Effect of iron deprivation on surface composition and virulence determinants of Candida albicans

Six strains of Candida albicans were grown in defined medium which had been deferrated by ion-exchange chromatography and then supplemented with FeCl3 to give iron concentrations ranging from 0.026 microM to 0.8 microM. Growth in 0.026 microM-iron (measured as increase in biomass) was reduced by 26-59% as compared with that in excess (0.8 microM) iron. With five of the strains, adhesion to buccal epithelial cells was maximal after growth in 0.2-0.4 microM-iron, but strain GDH 2023 adhered best when grown in 0.026 microM-iron. Differences in yeast cell-wall composition were revealed by Zymolyase treatment of whole cells and by 125I-labelling of surface proteins. SDS-PAGE of iodinated proteins, followed by autoradiography, showed quantitative but no qualitative differences in protein profiles of iron-deficient and iron-replete organisms. The ability of all strains to form germ tubes in serum was near-maximal after growth in 0.2-0.4 microM-iron but was inhibited by up to 93% following growth in lower concentrations. These results indicate that expression of important virulence attributes by C. albicans is highly dependent on available iron and that expression in vivo may therefore be significantly different from that observed under conventional laboratory conditions.     

产油微藻的分离、筛选及自养培养氮源、碳源的优化

从云南滇池的水样中分离筛选得到一株自养产油小球藻(Chlorella vulgaris,C.vulgaris),其油脂产率可达28.6mg/(L·d),进一步考察了不同氮源、氮源浓度和添加无机碳源对其自养生长和油脂积累的影响。结果表明,硝酸钠为优化氮源,氮元素的优化浓度为123mg/L,油脂含量随氮元素浓度升高而降低;添加NaHCO3显著提高了C.vulgaris生物量产率和油脂产率,其优化浓度为800mg/L。在氮源和碳源的优化浓度下,C.vulgaris的最大生物量产率和油脂产率可达332.8mg/(L·d)和100.2mg/(L·d),分别是对照组的3.6和3.4倍。     

氧化铝气体分布器应用小球藻培养的研究

光生物反应器设计中,气体分布器对微藻生长有较大的影响,尤其是在鼓泡式光生物反应器中更为显著。实验考察了采用氧化铝烧制的多孔气体分布器的5L鼓泡式光生物反应器中通气速率、CO₂ 浓度对小球藻LICME002生物量、叶绿素含量、油脂积累的影响。对该气体分布器下的CO₂浓度和通气速率对小球藻的作用机理进行了初步的探讨。结果表明,CO₂浓度为3%时,该株微藻生物量、叶绿素、油脂积累的最佳;CO₂浓度超过6%时各项指标显著下降。通过对0.1vvm,0.4vvm,0.7vvm、1.0vvm的通气速条件下的各项指标的分析,确定最佳通气条件为0.4vvm。结论显示,在最佳通气速率和CO₂浓度下,微藻生物量能达到1.52g/L,油脂含量达到31.5%。     

无机碳源对小球藻自养产油脂的影响

旨在研究小球藻利用无机碳自养产油脂,考察了3种无机碳源 (Na2CO3、NaHCO3和CO2) 及其初始浓度对小球藻产油特性的影响。结果表明,小球藻能利用Na2CO3、NaHCO3和CO2产油;经Na2CO3、NaHCO3和CO2培养10 d后,随着每种无机碳源浓度的增加,小球藻产量均先增加后减少。小球藻经3种无机碳源培养后,其培养液pH值上升。最适宜的Na2CO3和NaHCO3添加量均为40 mmol/L,其生物量分别达到0.52 g/L和0.67 g/L,产油量分别达到0.19 g/L和0.22 g/L。在3种无机碳源中,CO2是最佳无机碳源,当CO2浓度为6％时,小球藻生长最快,生物量达2.42 g/L,产油量最高达0.72 g/L;当CO2浓度过低时,无机碳供应不足,油脂产量低;当CO2浓度过高时,培养液pH偏低,小球藻油脂积累受到抑制。Na2CO3和NaHCO3较CO2更有利于小球藻积累不饱和脂肪酸。     

Lipid accumulation and CO2 utilization of Nannochloropsis oculata in response to CO2 aeration

In order to produce microalgal lipids that can be transformed to biodiesel fuel, effects of concentration of CO(2) aeration on the biomass production and lipid accumulation of Nannochloropsis oculata in a semicontinuous culture were investigated in this study. Lipid content of N. oculata cells at different growth phases was also explored. The results showed that the lipid accumulation from logarithmic phase to stationary phase of N. oculata NCTU-3 was significantly increased from 30.8% to 50.4%. In the microalgal cultures aerated with 2%, 5%, 10% and 15% CO(2), the maximal biomass and lipid productivity in the semicontinuous system were 0.480 and 0.142 g L(-1)d(-1) with 2% CO(2) aeration, respectively. Even the N. oculata NCTU-3 cultured in the semicontinuous system aerated with 15% CO(2), the biomass and lipid productivity could reach to 0.372 and 0.084 g L(-1)d(-1), respectively. In the comparison of productive efficiencies, the semicontinuous system was operated with two culture approaches over 12d. The biomass and lipid productivity of N. oculata NCTU-3 were 0.497 and 0.151 g L(-1)d(-1) in one-day replacement (half broth was replaced each day), and were 0.296 and 0.121 g L(-1)d(-1) in three-day replacement (three fifth broth was replaced every 3d), respectively. To optimize the condition for long-term biomass and lipid yield from N. oculata NCTU-3, this microalga was suggested to grow in the semicontinuous system aerated with 2% CO(2) and operated by one-day replacement.     

Application of high-salinity stress for enhancing the lipid productivity of <Emphasis Type="Italic">Chlorella sorokiniana</Emphasis> HS1 in a two-phase process

Increased lipid accumulation of algal cells as a response to environmental stress factors attracted much attention of researchers to incorporate this stress response into industrial algal cultivation process with the aim of enhancing algal lipid productivity. This study applies high-salinity stress condition to a two-phase process in which microalgal cells are initially grown in freshwater medium until late exponential phase and subsequently subjected to high-salinity condition that induces excessive lipid accumulation. Our initial experiment revealed that the concentrated culture of Chlorella sorokiniana HS1 exhibited the intense fluorescence of Nile red at the NaCl concentration of 60 g/L along with 1 g/L of supplemental bicarbonate after 48 h of induction period without significantly compromising cultural integrity. These conditions were further verified with the algal culture grown for 7 days in a 1 L bottle reactor that reached late exponential phase; a 12% increment in the lipid content of harvested biomass was observed upon inducing high lipid accumulation in the concentrated algal culture at the density of 5.0 g DW/L. Although an increase in the sum of carbohydrate and lipid contents of harvested biomass indicated that the external carbon source supplemented during the induction period increased overall carbon assimilation, a decrease in carbohydrate content suggested the potential reallocation of cellular carbon that promoted lipid droplet formation under high-salinity stress. These results thus emphasize that the two-phase process can be successfully implemented to enhance algal lipid productivity by incorporating high-salinity stress conditions into the pre-concentrated sedimentation ponds of industrial algal production system.     

不同培养基及组成对2种小球藻生长和油脂的影响

研究了4种培养基及组成对蛋白核小球藻F-9和普通小球藻HYS-2的生长、油脂积累和脂肪酸组成的影响。结果发现knop、Provasoli、f/2、MAV 4种培养基中,f/2培养基更有利于小球藻的快速生长,而MAV培养基更适合油脂积累。在f/2培养基中F-9和HYS-2相对生长速率分别为0.156和0.171,培养9 d细胞干重为0.188 g/L和0.195 g/L。而在MAV培养基中F-9油脂含量最高可达19.67%,HYS-2油脂含量最高为21.91%,脂肪酸最高分别占干重的5.11%和8.71%。N/P为16∶1时小球藻生长最快,培养9 d后F-9和HYS-2的相对生长速率分别为0.23和0.239,最终细胞干重分别为0.107 g/L和0.143 g/L。而F-9和HYS-2在N/P为1∶1条件下积累油脂和脂肪酸含量最高,总脂含量分别占干重的为20.40%和27.39%,总脂肪酸占藻粉干重的含量为12.52%和16.94%。     

Enterobactin-mediated iron transport in Pseudomonas aeruginosa.

A pyoverdine-deficient strain of Pseudomonas aeruginosa was unable to grow in an iron-deficient minimal medium in the presence of the nonmetabolizable iron chelator ethylene diamine-di(omega-hydroxyphenol acetic acid) (EDDHA), although addition of enterobactin to EDDHA-containing minimal media did restore growth of the pyoverdine-deficient P. aeruginosa. Consistent with the apparent ability of enterobactin to provide iron to P. aeruginosa, enterobactin-dependent 55Fe3+ uptake was observed in cells of P. aeruginosa previously grown in an iron-deficient medium containing enterobactin (or enterobactin-containing Escherichia coli culture supernatant). This uptake was energy dependent, was observable at low concentrations (60 nM) of FeCl3, and was absent in cells cultured without enterobactin. A novel protein with a molecular weight of approximately 80,000 was identified in the outer membranes of cells grown in iron-deficient minimal medium containing enterobactin, concomitant with the induction of enterobactin-dependent iron uptake. A Tn501 insertion mutant lacking this protein was isolated and shown to be deficient in enterobactin-mediated iron transport at 60 nM FeCl3, although it still exhibited enterobactin-dependent growth in iron-deficient medium containing EDDHA. It was subsequently observed that the mutant was, however, capable of enterobactin-mediated iron transport at much higher concentrations (600 nM) of FeCl3. Indeed, enterobactin-dependent iron uptake at this concentration of iron was observed in both the mutant and parent strains irrespective of whether they had been cultured in the presence of enterobactin. Apparently, at least two uptake systems for ferrienterobactin exist in P. aeruginosa: one of higher affinity which is specifically inducible by enterobactin under iron-limiting conditions and the second, of lower affinity, which is also inducible under iron-limiting conditions but is independent of enterobactin for induction.     

Effect of oxidative stress and exogenous beta-carotene on sclerotial differentiation and carotenoid yield of Penicillium sp. PT95

AIMS: To determine the effect of oxidative stress and exogenous beta-carotene on sclerotial differentiation and carotenoid yield of Penicillium sp. PT95. METHODS AND RESULTS: In this experiment, high oxidative stress was applied by inclusion of FeCl(3) (10 micromol l(-1)) in the growth medium and by light exposure. Low oxidative stress was applied by omitting iron from the growth medium and by incubation in the dark. Supplementation of exogenous beta-carotene (as antioxidant) to the basal medium caused a concentration-dependent delay of sclerotial differentiation (up to 72 h), decrease of sclerotial biomass (up to 43%) and reduction of carotenoid yield (up to 92%). On the contrary, the exogenous beta-carotene also caused a concentration-dependent decrease of lipid peroxidation in colonies of this fungus. CONCLUSIONS: Under high oxidative stress growth condition, the sclerotial biomass and carotenoid yield of PT95 strain in each plate culture reached 141 mg and 30.03 microg, which were 1.53 and 3.51 times higher respectively, than that at low oxidative stress growth condition. SIGNIFICANCE AND IMPACT OF THE STUDY: These data prompted us to consider that in order to attain higher sclerotial biomass and pigment yield, the strain PT95 should be grown under high oxidative stress and in the absence of antioxidants.     

Siderophore containing 2,3-dihydroxybenzoic acid and threonine formed by Rhizobium trifolli

An iron-binding compound was isolated from ethyl acetate extract of culture supernatant fluid of Rhizobium trifolii AR6 and was purified by iron-exchange chromatography. The compound was characterized by UV and IR. It contained 2,3-dihydroxy-benzoic acid and threonine and was accumulated during stationary phase of growth in iron-deficient media. Synthesis of the siderophore was repressed by FeCl3. In iron limited medium the compound promoted growth of R. trifolii strains.     

利用市政污水培养Chlorella vulgaris生产生物柴油

为了考察利用南昌市政污水规模化培养富油微藻生产生物柴油,同时达到净化污水的目的,取南昌市青山湖污水处理厂未经任何处理的市政污水作为普通小球藻(Chlorella vulgaris)生长的培养液。监测了C.vulgaris在市政污水中连续培养10 d的特定生长率、生物质产量以及与之相关的市政污水中氨氮(NH4+-N)、总磷(TP)、化学需氧量(COD)、总悬浮固体(TSS)和挥发性悬浮固体(VSS)的清除情况。实验表明:营养物质的水平显著地影响了C.vulgaris的生长。C.vulgaris的生长率在培养8 d后达到最大,OD680为2.856,总的生物质产量日均最大积累速率为0.01 g/L,油脂含量为干质量的18%,油脂的平均日产量为0.001 g/L。培养10 d内NH4+-N、TP和COD的去除率分别为50.0%、32.1%和26.0%,TSS和VSS的日平均去除速率分别为0.01 g/L和0.006 1 g/L。     

Effects of Temperature and pH on Cell Growth of a Flocculating Microalga (Chlorella vulgaris) JSC-7

微藻是可广泛用于健康食品及水产养殖的饵料,同时,微藻细胞内积累的油脂可作为可再生生物燃料,因此微藻的生长和代谢受到广泛关注。温度和pH对微藻的生物量积累有很大影响,考察不同温度和pH条件下微藻细胞的生长有助于寻找最佳的条件进行微藻的培养。自絮凝小球藻JSC-7（Chlorella vulgaris JSC-7）可实现自沉降采收,有利于降低微藻生产成本,优化其生长条件对更好地利用该微藻具有重要意义。考察了温度（22∽40℃）及pH（6.0∽10.0）对其细胞生长、叶绿素含量和油脂产量的影响。在所选取的温度及pH范围内,JSC-7细胞均可生长,显示该藻种可以适应广泛的温度和pH条件。适合细胞生长的温度依次为31℃〉28℃〉35℃〉25℃,pH依次为7.0〉8.0〉6.0。pH 8.0时生物量和油脂的积累量最多,说明该藻株在弱碱条件下更适合生长和产油。当温度为31℃、pH为7.0时,可获得最高的生长量（OD690=0.941）、叶绿素含量（19 mg/L）及油脂产量（39.07%/克干重）。     

Biomass yields of Chlorella from iron (Y x/Fe) in iron-limited batch cultures

The maximum biomass in iron-limited photosynthetic batch cultures of chlorella increased as the logarithm of the iron concentration. The growth yield from iron (Y _x/Fe) showed a marked inverse relation to the specific growth rate. The maximum biomass yield, g dry biomass/g iron consumed, was 7.5x10³ with specific growth rate 0.108 h^-1; the minimum was 0.79×10³ with specific growth rate 0.145 h^-1. The maximum specific growth rate in the exponential phase of Fe limited cultures varied as the initial Fe concentration. Fe-limited growth made the cells adhere to a glass surface.Abbreviation O.D. optical density     

含氮类培养基对海洋微藻Isochrysis zhanjiangensis 油脂与碳水化合物积累的影响

考察了8种含氮培养基对湛江等鞭金藻(I. zhanjiangensis)生长、PSⅡ活性、油脂及碳水化合物积累的影响。结果显示,当培养基中氮浓度为1.5 g/L,藻细胞的总脂肪含量和产量分别达到最高值为39.8 %和 0.92 g/L, 碳水化合物的含量为最低11.6 %;而当培养基中氮浓度为 0.016 g/L,藻细胞的总脂肪含量和产量分别达到最低值为21.1 %和0.16 g/L。而此时总碳水化合物含量最高达到44.4 %。同时线性拟合方程的结果表明培养基中NO₃^-的浓度与藻细胞的总脂含量呈较好的正相关性。因此,通过研究不同含氮水平的培养基实现了脂肪或碳水化合物产量的调控。     

Effect of phosphorus on lipid accumulation in freshwater microalga Chlorella sp.

Microalgae have already been investigated as a potential resource for biofuel in many reports. In this study, the effect of phosphorus concentration on lipid content was analyzed using the freshwater microalga Chlorella sp as a model. In addition, the carbohydrate and protein content were also analyzed in order to investigate the variations of biochemical composition under different phosphorus levels. Results showed that both lipid content and lipid productivity were increased under low phosphorus conditions. Furthermore, it was also found that lipid accumulation in cells decreased by supplementing the growth media with K₂HPO₄ in the late growth phase. The analysis of the total protein and the carbohydrate content showed that the former remained unaffected by external phosphorus variation; while the latter was directly correlated to phosphorus concentration. In summary, lipid accumulation had significant relationship with phosphorus concentration.     

Effect of nutrients on growth and lipid accumulation in the green algae Dunaliella tertiolecta

Production of biofuel from algae is dependent on the microalgal biomass production rate and lipid content. Both biomass production and lipid accumulation are limited by several factors, of which nutrients play a key role. In this research, the marine microalgae Dunaliella tertiolecta was used as a model organism and a profile of its nutritional requirements was determined. Inorganic phosphate PO4(3-) and trace elements: cobalt (Co2+), iron (Fe3+), molybdenum (Mo2+) and manganese (Mn2+) were identified as required for algae optimum growth. Inorganic nitrogen in the form of nitrate NO3- instead of ammonium (NH4+) was required for maximal biomass production. Lipids accumulated under nitrogen starvation growth condition and this was time-dependent. Results of this research can be applied to maximize production of microalgal lipids in optimally designed photobioreactors.     

Regulation of iron uptake in Saccharomyces cerevisiae. The ferrireductase and Fe(II) transporter are regulated independently.

Iron is required for the growth of Saccharomyces cerevisiae. High concentrations of iron, however, are toxic, forcing this yeast to tightly regulate its concentration of intracellular free iron. We demonstrate that S. cerevisiae accumulates iron through the combined action of a plasma membrane ferrireductase and an Fe(II) transporter. This transporter is highly selective for Fe(II). Several other transition metals did not inhibit iron uptake when these metals were present at a concentration 100-fold higher than the Km (0.15 microM) for iron transport. Pt(II) inhibited ferrireductase activity but not the ability of cells to transport iron that was chemically reduced to Fe(II). Incubation of cells in a synthetic iron-limited media resulted in the induction of both ferrireductase and Fe(II) transporter activities. In complex media, Fe(II) transport activity was regulated in response to media iron concentration, while the activity of the ferrireductase was not. When stationary phase cells were inoculated into fresh media, ferrireductase activity increased independent of the iron content of the media; in contrast, transporter activity varied inversely with iron levels. These results demonstrate that the ferrireductase and Fe(II) transporter are separately regulated and that iron accumulation may be limited by changes in either activity.     

Optimisation of docosahexaenoic acid production in batch cultivations by Crypthecodinium cohnii

The heterotrophic micro alga Crypthecodinium cohnii was cultivated in media containing glucose, yeast extract and sea salt. Increasing amounts of yeast extract stimulated growth but influenced lipid accumulation negatively. Sea salt concentrations above half the average seawater salinity were required for good growth and lipid accumulation. C. cohnii was able to grow on a glucose concentration as high as 84.3 g l⁻¹, although concentrations above 25 g l⁻¹ decreased the growth rate. Comparison of growth at 27 and 30°C showed that the higher incubation temperature was more favourable for growth. However, lipid accumulation was higher at the lower incubation temperature. In a bioreactor the biomass concentration increased from 1.5 to 27.7 g l⁻¹ in 74 h. In the final 41 h of the process the lipid content of the biomass increased from 7.5 to 13.5%. In this period the percentage of docosahexaenoic acid of the lipid increased from 36.5 to 43.6%. The total amounts of lipid and docosahexaenoic acid after 91 h were 3.7 and 1.6 g l⁻¹, respectively.     

Response surface methodology as a decision-making tool for optimization of culture conditions of green microalgae Chlorella spp. for biodiesel production

We have evaluated process optimization and the interactive effects of a number of variables using a Box–Behnken design of response surface methodology (RSM). The process variables nitrate, phosphate, glucose and pH were optimized to enhance the cell growth rate, lipid accumulation and other biochemical parameters of Chlorella spp. The most significant increase in lipid production (dry cell weight basis) occurred at limited concentrations of nitrate and phosphate, 1 % glucose and pH 7.5. The addition of nitrates during the mid-lag and mid-exponential phases produced the maximum inhibitory effect on lipid accumulation and the presence of yeast extract led to a further enhancement of lipid accumulation. Of all the media tested, BG-11 was the best suited medium for algal biomass production and chlorophyll content. A significant increase in algal biomass was observed in BG-11 supplemented with bicarbonate and glucose (1 %). The maximum specific growth rate observed was on 9th day of culturing. Results of optimization of process variables through response surface methodology and optimization of various other conditions reflect cutting edge research directed towards increasing algal biomass and lipid content for biodiesel production using an efficient economical technological approach.