Maximum Cell Density Research Articles

Optimization of culture conditions for human bone marrow-derived mesenchymal stromal cell expansion in macrocarrier-based Tide Motion system.

With high cell doses required for mesenchymal stromal cell (MSC) clinical trials, there is a need to upgrade technologies that facilitate efficient scale up of MSCs for cell therapy. Conventional expansion with 2D culture vessels becomes the bottleneck when large cell dosages are required. Tide Motion bioreactors offer a robust, scalable platform using BioNOC II macrocarriers developed for the production of adherent cells. We evaluated the growth and expansion of bone marrow-derived MSCs (BM-MSCs) on the macrocarrier-based culture system by optimizing key parameters such as cell seeding densities, culturing conditions, and harvesting procedures to achieve optimal cell growth. BM-MSCs expanded in conventional 2D adherent cultures were seeded into BioNOC II macrocarriers and grown in serum-containing or serum-free medium. BM-MSCs attained a maximum cell density of 0.49 ± 0.07×106 cells/carrier after 12 days of culture in BioNOC II macrocarriers with cell viability > 86% while retaining MSC specific characteristics such as surface marker expression, tri-lineage differentiation potential, immunosuppressive properties, and potency. These results reveal the feasibility of BM-MSC expansion in the scalable macrocarrier-based Tide Motion system both under serum and serum-free conditions and represent an important step for the large-scale production system of BM-MSC based cellular therapies.

Pemanfaatan Hidrolisat Talas (Colocasia esculenta L.) pada Kultur Miksotrofik Mikroalga Tetraselmis chui: Pengamatan Pertumbuhan dan Kadar Lipida

This study aims to observe the potential use of taro hydrolysate (Colocasia esculenta L.) as a source of complex organic carbon to produce optimum cell density, biomass, lipid and chlorophyll content from T. chui microalgae under myxotrophic conditions. The culture was carried out in a vial containing 400 mL of bold basal medium. Taro hydrolysate is given in five concentrations, namely: 0, 5, 10, 15 and 20 g/L. The results showed that T. chui microalgae could grow in myxotrophic conditions with the addition of taro hydrolysate in the concentration range of 5 to 20 g/L. The maximum cell density and dry weight in the addition of 10 g/L taro hydrolysate were 4.23 x 105 cells/ml and 0.57 g/L, respectively. Meanwhile, the maximum fresh weight and lipid content were achieved at the addition of 15 g/L taro hydrolysate, namely 4.85 g/L and 67.4%. Chlorophyll content decreased with increasing concentration of taro hydrolysate. In conclusion, the use of taro hydrolysate can increase cell density, fresh weight and dry weight, lipid content and decrease the chlorophyll content of T.chui microalgae in myxotrophic culture.
 Keywords: Taro Hydrolysate, Lipid, Mixotrophic, Growth, Tetraselmis chui

Chemically Defined Xeno- and Serum-Free Cell Culture Medium to Grow Human Adipose Stem Cells.

Adipose tissue is an abundant source of stem cells. However, liposuction cannot yield cell quantities sufficient for direct applications in regenerative medicine. Therefore, the development of GMP-compliant ex vivo expansion protocols is required to ensure the production of a “cell drug” that is safe, reproducible, and cost-effective. Thus, we developed our own basal defined xeno- and serum-free cell culture medium (UrSuppe), specifically formulated to grow human adipose stem cells (hASCs). With this medium, we can directly culture the stromal vascular fraction (SVF) cells in defined cell culture conditions to obtain hASCs. Cells proliferate while remaining undifferentiated, as shown by Flow Cytometry (FACS), Quantitative Reverse Transcription PCR (RT-qPCR) assays, and their secretion products. Using the UrSuppe cell culture medium, maximum cell densities between 0.51 and 0.80 × 105 cells/cm2 (=2.55–4.00 × 105 cells/mL) were obtained. As the expansion of hASCs represents only the first step in a cell therapeutic protocol or further basic research studies, we formulated two chemically defined media to differentiate the expanded hASCs in white or beige/brown adipocytes. These new media could help translate research projects into the clinical application of hASCs and study ex vivo the biology in healthy and dysfunctional states of adipocytes and their precursors. Following the cell culture system developers’ practice and obvious reasons related to the formulas’ patentability, the defined media’s composition will not be disclosed in this study.

Flexible A-site doping La0.6-xMxSr0.4Co0.2Fe0.8O3 (M=Ca, Ba, Bi; x=0, 0.1, 0.2) as novel cathode material for intermediate-temperature solid oxide fuel cells: A first-principles study and experimental exploration

To address both challenges of insufficient oxygen vacancies and excessive interface resistance in intermediate-temperature solid oxide fuel cells (IT-SOFCs), in this study, we apply the first-principle density functional study to choose the A-site cation doping M(M = Ca, Ba, Bi) for conventional La0.6Sr0.4Co0.2Fe0.8O3 (LSCF) and find that Bi doping could produce the smallest generation energy of oxygen vacancy. Then novel Bi-doped La0.6-xBixSr0.4Co0.2Fe0.8O3 (LBSCFx, x = 0,0.1,0.2) cathode materials are investigated, revealing Bi3+ doping can promote the electrochemical performance of LBSCFx cathode by the enrichment of oxygen vacancies and the triple-phase boundaries. Attributed to the accelerated oxygen transportation and the increased oxygen reduction reaction sites, the effectiveness of Bi3+ doping LSCF on the reduction of polarization resistant (Rp) and activation energy (Ea) is superior than most of other LSCF doping strategies. The Rp and Ea values of LBSCF0.2 are reduced more than 58% and 27% compared to that of undoped LSCF respectively, and the maximum power density of the anode-supported single cells based on LBSCF0.2 outperforms 1 W⋅cm−2 at 750 °C. Both Rp and power density suggest the effectiveness of Bi doping strategy for developing cathode materials in IT-SOFCs.

Evaluation of the influence of different culture media on growth, life cycle, biochemical composition, and astaxanthin production in Haematococcus pluvialis

Haematococcus pluvialis is known as the richest natural source of carotenoid astaxanthin, whose synthesis is related to changes in cells according its complex life cycle and the availability of nutrients present in the culture media. This study’s objective was to evaluate the influence of different culture media under photoautotrophic and mixotrophic conditions on the growth, life cycle, biochemical composition, and astaxanthin production in H. pluvialis. Cultures were performed using the following media: KM1, MM2, Provasoli, modified Provasoli, and how to control the BBM, all kept at 24 ± 1 °C, with constant aeration, light/dark photoperiod 24:0 and irradiance of 60 μmol photons/m2/s. Growth and life cycle were evaluated by daily cell counts under an optical microscope; values of maximum cell density (MCD) and dry biomass were also assessed. Biochemical analyses were chlorophyll (a and b), astaxanthin, total proteins, and fatty acids. Cultivation under photoautotrophic conditions in BBM medium showed higher concentration of chlorophylls a (33 ± 4.0 μg/mL) and b (18 ± 1.6 μg/mL) and protein (62.7 ± 3.38%). Cultivation in modified Provasoli medium, under mixotrophic conditions, showed higher MCD (84.5 ± 11.7), biomass production (4.9 ± 0.0004 mg/mL), fatty acid methyl esters, and astaxanthin productivity (9.28 ± 0.4 mg/L/day). These results demonstrate that the culture media and the culture conditions to which H. pluvialis is submitted stimulate specific metabolic and biosynthetic pathways of the cells, which directly affect the biochemical composition of the microalgae. Modified Provasoli medium proved to be the most efficient in increasing astaxanthin productivity for this species, as it has shown better growth parameters and biomass production.

Coupled flow and biomass-nutrient growth at pore-scale with permeable biofilm, adaptive singularity and multiple species.

In this paper we describe a coupled model for flow and microbial growth as well as nutrient utilization. These processes occur within and outside the biofilm phase formed by the microbes. The primary challenge is to address the volume constraint of maximum cell density but also to allow some microbial presence outside the contiguous biofilm phase. Our model derives from the continuum analogues of the mechanism of cell shoving introduced in discrete biomass models, and in particular from the models exploiting singular diffusivity as well as from models of variational inequality type which impose explicit constraints. We blend these approaches and propose a new idea to adapt the magnitude of the diffusivity automatically so as to ensure the volume constraint without affecting the reactions; this construction can be implemented in many variants without deteriorating the overall efficiency. The second challenge is to account for the flow and transport in the bulk fluid phase adjacent to the biofilm phase. We use the Brinkman flow model with a spatially variable permeability depending on biomass amount. The fluid flow allows some advection of the nutrient within the biofilm phase as well as for the flow even when the pores are close to being plugged up. Our entire model is monolithic and computationally robust even in complex pore-scale geometries, and extends to multiple species. We provide illustrations of our model and of related approaches. The results of the model can be easily post-processed to provide Darcy scale properties of the porous medium, e.g., one can predict how the permeability changes depending on the biomass growth in many realistic scenarios.

Performance of microbial fuel cell operating with clay-manihot starch composite proton exchange membrane using RSM

This study optimized the performance of a microbial fuel cell (MFC) operating with raw clay sample (RCS)–manihot starch composite functioning as proton exchange membrane for electric power generation and bio-treatment of wastewater using central composite design (CCD) technique of the response surface methodology (RSM). The clay sample was heated at different temperatures ranging from 100 ​°C to 900 ​°C. The responses, power density and biochemical oxygen demand (BOD) removal efficiency were functions of four critical quantitative variables: pH, proton exchange membrane (PEM) preparation temperature (PPT), anolyte concentration and relative mass of clay in the PEM manihot-clay composite. A 24 CCD was employed to model and predict the process parameters. Sanitary wastewater of maximum cell density 4.25 ​× ​104/100 ​mL sustained the cell. Optimal responses of 82.4 ​mW/m2 power density and 72.3% BOD removal efficiency were recorded at clay PPT (RCS – 300 ​°C), 80 v/v wastewater to 10% glucose solution anolyte concentration, pH of 6.5 and clay component of PEM of mass 70 ​g optimum conditions. The study therefore suggests that RSM is an effective tool for evaluating and optimizing the Rsc-manihot composite PEM-MFC device for clean energy recovery and wastewater treatment, thereby providing the necessary leeway to overcoming the challenge of MFC scalability and greater performance.

Improved Isolation Procedures for Okadaic Acid Group Toxins from Shellfish (Mytilus edulis) and Microalgae (Prorocentrum lima).

Okadaic acid (OA) group toxins may accumulate in shellfish and can result in diarrhetic shellfish poisoning when consumed by humans, and are therefore regulated. Purified toxins are required for the production of certified reference materials used to accurately quantitate toxin levels in shellfish and water samples, and for other research purposes. An improved procedure was developed for the isolation of dinophysistoxin 2 (DTX2) from shellfish (M. edulis), reducing the number of purification steps from eight to five, thereby increasing recoveries to ~68%, compared to ~40% in a previously reported method, and a purity of >95%. Cell densities and toxin production were monitored in cultures of Prorocentrum lima, that produced OA, DTX1, and their esters, over ~1.5 years with maximum cell densities of ~70,000 cells mL−1 observed. Toxin accumulation progressively increased over the study period, to ~0.7 and 2.1 mg L−1 of OA and DTX1 (including their esters), respectively, providing information on appropriate harvesting times. A procedure for the purification of OA and DTX1 from the harvested biomass was developed employing four purification steps, with recoveries of ~76% and purities of >95% being achieved. Purities were confirmed by LC-HRMS, LC-UV, and NMR spectroscopy. Additional stability observations led to a better understanding of the chemistry of these toxins.

Occurrence of typical antibiotics, representative antibiotic-resistant bacteria, and genes in fresh and stored source-separated human urine

Human urine is a source of fertilizer and, with proper management, it can be reused in agriculture. Determining the contamination issue of antibiotics in source-separated urine is important because the majority of antibiotics are excreted with urine. In this study, source-separated urine samples were randomly collected from a male toilet in a university building and analyzed in terms of 30 typical antibiotics (including 14 sulfonamides, 4 tetracyclines, and 12 fluoroquinolones) and tetracycline-resistant Escherichia coli, as well as its antibiotic-resistant genes to determine the contamination characteristics of antibiotic-related pollution in fresh and stored urine. Results showed that 18 out of 30 typical antibiotics were detected in fresh source-separated human urine. The dominant antibiotic was oxytetracycline with a frequency of 100%, followed by tetracycline, sparfloxacin, enrofloxacin, and ofloxacin, which demonstrated a detection frequency of 55%. Among the detected values, sulfonamides (2 antibiotics), tetracyclines (4 antibiotics), and fluoroquinolones (12 antibiotics) had a concentration range of 0.25–2.94, 0.94–41.2, and 0.06–163.16 ng/mL, respectively. Furthermore, tetracycline-resistant Escherichia coli, which was measured using plate count method, and its related gene, tet M, exhibited a maximum cell density of (200,000 ± 5000) CFU/100 mL and (2.73 ± 0.261) × 107 copies/mL, respectively. When the fresh urine was stored in an ambient environment for 30 days to simulate the real circumstances of urine management, a significant reduction in antibiotics and antibiotic-resistant bacteria was observed, while the change in antibiotic-resistant genes was insignificant. The results of this study suggest that risks associated with antibiotics and their antibiotic-resistant bacteria and genes are retained during collection and storage. Hence, these kinds of microcontaminants must be considered in further urine utilization.

Primary role of increasing urea-N concentration in a novel Microcystis densa bloom: Evidence from ten years of field investigations and laboratory experiments

A novel Microcystis bloom caused by Microcystis densa has occurred in a typical subtropical reservoir every spring and summer since 2012, and it has caused several ecological and economic losses. To determine the environmental factors that influence the growth and physiological characteristics of M. densa, we investigated the variations in physicochemical factors and M. densa cell density from 2007 to 2017. The results showed that the urea-N concentration increased significantly (from 0.02 ± 0.00–0.20 ± 0.01 mg N l−1), whereas other factors did not vary significantly. NO3−-N and urea-N concentrations were higher than the NH4+-N concentration during the M. densa bloom. The nitrogen composition changed, and urea-N and NO3−-N became a major nitrogen sources in the reservoir. Water temperature and increased urea-N concentrations were the primary factors that influenced variations in M. densa cell density (45.5%, p < 0.05). Laboratory experiments demonstrated that M. densa cultured with urea-N exhibited a higher maximum cell density (9.8 ± 0.5 × 108 cells l−1), more cellular pigments for photosynthesis (chlorophyll a and phycocyanin) and photoprotection (carotenoid), and more proteins than those cultured with NH4+-N and NO3−-N. These results suggested that M. densa cultured with urea-N exhibited preferable growth and physiological conditions. Moreover, M. densa exhibited an increased maximum specific uptake rate (0.93 pg N cell−1 h−1) and reduced half-saturation constant (0.03 mg N l−1) for urea-N compared with NH4+-N and NO3−-N, suggesting that M. densa preferred urea-N as its major nitrogen source. These results collectively indicated that the increasing urea-N concentration was beneficial for the growth and physiological conditions of M. densa. This study provided ten years of field data and detailed physiological information supporting the critical effect of urea-N on the growth of a novel bloom species M. densa. These findings helped to reveal the mechanism of M. densa bloom formation from the perspective of dissolved organic nitrogen.

Studying the Radial and Tangential Velocity Components of the Epithelization Healing Post Photorefractive Keratectomy Surgery of the Human Eye

&#x0D; Photorefractive keratectomy (PRK) is the refractive technique that began with a physical scraping of the epithelial layer of cornea subsequent by laser treatment. Post this procedure to about 48 hours the removed epithelial layer regenerated to protect the eye again. The regeneration process (called re-epithelization) started from the limbus of the cornea toward the central part of it. The re-epithelization mechanism consists of a change in cell density (mitosis) and cell concentration (migration) with a velocity in two directions: radial and tangential. In the present study, an estimation for both radial (responsible for the overlapped layers toward the outward direction of the cornea) and tangential components (contour shape wave from limbus to the center) has been done for the first time, not like the previous studies that always estimate the velocity values of the re-epithelization only. Results showed that the trend shape of both components agrees with the kinematic behaviour of the mitosis and migration, where the maximum cell density fluctuated toward the central part in exponential decay shape. For a healing diameter of 2mm, the maximum redial velocity was 16.85 µm/h, while the maximum tangential velocity was 55.48 µm/h. These two components give a speed of re-epithelization of 58 µm/h which agrees with the biological and practical healing speed measured of 60 µm/h. Estimating these two components will open the way to understand the relationship between the total epithelial layer required and the total healing time to control the medication period for the patient post-surgery.

Optimization of resuscitation-promoting broths for the revival of Vibrio parahaemolyticus from a viable but nonculturable state.

This study was conducted to examine the effect of formulated resuscitation-promoting broths on the revival of viable but nonculturable Vibrio parahaemolyticus induced by cold and starvation stresses. Vibrio parahaemolyticus was incubated in artificial sea water at 4°C for more than 8months until this bacterium became undetectable, while retaining its intact cell count of more than 105CFU/field over time. On day 250, V. parahaemolyticus was collected and enriched in tryptic soy broth supplemented with 3% NaCl, 10,000 U/mg catalase, 2% sodium pyruvate, 20mM MgSO4, 5mM EDTA, and a cell-free supernatant taken from V. parahaemolyticus ATCC 17802 in the stationary phase (pH 8). V. parahaemolyticus returned partially to a culturable state with a maximal cell density of 7.91 log CFU/mL in this formulated medium following 7days of enrichment at 25°C. In contrast, no V. parahaemolyticus was resuscitated when enriched in alkaline peptone water and tryptic soy broth.

Research Article: Optimization of production and antioxidant activity of fucoxanthin from marine haptophyte algae, Isochrysis galbana

This study compared the biomass production, fucoxanthin production and antioxidant capacity of the fucoxanthin from the marine haptophyte algae, Isochrysis galbana under different nitrogen concentrations. At first step in the salinity test, I. galbana could grow in 20‰ and 35‰ but the 35‰ salinity was optimal. At second step, five different nitrogen concentrations (N-NO3) of 2, 4, 8, 12 12 mM, at the salinity of 35‰, were investigated. Algal cell density increased as nitrogen concentrations increased, but a low growth rate occurred in the culture with the highest nitrogen concentration (12 mM). The maximum cell density of 72× 12105> and the maximum amount of fucoxanthin (18.1 mg g-1) was obtained in I. galbana cultured in media containing four mM nitrogen (N-NO3). The purified fucoxanthin exhibited strong antioxidant properties, with the effective concentration for 50% scavenging (EC50) of 1, 1-dihpenyl-2-picrylhydrazyl (DPPH) radical, being 0.2 mg/ml. This study suggests that the production and fucoxanthin concentration of I. galbana can be improved using nitrogen-replete culture in 35‰ salinity. Also under this condition this microalgaecan be a commercial source of fucoxanthin for human health and nutrition.

Batch kinetics of nutrients removal for palm oil mill effluent and recovery of lipid by Nannochloropsis sp

Batch experiments were investigated for the effect of initial nutrients concentration of palm oil mill effluent (POME) on nutrients removals, growth rate, and lipid content recovery by Nannochloropsis sp. Bio-kinetic coefficients, k; reaction rate constant, Km, half-saturation constant, and Y, yield coefficient were determined. The concentrations of POME chosen were 0, 20, 40, 60, 80 % diluted with seawater (POME + SW) and Walne’s medium (POME + WM). Nannochloropsis sp. demonstrated the highest specific growth rate (0.39 d−1), maximum cell density (7.93 × 107 cell/mL) and lipid content (61.60 %) in 60 % POME + WM. Chemical oxygen demand (COD) can be removed effectively with k =11.31 mg COD mg−1 DCW d−1, and Km = 3883.04 mgL−1. The highest polyunsaturated fatty acid (PUFA) of microalgae treated in 60 % POME + WM was 59.13 %. For conclusion, 60 % POME + WM medium can be selected for POME remediation for high nutrients removal, growth rate and lipid content recovery.

A Comparison of CO2 and N2 Foaming Behaviors of PP in a Visualization System

Abstract Understanding of polypropylene (PP) foaming is critically important to reduce the weight of automotive parts. In this study, we used a batch foaming simulation system with visualization cell, to observe the foaming behaviors of PP that is blown with CO2 and N2 under various experimental conditions. We found that the nucleating agent content, initial temperature, pressure (i. e., gas content), and pressure drop rate during foaming have a significant effect on cell nucleation and cell growth. The cell density and the void fraction of PP foamed with CO2 and N2, respectively, were separately observed and compared. It was found that under the same experimental conditions, the maximum cell density of PP foamed with CO2 was higher than that of PP foamed with N2. However, the maximum cell density of PP foamed with CO2 was determined to be lower than that of PP foamed with N2, when the same gas mole numbers were employed. Based on the experimental results, optimum foaming conditions and effective processing strategies for PP-CO2 system are suggested.

Enhanced degradation and mineralization of phenol by combining two highly efficient strains with divergent ring-cleavage pathways

Pseudomonas stutzeri N2 and Rhodococcus qingshengii FF were combined to enhance phenol degradation, and the interaction mechanism of microorganisms was investigated. The cells in the culture of mixed strain degrading 1000 mg/L phenol exhibited a rapid growth and proliferation, and the maximum cell density of mixed strain was 34.6 ± 0.3% and 60.8 ± 0.2% higher than the single strain N2 and strain FF respectively. The degradation of phenol by mixed strain was completed within 24 h, and the phenol mineralization efficiency was up to 84.9 ± 0.4%. In addition, two ring-cleavage products of catechol accumulating from the culture of mixed strain were markedly reduced. Through the analysis of intermediates and functional groups, the enhanced phenol degradation by mixed strain was found to mainly depend on the synergistic effect of strain N2 served as an oxidant and strain FF acted as a reductant. Based on the synergic mechanism, the mixed strain might be used as a promising bacterial agent for removing phenolic compounds from the industrial wastewater.

Novel external-loop-airlift milliliter scale bioreactors for cell growth studies: Low cost design, CFD analysis and experimental characterization

Many researchers have limited access to fully equipped laboratory-scale batch bioreactors and chemostats due to their relatively high cost. This becomes particularly prohibitive when multiple replicas of the same experiment are required, but not enough bioreactors are available to operate simultaneously. Additionally, experiments using shaken flasks are common but show significant limitations in terms of maintaining homogeneous conditions in liquid cultures or installing instrumentation for monitoring. Here, we proposed to tackle this significant hurdle by providing a route to make available the manufacture of low-cost, milliliter-scale bioreactors. This approach seems plausible for enabling proof-of-concept experiments before moving to a larger scale without significant investments. The conceptually designed systems were based on external-loop bioreactors due to their flexibility, simplicity, and ease of assembling and testing. Designs were initially evaluated in silico with the aid of COMSOL Multiphysics. The successfully evaluated systems were then constructed via additive manufacturing and assembled for hydrodynamics testing via tracer methods. This was enabled by a newly home-made optical absorbance sensor (OAS) for in-line and real-time measurements. Both the in silico and experimental results indicated close to ideal mixing conditions and low shear stress. Cell growth curves were prepared by culturing Escherichia coli and following its cell density in real-time. Our cell growth rate and maximum cell density were similar to those previously obtained in closely related systems. Therefore, the proposed bioreactors are an affordable alternative for batch and continuous cell growth studies rapidly and inexpensively.

Denizel kuluçkahanede Nannochloropsis oculata dış ortam kültüründe endüstriyel ölçekli tübüler fotobiyoreaktör ile FRP (fiberglas ile güçlendirilmiş plastik) panel fotobiyoreaktörün karşılaştırılması

Microalgal culture is a key procedure in marine fish hatcheries, but this activity is far from optimized and has several problems remain to be solved. Nannochloropsis oculata are important to live feed organisms, which are used to rear the larvae of marine finfish. N. oculata were cultivated in tubular PBR and FRP panel PBR in a greenhouse. Tubular PBR was reached 701.7 x 106 cells mL-1 as its maximum cell density and FRP panel PBR was reached 245 x 106 cells mL-1 as maximum. Also, estimated maximum dry weights of tubular and FRP panel PBRs were calculated as 3.249 g L-1 and 1.47 g L-1, respectively. Consequently, tubular PBR was showed that it is more efficient than FRP panel PBR in this study.

Effects of the Culture Conditions on Growth and Photosynthesis Indices of Thalassiosira weissflogii

Dou, Y.; Shao, P.; Gao, J.W.; Jia, X.Y., and Zhou, W.L., 2020. Effects of the culture conditions on growth and photosynthesis indices of Thalassiosira weissflogii. In: Bai, X. and Zhou, H. (eds.), Advances in Water Resources, Environmental Protection, and Sustainable Development. Journal of Coastal Research, Special Issue No. 115, pp. 696-699. Coconut Creek (Florida), ISSN 0749-0208.Thalassiosira weissflogii is a marine resource microalga with practical applications in aquaculture and preparation of new nanomaterials, therefore the approach to culture conditions of T. weissflogii is quite important. Batch culture methods were used to study the effects of salinity and light intensity on T. weissflogii cell density and chlorophyll-a (chl-a) concentration. The results showed that: (1) The optimal salinity level for T. weissflogii growth was 30‰, under which cell density and chl-a concentration were up to 8.22 × 105 cells·mL-1 and 887.5 µg·L-1, respectively; the relative growth rate was 0.183. (2) The optimal light intensity level was 36 µmol·m-2s-1, under which cell density and chl-a concentration were up to 6.83 × 105 cells·mL-1 and 1431.7 µg·L-1, respectively; the relative growth rate was 0.146. (3) Compared with inorganic nitrogen sources, (NH2)2CO could better increase the cell density and chl-a concentration of T. weissflogii. In the experiment, the maximum cell density and chl-a concentration of T. weissflogii in the (NH2)2CO treatment group were 3.67 × 104 cells·mL-1 and 279.25 mg·L-1, respectively. These findings determined the optimal salinity and light intensity levels for growth of T. weissflogii, and reflected the effects of nitrogen source composition on T. weissflogii, accordingly, provided a new insight and important references to growth regulation and intensive culture of T. weissflogii in the lab.

Tolerance of Bradyrhizobium sp. BR 3901 to herbicides and their ability to use these pesticides as a nutritional source

Several groups of microorganisms degrade and use herbicide residues as a source of carbon and nitrogen. Identification of new strains capable of tolerating and degrading these pesticides can make strategic planning more flexible in environmental decontamination programs. Our objective was to evaluate the tolerance and growth in vitro of Bradyrhizobium sp BR 3901 strain in media without carbon and nitrogen sources, exposed to different herbicides. The biochemical activity of enzymes catalase, esterase, oxidase, reductase, and urease was determined for BR 3901. The time of maximum growth, maximum cell density, and growth in media without carbon and nitrogen sources in the presence of herbicides were evaluated for BR 3901. Formulated products based on glyphosate, sulfentrazone, and diuron were toxic to BR 3901. The presence of glyphosate, sulfentrazone, and diuron decreased maximum cell density and time for maximum cell growth of BR 3901. BR 3901 can use products based on diuron, sulfentrazone, and 2,4-D as a carbon source, even the last two, causing toxicity to this bacterial strain. The oxyfluorfen-based product can serve as a nitrogen source for BR 3901, degrading this pesticide.