Effects of carbon source and light intensity on the growth and total lipid production of three microalgae under different culture conditions.

We attempted to enhance the growth and total lipid production of three microalgal species, Isochrysis galbana LB987, Nannochloropsis oculata CCAP849/1, and Dunaliella salina, which are capable of accumulating high content of lipid in cells. Low nitrogen concentration under photoautotrophic conditions stimulated total lipid production, but a decreasing total lipid content and an increasing biomass were observed with increasing nitrogen concentration. Among the different carbon sources tested for heterotrophic cultivation, glucose improved the growth of all three strains. The optimal glucose concentration for growth of I. galbana LB987 and N. oculata CCAP849/1 was 0.02 M, and that of D. salina was 0.05 M. Enhanced growth occurred when they were cultivated under heterotrophic or mixotrophic conditions compared with photoautotrophic conditions. Meanwhile, high total lipid accumulation in cells occurred when they were cultivated under photoautotrophic or mixotrophic conditions. During mixotrophic cultivation, biomass production was not affected significantly by light intensity; however, both chlorophyll concentration and total lipid content increased dramatically with increasing light intensity up to 150 µmol/m(2)/s. The amount and composition ratio of saturated and unsaturated fatty acids in cells were different from each other depending on both species and light intensity. The highest accumulation of total fatty acid (C16-C18) among the three strains was found from cells of N. oculata CCAP849/1, which indicates that this species can be used as a source for production of biodiesel.

Enhanced method for microbial community DNA extraction and purification from agricultural yellow loess soil.

In this study, novel DNA extraction and purification methods were developed to obtain high-quantity and reliable quality DNA from the microbial community of agricultural yellow loess soil samples. The efficiencies of five different soil DNAextraction protocols were evaluated on the basis of DNA yield, quality and DNA shearing. Our suggested extraction method, which used CTAB, EDTA and cell membrane lytic enzymes in the extraction followed by DNA precipitation using isopropanol, yielded a maximum DNA content of 42.28 ± 5.59 µg/g soil. In addition, among the five different purification protocols, the acid-treated polyvinyl polypyrrolidone (PVPP) spin column purification method yielded high-quality DNA and recovered 91% of DNA from the crude DNA. Spectrophotometry revealed that the ultraviolet A 260/A 230 and A 260/A 280 absorbance ratios of the purified DNA were 1.82 ± 0.03 and 1.94 ± 0.05, respectively. PCR-based 16S rRNA amplification showed clear bands at ~1.5 kb with acid-treated PVPP-purified DNA templates. In conclusion, our suggested extraction and purification protocols can be used to recover high concentration, high purity, and high-molecular-weight DNA from clay and silica-rich agricultural soil samples.

Biodegradation of Methyl Orange by alginate-immobilized Aeromonas sp. in a packed bed reactor: external mass transfer modeling.

Azo dyes are recalcitrant and xenobiotic nature makes these compounds a challenging task for continuous biodegradation up to satisfactorily levels in large-scale. In the present report, the biodegradation efficiency of alginate immobilized indigenous Aeromonas sp. MNK1 on Methyl Orange (MO) in a packed bed reactor was explored. The experimental results were used to determine the external mass transfer model. Complete MO degradation and COD removal were observed at 0.20 cm bead size and 120 ml/h flow rate at 300 mg/l of initial dye concentration. The degradation of MO decreased with increasing bead sizes and flow rates, which may be attributed to the decrease in surface of the beads and higher flux of MO, respectively. The experimental rate constants (k ps) for various beads sizes and flow rates were calculated and compared with theoretically obtained rate constants using external film diffusion models. From the experimental data, the external mass transfer effect was correlated with a model J D = K Re (-(1 - n)). The model was tested with K value (5.7) and the Colburn factor correlation model for 0.20, 0.40 and 0.60 bead sizes were J D = 5.7 Re (-0.15), J D = 5.7 Re (-0.36) and J D = 5.7 Re (-0.48), respectively. Based on the results, the Colburn factor correlation models were found to predict the experimental data accurately. The proposed model was constructive to design and direct industrial applications in packed bed reactors within acceptable limits.

Comparison of biomass production and total lipid content of freshwater green microalgae cultivated under various culture conditions.

The growth and total lipid content of four green microalgae (Chlorella sp., Chlorella vulgaris CCAP211/11B, Botryococcus braunii FC124 and Scenedesmus obliquus R8) were investigated under different culture conditions. Among the various carbon sources tested, glucose produced the largest biomass or microalgae grown heterotrophically. It was found that 1% (w/v) glucose was actively utilized by Chlorella sp., C. vulgaris CCAP211/11B and B. braunii FC124, whereas S. obliquus R8 preferred 2% (w/v) glucose. No significant difference in biomass production was noted between heterotrophic and mixotrophic (heterotrophic with light illumination/exposure) growth conditions, however, less production was observed for autotrophic cultivation. Total lipid content in cells increased by approximately two-fold under mixotrophic cultivation with respect to heterotrophic and autotrophic cultivation. In addition, light intensity had an impact on microalgal growth and total lipid content. The highest total lipid content was observed at 100 µmol m(-2)s(-1) for Chlorella sp. (22.5%) and S. obliquus R8 (23.7%) and 80 µmol m(-2)s(-1) for C. vulgaris CCAP211/11B (20.1%) and B. braunii FC124 (34.9%).

Enhanced indirubin production in recombinant Escherichia coli harboring a flavin-containing monooxygenase gene by cysteine supplementation.

In our previous study, a batch fermentation of recombinant Escherichia coli DH5α cells harboring the fmo gene from Methylophaga aminisulfidivorans MP(T) produced indirubin (5.0mg/L) and indigo (920mg/L) in a 5L fermenter containing tryptophan medium (2g/L tryptophan, 5g/L yeast extract, 10g/L NaCl). In this study, it was found that indirubin production greatly increased when 0.36g/L cysteine was added to the tryptophan medium, although cysteine inhibited the growth of the recombinant E. coli harboring the fmo gene. However, the addition of cysteine did not inhibit the expression level and activity of FMO in the cell. Indigo was synthesized by the dimerization of two 3-hydroxyindole molecules under the non-enzymatic reaction. Cysteine influenced the regioselectivity of FMO and enhanced the synthesis of 2-hydroxyindole instead of 3-hydroxyindole, which might function to increase indirubin production. The optimal culture conditions for indirubin production in tryptophan medium were determined from the response surface methodology analysis: 2g/L tryptophan, 5g/L yeast extract, 10g/L NaCl, 0.36g/L (3mM) cysteine, pH 8.0 at 35°C. Under these conditions, the recombinant E. coli cells were capable of producing 223.6mg/L of indirubin from 2g/L of tryptophan. The intracellular accumulation of the indirubin crystals might stress the cell, which may be a main reason for the poor growth of the recombinant E. coli pBlue 1.7.

Optimization of culture conditions and comparison of biomass productivity of three green algae.

Culture conditions for the mass production of three green algae, Chlorella sp., Dunaliella salina DCCBC2 and Dunaliella sp., were optimized using a response surface methodology (RSM). A central composite design was applied to investigate the effects of initial pH, nitrogen and phosphate concentrations on the cultivation of microalgae. The optimal growth conditions estimated from the design are as follows: Chlorella sp. (initial pH 7.2, ammonium 17 mM, phosphate 1.2 mM), D. salina DCCBC2 (initial pH 8.0, nitrate 3.3 mM, phosphate 0.0375 mM) and Dunaliella sp. (initial pH 8.0, nitrate 3.7 mM, phosphate 0.17 mM). Culturing the microalgae with the optimized conditions confirmed that the maximum growth rates were attained for these parameters. The optimum CO(2) concentrations of Chlorella sp., D. salina DCCBC2 and Dunaliella sp. were 1.0, 3.0 and 1.0% (v/v), respectively. The specific growth rates (µ) of Chlorella sp., D. salina DCCBC2 and Dunaliella sp. were 0.58, 0.78 and 0.56 day(-1), respectively, and the biomass productivities were 0.28, 0.54 and 0.30 g dry cell wt l(-1) day(-1), respectively. The CO(2) fixation rates of Chlorella sp., D. salina DCCBC2 and Dunaliella sp. were 42.8, 90.9 and 45.5 mg l(-1) day(-1), respectively. Mixotrophic cultivation of Chlorella sp. with glucose increased biomass productivity from 0.28 to 0.51 g dry cell wt l(-1) day(-1). However, D. salina DCCBC2 and Dunaliella sp. were not stimulated by several organic compounds tested.