Reduced gene expression at the branch point of chlorophyll and heme biosynthesis in Arctic <Emphasis Type="Italic">Chlorella</Emphasis> ArM0029B

The gene expression at the branch point of chlorophyll and heme synthesis in the model microalga, Chlamydomonas reinhardtii, is different from that of higher plants. Another green alga, Arctic Chlorella, was recently isolated from Arctic sea ice and may be a promising candidate for a biofuel. To understand the chlorophyll metabolic pathway and relevant nuclear gene expression in Chlorella sp., we characterized chlorophyll-deficient mutants of the Arctic Chlorella sp. ArM0029B. First, we characterized the chlorophyll and heme biosynthetic pathways based on genes identified by bioinformatics analysis of the genome of Arctic Chlorella sp. ArM0029B. Then, we isolated and analyzed nine chlorophyll-deficient mutants that showed reduced expression of the ChlM gene, which encodes Mg-protoporphyrin methyltransferase. Expression of 5-amino levulinic acid dehydratase (encoded by ALAD) and glutamyl-tRNA reductase (encoded by HemA) was reduced in all nine independent mutants compared to wild type. These results indicated that Arctic Chlorella ArM0029B may have a regulatory mechanism of gene expression at earlier steps of the Mg-porphyrin branch that is more similar to higher plants than to the microalga C. reinhardtii. This study provides useful insight into the regulation of porphyrin precursor formation in Chlorella and related microalgae.     

Lipid Profile Remodeling in Response to Nitrogen Deprivation in the Microalgae Chlorella sp. (Trebouxiophyceae) and Nannochloropsis sp. (Eustigmatophyceae)

Many species of microalgae produce greatly enhanced amounts of triacylglycerides (TAGs), the key product for biodiesel production, in response to specific environmental stresses. Improvement of TAG production by microalgae through optimization of growth regimes is of great interest. This relies on understanding microalgal lipid metabolism in relation to stress response in particular the deprivation of nutrients that can induce enhanced TAG synthesis. In this study, a detailed investigation of changes in lipid composition in Chlorella sp. and Nannochloropsis sp. in response to nitrogen deprivation (N-deprivation) was performed to provide novel mechanistic insights into the lipidome during stress. As expected, an increase in TAGs and an overall decrease in polar lipids were observed. However, while most membrane lipid classes (phosphoglycerolipids and glycolipids) were found to decrease, the non-nitrogen containing phosphatidylglycerol levels increased considerably in both algae from initially low levels. Of particular significance, it was observed that the acyl composition of TAGs in Nannochloropsis sp. remain relatively constant, whereas Chlorella sp. showed greater variability following N-deprivation. In both algae the overall fatty acid profiles of the polar lipid classes were largely unaffected by N-deprivation, suggesting a specific FA profile for each compartment is maintained to enable continued function despite considerable reductions in the amount of these lipids. The changes observed in the overall fatty acid profile were due primarily to the decrease in proportion of polar lipids to TAGs. This study provides the most detailed lipidomic information on two different microalgae with utility in biodiesel production and nutraceutical industries and proposes the mechanisms for this rearrangement. This research also highlights the usefulness of the latest MS-based approaches for microalgae lipid research.     

Effects of <Emphasis Type="Italic">Ascophyllum nodosum</Emphasis> extract on growth and antioxidant defense systems of two freshwater microalgae

Microalgae in genus Chlorella and Scenedesmus are common in aquatic ecosystems and are widely used for various studies on algal growth and applications. Macroalgae may play an important role for control of microalgal growth, attributable to their rich content of bioactive compounds. In this study, the brown seaweed Ascophyllum nodosum was extracted with 70% acetone and the extract was used to treat the green microalgae, Chlorella vulgaris and Scenedesmus sp. Cell density and chlorophyll a concentration were used as growth indexes to evaluate the effects of A. nodosum extract (ANE) on the microalgae. The ANE with concentrations > 1% exhibited significant capability of inhibition of the growth of microalgae by over 80%. On the contrary, 1% ANE caused varying degrees of acceleration of cell proliferation and chlorophyll a synthesis in C. vulgaris and Scenedesmus sp., respectively. Analysis of antioxidant activities of the enzymes superoxide dismutase (SOD) and catalase (CAT) revealed the impact of ANE on the antioxidant defense system of the microalgae. The SOD and CAT activities were significantly depressed by high concentrations (> 2%) ANE, while a slight increase of the enzyme activities was observed with 1% ANE at the early period, which could be correlated to the growth response. Therefore, the mechanism of microalgae control could be related to the interaction between the ANE and the antioxidant defense systems. Phlorotannins are proposed as the principal algistatic components in the ANE which could be utilized in controlling microalgae growth.     

Microalgal Biomass and Lipid Production on Dairy Effluent Using a Novel Microalga, <Emphasis Type="Italic">Chlorella</Emphasis> sp. Isolated from Dairy Wastewater

The present study focused on cost-effective production of microalgal biomass and lipid production on dairy effluent. The novel microalga, Chlorella sp. isolated from the dairy effluent showed high growth and lipid production on the undiluted and two-fold diluted dairy effluent which were four to five times higher than those of Chlorella vulgaris (control). The high growth of Chlorella sp. was thought to be possibly due to its heterotrophic growth capacity, high turbidity, COD, nutrients and trace elements. In contrast, C. vulgaris showed poor heterotrophic and photoautotrophic growth under the highly turbid conditions of dairy effluent. Both Chlorella sp. and C. vulgaris showed similar total FAME (mg FAME/g algal cells). The fatty acid composition analysis revealed that both Chlorella sp. and C. vulgaris possessed major C18 and C20 fatty acids which will be used for biodiesel production. Overall, the novel microalga, Chlorella sp. isolated from the dairy effluent showed high potential for cost-effective algal cultivation and lipid production on dairy effluent without any modification of process.     

Nitrogen deprivation of microalgae: effect on cell size,cell wall thickness,cell strength,and resistance to mechanical disruption

Nitrogen deprivation (N-deprivation) is a proven strategy for inducing triacylglyceride accumulation in microalgae. However, its effect on the physical properties of cells and subsequently on product recovery processes is relatively unknown. In this study, the effect of N-deprivation on the cell size, cell wall thickness, and mechanical strength of three microalgae was investigated. As determined by analysis of micrographs from transmission electron microscopy, the average cell size and cell wall thickness for N-deprived Nannochloropsis sp. and Chlorococcum sp. were ca. 25% greater than the N-replete cells, and 20 and 70% greater, respectively, for N-deprived Chlorella sp. The average Young’s modulus of N-deprived Chlorococcum sp. cells was estimated using atomic force microscopy to be 775 kPa; 30% greater than the N-replete population. Although statistically significant, these microstructural changes did not appear to affect the overall susceptibility of cells to mechanical rupture by high pressure homogenisation. This is important as it suggests that subjecting these microalgae to nitrogen starvation to accumulate lipids does not adversely affect the recovery of intracellular lipids.     

Interactive Effects of Temperature and UV Radiation on Photosynthesis of Chlorella Strains from Polar,Temperate and Tropical Environments: Differential Impacts on Damage and Repair

Global warming and ozone depletion, and the resulting increase of ultraviolet radiation (UVR), have far-reaching impacts on biota, especially affecting the algae that form the basis of the food webs in aquatic ecosystems. The aim of the present study was to investigate the interactive effects of temperature and UVR by comparing the photosynthetic responses of similar taxa of Chlorella from Antarctic (Chlorella UMACC 237), temperate (Chlorella vulgaris UMACC 248) and tropical (Chlorella vulgaris UMACC 001) environments. The cultures were exposed to three different treatments: photosynthetically active radiation (PAR; 400–700 nm), PAR plus ultraviolet-A (320–400 nm) radiation (PAR + UV-A) and PAR plus UV-A and ultraviolet-B (280–320 nm) radiation (PAR + UV-A + UV-B) for one hour in incubators set at different temperatures. The Antarctic Chlorella was exposed to 4, 14 and 20°C. The temperate Chlorella was exposed to 11, 18 and 25°C while the tropical Chlorella was exposed to 24, 28 and 30°C. A pulse-amplitude modulated (PAM) fluorometer was used to assess the photosynthetic response of microalgae. Parameters such as the photoadaptive index (E_k) and light harvesting efficiency (α) were determined from rapid light curves. The damage (k) and repair (r) rates were calculated from the decrease in ΦPSII_eff over time during exposure response curves where cells were exposed to the various combinations of PAR and UVR, and fitting the data to the Kok model. The results showed that UV-A caused much lower inhibition than UV-B in photosynthesis in all Chlorella isolates. The three isolates of Chlorella from different regions showed different trends in their photosynthesis responses under the combined effects of UVR (PAR + UV-A + UV-B) and temperature. In accordance with the noted strain-specific characteristics, we can conclude that the repair (r) mechanisms at higher temperatures were not sufficient to overcome damage caused by UVR in the Antarctic Chlorella strain, suggesting negative effects of global climate change on microalgae inhabiting (circum-) polar regions. For temperate and tropical strains of Chlorella, damage from UVR was independent of temperature but the repair constant increased with increasing temperature, implying an improved ability of these strains to recover from UVR stress under global warming.     

High biomass production and CO<Subscript>2</Subscript> fixation from biogas by <Emphasis Type="Italic">Chlorella</Emphasis> and <Emphasis Type="Italic">Scenedesmus</Emphasis> microalgae using tequila vinasses as culture medium

Tequila vinasses (TVs) generated during Tequila production are brown liquid residues rich in nutrients. The nutrient content of agro-industrial effluents represents an excellent resource to support low-cost biomass production of microalgae; nonetheless, it is crucial to select the suitable microalgal strain to attain the highest biomass production in each residue used. In this study, biomass production, CO₂ fixation from biogas, and cell compound accumulation by Chlorella vulgaris U162, Chlorella sp., Scenedesmus obliquus U169, and Scenedesmus sp. using biodigested and filtered TVs as culture medium were evaluated and compared with the conventional microalgal culture media, C30, BG-11, Bold 3N, and Bristol. The four microalgae evaluated attained the highest biomass production and CO₂ fixation rate cultured in both residues, accumulating mainly carbohydrates and proteins although the most appropriate microalga to be cultured in TVs was Chlorella sp., recording 2.30 g L^?1. Moreover, the nutrient ratio of filtered TVs was ideal to support biomass production while biodigested TVs need to be supplemented with nitrogen. Overall, these results demonstrated that tequila vinasses are an excellent resource to support high and quick biomass production of microalgae, which can be used to obtain biofuels as ethanol, biogas, and supplement food depicting an extra benefit during the appropriate disposal of this residue.     

Antioxidant responses of different microalgal species to nonylphenol-induced oxidative stress

The antioxidant responses of four green microalgae, i.e., Chlorella vulgaris, Chlorella sp., Selenastrum capricornutum and Scenedesmus quadricauda, under control, low (0.1 mg L^?1) and high (1.0 mg L^?1) nonylphenol (NP) concentration were studied. The antioxidant responses of microalgae to NP depended on both NP concentrations and exposure time. The effects of NP on antioxidant responses were most obvious on the first day of exposure and the effects decreased with prolonged exposure time. At low NP concentration, there were no significant changes in activities of superoxide dismutase (SOD), catalase (CAT), and peroxidase (POD), or in glutathione (GSH) content, in all four species, while high concentration of NP led to different changes in these parameters. In NP-tolerant species, i.e., C. vulgaris and Chlorella sp., activities of SOD, CAT and POD increased remarkably when exposed to high NP concentration, while the increase was less evident or insignificant in Se. capricornutum and Sc. quadricauda, the two NP-sensitive species. On the other hand, the malondialdehyde (MDA) content declined gradually with increase in NP concentrations, particularly in C. vulgaris and Chlorella sp. Similarly, NP exposure caused an inhibition of glutathione peroxidase (GPX) activity in all four species. However, the changes of glutathione reductase (GR) and glutathione S-transferase (GST) activity did not seem to correlate with the NP tolerance of microalgae. These results suggested that various antioxidant mechanisms were involved in microalgae when exposed to NP, and the NP-tolerant species displayed more evident and rapid changes in some antioxidant responses than the NP-sensitive ones.     

<Emphasis Type="Italic">Scenedesmus</Emphasis> sp. cultivation using commercial-grade ammonium sources

The use of commercial-grade nutrients such as agricultural fertilizers is important for commercial microalgae cultivation, and this is particularly the case for biofuel production which is associated with low added value. Nitrogen is a very important macronutrient in microalgae cultivation, and ammonium sources are cheaper than nitrate sources. However, the growth response and cellular composition can be altered by the different nutrient sources. In the study reported here, we investigated the effects of different ammonium doses and commercial-grade macronutrients from agricultural fertilizers on the growth of Scenedesmus sp. BR003, a promising genus for biofuel production. Five growth media were developed using fertilizers and evaluated during Scenedesmus sp. cultivation under autotrophic conditions. The growth media differed in terms of their composition and concentration of macronutrients. We found that all commercial-grade media supported equal or higher cell concentrations, dry weight, water-soluble proteins, neutral carbohydrates, and total lipid production compared to the conventional BG11 medium. However, the commercial-grade growth medium with the highest ammonium content affected the coenobium pattern of Scenedesmus sp. BR003. Commercial-grade nutrient sources were a low-cost alternative to improve the growth of Scenedesmus sp. BR003. The different fertilizers also allowed for manipulation of microalgae chemical composition and phenotypic plasticity to target traits of commercial interest. Our results demonstrate the potential of using ammonium from agricultural fertilizers as a nitrogen source in combination with other commercial-grade macronutrients sources. In addition, this work demonstrates the ability of a robust Scenedesmus strain to grow in media of different compositions, even when a high dosage of ammonium was used.     

A (too) bright future? Arctic diatoms under radiation stress

Decreasing Arctic sea ice cover and increasing stratification of ocean surface waters make the exposure of pelagic microalgae to high irradiances more likely. Apart from light being a necessary prerequisite for photosynthesis, rapidly changing and/or high irradiances are potentially detrimental. An in situ study was performed in the high Arctic (79°N) to determine the effect of high irradiances in general, and ultraviolet radiation (UVR, 280–400 nm) in particular, on cell concentrations, fatty acid composition, and photoprotective pigments of three diatom species isolated from seawater around Svalbard. Unialgal cultures were exposed in situ at 0.5- and 8 m-depth. After 40 h, cell concentrations of Synedropsis hyperborea and Thalassiosira sp., were lower at 0.5 than at 8 m, and the content of the photoprotective xanthophyll-cycle pigment diatoxanthin in all species (S. hyperborea, Thalassiosira sp., Porosira glacialis) was higher in the 0.5 m exposure compared to 8 m. In S. hyperborea, growth was additionally inhibited by UVR at 0.5-m depth. In situ radiation conditions led, furthermore, to a significant decrease in polyunsaturated fatty acids (PUFAs) in all three species, but UVR had no additional effect. Hence, we conclude that natural radiation conditions close to the surface could reduce growth and PUFA concentrations, but the effects are species specific. The diatoms’ potential to acclimate to these conditions over time has to be evaluated.     

High pH-induced flocculation of marine <Emphasis Type="Italic">Chlorella</Emphasis> sp. for biofuel production

Microalgae are being considered as a promising raw material for biofuel production. However, rapid, efficient, and economic technologies for harvesting microalgae are essential for successful applications. In this study, the high–pH-induced flocculation method was applied to harvest marine Chlorella sp. strains. These algae could be concentrated up to approximately 20-fold by increasing pH using NaOH, with a flocculation efficiency of 90 %. When NaOH dosage was low (1 or 3 mM), the flocculation efficiency decreased considerably with the increase of biomass concentration. At higher NaOH dosage tested (5 or 7 mM), flocculation occurred quickly and efficiently, which tended to be independent of biomass concentration. In larger volumes, all strains were flocculated with similar efficiencies (approximately 90 %) after adding 5 mM NaOH. After flocculation, the flocculated algae cells could be re-cultured as inoculum, and the growth yields in flocculated medium were slightly higher than those from fresh medium. Additionally, for each strain, there were no significant differences in lipid extraction yield and fatty acid composition according to different harvesting methods. These results showed that the high–pH-induced flocculation method could be used to harvest marine Chlorella sp. for biofuel production successfully.     

The eurythermal adaptivity and temperature tolerance of a newly isolated psychrotolerant Arctic <Emphasis Type="Italic">Chlorella</Emphasis> sp.

A new strain of Chlorella sp. (Chlorella-Arc), isolated from Arctic glacier melt water, was found to have high specific growth rates (μ) between 3 and 27 °C, with a maximum specific growth rate of 0.85 day^?1 at 15 °C, indicating that this strain was a eurythermal strain with a broad temperature tolerance range. To understand its acclimation strategies to low and high temperatures, the physiological and biochemical responses of the Chlorella-Arc to temperature were studied and compared with those of a temperate Chlorella pyrenoidosa strain (Chlorella-Temp). As indicated by declining F _v/F _m, photoinhibition occurred in Chlorella-Arc at low temperature. However, Chlorella-Arc reduced the size of the light-harvesting complex (LHC) to alleviate photoinhibition, as indicated by an increasing Chl a/b ratio with decreasing temperatures. Interestingly, Chlorella-Arc tended to secrete soluble sugar into the culture medium with increasing temperature, while its intracellular soluble sugar content did not vary with temperature changes, indicating that the algal cells might suffer from osmotic stress at high temperature, which could be adjusted by excretion of soluble sugar. Chlorella-Arc accumulated protein and lipids under lower temperatures (<15 °C), and its metabolism switched to synthesis of soluble sugar as temperatures rose. This reflects a flexible ability of Chlorella-Arc to regulate carbon and energy distribution when exposed to wide temperature shifts. More saturated fatty acids (SFA) in Chlorella-Arc than Chlorella-Temp also might serve as the energy source for growth in the cold and contribute to its cold tolerance.     

Microalgae from the Selenastraceae as emerging candidates for biodiesel production: a mini review

Over the years, microalgae have been identified to be a potential source of commercially important products such as pigments, polysaccharides, polyunsaturated fatty acids and in particular, biofuels. Current demands for sustainable fuel sources and bioproducts has led to an extensive search for promising strains of microalgae for large scale cultivation. Prospective strains identified for these purposes were among others, mainly from the genera Hematococcus, Dunaliella, Botryococcus, Chlorella, Scenedesmus and Nannochloropsis. Recently, microalgae from the Selenastraceae emerged as potential candidates for biodiesel production. Strains from the Selenastraceae such as Monoraphidium sp. FXY-10, M. contortum SAG 47.80, Ankistrodesmus sp. SP2-15 and M. minutum were high biomass and lipid producers when cultivated under optimal conditions. A number of Selenastraceae strains were also reported to be suitable for cultivation in wastewater. This review highlights recent reports on potential strains from the Selenastraceae for biodiesel production and contrasts their biomass productivity, lipid productivity as well as fatty acid profile. Cultivation strategies employed to enhance their biomass and lipid productivity as well as to reduce feedstock cost are also discussed in this paper.     

Contaminated bacterial effects and qPCR application to monitor a specific bacterium in <Emphasis Type="Italic">Chlorella</Emphasis> sp. KR-1 culture

To investigate the effects of bacteria contaminated in microalgal cultivation, several bacteria were isolated from four photobioreactors for Chlorella sp. KR-1 culture. A total of twenty-one bacterial strains isolated from the reactors and identified by 16S rRNA gene sequencing. Six bacteria, which were found from more than two reactors of the four photobioreactors, were introduced into co-culturing experiments with Chlorella sp. KR-1. Then, the bacterial influences on the productivity of microalgal biomass and lipids were assessed in the photoautotrophic- and mixotrophic microalgal cultivation by comparing them with axenic culture of Chlorella sp. KR-1. The results showed that both biomass and lipid production were significantly enhanced under mixotrophic conditions compared to photoautotropic conditions. However, an excess ratio (more than 10%) of bacterial cells to microalgal cells at the initial stage of mixotrophic cultivation has limited the growth of Chlorella sp. KR-1 because of the relatively fast growth of bacteria, especially under mixotrophic conditions. Moreover, it was proven that the strong biofilm formability of Sphingomonas sp. MB6 is the responsible strain to cause the biomass aggregation observed during the early stage of co-culture. The high abundance of Sphingomonas sp. MB6 during early cultivation period shown by qPCR results was also well corresponded with the period shown a strong biofilm formation, which suggested the applicability of qPCR to monitor a specific bacterial group in a microalgal culture.     

Toxicity and bioaccumulation of iron in soil microalgae

Microalgae are extensively used in the remediation of heavy metals like iron. However, factors like toxicity, bioavailability and iron speciation play a major role in its removal by microalgae. Thus, in this study, toxicity of three different iron salts (FeSO₄, FeCl₃ and Fe(NO₃)₃) was evaluated towards three soil microalgal isolates, Chlorella sp. MM3, Chlamydomonas sp. MM7 and Chlorococcum sp. MM11. Interestingly, all the three iron salts gave different EC50 concentrations; however, ferric nitrate was found to be significantly more toxic followed by ferrous sulphate and ferric chloride. The EC₅₀ analysis revealed that Chlorella sp. was significantly resistant to iron compared to other microalgae. However, almost 900 μg g^?1 iron was accumulated by Chlamydomonas sp. grown with 12 mg L^?1 ferric nitrate as an iron source when compared to other algae and iron salts. The time-course bioaccumulation confirmed that all the three microalgae adsorb the ferric salts such as ferric nitrate and ferric chloride more rapidly than ferrous salt, whereas intracellular accumulation was found to be rapid for ferrous salts. However, the amount of iron accumulated or adsorbed by algae, irrespective of species, from ferrous sulphate medium is comparatively lower than ferric chloride and ferric nitrate medium. The Fourier transform infrared spectroscopy (FTIR) analysis shows that the oxygen atom and P?=?O group of polysaccharides present in the cell wall of algae played a major role in the bioaccumulation of iron ions by algae.     

Nutrient removal from high strength nitrate containing industrial wastewater using <Emphasis Type="Italic">Chlorella</Emphasis> sp. strain ACUF_802

the research aim of this study was to characterize an isolated native strain of Chlorella sp. ACUF_802, well adapted to a high nitrate concentration environment and to investigate its potential to nitrate and phosphate removal from industrial wastewaters with the minimal addition of chemical reagents and energy. The isolated strain was identified and evaluated for its capability to support biomass growth and nutrient removal from synthetic wastewater in batch tests using different concentrations of carbon and nitrogen, different carbon sources and N:P ratios. The strain was isolated via the plating method from the settler of a pilot scale moving bed biofilm reactor performing a nitrification process. The strain was identified using molecular analysis with rDNA primers. Using sodium bicarbonate as carbon source, the batch productivity (71.43 mg L^?1 day^?1) of the strain Chlorella sp. ACUF_802 was calculated with a logistic model and compared to the values reported in the literature. Assays on the effect of the N:P ratio indicated that the productivity was increased 36% when the N:P ratio was close to 1 (111.96 mg L^?1 day^?1), but for a complete phosphorus removal a 5:1 N:P ratio with nitrate concentrations ≤125 mg?L^?1 is recommended. The isolated microalgae strain Chlorella sp. ACUF_802 showed versatility to grow in the synthetic industrial wastewaters tested and can be considered as an appropriate organism for nitrogen removal from industrial wastewaters in the presence of an organic or inorganic carbon source.     

Effect of elevated temperature on the physiological responses of marine <Emphasis Type="Italic">Chlorella</Emphasis> strains from different latitudes

The increased frequency of heat waves due to climate change poses a threat to all organisms. Microalgae are the basis of aquatic food webs, and high temperatures have significant impacts on their adaptation and survival rates. Algae respond to environmental changes by modulating their photosynthetic rates and biochemical composition. This study aims to examine the effect of elevated temperature on similar taxa of marine Chlorella originating from different latitudes. Strains from the Antarctic, temperate zone, and the tropics were grown at various temperatures, ranging from 4 to 38, 18 to 38, and 28 to 40 °C, respectively. A pulse-amplitude modulated (PAM) fluorometer was used to assess their photosynthetic responses. Parameters including maximum quantum efficiency (F _v/F _m), relative electron transport rate (rETR), and light harvesting efficiency (α) were determined from the rapid light curves (RLCs). In addition, the composition of fatty acids was compared to evaluate changes induced by the temperature treatments. Increasing the temperature from 35 to 38 °C for both Antarctic and temperate strains and from 38 to 40 °C for the tropical strain resulted in severe inhibition of photosynthesis and suppressed growth. Although all the strains demonstrated the ability to recover from different stress levels, the tropical strain was able to recover most rapidly while the Antarctic strain had the slowest recovery. The results underline that the thermal threshold for the analysed Chlorella strains temperature ranges between 38 and 40 °C. Furthermore, the analysed strains exhibited different trends in their response to elevated temperatures and recovery capabilities.     

Phosphopantetheinylation in the green microalgae <Emphasis Type="Italic">Chlamydomonas reinhardtii</Emphasis>

Microalgal biofuel is a promising solution to the decline of fossil fuels. However, algal fatty acid metabolism, the machinery producing the raw material for biofuels, remains poorly understood. The central unit of the fatty acid synthase (FAS) is the acyl carrier protein (ACP), which is responsible for holding the product. Fatty acid biosynthesis is initiated through posttranslational modification of the ACP by the phosphopantetheinyl transferase (PPTase). We identified two PPTases, PptC1 and PptC2, in the model alga Chlamydomonas reinhardtii by genome analysis and phylogenetic and structural comparison. Both PPTases are of Sfp-type, the archetypical PPTase type for non-ribosomal peptide and polyketide biosynthetic pathways in bacteria and cyanobacteria. In vitro analysis revealed that PptC2 has a broader substrate range than PptC1. Both PPTases were able to activate the cognate ACP of the type II FAS, while PptC2 also recognized ACP of Escherichia coli type II FAS and actinorhodin type II polyketide synthase. Besides FAS as PPTase target, the C. reinhardtii genome encodes a single type I PKS, and we hypothesize that PptC2 is responsible for its activation. Screening of the currently available microalgal genome data revealed that most green microalgae appear to carry two PPTases forming clusters with each C. reinhardtii PPTase, while microalgae of other divisions carry one or two PPTases and do not cluster in the pattern of the green algal data. This new understanding on the PPTases in microalgae shows that microalgae are already primed for biotechnological applications in contrast to other organisms. Thus, microalgae have great potential for metabolic engineering efforts in the realm of biofuel and high-value products including direct engineering of the fatty acid or secondary metabolism using the natural genomic reservoir and as biotechnological platform for heterologous expression.     

Potential Outdoor Cultivation of Green Microalgae Based on Response to Changing Temperatures and by Combining with Air Temperature Occurrence

In this study, our working hypothesis was to examine whether temperature alters biomass and metabolite production by microalgae according to strain. We also addressed whether it is possible to choose a strain suitable for growing in each season of a given region. A factorial experiment revealed a significant interaction between chlorophylls a and b (Chl a and Chl b), carotenoid/Chl (a?+?b) ratio, biomass and total lipid productivity of six green microalgae (four Chlorella spp., Chlorella sorokiniana and Neochloris oleoabundans) after 15 days at four temperatures. At 39/35 °C, two Chlorella sp. strains (IPR7115 and IPR7117) showed higher total carotenoids/Chl (a?+?b) (0.578 and 0.830), respectively. N. oleoabundans had the highest Chl a (8210 μg L^?1) and Chl b (1909 μg L^?1) at 19/15 °C and highest maximum dry biomass (2900 mg L^?1), specific growth rate (0.538 day^?1) and total lipids (1003 mg L^?1) at 15/8 °C. We applied a method to infer the growth of these six green microalgae in outdoor ponds, as based on their response to changing temperatures and by combining with historical data on day/night air temperature occurrence for a given region. We conclude that the use of regionalized maps based on air temperature is a good strategy for predicting microalgal cultivation in outdoor ponds based on their features and tolerance to changing temperature.