Enhancement of fatty acid production of Chlorella sp. (Chlorophyceae) by addition of glucose and sodium thiosulphate to culture medium

Mitigation of oxidative stress damage caused by abiotic stress to improve biomass yield of microalgae: A review

Microalgae have been recognized as emerging cell factories due to the high value-added bio-products. However, the balance between algal growth and the accumulation of metabolites is always the main contradiction in algal biomass production. Hence, the security and effectiveness of regulating microalgal growth and metabolism simultaneously have drawn substantial attention. Since the correspondence between microalgal growth and reactive oxygen species (ROS) level has been confirmed, improving its growth under oxidative stress and promoting biomass accumulation under non-oxidative stress by exogenous mitigators is feasible. This paper first introduced ROS generation in microalgae and described the effects of different abiotic stresses on the physiological and biochemical status of microalgae from these aspects associated with growth, cell morphology and structure, and antioxidant system. Secondly, the role of exogenous mitigators with different mechanisms in alleviating abiotic stress was concluded. Finally, the possibility of exogenous antioxidants regulating microalgal growth and improving the accumulation of specific products under non-stress conditions was discussed.

Potentiality of Self-Cloned Lactobacillus plantarum Taj-Apis362 for Enhancing GABA Production in Yogurt under Glucose Induction: Optimization and Its Cardiovascular Effect on Spontaneous Hypertensive Rats

The current study evaluated the γ-aminobutyric acid (GABA) producing ability from three novel strains of lactic acid bacteria (L. plantarum Taj-Apis362, assigned as UPMC90, UPMC91, and UPMC1065) co-cultured with starter culture in a yogurt. A combination of UPMC90 + UPMC91 with starter culture symbiotically revealed the most prominent GABA-producing effect. Response surface methodology revealed the optimized fermentation conditions at 39.0 °C, 7.25 h, and 11.5 mM glutamate substrate concentration to produce GABA-rich yogurt (29.96 mg/100 g) with desirable pH (3.93) and water-holding capacity (63.06%). At 2% glucose to replace pyridoxal-5-phosphate (PLP), a cofactor typically needed during GABA production, GABA content was further enhanced to 59.00 mg/100 g. In vivo study using this sample revealed a blood pressure-lowering efficacy at 0.1 mg/kg GABA dosage (equivalent to 30 mg/kg GABA-rich yogurt) in spontaneously hypertensive rats. An improved method to produce GABA-rich yogurt has been established, involving shorter fermentation time and lower glutamate concentration than previous work, along with glucose induction that omits the use of costly PLP, fostering the potential of developing a GABA-rich functional dairy product through natural fermentation with desirable product quality and antihypertensive property.

A Review on the Assessment of Stress Conditions for Simultaneous Production of Microalgal Lipids and Carotenoids

Microalgal species are potential resource of both biofuels and high-value metabolites, and their production is growth dependent. Growth parameters can be screened for the selection of novel microalgal species that produce molecules of interest. In this context our review confirms that, autotrophic and heterotrophic organisms have demonstrated a dual potential, namely the ability to produce lipids as well as value-added products (particularly carotenoids) under influence of various physico-chemical stresses on microalgae. Some species of microalgae can synthesize, besides some pigments, very-long-chain polyunsaturated fatty acids (VL-PUFA,>20C) such as docosahexaenoic acid and eicosapentaenoic acid, those have significant applications in food and health. Producing value-added by-products in addition to biofuels, fatty acid methyl esters (FAME), and lipids has the potential to improve microalgae-based biorefineries by employing either the autotrophic or the heterotrophic mode, which could be an offshoot of biotechnology. The review considers the potential of microalgae to produce a range of products and indicates future directions for developing suitable criteria for choosing novel isolates through bioprospecting large gene pool of microalga obtained from various habitats and climatic conditions.

Heterotrophic cultivation of Nannochloropsis salina for enhancing biomass and lipid production

Response surface methodology (RSM) was used to enhance the biomass and lipid content in Nannochloropsis salina due to its economic importance. Preliminary screening results revealed that the heterotrophically cultivated N. salina with various carbon and nitrogen sources yielded higher biomass (0.91 ± 0.0035 g/L) and lipid content (37.1 ± 0.49 mg/L) than that of the photoautotrophical cultivation (0.21 ± 0.009 g/L and 22.16 ± 0.27 mg/L). Significant sources that greatly influenced on biomass and lipid content of the alga were optimized through RSM. The medium consisting of glucose (7.959 g/L), sodium acetate (1.46 g/L), peptone (7.6 g/L) and sodium thiosulphate (1.05 g/L) was found to be the optimal concentration for heterotrophic cultivation by response optimizer. Confirmation experiment results for the RSM optimized concentration yielded the biomass of 1.85 g/L and total lipid content of 48.6 mg/L. In this study, we provide with a strategy for enhancing the biomass and lipid content in N. salina.

Production of biodiesel from Chlorella sp. enriched with oyster shell extracts

This study investigated the cultivation of the marine microalga Chlorella sp. without supplying an inorganic carbon source, but instead with enriching the media with extracts of oyster shells pretreated by a high-pressure homogenization process. The pretreated oyster shells were extracted by a weak acid, acetic acid, that typically has harmful effects on cell growth and also poses environmental issues. The concentration of the residual dissolved carbon dioxide in the medium was sufficient to maintain cell growth at 32 ppm and pH 6.5 by only adding 5% (v/v) of oyster shell extracts. Under this condition, the maximum cell density observed was 2.74 g dry wt./L after 27 days of cultivation. The total lipid content was also measured as 18.1 (%, w/w), and this value was lower than the 23.6 (%, w/w) observed under nitrogen deficient conditions or autotrophic conditions. The fatty acid compositions of the lipids were also measured as 10.9% of C16:1 and 16.4% of C18:1 for the major fatty acids, which indicates that the biodiesel from this culture process should be a suitable biofuel. These results suggest that oyster shells, environmental waste from the food industry, can be used as a nutrient and carbon source with seawater, and this reused material should be important for easily scaling up the process for an outdoor culture system.

Rational design of a culture medium for the intensification of lipid storage in Chlorella sp. Performance evaluation in air-lift bioreactor

An optimal medium to culture Chlorella sp., microalgae capable of storage intracellular lipids was obtained. This culture medium consists of a saline base plus carbon-energy and nitrogen sources. Significant factors exerting influence on the culture parameters were selected. Then, by applying response surface methodology coupled to desirability function, an optimal formulation, specific for the heterotrophic growth of Chlorella sp. that allows maximizing lipid concentration was obtained. During the experimental verification, the possibility of replacing commercial glucose by hydrolysates obtained from lignocellulosic materials was evaluated. Biochemical hydrolysate of corn bran allowed obtaining important improvements in lipid concentration. Finally, the optimal formulation was evaluated in an air-lift bioreactor performing a fed-batch culture. Culturing the strain in these conditions allowed rising lipid concentrations.

Biochemical composition of green alga Chlorella minutissima in mixotrophic cultures under the effect of different carbon sources

Mixotrophic growth of Chlorella minutissima with carbon supplements such as glucose, glycerol, succinate, molasses and press mud resulted in maximum biomass accumulation in glucose supplemented culture. Lipid content was maximum with molasses followed by press mud, fatty acid compositions of which also were best suited for biodiesel production.

Evaluation of FT-IR and Nile Red methods for microalgal lipid characterization and biomass composition determination

To characterize lipid content of microalgal cells rapidly and accurately, the gravimetric determination, FT-IR and Nile Red (NR) staining were investigated on six typical eukaryotic and prokaryotic algae species. FT-IR and Nile Red were relative quantification methods and a standard curve was required in contrast to the gravimetric method. The FT-IR method determined the lipid, carbohydrate and protein contents simultaneously assuming that the algal cells only consisted of those three components. The Nile Red method was a relatively rapid method for neutral lipid content characterization by spectrofluorometry and could locate lipid body of the algal cell by fluorescence microscopy. According to sample sources and processing purposes, the gravimetric determination was preferable for large-scale cultivation with low-frequency monitoring, while FT-IR and Nile Red were suitable for general laboratory cultivation with medium-frequency monitoring, in particularly Nile Red was appropriate for small samples when high-frequency screening was required.

Biochemical modulation of growth, lipid quality and productivity in mixotrophic cultures of Chlorella sorokiniana

The genus Chlorella is a widely employed microalga for biodiesel, as it can be grown using photo/mixo/heterotrophic mode of cultivation. The present investigation was undertaken with the hypothesis that addition of different substrates (amino acids, carbon sources, vitamins) along with reducing agents may aid in diverting Acetyl CoA to malonyl CoA or fatty acid biosynthesis, under mixotrophic conditions in Chlorella sorokiniana. Preliminary investigations undertaken with two reducing agents individually (sodium thiosulphate and methyl viologen) along with selected substrates revealed the promise of sodium thiosulphate (1%) in enhancing lipid accumulation significantly. Further, the role of inclusion of twelve substrates and sodium thiosulphate revealed that supplementation with tryptophan (0.1%) recorded 57.28% enhancement in lipid productivity on 4(th) day. Highest values of lipid productivity of 33% were recorded on 8(th) day in 0.1% glucose supplemented medium containing sodium thiosulphate. Fatty Acid Methyl Ester (FAME) profiles generated revealed significant reduction in the content of Poly unsaturated fatty acids (PUFA) and enhanced Mono unsaturated fatty acids (MUFA) (especially oleic acid) in the treatments involving tryptophan, Vitamin B12, sodium pyruvate and glucose. This study reveals the promise of using sodium thiosulphate along with selected substrate for enriching the quality and quantity of lipids, which can be valuable for exploiting algae as a source of biodiesel.

Harvesting of Chlorella sp. using hollow fiber ultrafiltration

INTRODUCTION

The suitability of the application of ultrafiltration (UF) to harvest Chlorella sp. from the culture medium was examined. We investigated the effects of two improved UF system, forward air-water flushing and backwash with permeate, on the concentration process.

MATERIALS AND METHODS

Backwash with permeate was selected as an optimization of the improved UF system, which was more effective for permeate flux recovery. Moreover, the hollow fiber UF system by adding periodical backwash with permeate was examined for Chlorella sp. harvesting.

RESULTS AND DISCUSSION

It was found that Chlorella sp. could be concentrated with high recovery in a lab-scale experiment. An overall algal biomass recovery of above 90% was achieved when the volume concentration factor was 10. For an original biomass of 1.3 ± 0.05 g/L, 1 min backwash followed by 20 min forward concentrating was more effective, which resulted in a recovery of 94% and a high average flux of 30.3 L/m(2)/h. In addition, the algal recovery was highly correlated to the volume concentration factor and the initial biomass. A high concentration factor or a high initial biomass resulted in a low biomass recovery.

Best practices in heterotrophic high-cell-density microalgal processes: achievements, potential and possible limitations

Microalgae of numerous heterotrophic genera (obligate or facultative) exhibit considerable metabolic versatility and flexibility but are currently underexploited in the biotechnological manufacturing of known plant-derived compounds, novel high-value biomolecules or enriched biomass. Highly efficient production of microalgal biomass without the need for light is now feasible in inexpensive, well-defined mineral medium, typically supplemented with glucose. Cell densities of more than 100 g l(-1) cell dry weight have been achieved with Chlorella, Crypthecodinium and Galdieria species while controlling the addition of organic sources of carbon and energy in fedbatch mode. The ability of microalgae to adapt their metabolism to varying culture conditions provides opportunities to modify, control and thereby maximise the formation of targeted compounds with non-recombinant microalgae. This review outlines the critical aspects of cultivation technology and current best practices in the heterotrophic high-cell-density cultivation of microalgae. The primary topics include (1) the characteristics of microalgae that make them suitable for heterotrophic cultivation, (2) the appropriate chemical composition of mineral growth media, (3) the different strategies for fedbatch cultivations and (4) the principles behind the customisation of biomass composition. The review confirms that, although fundamental knowledge is now available, the development of efficient, economically feasible large-scale bioprocesses remains an obstacle to the commercialisation of this promising technology.

Productivity and selective accumulation of carotenoids of the novel extremophile microalga Chlamydomonas acidophila grown with different carbon sources in batch systems

Cultivation of extremophile microorganisms has attracted interest due to their ability to accumulate high-value compounds. Chlamydomonas acidophila is an acidophile green microalga isolated by our group from Tinto River, an acidic river that flows down from the mining area in Huelva, Spain. This microalga accumulates high concentrations of lutein, a very well-known natural antioxidant. The aim of this study is to assess use of different carbon sources (CO(2), glucose, glycerol, starch, urea, and glycine) for efficient growth of and carotenoid production by C. acidophila. Our results reveal that growth of the microalga on different carbon sources resulted in different algal biomass productivities, urea being as efficient as CO(2) when used as sole carbon source (~20 g dry biomass m(-2) day(-1)). Mixotrophic growth on glucose was also efficient in terms of biomass production (~14 g dry biomass m(-2) day(-1)). In terms of carotenoid accumulation, mixotrophic growth on urea resulted in even higher productivity of carotenoids (mainly lutein, probably via α-carotene) than obtained with photoautotrophic cultures (70% versus 65% relative abundance of lutein, respectively). The accumulated lutein concentrations of C. acidophila reported in this work (about 10 g/kg dry weight, produced in batch systems) are among the highest reported for a microalga. Glycerol and glycine seem to enhance β-carotene biosynthesis, and when glycine is used as carbon source, zeaxanthin becomes the most accumulated carotenoid in the microalga. Strategies for production of lutein and zeaxanthin are suggested based on the obtained results.

Marine diatom, Navicula sp. strain JPCC DA0580 and marine green alga, Chlorella sp. strain NKG400014 as potential sources for biodiesel production

Marine diatom, strain JPCC DA0580, and marine green microalga strain NKG400014 were selected as high neutral lipid-producers from marine microalgal culture collection toward biodiesel production. These strains were tentatively identified as Navicula sp. and Chlorella sp., respectively, by 18S rDNA analysis. Growth and lipid accumulation conditions of both strains were analyzed by changing nutrient concentrations in growth media and initial illuminance intensity. The highest productivity of fatty acid methyl ester (FAME) reached to 154 mg/L/week for NKG400014 and 185 mg/L/week for JPCC DA0580. Gas chromatography/mass spectrometry analysis indicates that FAME fraction from NKG400014 mainly contained 9-12-15-octadecatrienoate (C18:3) and that from JPCC DA0580 mainly contained methyl palmitate (C16:0) and methyl palmitoleate (C16:1). Furthermore, calorimetric analysis revealed that the energy content of strain was 4,233 +/- 55 kcal/kg (i.e., 15.9 +/- 0.2 MJ/kg) for NKG400014 and 6,423 +/- 139 kcal/mg (i.e., 26.9 +/- 0.6 MJ/kg) for JPCC DA0580, respectively. The value from JPCC DA0580 was equivalent to that of coal. The strains NKG400014 and JPCC DA0580 will become a promising resource that can grow as dominant species in the open ocean toward production of both liquid and solid biofuels.

Studies on lipid production by Rhodotorula glutinis fermentation using monosodium glutamate wastewater as culture medium

Microbial lipid, as a raw material for biodiesel, can be produced by Rhodotorula glutinis with the monosodium glutamate (MSG) wastewater. The effect of adding glucose to MSG wastewater on lipid production was studied in this paper. Three different strategies, including initial addition, fed-batch addition and glucose feedback addition were attempted. The results show that addition of glucose was found favorable not only for cell growth but also for lipid synthesis. Of the three adding methods glucose feedback addition was the most effective one: about 25 g/L of biomass, 20% of lipid content and 45% of COD degradation were obtained respectively. And the components of the resulted lipid using different addition strategies were further studied.