Regulation of carbon source metabolism in mixotrophic microalgae cultivation in response to light intensity variation.

Microalgae are one of the promising sources for renewable energy production, and the light intensity variation can affect the biofuel generation and carbon assimilation of mixotrophic microalgae. To reveal the response of carbon assimilation to light intensity, the effect of light intensity on the carbon source metabolism of Chlorella vulgaris under mixotrophic cultivation was investigated in this study. Moreover, the optimal carbon source composition for mixotrophic microalgae cultivation was evaluated using bicarbonate (HCO3-) and carbonate (CO32-) as inorganic carbon sources, and glucose and acetate as organic carbon sources. The optimal light intensity for Chlorella vulgaris growth was at the range of 8000-12000 lux. For the accumulation of biochemical components, low light intensity was beneficial to protein accumulation, and high light intensity was advantageous for carbohydrate and lipid accumulation. With HCO3- and glucose, the maximum lipid content reached 37.0% at a light intensity of 12000 lux. The citrate synthase activity was negatively correlated with light intensity, showing an opposite trend to biomass production. High light intensity had a positive impact on Rubisco expression, which promoted the microalgae growth and carbon fixing. The energy produced by heterotrophic metabolic activities increased at low light intensity, and the enhancement of biomass production with high light intensity was mainly caused by the improved photoreaction efficiency during the mixotrophic cultivation.

Thermophilic bacteria combined with alkyl polyglucose pretreated mariculture solid wastes using as denitrification carbon source for marine recirculating aquaculture wastewater treatment.

In marine recirculating aquaculture systems (RAS), efficient nitrogen removal is challenging due to the high NO3--N concentration, low organic matters content, and high salinity. In this study, mariculture solid wastes (MSW) acidogenic liquid pretreated by thermophilic bacteria (TB) combined with alkyl polyglucose (APG) was first used as carbon source for denitrification to remove NO3--N. TB + APG pretreatment could accelerate the hydrolysis of MSW, and the highest volatile fatty acids (VFAs) yield (40.3%) was obtained with TB + 0.2 g/g VSS APG pretreatment. MSW acidogenic liquid pretreated by TB + 0.2 g/g VSS APG was a reliable carbon source for denitrification, and the optimum COD/NO3--N ratio (C/N) was 8 with no residue of NOx--N. VFAs were more effectively utilized by denitrifiers than carbohydrate and protein. The high denitrification potential (PDN) and denitrification rate (VDN) indicated the higher denitrification ability at C/N of 8 using MSW acidogenic liquid as carbon source. The outcomes of this work could provide useful information for promoting technological innovation in marine RAS wastewater treatment.

Enhancing microalgae growth and product accumulation with carbon source regulation: New perspective for the coordination between photosynthesis and aerobic respiration.

The coordination between photosynthesis and aerobic respiration under mixotrophic cultivation can make a difference to the growth and biochemical composition of microalgae. However, the response of carbon metabolism to carbon source composition under mixotrophic microalgae cultivation has not been well studied. In this study, the synergistic effects of inorganic carbon (IC) and organic carbon (OC) supply on the growth and carbon metabolism of Chlorella vulgaris under mixotrophic cultivation were investigated. The increase of the proportion of HCO3- had a positive effect on the expression of ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO), which promoted the biomass production and carbon fixing. The activity of citrate synthase was attenuated with the increase of IC/OC ratio, indicating that the energy needed for the biomass production in groups with high IC/OC ratio was contributed by photoreaction. Biochemical analysis showed that CO32- was more efficient than HCO3- for carbohydrate and lipid accumulation of Chlorella vulgaris, and the highest amount of carbohydrate (30.2%) and lipid (35.8%) was recorded with the combined use of CO32- and glucose. The results could provide a new perspective on carbon metabolism and enzyme regulation in mixotrophic microalgae cultivation.

Elucidating temperature on mixotrophic cultivation of a Chlorella vulgaris strain: Different carbon source application and enzyme activity revelation.

With depletion of fossil fuel, microalgae is considered as a promising substitute due to high growth rate, efficient cost and high biofuels content. This study investigated the effect of temperature on mixotrophic cultivation of Chlorella vulgaris. In addition, the combination carbon source of inorganic (HCO3- or CO32-) and organic (glucose or acetate) for microalgae cultivation was evaluated to obtain the optimum carbon source for mixotrophic cultivation. The results showed that the optimum temperature of microalgae cultivation was at the range of 15-20 °C. The activity of Rubisco was obviously inhibited at the temperature of 30 °C, however, citrate synthase was not susceptible to the increasing temperature. COD removal efficiency was all higher than 64.0%. Low temperature was benefit for protein formation, and the lipid accumulation occurred at high temperature. The results provide a fresh perspective between enzyme activity and temperature variation for product accumulation of microalgae.

Effect of alkyl polyglycosides on the performance of thermophilic bacteria pretreatment for saline waste sludge hydrolysis.

In this study, alkyl polyglycosides (APG) was used to further accelerate the hydrolysis of saline waste sludge with thermophilic bacteria (TB) pretreatment. In the presence of 0.4 g/g TSS APG, the concentrations of soluble chemical oxygen demand (SCOD), soluble carbohydrate and soluble protein in dissolved organic matters (DOM) were 0.4, 2.4 and 1.3 times of that without APG addition, respectively. Excitation emission matrix (EEM) fluorescence spectroscopy revealed that the addition of APG led to the increase of soluble microbial materials and the decrease of fulvic acid-like substances in DOM, which was beneficial for the subsequent process of anaerobic digestion. Using APG promoted the releasing of enzymes trapped in saline waste sludge and improved the activity of enzymes during hydrolysis. The activities of α-glucosidase and protease increased by 8.8% and 21.3% respectively in the presence of 0.4 g/g TSS APG comparing no APG addition.

Accelerating waste sludge hydrolysis with alkyl polyglucose pretreatment coupled with biological process of thermophilic bacteria: Hydrolytic enzyme activity and organic matters transformation.

A novel pretreatment method combining thermophilic bacteria (TB) with alkyl polyglucose (APG) was employed to pretreat waste sludge for enhancing the sludge hydrolysis. TB combined with APG pretreatment was effective in the releasing of soluble chemical oxygen demand (SCOD), protein and carbohydrate in extracellular polymeric substances (EPS) when the dosage of APG was below 0.1 g/g TSS. The enhancement of SCOD, carbohydrates and protein in dissolved organic matter (DOM) was promoted by the synthetic effect of APG and TB, which provides more carbon and energy source to the subsequent biochemical processes in sludge digestion. Excitation-emission matrix (EEM) fluorescence spectroscopy revealed that the combined pretreatment was beneficial for the decrease of non-biodegradable materials and the increase of biodegradable materials in DOM, resulting in the enhancement of the biodegradation of waste sludge. The combined use of TB and 0.4 g/g TSS APG achieved the maximal activities of protease (1.8) and α-glucosidase (1.9), and the activities of protease and α-glucosidase were positively correlated to the dosage of APG. The combined pretreatment was advantageous for the sludge reduction and sludge stabilization.

Enhancing the hydrolysis of saline waste sludge with thermophilic bacteria pretreatment: New insights through the evolution of extracellular polymeric substances and dissolved organic matters transformation.

Recently, the treatment and utilization of saline waste sludge has drawn growing attention because large amounts of saline waste sludge were generated with the increase of saline wastewater discharge. In this study, thermophilic bacteria (TB) pretreatment was applied to accelerate the hydrolysis of saline waste sludge and the efficiency of hydrolysis at different salinities was evaluated. Compared with the group without salinity, the releasing of carbohydrate (up to a 67.0% decrease) in extracellular polymeric substances (EPS) was inhibited at the salinity ranging from 1.0% to 2.5%, and the releasing of protein (up to a 17.6% decrease) was inhibited under salinity conditions. Excess salinity (4.0%) caused the cell lysis, and the content of soluble chemical oxygen demand (SCOD), soluble carbohydrate and protein in dissolved organic matter (DOM) increased by 44.9%, 38.8% and 20.8% than that obtained without salinity, respectively. According to the excitation-emission matrix (EEM) fluorescence spectroscopy, the biodegradability of sludge was improved at 2.0% salinity. At 2.0% salinity, the maximum fluorescence intensity of soluble microbial byproduct substances (76,358.9 (au)) and the minimum fluorescence intensity of humic acid-like substances (173,424 (au)) were obtained. The increased salinity was beneficial for the sludge stabilization and was disadvantageous for the sludge reduction.

Simultaneous determination of acetaminophen and dihydrocodeine in human plasma by UPLC-MS/MS: Its pharmacokinetic application.

An ultra performance liquid chromatography tandem mass spectrometry (UPLC-MS/MS) method was developed and validated to determine acetaminophen (AAP) and dihydrocodeine (DHC) in human plasma simultaneously. Plasma samples were prepared using protein precipitation with acetonitrile, the two analytes and the internal standard midazolam were separated on an Acquity UPLC BEH C18 column and mass spectrometric analysis was performed using a QTrap5500 mass spectrometer coupled with an electro-spray ionization (ESI) source in the positive ion mode. The MRM transitions of m/z 151.2→110.0 and m/z 302.3→199.2 were used to quantify for AAP and DHC, respectively. The linearity of this method was found to be within the concentration range of 50-10000ng/mL for AAP, and 1-100ng/mL for DHC in human plasma, respectively. The lower limit of quantification (LLOQ) was 50ng/mL and 1ng/mL for AAP and DHC in human plasma, respectively. The relative standard deviations (RSD) of intra and inter precision were less than 10% for both AAP and DHC. The analysis time of per sample was 1.0min. The developed and validated method was successfully applied to a pharmacokinetic study of AAP (500mg) with DHC (20mg) capsule in Chinese healthy volunteers (N=20).