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. 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. 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. 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.

中文翻译：

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温度和溶解氧对单细胞藻类盐生杜氏藻重力沉降的影响

微藻盐生杜氏藻主要作为天然β-胡萝卜素的来源进行栽培，但它也可以是蛋白质、碳水化合物和脂质等其他营养素的重要来源。收获和脱水被认为是生物质生产中最昂贵的过程，因此我们建议重力沉降作为一种具有成本效益的方法。本研究考察了温度和溶解氧浓度对盐生杜氏藻正常细胞和类胡萝卜素蓄积细胞重力沉降的影响。盐生杜氏藻在 f/2 培养基中以两种不同的盐度进行培养，12.5% (2.2 M NaCl) 和 17.5% (3.3 M NaCl)。通过从 f/2 培养基中去除 NaNO3 并在两种不同的盐度（12.5% 和 17.5%）下，在无氮源的培养基中培养类胡萝卜素积累细胞。对于重力沉降试验，将 10 mL 悬浮培养基转移到锥形管中并用铝箔包裹遮光。试管在 4 °C、10 °C、15 °C、20 °C、25 °C、30 °C、35 °C、40 °C、45 °C 和 50 °C 下孵育 4 小时和 18 H。对于好氧和厌氧条件下的重力沉降，将 10 mL 悬浮培养基转移到锥形管中，然后用 20% 氧气和 80% 氮气或 100% 氮气吹扫 10 分钟，并用铝箔包裹。将管在 25°C 下孵育 0.5 小时、1 小时、2 小时和 3 小时。采收率随温度、盐度和时间的不同而不同。正常细胞和类胡萝卜素蓄积细胞在20℃、25℃和30℃、12.5%和17.5%盐度、4小时后的恢复率达到79%～96%。在重力沉降实验中，正常细胞和类胡萝卜素积累细胞的恢复率不受细胞培养基中初始溶解氧变化的显着影响。考虑到在 D. salina 最佳生长温度下的重力沉降具有较高的回收率，重力沉降有望成为从开放池塘养殖系统中收获 D. salina 的一种经济有效的方法。