Production of bioactive proteins and peptides from the diatom Nitzschia laevis and comparison of their in vitro antioxidant activities with those from Spirulina platensis and Chlorella vulgaris

This research focuses on green production of bioactive proteins and hydrolysates from Nitzschia. A comparison of antioxidant activities was established between protein extracts and hydrolysates from Nitzschia and two other well‐known microalgae, chlorella and spirulina. Protein hydrolysates from these microalgae were produced using Alcalase^®, Flavourzyme^® and Trypsin. The hydrolysis process enhanced the antioxidant activities in general, especially those obtained using Alcalase^®. Nitzschia showed the highest (P < 0.05) total phenolic content/reducing capacity (2.4 ± 0.02 mg GAE/100 g) after 90 min of hydrolysis with Alcalase^®. The ABTS [2,2′‐Azino‐bis(3‐ethylbenzothiazoline‐6‐sulphonic acid)] radical scavenging activity (66.77 ± 0.00%) was highest (P < 0.05) after 120 min of hydrolysis, but DPPH (2,2‐Diphenyl‐1‐picrylhydrazyl radical) was low (29.59 ± 0.02%). A correlation between ABTS activity and total phenolic contents was the highest (P < 0.05) for protein hydrolysates from all three organisms using Alcalase^®, but superoxide anion radical scavenging activity was intermediate for Nitzschia. Therefore, Nitzschia protein hydrolysates have the potential to be used as antioxidants.     

新月菱形藻遗传重组标记的选择

为了选择抗生素G418作为新月菱形藻的遗传重组标记,分别研究G418对新月菱形藻生长的最小抑制浓度,以及G418对携有质粒载体pBI121的遗传重组受体新月菱形藻的最大抗性浓度。结果表明:25μg/mLG418能完全抑制新月菱形藻在液体培养基中的生长;50μg/mLG418能完全抑制新月菱形藻在固体培养基上长出藻落;而G418对携有质粒载体pBI121的遗传重组受体新月菱形藻的最大抗性浓度在液体培养基和固体培养基中均是400μg/mL。     

Fatty acid and lipid class composition of the eicosapentaenoic acid-producing microalga, Nitzschia laevis

The diatom Nitzschia laevis is a potential producer of eicosapentaenoic acid (EPA, C20:5n − 3). In order to further adopt this alga in the functional food and aquaculture industries, the lipid class composition and fatty acid distribution in the lipid pool of N. laevis were studied using thin-layer chromatography and gas chromatography. The total lipids of N. laevis were fractionated into neutral lipids (NLs), glycolipids (GLs) and phospholipids (PLs). NLs were the major constituents and accounted for 78.6% of the total lipids. Triacylglycerol (TAG) was the predominant component of NLs (87.9%). GLs and PLs accounted for 8.1% and 11.6% of the total lipids, respectively. Phosphatidylcholine (PC) was the major component of PLs (69.7%). The principal fatty acids identified in most lipid classes were tetradecanoic acid (C14:0), hexadecanoic acid (C16:0), palmitoleic acid (C16:1) and EPA. EPA was distributed widely among the various lipid classes with the major proportion (75.9% of the total EPA) existing in TAG, monoacylglycerol and PC.     

不同环境因子对谷皮菱形藻生长的影响

本实验研究了不同环境因子包括氮源种类、氮源浓度、硅盐浓度、光强、盐度和pH值对谷皮菱形藻生长的影响。结果表明,以CO(NH2)2为氮源生长最快,最大比生长速率和最大细胞浓度最大,分别为0.49d-1和0.54g/L;NaNO3浓度为0.72g/L时,有利于谷皮菱形藻生长;在硅酸钠浓度0～0.4g/L的范围内,随着硅浓度的增加,谷皮菱形藻生长明显加快;光强对谷皮菱形藻的影响十分显著,易成为其生长的限制因素;NaCl浓度0.15mol/L时,谷皮菱形藻最大比生长速率和最大细胞浓度最大;碱性的培养液最利于谷皮菱形藻生长。     

小新月菱形藻固定化培养初步研究

用褐藻酸钙对小新月菱形藻进行固定化培养实验,测定不同胶粒大小、胶珠密度、CaCl2浓度及不同接种量对该藻的影响,比较了自由化生长与固定化细胞的生长曲线。小新月菱形藻在褐藻酸钙凝胶中仍具有呼吸和光合作用的能力。球径为3.5mm,CaCl2浓度为2%时,细胞生长快,每50mL培养液中加入200个胶珠时细胞生长量大,接种量不能低于104个细胞/mL。与游离的小新月菱形藻相比,固定化小新月菱形藻生长慢,但生长周期长。     

Variation of lipid class composition in Nitzschia laevis as a response to growth temperature change

The lipid composition and the distribution of fatty acids in the lipid pool were determined in eicosapentaenoic acid (EPA)-producing microalga (Nitzschia laevis) grown under different temperatures. Both the relative amounts of lipid classes and the degree of fatty acid unsaturation in various lipid species were not greatly changed under tested growth conditions. Higher temperature up to 23 °C benefited the growth of N. laevis but only had a slight influence on EPA and lipid contents. Further increasing the culture temperature caused a serious inhibition of both the cell growth and fatty acid biosynthesis. Under all temperatures tested, triacylglycerol (TAG) was the predominant lipid constituent (64.5–69.1% of total lipid) and was highly saturated. Lower temperature favored the formation of polar lipids. The highest content of phosphatidylcholine (PC), the major phospholipids component, was reached at 15 °C (10.9% of total lipid). In sharp contrast to TAG, PC was highly unsaturated and contained a higher amount of EPA under lower temperature. The highest EPA content in polar lipid was achieved at 19 °C. The results from this investigation suggested that the low temperature could improve the distribution of polyunsaturated fatty acids in phospholipids, though it could not significantly influence their amount, especially in PC.     

The growth inhibition of planktonic algae due to surfactants used in washing agents

A survey of inhibitory effects of nonionic and anionic surfactants, including a soap, used in washing agents, on the growth on three species of freshwater phytoplankton, Selenastrum capricornutum, Nitzschia fonticola and Microcystis aeruginosa was conducted. Based on the specific growth rate, μu estimated from a short period (2 or 3 days) cultivation of test algae, the growth inhibition was determined using EC₅₀ values where μu in the culture medium with surfactant decreased 50% of that without surfactant.The EC₅₀ values of nonionic and anionic surfactants tested here for S. capricornutum ranged from 2 to 50 mg l⁻¹ and from 10 to 100 mg l⁻¹, respectively. The tolerances of three species of algae tested with three surfactants, LAS, AE (EO:9) and soap, were different and the inhibitory effects were species specific. EC₅₀ values of LAS, AE (EO:9) and soap for S. capricornutum were 50–100, 4–8 and 10–50 mg l⁻¹, respectively. Those for N. fonticola were 20–50, 5–10 and 20–50 mg l⁻¹, and those for M. aeruginosa were 10–20, 10–50 and 10–20 mg l⁻¹, respectively.     

氮浓度和光照强度对小新月菱形藻生长和总脂含量的影响

以NaNO3为氮源,研究了氮浓度的五个水平及光照强度对小新月菱形藻的生长率及总脂含量的影响．结果表明：小新月菱形藻（Nitzschia closterium f.minutissima）（MACC／B222）在氮浓度为32mmol／L时平均生长率∥达到最大值0．7100d,脂肪含量在16mmol／L时达到最大值34．8％;在光强260-μmol／（s·m^2）处获得最大生长率0．6505d^-1,140μmol／（s·m^2）处获得最大总脂含量33．9％     

三种饵料微藻半连续培养条件的研究

文章从起始密度和更新率两个方面对三种经济饵料微藻:小球藻、牟氏角毛藻和小新月菱形藻进行半连续培养条件的研究。实验表明,三种饵料微藻均可实现半连续培养;小球藻的最佳半连续培养条件是细胞起始密度4.2×107个/mL,日更新率为30%;牟氏角毛藻的最佳半连续培养条件是起始密度3.8×106个/mL,日更新率为40%;小新月菱形藻的最佳半连续培养条件是起始密度7.8×106个/mL,日更新率为40%。