Algal Lipid Content Research Articles

PROLIFERATION OF THE DIATOM CYCLOTELLA MENEGHINIANA AFFECTED BY EXPOSURE TO LEAD

Elevated levels of pollutants, including heavy metals, resulting from human activities, have raised concerns regarding their adverse impacts on natural ecosystems. Among these, aquatic organisms, particularly non-target microalgae, bear substantial consequences from such contaminants. This study endeavored to evaluate the impact of the heavy metal lead (Pb) at concentrations of 2.5, 25, and 250 μg L−1 on the growth and lipid content of the diatom Cyclotella meneghiniana in a 14-day toxicity test conducted under controlled laboratory conditions. The findings indicate that lower Pb concentrations (2.5 and 25 μg L−1 ) fostered algal proliferation, whereas exposure to 250 μg L−1 resulted in complete inhibition in two distinct endpoints. Additionally, no significant fluctuations in algal lipid content were discernible between exposure to 2.5 and 25 μg Pb L−1 and the control group. This study stands as a pioneering effort in unveiling the toxicity of Pb on C. meneghiniana, shedding light on the species’ susceptibility to this heavy metal and underscoring the necessity of incorporating this species into ongoing ecological risk assessments of Pb.

Simultaneous enhancement of lipid biosynthesis and solvent extraction of Chlorella using aminoclay nanoparticles

Magnesium aminoclay nanoparticles (MgANs) exert opposing effects on photosynthetic microalgae by promoting carbon dioxide (CO2) uptake and inducing oxidative stress. This study explored the potential application of MgAN in the production of algal lipids under high CO2 concentrations. The impact of MgAN (0.05–1.0 g/L) on cell growth, lipid accumulation, and solvent extractability varied among three tested oleaginous Chlorella strains (N113, KR-1, and M082). Among them, only KR-1 exhibited significant improvement in both total lipid content (379.4 mg/g cell) and hexane lipid extraction efficiency (54.5%) in the presence of MgAN compared to those of controls (320.3 mg/g cell and 46.1%, respectively). This improvement was attributed to the increased biosynthesis of triacylglycerols and a thinner cell wall based on thin-layer chromatography and electronic microscopy, respectively. These findings suggest that using MgAN with robust algal strains can enhance the efficiency of cost-intensive extraction processes while simultaneously increasing the algal lipid content.

Optimization of hydrolysis conditions of crop straw and its effect in Chlorellasorokiniana culture.

Taking straws of corn, wheat, and millet as raw materials, we pretreated them with alkaline hydrogen peroxide, and then hydrolyzed by cellulase and xylanase. We selected the total sugar content in the hydrolysate as the indicator to evaluate the hydrolysis of the straws from three crop species, and further optimized the conditions. Then, the hydrolysates of three types of crop straws were used as carbon source for Chlorella sorokiniana culture to assess their effects on microalgal cultivation. The results showed that the optimal hydrolysis conditions for the three crop straws were identified as solid-liquid ratio of 1:15, temperature of 30 ℃, and treatment time of 12 h. Under such optimal condition, the total sugar contents increased up to 1.677, 1.412, and 1.211 g·L-1 in the corn, millet and wheat straw hydrolysate, respectively. The hydrolysates from the three crop straw could significantly increase both algal biomass and lipid content of C. sorokiniana. Corn straw hydrolysate had the best effect, with high levels of algal biomass (1.801 g·L-1) and lipid content (30.1%). Therefore, we concluded that crop straw hydrolysates as carbon source could significantly promote microalgal biomass and lipid enrichment. The results could lay the foundation for the efficient conversion and utilization of straw lignocellulose raw materials, provide new knowledge for the resource utilization of agricultural wastes, as well as the theoretical basis for the efficient cultivation of microalgae using crop straw hydrolysates.

Municipal Wastewater Effects on the Performance of Nutrient Removal, and Lipid, Carbohydrate, and Protein Productivity of Blue-Green Algae Chroococcus turgidus

The use of microalgae in wastewater treatment (WWT) is seen as a promising and sustainable alternative to conventional WWTs, and the obtained biomass is gaining importance as a bio-product. The present study aimed to investigate the effectiveness of using municipal wastewater (MWW) as a nutritional supplement for the cultivation of the cyanobacteria Chroococcus turgidus (Kützing) Nägeli 1849 and the pollutant removal potential of the microalgae. The WW received from the different treatment stages (primary, secondary, and final effluent) was applied to the microalgae culture, and algal growth was compared with regard to growth rate, nutrient removal efficiency, and final algal lipid (%) and protein (%) content. In 7-day batch experiments, except for BOD5 analysis, COD, PO4-P, and N forms analyses were carried out daily in parallel with in vivo Chl-a and Chl-b, DO, pH, temperature, and conductivity measurements. The growth rates and Chl-a quotas of the microalgae grown in trials were different, and the highest growth rate was with a 1.03 ± 0.06 d−1 in the primary effluent (PE). The highest Chl-a and Chl-b quotas among WW trials of microalgae were obtained from the PE trial as 252.4 ± 2 µg L−1 and 112 ± 18 µgL−1, respectively. NH4-N, NO3-N, NO2-N, PO4-P, BOD5, and COD treatment efficiencies were in the ranges of (74.6–83%), (16–71.2%), (22.2–63.6%), (89–95.3%), (50–76.2%), and (70.3–78.6%), respectively. The microalgae were observed to accumulate the highest lipid (28.05 ± 2.26%DW) content in secondary effluent (SE), the highest carbohydrate (43.93 ± 1.02%DW) content in the effluent (E), and the highest protein content (35.25 ± 1.22%DW) in the PE. The results of this study suggested that C. turgidus is a new candidate for bioremediate pollution load of MWW, and its biomass has the potential to offer options in bio-product applications.

Screening of symbiotic Streptomyces spp. and optimization of microalgal growth in a microalgae-actinomycetes co-culture system

Microalgal biodiesel as a substitute for fossil energy has attracted extensive attention. However, the high cost of microalgae cultivation limits the industrial production of microalgal biodiesel. The co-culture system may offer a means to increase microalgae’s biomass production. In this study, Streptomyces strains were selected to construct and optimize co-culture systems with Monoraphidium sp. HDMA-11 and the algal cell biomass, lipid content, phycocyanin content, starch content, and fatty acid composition were determined. The results showed that Streptomyces nojiriensis significantly promoted Monoraphidium sp. HDMA-11 growth and a co-culture system were established. Orthogonal experiments showed that the Monoraphidium sp. HDMA-11 biomass was further increased when the initial culture pH was 7.5, the inoculation time of Streptomyces strain supernatants was 36 h, the volume ratio of microalgal actinomycetes was 1:1, and no additional acetic acid was added. Under these conditions, compared with monocultured Monoraphidium sp. HDMA-11, the cell biomass and lipid productivity of the co-culture system increased by 525.8 and 155.1%, respectively. These results suggest that S. nojiriensis supernatant potentially enhances microalgae biomass and may represent a new method to improve microalgae growth.

Investigating the effects of eleven key physicochemical factors on growth and lipid accumulation of Chlorella sp. as a feedstock for biodiesel production

Biodiesel, as a renewable and eco-friendly energy source that can be produced through algae oil esterification, has recently received much attention. Maximization of algal biomass and lipid content is crucial for commercial biodiesel production. In this study, Chlorella sp. PG96, a microalgal strain isolated from urban wastewater, was identified considering its morphological and molecular characteristics. Fractional factorial design (211-7) was employed to screen medium and environmental factors for achieving high lipid productivity. The effects of eleven factors including light intensity, light spectrum, aeration rate, temperature, salinity, NaHCO3, CO2, NaNO3, NH4Cl, MgSO4.7H2O, and K2HPO4 and their interactions on growth characteristics of Chlorella sp. PG96 (biomass and lipid production) were statistically assessed. Based on the experimental results, lipid productivity was at its maximum (54.19 ± 8.40 mglipid L−1 day−1) under a combination of high levels of all factors. The analysis also showed that physical parameters of light intensity and temperature were more effective on algal growth compared to nutritional parameters. Furthermore, nitrogen source of ammonium and carbon source of bicarbonate played more significant roles in biomass and lipid production, compared with nitrate and CO2, respectively. Although the effect of sulfur limitation on cellular growth was similar to phosphorus deficiency, S-limitation had a greater impact on lipid accumulation. The interaction between NaHCO3 and NH4Cl was the most prominent interaction affecting all responses. It is concluded that Chlorella sp. PG96 at a high level of light intensity and temperature (22500 Lux and 32 °C, respectively) can be a prospective candidate for biodiesel production.

The Influence of Bacteria on the Growth, Lipid Production, and Extracellular Metabolite Accumulation by Phaeodactylum tricornutum (Bacillariophyceae).

To examine the impact of heterotrophic bacteria on microalgal physiology, we co-cultured the diatom Phaeodactylum tricornutum with six bacterial strains to quantify bacteria-mediated differences in algal biomass, total intracellular lipids, and for a subset, extracellular metabolite accumulation. A Marinobacter isolate significantly increased algal cell concentrations, dry biomass, and lipid content compared to axenic algal cultures. Two other bacterial strains from the Bacteroidetes order, of the genera Algoriphagus and Muricauda, significantly lowered P. tricornutum biomass, leading to overall decreased lipid accumulation. These three bacterial co-cultures (one mutualistic, two competitive) were analyzed for extracellular metabolites via untargeted liquid chromatography mass spectrometry to compare against bacteria-free cultures. Over 80% of the extracellular metabolites differentially abundant in at least one treatment were in higher concentrations in the axenic cultures, in agreement with the hypothesis that the co-cultured bacteria incorporated algal-derived organic compounds for growth. Furthermore, the extracellular metabolite profiles of the two growth-inhibiting cultures were more similar to one another than the growth-promoting co-culture, linking metabolite patterns to ecological role. Our results show that algal-bacterial interactions can influence the accumulation of intracellular lipids and extracellular metabolites, and suggest that utilization and accumulation of compounds outside the cell play a role in regulating microbial interactions.

Molecular Mechanism of Lipid Accumulation and Metabolism of Oleaginous Chlorococcum sphacosum GD from Soil under Salt Stress.

The oleaginous microalgae species Chlorococcum sphacosum GD is a promising feedstock for biodiesel production from soil. However, its metabolic mechanism of lipid production remains unclear. In this study, the lipid accumulation and metabolism mechanisms of Chlorococcum sphacosum GD were analyzed under salt stress based on transcriptome sequencing. The biomass and lipid content of the alga strain were determined under different NaCl concentrations, and total RNA from fresh cells were isolated and sequenced by HiSeq 2000 high throughput sequencing technology. As the salt concentration increased in culture medium, the algal lipid content increased but the biomass decreased. Following transcriptome sequencing by assembly and splicing, 24,128 unigenes were annotated, with read lengths mostly distributed in the 200–300 bp interval. Statistically significant differentially expressed unigenes were observed in different experimental groups, with 2051 up-regulated genes and 1835 down-regulated genes. The lipid metabolism pathway analysis showed that, under salt stress, gene-related fatty acid biosynthesis (ACCase, KASII, KAR, HAD, FATA) was significantly up-regulated, but some gene-related fatty acid degradation was significantly down-regulated. The comprehensive results showed that salt concentration can affect the lipid accumulation and metabolism of C. sphacosum GD, and the lipid accumulation is closely related to the fatty acid synthesis pathway.

Long-Term Toxicity of ZnO Nanoparticles on Scenedesmus rubescens Cultivated in Semi-Batch Mode.

The scope of this study was to investigate the toxic effects of zinc oxide (ZnO) nanoparticles (NPs) on freshwater microalgae, in long-term semi-batch feeding mode at two different hydraulic retention times (HRTs) (20 and 40 days). A freshwater microalgae, Scenedesmus rubescens, was employed and exposed to a semi-continuous supply of ZnO NPs at a low concentration of 0.081 mg/L for a period of 28 d. Experiments were conducted under controlled environmental conditions. Τhe impact of ZnO NPs on S. rubescens, which was assessed in terms of nutrient removal, biomass growth, and algal lipid content. Semi-batch mode cultures showed that low ZnO NP concentrations at an HRT of 40 d did not have any negative effect on microalgae growth after the fourth day of culture. In contrast, algal growth was inhibited up to 17.5% at an HRT of 20 d in the presence of ZnO NPs. This might be attributed to the higher flow rate applied and ZnO NPs load. A positive correlation between nutrient removal and microalgae growth was observed. The algal lipid content was, in most cases, higher in the presence of ZnO NPs at both HRTs, indicating that even low ZnO NPs concentration cause stress resulting in higher lipid content.

Interactive effect of light quality and temperature on Chlamydomonas reinhardtii growth kinetics and lipid synthesis

The efficient operation of an algal photobioreactor (PBR) requires appropriate lighting conditions. Despite recent advantages in PBR design and operation, optimal lighting conditions are still not fully understood. This work focuses on the effect of light quality and culturing temperature on the algal growth kinetics and lipid content. The green alga Chlamydomonas reinhardtii was grown in batch culture in a constant-temperature incubator-shaker under LED light. Three light wavelength regimes were studied: blue light (peaking at 433 nm–447 nm, 458 nm–470 nm), white-yellow light (peaking at 456–458 nm in blue, 545 nm in green and 570 nm in yellow) and red-orange light (peaking at 580 nm–594 nm and 604 nm in yellow-orange, 630 nm and 656 nm in red, and 735 nm in IR). Results show that red-orange light obtained 38% higher biomass productivity than blue light at 24 °C, and blue light obtained 13% higher biomass productivity than red-orange light at 32 °C. Red-orange light or temperatures of 30–32 °C favored lipid accumulation with a lipid mass fraction and lipid concentration of 44% and 80% higher, respectively, compared to blue light at 24 °C. In the late exponential phase, when nutrients in the medium were still sufficient, light quality was the predominant factor controlling the lipid synthesis and accumulation. While in the late stationary phase under nutrient starvation, a strong interactive effect was detected between the light quality and temperature (P = 0.02) for lipid synthesis and accumulation. Under both temperature and nutrient stress, there was a reduced effect of the light quality on the lipid synthesis.

Growth and lipid levels of Tetraselmis tetrahele and Nannochloropsis sp. cultured under commercial fertilizers

Microalgae are aquatic photosynthetic organisms that contain high amounts of lipid and are potential sources of biofuels as well as feed additives for aquaculture. This study analyzed the growth and algal lipid content of two microalgae species (Tetraselmis tetrahele and Nannochloropsis sp.) using commercial fertilizers and nutrient enrichment. The samples were cultured for 5 days in 1 L dextrose bottles fertilized using Tongkang Marine Research Laboratory (TMRL) enrichment media, inorganic fertilizers such as 14-14-14, and a combination of 14-14-14 and 21-0-0. The relative growth rate of two algae were measured by computing the k value while the lipid components were extracted using the Bligh and Dyer Method, and the lipid content of each sample was determined using the gravimetric method. The use of 14-14-14 fertilizer produced the highest growth rates (k=1.810) and lipid composition (14.789%) for T. tetrahele. By contrast, Nannochloropsis sp., grew well under TMRL enrichment media (k=9.708), and the use of 14-14-14 fertilizer resulted to high lipid content (5.000%).

Optimized process parameters for production of Chlorella pyrenoidosa biomass and lipids using response surface methodology

To utilize microalgae as a valuable bioresource, the effect of growth conditions on their yield and biochemical product production must be determined. We employed response surface methodology in the function of a Box-Behnken design to derive the functional relationship between environmental conditions and the microalgal biomass and lipid content of Chlorella pyrenoidosa. C. pyrenoidosa was grown in BG-11 medium from 20 to 30 °C, 100 to 200 μmol photons m−2 s−1 light intensity, and 7.5 to 9.5 pH. A total of 17 experimental runs were analyzed for the effect of three parameters of interest (temperature, light intensity, and pH). The statistical model and regression equation of the program predicted the optimal conditions for accumulating the highest biomass and lipid content. As predicted by the model, the optimized conditions of 24.70 °C, 178 μmol photons m−2 s−1 of light intensity, and a pH of 8.74 produced the maximal experimental results of C. pyrenoidosa algal biomass and lipid content, 2.90 g L−1 and 27.12%, respectively. Under optimal conditions, C. pyrenoidosa synthesized 53.25% of total polyunsaturated fatty acids, 23.53% of total monounsaturated fatty acids, and 23.07% of saturated fatty acids; α-linolenic acid was the most abundant fatty acid (39.93%) and is an essential ω-3 polyunsaturated fatty acid for commercial algal products. The optimized process parameters obtained in this work have provided a basis for further large volume photobioreactor culturing for biomass and lipid content.

Engineering the metabolic pathways of lipid biosynthesis to develop robust microalgal strains for biodiesel production.

Algal lipids have shown promising feedstock to produce biodiesel due to higher energy content, higher cetane number, and renewable nature. However, at present, the lipid productivity is too low to meet the commercial needs. Various approaches can be employed to enhance the lipid content and lipid productivity in microalgae. Stress manipulation is an attractive option to modify the algal lipid content, but it faces the drawback of time-consuming production processing and lack of information about molecular mechanisms related to triacylglycerides production in response to stress. Developing the robust hyper lipid accumulating algal strains has gained momentum due to advances in metabolic engineering and synthetic biology tools. Understanding the molecular basis of lipid biosynthesis followed by reorienting the related pathways through genomic modification is an alluring strategy that is believed to achieve the industrial and economic robustness. This review portrays the use of integrated OMIC approaches to elucidate the molecular mechanisms of strain adaptability in response to stress conditions, and identification of molecular pathways that should become novel targets to develop novel algal strains. Moreover, an update on the metabolic engineering approaches to improve the lipid production in microalgae is also provided.

Quorum-sensing mediated signals: A promising multi-functional modulators for separately enhancing algal yield and power generation in microbial fuel cell

Quorum-sensing molecules (QSMs) extracted from anaerobic sludge can help to enhance the overall productivity of algal culture, thus diminishing the per unit production cost of algae based-biofuel. In this investigation, QSMs extracted from anaerobic bacterial sludge of microbial fuel cell (MFC) was used to enhance the overall productivity of Chlorella sorokiniana cultivated in a separate bubble column photobioreactor. With the dosage of QSMs, algal biomass productivity and lipid content were increased by 2.25 times and 1.28 times, respectively. Further, lipid extracted biomass of quorum-sensing induced algae (LEB-QSA) was applied in anodic chamber of MFC to function as substrate and mediator, which enhanced the coulombic efficiency of this MFC by 74% as compared to the control MFC operated without LEB-QSA. Thus, this exploration demonstrated successful improvement in the macromolecular properties of algal culture dosed with QSMs and improved performance of MFC with the application of LEB-QSA as mediator and substrate.

The effect of glycerol and carbonate on the growth and lipid production of Isochrysis galbana under different cultivation modes

This study aimed to investigate the potential of using glycerol and carbonate as different carbon sources for the production of biomass and the lipid content of Isochrysis galbana under heterotrophic, mixotrophic and phototrophic conditions. Glycerol as the carbon source inhibited the growth of I. galbana in the heterotrophic mode, while growth was enhanced in the mixotrophic conditions as compared to phototrophic conditions. Algal dry weight and lipid content were enhanced as glycerol concentration was increased from 0 to 100 mM; this was such that the highest biomass production and lipid content occurred at 50 mM glycerol under mixotrophic conditions (0.23 g L−1, 29% of dry weight) and at 25 mM glycerol under heterotrophic conditions (0.25 g L−1, 19.6% of dry weight). The effect of carbonate as the inorganic carbon source on the growth of I. galbana under mixotrophic conditions was investigated; the highest biomass (0.38 g L−1) and lipid content (30.7% of dry weight) were achieved at 1 g L−1 carbonate. It was, therefore, demonstrated that the growth and lipid content of I. galbana could be improved by using the mixotrophic culture at 50 mM glycerol; especially, carbonate as the inorganic carbon could enhance CO2 biofixation to 1 g L−1.

Isolation and Characterization of Microalgae from Diverse Pakistani Habitats: Exploring Third-Generation Biofuel Potential

Production of microalgae as feedstock for biofuels must deal with a number of challenges including constraints imposed by local conditions. One solution is to use indigenous strains adapted to local climatic conditions. The present report describes the isolation, identification, and characterization of 32 microalgal strains from different ecological habitats: desert freshwater channels, northern region, and saline regions of Pakistan. The effects of temperature on algal growth rates, biomass productivity, and lipid content were determined through growth at 12, 20, and 35 °C for 15 days under 2% CO2 Responses to temperature varied among species with 20 °C being the optimum temperature in general, although, exceptionally, the best overall growth rate was found for strain S29 (0.311 d−1) at 12 °C. In some cases high biomass productivity was observed at 35 °C, and, depending upon the strain, the maximum lipid content was obtained at different temperatures, including 12 °C. Fatty acid methyl ester (FAME) analysis showed that the major fatty acids present were palmitic, stearic, oleic, linoleic, and linolenic. Oleic acid (C18:1) was the predominant fatty acid, with the specific FAME profile varying with strain. Thus, there is a rich diversity of microalgal strains native to Pakistan, some of which, characterized here, could be suitable for biodiesel production or other biotechnological applications.

Outdoor cultivation of the green microalga Chlorella vulgaris under stress conditions as a feedstock for biofuel.

The present work investigated the potential of the green alga Chlorella vulgaris to produce high-quality biofuel under culture stress conditions. The cultivation was carried out in a 1000 lopen plate tank system, which provides biomass yields comparable to open pond systems, but with less area needed. Algal biomass and lipid content were measured repeatedly. We compared the two solvent systems n-hexane and hexane/isopropanol (HIP) for extraction efficiency of lipids and applied three different extraction methods Soxhlet, soaking, and soaking followed by Soxhlet (soak-Sox). The combination of the HIP solvent and the soak-Sox provided the highest lipid yield (15.8 ± 0.174). Volumetric biomass and lipid productivity were 0.201gl-1day-1 and 31.71mgl-1day-1, respectively, whereas areal biomass and lipid productivity were 25.73gm-2day-1 and 4.066gm-2day-1, respectively. The fatty acid profile by means of gas chromatography resulted in seven fatty acids from C12 to C18. The most abundant fatty acid methyl esters (FAMES) were palmitic (C16:0), oleic (C18:1), and stearic (C18:0) acids. Lipid synthesis enhanced by optimizing the Kuhl growth medium with replacing nitrate by urea (50% N compared to the original recipe) increased salt content (10g/l NaCl), ferrous sulfate (0.5g/l), and sodium acetate addition (1g/l). With regard to density, kinematic viscosity, gravity, pour point, flash point, and cetane number, the Chlorella-biodiesel comply with ASTM and EN standards thus pointing at the high potential of lipids synthesized by Chlorella as a feedstock for biodiesel production.

Monitoring oil production for biobased feedstock in the microalga Nannochloropsis sp.: a novel method combining the BODIPY BD-C12 fluorescent probe and simple image processing

A simple reliable method with fast response for lipid detection and quantification is proposed, combining a new highly lipophilic fluorescent probe BODIPY BD-C12 and image analysis to determine the algal lipid content and the lipid production in the microalgae Nannochloropsis sp. Lipid bodies stained with BODIPY BD-C12 have a characteristic multicolor fluorescence, and their volumes were determined using a sphere volume approach. The method developed was applied in the evaluation of lipid accumulation by Nannochloropsis sp. under different cultivation conditions (varying nitrate and salinity concentrations and combined effect of these two variables). The results show an increase of lipid content in Nannochloropsis sp. cultivated in nitrogen replete and depleted conditions, from 9.4 to 40.8 μm3 cell−1 and 35.5 to 73.5%, respectively. The findings are also compared with conventional methods for determination of neutral lipids and with results obtained from the dyes Nile Red and BODIPY 505/515. A reasonable agreement between neutral lipid production measured by BODIPY BD-C12 and gravimetric methods (correlation coefficient of 0.98) was obtained. The neutral lipids production decreased from 964.6 to 244.8 mg L−1 and from 809.1 to 396.7 mg L−1, as the nitrate concentration increased from 0 to 0.3 g L−1. It is observed that, with the two commercially available dyes, lipid quantification using Nile Red leads to an overestimation of lipids, while the use of BODIPY 505/515 promoted unreliable measures due to rapid bleaching of the chromophore. The method proposed shows excellent potential to become a standard, yet advanced, strategy for rapid evaluation and quantification of intracellular lipids in microalgae, a crucial step of the scaling-up process involved in the production of biobased products.

Continuous energy recovery and nutrients removal from molasses wastewater by synergistic system of dark fermentation and algal culture under various fermentation types

Synergistic system of dark fermentation and algal culture was initially operated at batch mode to investigate the energy production and nutrients removal from molasses wastewater in butyrate-type, ethanol-type and propionate-type fermentations. Butyrate-type fermentation was the most appropriate fermentation type for the synergistic system and exhibited the accumulative hydrogen volume of 658.3 mL L−1 and hydrogen yield of 131.7 mL g−1 COD. By-products from dark fermentation (mainly acetate and butyrate) were further used to cultivate oleaginous microalgae. The maximum algal biomass and lipid content reached 1.01 g L−1 and 38.5%, respectively. In continuous operation, the synergistic system was stable and efficient, and energy production increased from 8.77 kJ L−1 d−1 (dark fermentation) to 17.3 kJ L−1 d−1 (synergistic system). Total COD, TN and TP removal efficiencies in the synergistic system reached 91.1%, 89.1% and 85.7%, respectively. This study shows the potential of the synergistic system in energy recovery and wastewater treatment.

Lytic and Chemotactic Features of the Plaque-Forming Bacterium KD531 on Phaeodactylum tricornutum.

Phaeodactylum tricornutum is a dominant bloom forming species and potential biofuel feedstock. To control P. tricornutum bloom or to release lipids from P. tricornutum, we previously screened and identified the lytic bacterium Labrenzia sp. KD531 toward P. tricornutum. In the present study, we evaluated the lytic activity of Labrenzia sp. KD531 on microalgae and investigated its lytic mechanism. The results indicated that the lytic activity of KD531 was temperature- and pH-dependent, but light-independent. In addition to P. tricornutum, KD531 also showed lytic activity against other algal species, especially green algae. A quantitative analysis of algal cellular protein, carbohydrate and lipid content together with measurements of dry weight after exposure to bacteria-infected algal lysate indicated that the bacterium KD531 influenced the algal biomass by disrupting the algal cells. Both chemotactic analysis and microscopic observations of subsamples from different regions of formed plaques showed that KD531 could move toward and then directly contact algal cells. Direct contact between P. tricornutum and KD531 cells was essential for the lytic process.