Ultrasound for microalgal cell disruption and product extraction: A review.

Microalgae are a promising feedstock for the production of biofuels, nutraceuticals, pharmaceuticals and cosmetics, due to their superior capability of converting solar energy and CO2 into lipids, proteins, and other valuable bioactive compounds. To facilitate the release of these important biomolecules from microalgae, effective cell disruption is usually necessary, where the use of ultrasound has gained tremendous interests as an alternative to traditional methods. This review not only summarizes the mechanisms of and operation parameters affecting cell disruption, but also takes an insight into measuring techniques, synergistic integration with other disruption methods, and challenges of ultrasonication for microalgal biorefining. Optimal conditions including ultrasonic frequency, intensity, and duration, and liquid viscosity and sonochemical reactor are the key factors for maximizing the disruption and extraction efficiency. A combination of ultrasound with other disruption methods such as ozonation, microwave, homogenization, enzymatic lysis, and solvents facilitates cell disruption and release of target compounds, thus provides powerful solutions to commercial scale-up of ultrasound extraction for microalgal biorefining. It is concluded that ultrasonication is a sustainable "green" process, but more research and work are needed to upscale this process without sacrificing performance or consuming more energy.

Understanding and Engineering Glycine Cleavage System and Related Metabolic Pathways for C1-Based Biosynthesis.

The glycine cleavage system (GCS) is a fundamental component of life, widely existing in microbes, plants, animals, and humans. A better understanding of the functionality and working mechanisms, and the engineering of the GCS have both scientific and practical impacts, which may lead to new knowledge and findings in life sciences, improved biomass production and human/animal health, efficient biosynthesis of chemicals, effective carbon fixation and global climate change mitigation. In this chapter, the GCS is first discussed in the context of the reductive glycine pathway (rGlyP), a recently proposed and appealing assimilation pathway of CO2 and formate, and its implementation and optimization in microorganisms for formatotrophic growth. Then, the present knowledge about the components, reactions, and working mechanisms of the GCS and related enzymes is reviewed. Particular emphasis is also placed on the conformational and structural features of the GCS proteins, especially the different forms of lipoylated H protein and its lipoylation by lipoate protein ligase (LplA). Subsequently, existing analytic methods for the components and reactions of the GCS and recent advances in quantitatively understanding and purposefully engineering the GCS are presented. Finally, perspectives of current state of the art in the GCS research are given and future research needs are highlighted.

Dynamics of microbial community and changes of metabolites during production of type Ι sourdough steamed bread made by retarded sponge-dough method.

Dynamics of microbial community and changes of metabolites during production of type Ι sourdough steamed bread made by retarded sponge-dough method (SSB) were studied. Lactobacillus sanfranciscensis and Lactobacillus pontis were the dominant bacterial species. Particularly, relative abundances of Lactobacillus sanfranciscensis were significantly higher than that of other sub-dominant bacterial species. The dominant fungal species were Saccharomyces cerevisiae and Kazachstania humilis, and the latter was the most predominant. A stable bacterial and fungal consortia was established in sponge dough retarded from 12 to 24 h and main dough proofed from 30 to 60 min. Metabolism preference for maltose of Lactobacillus sanfranciscensis favoured a mutualistic association with maltose-negative Kazachstania humilis, and hence contributing to their competitiveness and dominance. Volatile compounds became more abundant with much more esters as sponge retarding time extended. Probably, the accumulation of organic acids and ethanol contributed mostly to formation of ethyl esters in sponge dough during retarding.

Biochar production and applications in agro and forestry systems: A review.

Biochar is a product of biomass thermochemical conversion. Its yield and quality vary significantly with the production technology and process parameters, which also affect its performance in agro and forestry systems. In this review, biochar production technologies including slow pyrolysis, fast pyrolysis, gasification, and torrefaction were compared. The yield of biochar was found to decrease with faster heating rate or more oxygen available. The benefits of biochar application to agro and forestry systems were discussed. Improvements in soil health, plant growth, carbon sequestration, and greenhouse gas mitigation are apparent in many cases, but opposite results do exist, indicating that the beneficial aspect of biochar are limited to particular conditions such as the type of biochar used, the rate of application, soil type, climate, and crop species. Limitations of current studies and future research needed on biochar are also discussed. Specifically, the relationships among biochar production technologies, biochar properties, and biochar performance in agro and forestry systems must be better understood.

Changes of nutrients and potentially toxic elements during hydrothermal carbonization of pig manure.

The effects of reaction temperature, residence time, sulfuric acid and potassium hydroxide on the total concentration and speciation of N and P, potentially toxic elements (salts and metal elements) of pig manure during its hydrothermal carbonization (HTC) were investigated. Concentrations of Cl, K, Na and Mg in the hydrochars were much lower but total N, P and nitrate-nitrogen (NO3--N) contents were significantly higher than in untreated pig manure. The acid-extractable fractions of Cu and Zn in hydrochars were 0.03-0.63 and 0.17-0.66 times lower than those in pig manure and decreased significantly with increasing reaction temperature. The addition of sulfuric acid (H2SO4) or potassium hydroxide (KOH) in HTC reduced the contents of P, Ca, Mg, Cl and heavy metal elements (HMEs) in hydrochars, and the removal rates of Cu and Zn were up to 55% and 59%, respectively. Overall, the rapid treatment of pig manure by HTC reduced the harm of salts and HMEs, and effectively recovered the nutrients in pig manure. The HTC under alkaline conditions was desirable for optimizing the main elemental composition of the hydrochars.

Type I sourdough steamed bread made by retarded sponge-dough method.

A retarded sponge-dough method was adopted to make type I sourdough steamed bread (SSB). When matured from 9 to 21 h, sourdoughs attained a properly developed state with desirable acidifying and leavening capacity. Optimal parameters were obtained as follows: sourdough maturing time of 15 h, 40% of sourdough, 72% of flour in sponge dough and retarding time of 24 h. SSB under optimized parameters had large specific volume, fine crumb texture and a high sensory score. Flavor compounds in SSB (a total of 85) were more abundant than that in the control. Many aroma-active esters were identified of which ethyl hexanoate was the most abundant. Anti-staling effects were observed, including a great delay of crumb firmness and starch retrogradation. Retarding up to 24 h of sponge-dough allowed sufficient time for microbial metabolism and endogenous enzyme bioconversion, providing SSB with desirable balanced flavor and aromatic characteristics.

Kinetic modeling of butyric acid effects on butanol fermentation by Clostridium saccharoperbutylacetonicum.

A kinetic model of acetone-butanol-ethanol (ABE) fermentation taking into account butyric acid effects was developed and implemented in COPASI. The model was validated by comparing the simulation results with experimental data in batch cultures of Clostridium saccharoperbutylacetonicum under various concentrations of initial glucose (97.1 to 152.6 mM) and butyric acid (90.7 to 153.2 mM). The modeling results suggested that increasing the conversion rates from butyryl-CoA (BCoA) to butanol, from butyrate to BCoA, or from pyruvate to lactate would increase butanol synthesis. Similarly, reducing glucose uptake rate or the reaction rates from pyruvate to acetyl CoA (ACoA), from acetoacetyl CoA (AACoA) to BCoA, or from BCoA to butyrate would improve butanol production. Overall, the kinetic model developed can accurately predict the dynamic behavior of metabolites in ABE fermentation with butyric acid addition, which may subsequently be used to identify genetic manipulation strategies for higher bio-butanol production.

Microalgal-biochar immobilized complex: A novel efficient biosorbent for cadmium removal from aqueous solution.

The feasibility of the bioremediation of cadmium (Cd) using microalgal-biochar immobilized complex (MBIC) was investigated. Major operating parameters (e.g., pH, biosorbent dosage, initial Cd(II) concentration and microalgal-biochar ratio) were varied to compare the treatability of viable algae (Chlorella sp.), biochar and MBIC. The biosorption isotherms obtained by using algae or biochar were found to have satisfactory Langmuir predictions, while the best fitting adsorption isotherm model for MBIC was the Sips model. The maximum Cd(II) adsorption capacity of MBIC with a Chlorella sp.: biochar ratio of 2:3 (217.41mgg-1) was higher than that of Chlorella sp. (169.92mgg-1) or biochar (95.82mgg-1) alone. The pseudo-second-order model fitted the biosorption process of MBIC well (R2>0.999). Moreover, zeta potential, SEM and FTIR studies revealed that electrostatic attraction, ion exchange and surface complexation were the main mechanisms responsible for Cd removal when using MBIC.

The biological responses and metal phytoaccumulation of duckweed Spirodela polyrhiza to manganese and chromium.

The phytoaccumulation ability of duckweed Spirodela polyrhiza on manganese (Mn) and chromium (Cr) was assessed by exposing the plant to various concentrations of single or dual metals (5-70 mg L-1 Mn, 2-12 mg L-1 Cr(VI)) under laboratory conditions. The results showed that S. polyrhiza can tolerate Mn at high concentrations of up to 70 mg L-1, and its growth rate was barely affected by Mn. The effects of Cr on S. polyrhiza growth were dose-dependent, and the growth was completely inhibited in the presence of 12 mg L-1 Cr. Analysis of metal content in the plant biomass revealed a high accumulation of Mn (up to 15.75 mg per g of duckweed dry weight). The Cr bioaccumulation (from below detection limit to 2.85 mg Cr (11.84 mg Cr2O72-) per g of duckweed dry weight) increased with cultivation time and metal concentration in the medium. Further study with the concurrence of Mn and Cr showed increased toxicity to plant growth and photosynthesis. The metal accumulations in the dual metal treatments were also significantly decreased as compared to the single metal treatments. Nevertheless, the phytoaccumulation of these two metals in S. polyrhiza in the dual metal treatments were still comparable to or higher than in previous reports. Thus, it was concluded that duckweed S. polyrhiza has the potential to be used as a phytoremediator in aquatic environments for Mn and Cr removal.

Modeling the Growth of Archaeon Halobacterium halobium Affected by Temperature and Light.

The objective of this study was to develop sigmoidal models, including three-parameter (Quadratic, Logistic, and Gompertz) and four-parameter models (Schnute and Richards) to simulate the growth of archaeon Halobacterium halobium affected by temperature and light. The models were statistically compared by using t test and F test. In the t test, confidence bounds for parameters were used to distinguish among models. For the F test, the lack of fit of the models was compared with the prediction error. The Gompertz model was 100 % accepted by the t test and 97 % accepted by the F test when the temperature effects were considered. Results also indicated that the Gompertz model was 94 % accepted by the F test when the growth of H. halobium was studied under varying light intensities. Thus, the Gompertz model was considered the best among the models studied to describe the growth of H. halobium affected by temperature or light. In addition, the biological growth parameters, including specific growth rate, lag time, and asymptote changes under Gompertz modeling, were evaluated.

Is biochar-manure co-compost a better solution for soil health improvement and N2O emissions mitigation?

Land application of compost has been a promising remediation strategy for soil health and environmental quality, but substantial emissions of greenhouse gases, especially N2O, need to be controlled during making and using compost of high N-load wastes, such as chicken manure. Biochar as a bulking agent for composting has been proposed as a novel approach to solve this issue, due to large surface area and porosity, and thus high ion exchange and adsorption capacity. Here, we compared the impacts of biochar-chicken manure co-compost (BM) and chicken manure compost (M) on soil biological properties and processes in a 120-d microcosm experiment at the soil moisture of 60% water-filled pore space. Our results showed that BM and M addition significantly enhanced soil total C and N, inorganic and KCl-extractable organic N, microbial biomass C and N, cellulase enzyme activity, abundance of N2O-producing bacteria and fungi, and gas emissions of N2O and CO2. However, compared to the M treatment, BM significantly reduced soil CO2 and N2O emissions by 35% and 27%, respectively, over the experimental period. The 15N-N2O site preference, i.e., difference between 15N-N2O in the center position (δ15Nα) and the end position (δ15Nß), was ~17‰ for M and ~26‰ for BM during the first week of incubation, suggesting that BM suppressed N2O from bacterial denitrification and/or nitrifier denitrification. This inference was well aligned with the observation that soil glucosaminidase activity and nirK gene abundance were lower in BM than M treatment. Further, soil peroxidase activity was greater in BM than M treatment, implying soil organic C was more stable in BM treatment. Our data demonstrated that the biochar-chicken manure co-compost could substantially reduce soil N2O emissions compared to chicken manure compost, via controls on soil organic C stabilization and the activities of microbial functional groups, especially bacterial denitrifiers.

The Effect of Light Stress and Other Culture Conditions on Photoinhibition and Growth of Dunaliella tertiolecta.

This work aimed to examine the effects of high light stress as well as other culture conditions including HCO3 − concentration, temperature, salinity, and pre-acclimation on photoinhibition and growth of halotolerant alga Dunaliella tertiolecta. Significant photoinhibition of D. tertiolecta was observed during a short period of exposure (6 hours) to high intensity of lights (1000, 1500, and 2000 µmol photons m-2 s-1); however, after 2 days of continuous light exposure, the alga adapted to high light stress and reached similar growth rates as low light exposure. The increase in HCO3 − concentration in the culture medium did not reduce photoinhibition, but the growth rate and chlorophyll contents increased with increasing HCO3 − concentrations. Temperature had significant effects on photoinhibition. Combined high temperature and high light intensity led to more serious photoinhibition and reduced cell growth rates, so did combined low salinity and high light intensity. Pre-acclimation by 50, 200, or 500 µmol photons m-2 s-1 each for 1, 3, or 6 hours (a total of nine treatments) did not significantly influence photoinhibition or cell growth of D. tertiolecta, probably because the acclimation periods were not long enough.

Modeling bubble dynamics and radical kinetics in ultrasound induced microalgal cell disruption.

Microalgal cell disruption induced by acoustic cavitation was simulated through solving the bubble dynamics in an acoustical field and their radial kinetics (chemical kinetics of radical species) occurring in the bubble during its oscillation, as well as calculating the bubble wall pressure at the collapse point. Modeling results indicated that increasing ultrasonic intensity led to a substantial increase in the number of bubbles formed during acoustic cavitation, however, the pressure generated when the bubbles collapsed decreased. Therefore, cumulative collapse pressure (CCP) of bubbles was used to quantify acoustic disruption of a freshwater alga, Scenedesmus dimorphus, and a marine alga, Nannochloropsis oculata and compare with experimental results. The strong correlations between CCP and the intracellular lipid fluorescence density, chlorophyll-a fluorescence density, and cell particle/debris concentration were found, which suggests that the developed models could accurately predict acoustic cell disruption, and can be utilized in the scale up and optimization of the process.

Microalgal cell disruption in a high-power ultrasonic flow system.

A 2-kW continuous ultrasonic flow system (UFS) was found effective in the disruption of two microalgal strains: Scenedesmus dimorphus and Nannochloropsis oculata. Compared to the control, cell debris concentration of UFS treatments increased up to 202% for S. dimorphus and 112% for N. oculata. Similarly, Nile red stained lipid fluorescence density (NRSLD) increased up to 59.5% and 56.3% for S. dimorphus and N. oculata, respectively. It was also found that increasing ultrasound intensity improved cell disruption efficiency indicated by up to 54% increase in NRSLFD of the two strains. Increasing sonication-processing time to 3-min resulted in 33.0% increase for S. dimorphus and 45.7% increase for N. oculata in NRSLFD compared to the control. Cell recirculation was found beneficial to cell disruption, however, higher initial cell concentration significantly reduced cell disruption efficiency, indicated by 98.2% decrease in NRSLFD per cell when initial cell concentration increased from 4.25 × 10(6) to 1.7 × 10(7)cells ml(-1).

Glucose Synthesis in a Protein-Based Artificial Photosynthesis System.

The objective of this study was to understand glucose synthesis of a protein-based artificial photosynthesis system affected by operating conditions, including the concentrations of reactants, reaction temperature, and illumination. Results from non-vesicle-based glyceraldehyde-3-phosphate (GAP) and glucose synthesis showed that the initial concentrations of ribulose-1,5-bisphosphate (RuBP) and adenosine triphosphate (ATP), lighting source, and temperature significantly affected glucose synthesis. Higher initial concentrations of RuBP and ATP significantly enhanced GAP synthesis, which was linearly correlated to glucose synthesis, confirming the proper functions of all catalyzing enzymes in the system. White fluorescent light inhibited artificial photosynthesis and reduced glucose synthesis by 79.2 % compared to in the dark. The reaction temperature of 40 °C was optimum, whereas lower or higher temperature reduced glucose synthesis. Glucose synthesis in the vesicle-based artificial photosynthesis system reconstituted with bacteriorhodopsin, F 0 F 1 ATP synthase, and polydimethylsiloxane-methyloxazoline-polydimethylsiloxane triblock copolymer was successfully demonstrated. This system efficiently utilized light-induced ATP to drive glucose synthesis, and 5.2 µg ml(-1) glucose was synthesized in 0.78-ml reaction buffer in 7 h. Light-dependent reactions were found to be the bottleneck of the studied artificial photosynthesis system.

Design, fabrication, and characterization of archaeal tetraether free-standing planar membranes in a PDMS- and PCB-based fluidic platform.

The polar lipid fraction E (PLFE) isolated from the thermoacidophilic archaeon Sulfolobus acidocaldarius contains exclusively bipolar tetraether lipids, which are able to form extraordinarily stable vesicular membranes against a number of chemical, physical, and mechanical stressors. PLFE liposomes have thus been considered appealing biomaterials holding great promise for biotechnology applications such as drug delivery and biosensing. Here we demonstrated that PLFE can also form free-standing "planar" membranes on micropores (∼100 µm) of polydimethylsiloxane (PDMS) thin films embedded in printed circuit board (PCB)-based fluidics. To build this device, two novel approaches were employed: (i) an S1813 sacrificial layer was used to facilitate the fabrication of the PDMS thin film, and (ii) oxygen plasma treatment was utilized to conveniently bond the PDMS thin film to the PCB board and the PDMS fluidic chamber. Using electrochemical impedance spectroscopy, we found that the dielectric properties of PLFE planar membranes suspended on the PDMS films are distinctly different from those obtained from diester lipid and triblock copolymer membranes. In addition to resistance (R) and capacitance (C) that were commonly seen in all the membranes examined, PLFE planar membranes showed an inductance (L) component. Furthermore, PLFE planar membranes displayed a relatively large membrane resistance, suggesting that, among the membranes examined, PLFE planar membrane would be a better matrix for studying channel proteins and transmembrane events. PLFE planar membranes also exhibited a sharp decrease in phase angle with the frequency of the input AC signal at ∼1 MHz, which could be utilized to develop sensors for monitoring PLFE membrane integrity in fluidics. Since the stability of free-standing planar lipid membranes increases with increasing membrane packing tightness and PLFE lipid membranes are more tightly packed than those made of diester lipids, PLFE free-standing planar membranes are expected to be considerably stable. All these salient features make PLFE planar membranes particularly attractive for model studies of channel proteins and transmembrane events and for high-throughput drug screening and artificial photosynthesis. This work can be extended to nanopores of PDMS thin films in microfluidics and eventually aid in membrane-based new lab-on-a-chip applications.

Disruption of microalgal cells using high-frequency focused ultrasound.

The objective of this study was to evaluate the effectiveness of high-frequency focused ultrasound (HFFU) in microalgal cell disruption. Two microalgal species including Scenedesmus dimorphus and Nannochloropsis oculata were treated by a 3.2-MHz, 40-W focused ultrasound and a 100-W, low-frequency (20kHz) non-focused ultrasound (LFNFU). The results demonstrated that HFFU was effective in the disruption of microalgal cells, indicated by significantly increased lipid fluorescence density, the decrease of cell sizes, and the increase of chlorophyll a fluorescence density after treatments. Compared with LFNFU, HFFU treatment was more energy efficient. The combination of high and low frequency treatments was found to be even more effective than single frequency treatment at the same processing time, indicating that frequency played a critical role in cell disruption. In both HFFU and LFNFU treatments, the effectiveness of cell disruption was found to be dependent on the cell treated.

Hydrothermal conversion of big bluestem for bio-oil production: the effect of ecotype and planting location.

Three ecotypes (CKS, EKS, IL) and one cultivar (KAW) of big bluestem (Andropogon gerardii) that were planted in three locations (Hays, KS; Manhattan, KS; and Carbondale, IL) were converted to bio-oil via hydrothermal conversion. Significant differences were found in the yield and elemental composition of bio-oils produced from big bluestem of different ecotypes and/or planting locations. Generally, the IL ecotype and the Carbondale, IL and Manhattan, KS planting locations gave higher bio-oil yield, which can be attributed to the higher total cellulose and hemicellulose content and/or the higher carbon but lower oxygen contents in these feedstocks. Bio-oil from the IL ecotype also had the highest carbon and lowest oxygen contents, which were not affected by the planting location. Bio-oils from big bluestem had yield, elemental composition, and chemical compounds similar to bio-oils from switchgrass and corncobs, although mass percentages of some of the compounds were slightly different.

Rapid quantitation of lipid in microalgae by time-domain nuclear magnetic resonance.

A specific strain of Chlorella protothecoides has been studied in heterotrophic fermentation for increasing cell growth rate and lipid content for biodiesel production. For optimizing the process of fermentation to reduce costs of alga-based biodiesel production, rapid determination of lipid content in microalgal cells is critical. Nile Red (NR) staining and time-domain nuclear magnetic resonance (TD-NMR) have been investigated to quantitate the lipid content in C. protothecoides. Both methods were found feasible and simpler than gravimetric methods that are commonly employed. The TD-NMR method showed better agreement (R(2)=0.9973) with the measured values from lipid extraction experiments than the NR staining method (R(2)=0.9067). Additionally, the smaller standard deviations of the samples (< or =0.36) analyzed by TD-NMR revealed that the method is accurate and reproducible. The application of TD-NMR for lipid quantitation in C. protothecoides opens up the possibility of determining lipid content in algal fermentation precisely and quickly.