Effect of temperature and dissolved oxygen on gravity sedimentation of the unicellular alga Dunaliella salina

Purpose The microalgae Dunaliella salina is mainly cultivated as a source of natural β-carotene, but it can also be an important source of other nutrients such as protein, carbohydrate, and lipids. Harvesting and dewatering are considered the most expensive processes in the biomass production, so we proposed gravity sedimentation as a cost-effective method. The effect of temperature and dissolved oxygen concentration on the gravity sedimentation of normal cells and carotenoid-accumulating cells of Dunaliella salina was investigated in this study. Methods Dunaliella salina was cultivated in an f/2 culture medium at two different salinities, 12.5% (2.2 M NaCl) and 17.5% (3.3 M NaCl). Carotenoid-accumulating cells were cultivated in a medium without a nitrogen source by removing NaNO3 from the f/2 medium and at two different salinities, 12.5% and 17.5%. For gravity sedimentation tests, 10 mL of the suspended culture media were transferred to conical tubes and wrapped with aluminum foil for shading. The tubes were incubated at 4 °C, 10 °C, 15 °C, 20 °C, 25 °C, 30 °C, 35 °C, 40 °C, 45 °C, and 50 °C for 4 h and 18 h. For the gravity sedimentation under aerobic and anaerobic conditions, 10 mL of the suspended culture media were transferred to conical tubes and then purged with 20% oxygen and 80% nitrogen or 100% nitrogen for 10 min and wrapped with aluminum foil. The tubes were incubated at 25 °C for 0.5 h, 1 h, 2 h, and 3 h. Result Recovery rates differed with temperature, salinity, and time. The recovery rate of normal cells and carotenoid-accumulating cells reached 79 to 96% at 20 °C, 25 °C, and 30 °C at 12.5% and 17.5% of salinity and after 4 h. The recovery rate of both normal and carotenoid-accumulating cells in gravity sedimentation experiments was not significantly affected by changing initial dissolved oxygen in the cell-cultured media. Conclusion Considering that gravity sedimentation at the optimum growth temperature for D. salina presented high recovery rates, gravity sedimentation is expected to be a cost-effective method to harvest D. salina from open pond cultivation systems.

The Simple One-Step (SOS) stool processing method for use with the Xpert MTB/RIF assay for a child-friendly diagnosis of tuberculosis closer to the point-of-care

Young children cannot easily produce sputum for diagnosis of pulmonary tuberculosis. Alternatively, Mycobacterium tuberculosis complex (MTB) bacilli can be detected in stool by using the Xpert MTB/RIF (Ultra) assay (Xpert). Published stool processing methods contain somewhat complex procedures and additional supplies. The aim of this study was to develop a simple one step (SOS) stool processing method, based on gravity sedimentation only, similar to sputum Xpert testing for the detection of MTB in stool. We first assessed if the SOS stool method could provide valid Xpert results without the need of bead-beating, dilution and filtration steps. We concluded that this was the case and, subsequently, validated the SOS stool method by testing spiked stool samples. By using the SOS stool method, of the 29 spiked samples, 27 gave valid Xpert results and MTB was recovered from all 27. The proof of principle of the SOS stool method was demonstrated in a routine setting in Addis Ababa, Ethiopia. Nine of 123 children with presumptive TB were MTB positive on nasogastric aspirate (NGA), and seven (77.8%) of these also had an MTB positive Xpert result on stool. Additionally, MTB was detected in the stool but not on the NGA of two children. The SOS stool processing method makes use of the standard Xpert assay kit, without the need for additional supplies or equipment. The method can potentially be rolled out to any Xpert site, bringing a bacteriologically confirmed diagnosis of TB in children closer to the point of care.

A Case Study on Settling Process in Inclined-Tube Gravity Sedimentation Tank for Drip Irrigation with the Yellow River Water

A sedimentation tank which can remove fine sediment with low cost and high efficiency is of great significance for the wide application of drip irrigation techniques with the Yellow River water. In this study, the settling process of an inclined-tube gravity sedimentation tank which has high removal efficiency for fine particles in practice was thoroughly investigated. The sediment concentration distribution in the tank was measured by an optical back-scattering turbidimeter. The sediment thickness at the tank bottom was also measured. In addition, the size grading of sediment deposited at different positions on the tank bottom and at different heights in the inclined tubes was also measured by a laser particle size analyzer. It was found that the removal efficiency of fine sediment was 64.7–69.7% in the inclined-tube gravity sedimentation tank, which was higher than that of the sedimentation tank without inclined tubes (with a sediment removal rate of 20.7–32%). The sediment was mainly deposited in the flow adjustment area and settlement area with inclined tubes. A suitable height for the inclined tubes was 70–90 cm. In addition, the water inlet, baffle, and overflow weir in the tank negatively affected the fine sediment settling in two experiment cases. The experimental results enhance our understanding of the sedimentation characteristics in the tank, and indicate the direction for the subsequent structural optimization of the tank.

Fabrication of Structural-Coloured Carbon Fabrics by Thermal Assisted Gravity Sedimentation Method

Structural-coloured poly(styrene-methyl methacrylate-acrylic acid) (Poly(St-MMA-AA)) deposited carbon fabrics (Poly(St-MMA-AA)/PCFs) with fascinating colours (salmon, chartreuse, springgreen, skyblue, mediumpurple) changing with the (Poly(St-MMA-AA) nanoparticle sizes can be facilely fabricated by the thermal-assisted gravity sedimentation method that facilitates the self-assembly of Poly(St-MMA-AA) colloidal nanoparticles to generate photonic crystals. The particle sizes of Poly(St-MMA-AA) copolymer with core/shell structure varying from 308.3 nm to 213.1 nm were controlled by adjusting the amount of emulsifier during emulsion polymerisation. The presence of the intrinsic chemical information of Poly(St-MMA-AA) copolymer has been ascertained by Raman and Fourier Transform Infrared (FT-IR) Spectroscopy analysis. Colour variation of the as-prepared structural-coloured carbon fabrics (Poly(St-MMA-AA)/PCFs) before and after dipping treatment were captured while using an optical microscope. The structural colours of Poly(St-MMA-AA)/PCFs were assessed by calculating the diffraction bandgap according to Bragg’s and Snell’s laws. The Poly(St-MMA-AA) photonic crystal films altered the electrical properties of carbon fabrics with the resistivity growing by five orders of magnitude. The differential electrical resistivity between Poly(St-MMA-AA)/PCFs and wet Poly(St-MMA-AA)/PCFs combined with the corresponding tunable colours can be potentially applied in several promising areas, such as smart displays, especially signal warning displays for traffic safety.

“Old School” Islet Purification Based on the Unit Gravity Sedimentation as a Rescue Technique for Intraportal Islet Transplantation—A Case Report

Here, we present a case that required a supplemental “old school” islet purification for a safe intraportal infusion. Following pancreas procurement from a brain-dead 26-year-old male donor (body mass index: 21.9), 24.6 ml of islet tissue was isolated after continuous density gradient centrifugation. The islet yield was 504,000 islet equivalent (IEQ), distributed among the following three fractions: 64,161 IEQ in 0.6 ml of pellet, 182,058 IEQ in 10 ml, and 258,010 IEQ in 14 ml with 95%, 20%, and 10% purity, respectively. After a 23-h culture, we applied supplemental islet purification, based on the separation of tissue subfractions during unit gravity sedimentation, a technique developed over 60 years ago (“old school”). This method enabled the reduction of the total pellet volume to 11.6 ml, while retaining 374,940 IEQ with a viability of over 90%. The final islet product was prepared in three infusion bags, containing 130,926 IEQ in 2.6 ml of pellet, 108,079 IEQ in 4 ml of pellet, and 135,935 IEQ in 5 ml of pellet with 65%, 40%, and 30% purity, respectively, and with the addition of unfractionated heparin (70 units/kg body weight). Upon the islet infusion from all three bags, portal pressure increased from 7 to 16 mmHg. Antithrombotic prophylaxis with heparin was continued for 48 h after the infusion, with target activated partial thromboplastin time 50–60 s, followed by fractionated heparin subcutaneous injections for 2 weeks. β-Cell graft function assessed on day 75 post-transplantation was good, according to Igls criteria, with complete elimination of severe hypoglycemic episodes and 50% reduction in insulin requirements. Time spent within the target glucose range (70–180 mg/dl) improved from 42% to 98% and HbA1c declined from 8.7% to 6.7%. Supplemental “old school” islet purification allowed for the safe and successful utilization of a robust and high-quality islet preparation, which otherwise would have been discarded.