturing of the virus every 3-4 days. Rabies virus caused typical CPE and RHDP-cell-lysis in monolayers which were easily observed by microscopy. Our results suggest that RHDP could be another cell substrate candidate for rabies virus titration. The maximum specific virus production in RHDP and MRC-5 were 5.243 FFU/cell/h and 3.625 FFU/cell/h respectively; both had lower titers than those reported for Vero cell.

Evaluation of physicochemical and biological properties of chitosan/poly (vinyl alcohol) polymer blend membranes and their correlation for Vero cell growth

The blend membranes with varying weight ratios of chitosan/poly (vinyl alcohol) (CS/PVA) (1:0, 1:1, 1:2.5, 1.5:1, 1.5: 2.5) were prepared using solvent casting method and were evaluated for their potential application in single-use membrane bioreactors (MBRs). The physicochemical properties of the prepared membranes were investigated for chemical interactions (FTIR), surface morphology (SEM), water uptake, protein sorption (qe), ammonia sorption and growth kinetics of Vero cells. CS/PVA blend membrane having weight ratio of 1.5:1 had shown enhanced membrane flexibility, reduced water uptake, less protein sorption and no ammonium sorption compared to CS membrane. This blend membrane also showed comparatively enhanced higher specific growth rate (0.82/day) of Vero cells. Improved physicochemical properties and growth kinetics obtrude CS/PVA (1.5:1) as a potential surface for adhesion and proliferation with possible application in single use membrane bioreactors. Additionally, new insight explaining correlation between water holding (%) of CS/PVA (1.5:1) blend membrane and doubling time (td) of Vero cells is proposed.

Enhancement of Cellulase and Xylanase Production Using pH-Shift and Dissolved Oxygen Control Strategy with Streptomyces griseorubens JSD-1.

In this study, the production of cellulase and xylanase by Streptomyces griseorubens JSD-1 was improved by integrating the pH-shift and dissolved oxygen (DO)-constant control strategies. The pH-shift control strategy was carried out by analyzing the specific cell growth rate (μ) and specific enzyme formation rate (Q p) of S. griseorubens JSD-1. The pH was controlled at 8.0 during the first 48h to maintain high cell growth, which then shifted to 7.5 after 48h to improve the production of cellulase and xylanase. Using this method, the maximum activities of cellulase, xylanase, and filter paper enzyme (FPase) increased by 47.9, 29.5, and 113.6%, respectively, compared to that obtained without pH control. On the basis of pH-shift control, the influence of DO concentrations on biomass and enzyme production was further investigated. The maximum production of cellulase, xylanase, and FPase reached 114.38±0.96UmL(-1), 330.57±2.54UmL(-1), and 40.11±0.38UmL(-1), which were about 1.6-fold, 0.6-fold, and 3.2-fold higher than that of neutral pH without DO control conditions. These results supplied a functional approach for improving cellulase and xylanase production.

A pH shift feeding strategy for increased enduracidin production during fed–batch fermentation by a deep–sea, bacterium, Streptomyces sp. MC079

The aim of this work is to enhance enduracidin production by Streptomyces sp. MC079. Based on the time course analysis of the specific cell growth rate and specific enduracidin formation rate, a two–stage pH control strategy was proposed to improve enduracidin production by shifting the culture pH from 5.5 to 5.8 after 112 h of cultivation. By applying this pH control strategy, enduracidin concentration and productivity was 51.2 and 65.0% higher than results with uncontrolled pH batch fermentation. For further enhancement of enduracidin production, the effects of constant–rate feeding and pH-shift feeding strategy were investigated. The results indicated that the pH-shift feeding strategy increased the maximum concentration and productivity of enduracidin to 61.37 mg/L and 0.697 mg/L/h in the constant–rate feeding fermentation process. This is 73.3 and 88.9% higher than results with uncontrolled pH batch fermentation, respectively. The obtained optimal pH shift feeding strategy may be useful for the industrial–scale microbial production of enduracidin.

Establishment and characterization of a Satureja khuzistanica Jamzad (Lamiaceae) cell suspension culture: a new in vitro source of rosmarinic acid.

An in vitro approach to the production of rosmarinic acid (RA), a medicinally important caffeic acid ester, in a cell suspension culture (CSC) of Satureja khuzistanica Jamzad (Lamiaceae) has been investigated for the first time. The CSC was established from friable calli derived from shoot tip explants in Gamborg's B5 liquid medium supplemented with 30g/L sucrose, 20mg/L L-glutamine, 200mg/L casein hydrolysate, 5mg/L benzyladenine (BA) and 1mg/L indole-3-butyric acid (IBA). The effect of nitrogen source (KNO3 and (NH4)2SO4) and their different concentrations on the fresh and dry weight (g/L), as well as RA content (mg/g dry weight) were measured. CSC growth measurements indicated a maximum specific cell growth rate of 1.5/day, a doubling time of 7.6days and a high percentage of cell viability (96.4%) throughout the growth cycle. Maximum cell fresh weight (353.5g/L), dry weight (19.7g/L) and RA production (180.0mg/g) were attained at day 21 of culture. Cell growth and RA content were affected by nitrogen deficiency. Media containing 8.3mM of total nitrogen (¼ of B5 standard medium) led to a minimum cell fresh weight (243.0g/L), dry weight (17.4g/L) and RA content (38.0mg/g) after 21 days. The established CSC provided useful material for further optimization experiments aimed at a large-scale production of RA.

Effect of specific light supply rate on photosynthetic efficiency of Nannochloropsis salina in a continuous flat plate photobioreactor.

In this work, Nannochloropsis salina was cultivated in a continuous-flow flat-plate photobioreactor, working at different residence times and irradiations to study the effect of the specific light supply rate on biomass productivity and photosynthetic efficiency. Changes in residence times lead to different steady-state cell concentrations and specific growth rates. We observed that cultures at steady concentration were exposed to different values of light intensity per cell. This specific light supply rate was shown to affect the photosynthetic status of the cells, monitored by fluorescence measurements. High specific light supply rate can lead to saturation and photoinhibition phenomena if the biomass concentration is not optimized for the selected operating conditions. Energy balances were applied to quantify the biomass growth yield and maintenance requirements in N. salina cells.

Evaluation of performance of Planococcus sp. TRC1 an indigenous bacterial isolate monoculture as bioremediator for tannery effluent

An indigenous bacterial isolate Planococcus sp. TRC1 was found to tolerate Cr(VI) solution up to 500 mg/L concentration when grown in mineral salt media. Gene sequencing of the isolated strain using 16S rDNA technique and phylogenetic analysis confirmed that the species was 96% close to Planococcus maritimus (KP8). Studies on cell dynamics in batch bioreactor showed the maximum specific cell growth rate (μmax) to be 0.276 h−1. Removal of Cr(VI) was observed to be dependent on initial chromium concentration and the maximum removal of Cr(VI) (75 ± 3%) was obtained at 25 mg/L Cr(VI) solution for an incubation period of 72 h. Above this value, the removal of Cr(VI) was declined. Scanning electron microscope and Fourier transform infrared spectroscopic studies indicated that the Cr(VI) removal took place by the adsorption process on the cell outer membrane. It is observed that the adsorption process follows the Freundlich adsorption isotherm (R2 = 0.987). Planococcus sp. TRC1 reduced 80 ± 5% chemical oxygen demand (COD) of tannery effluent (COD 7,270 ± 45 mg O2/L) within 48 h of batch treatment. The elimination of cytotoxicity and genotoxicity imparted by the raw tannery effluent and Cr(VI) solution after bacterial treatment is an important observation which reflects the eco-friendly behavior of the Planococcus sp. TRC1 mediated tannery effluent and aqueous Cr(VI) solution treatment. The results revealed the applicability of Planococcus sp. TRC1 in both tannery waste and Cr(VI) reduction without affecting our environment.

Intracellular nitrite accumulation: The cause of growth inhibition of Microcystis aeruginosa exposure to high nitrite level

SummaryThe aim of the present study is to test the role of intracellular nitrite in external nitrite suppressing algal growth. We examined the growth of Microcystis aeruginosa at different nitrite levels under high nitrate conditions and without nitrate conditions. There were higher intracellular nitrite and lower Pmchla, Rd chla, αchl, maximum cell density and specific growth rate in high nitrate group than nitrate absence group at 5 mg NO2−‐N L−1. At 10 and 15 mg NO2−‐N L−1, Pmchla, Rd chla, αchl, maximum cell densities and specific growth rates in the high nitrate group became higher than those of the nitrate absence group, while a lower intracellular nitrite in the high nitrate group than nitrate absence group was observed. In addition, the intracellular nitrite and the growth of M. aeruginosa in the high nitrate group did not change from 5 to 10 mg NO2−‐N L−1. In the nitrite uptake experiment, with nitrite concentration increasing from 5 to 15 mg NO2−‐N L−1, maximum nitrite uptake rate of alga increased, and half‐saturation constant of alga decreased. These results indicate that external nitrite inhibited algal growth through stimulating intracellular nitrite rise, which resulted from overexpression of nitrite transporter.