Cell Dry Weight Concentration Research Articles

Production of single cell protein rich in potassium by Nectaromyces rattus using biogas slurry and molasses

Single-cell protein (SCP) is a vital supplement for animal protein feed. This study utilized biogas slurry and sugarcane molasses to ferment Nectaromyces rattus for the production of SCP. The optimal batch fermentation conditions were obtained in a 5L jar with a tank pressure of 0.1 MPa, an initial speed of 300 rpm, and an inoculum volume of 30%. The highest cell dry weight concentrations of the fed-batch fermentation without reflux and the fed-batch fermentation with reflux were 46.33 g/L and 29.71 g/L, respectively. The nitrogen conversion rates (47.05% and 44.12%) and the cell yields of total organic carbon (1 g/g and 1.17 g/g) of both fermentation modes were compared. The SCP contained 42.32% amino acids. Its high concentrations of potassium (19859.96 mg/kg) and phosphorus (7310.44 mg/kg) present a novel approach for the extraction of these essential nutrients from biogas slurry. The enrichment of K was related to the H+ efflux and sugar transport.

Pilot Scale Production of Single Cell Oil by Apiotrichum brassicae and Pichia kudriavzevii from Acetic Acid and Propionic Acid

Volatile fatty acids can be used as a cheap carbon source for biotechnological lipid production with oleaginous yeasts, but one factor limiting their large-scale use is their inherent cytotoxicity. Developing a suitable cultivation strategy can help mitigate the adverse effect volatile fatty acids have, since these effects are strongly dependent on concentration and pH. This work shows that, by employing a pH-stat fed-batch approach for the cultivation of Apiotrichum brassicae V134 and Pichia kudriavzevii V194, lipid contents above 56 g/100 g dry cell weight and dry cell weight concentrations above 30 g/L can be reached. Furthermore, volumetric lipid productivities up to 0.29 g/Lh could be achieved using acetic and propionic acid as a sole carbon source. It was also demonstrated that the developed process is robust and scalable. Scale-up to the 500 L scale resulted in a similar lipid yield, dry cell weight (31–37 g/L), and single cell oil content (56 g/100 g dry cell weight–58 g/100 g dry cell weight). The main fatty acid present in the produced lipids was oleic acid (36–43%), but also odd-numbered fatty acids, especially heptadecanoic acid (7–15%), were present. Additionally, different methods for the pretreatment of biomass prior to lipid extraction were assessed, and the iodine value (48), peroxide value (7.3), and acid value (4.3) of the extracted single cell oil were determined.

Simultaneous photoautotrophic production of DHA and EPA by Tisochrysis lutea and Microchloropsis salina in co-culture

Marine microalgae have received much attention as a sustainable source of the two health beneficial omega-3-fatty acids docosahexaenoic acid (DHA, C22:6) and eicosapentaenoic acid (EPA, C20:5). However, photoautotrophic monocultures of microalgae can only produce either DHA or EPA enriched biomass. An alternative may be the photoautotrophic co-cultivation of Tisochrysis lutea as DHA-producer with Microchloropsis salina for simultaneous EPA production to obtain EPA- and DHA-rich microalgae biomass in a nutritionally balanced ratio. Photoautotrophic co-cultivation processes of T. lutea and M. salina were studied, applying scalable and fully controlled lab-scale gas-lift flat-plate photobioreactors with LED illumination for dynamic climate simulation of a repeated sunny summer day in Australia [day–night cycles of incident light (PAR) and temperature]. Monocultures of both marine microalgae were used as reference batch processes. Differences in the autofluorescence of both microalgae enabled the individual measurement, of cell distributions in co-culture, by flow cytometry. The co-cultivation of T. lutea and M. salina in artificial sea water with an inoculation ratio of 1:3 resulted in a balanced biomass production of both microalgae simultaneously with a DHA:EPA ratio of almost 1:1 (26 mgDHA gCDW−1, and 23 mgEPA gCDW−1, respectively) at harvest after depletion of the initially added fertilizer. Surprisingly, more microalgae biomass was produced within 8 days in co-cultivation with an increase in the cell dry weight (CDW) concentration by 31%, compared to the monocultures with the same amount of light and fertilizer. What is more, DHA-content of the microalgae biomass was enhanced by 33% in the co-culture, whereas EPA-content remained unchanged compared to the monocultures.Graphical

Cell Retention as a Viable Strategy for PHA Production from Diluted VFAs with Bacillus megaterium

The production of biodegradable and biocompatible materials such as polyhydroxyalkanoates (PHAs) from waste-derived volatile fatty acids (VFAs) is a promising approach towards implementing a circular bioeconomy. However, VFA solutions obtained via acidification of organic wastes are usually too diluted for direct use in standard batch or fed-batch processes. To overcome these constraints, this study introduces a cell recycle fed-batch system using Bacillus megaterium uyuni S29 for poly(3-hydroxybutyrate) (P3HB) production from acetic acid. The concentrations of dry cell weight (DCW), P3HB, acetate, as well as nitrogen as the limiting substrate component, were monitored during the process. The produced polymer was characterized in terms of molecular weight and thermal properties after extraction with hypochlorite. The results show that an indirect pH-stat feeding regime successfully kept the strain fed without prompting inhibition, resulting in a dry cell weight concentration of up to 19.05 g/L containing 70.21% PHA. After appropriate adaptations the presented process could contribute to an efficient and sustainable production of biopolymers.

Sustainable arabitol production by a newly isolated Debaryomyces prosopidis strain cultivated on biodiesel-derived glycerol

The purpose of this research was the bioconversion of biodiesel-derived glycerol to arabitol through the adoption of sustainable bioprocessing. Arabitol production by Debaryomyces prosopidis FMCC Y69 was significantly affected by initial glycerol concentrations. The highest arabitol concentration of 45.5 g/L was achieved in the case of 120 g/L initial glycerol combined with the highest yield (0.379 g arabitol/g initial glycerol). The yeast strain showed a non-typical oleaginous behavior with low accumulation of lipids (up to 20.9% w/w) despite nitrogen-limited condition that prevailed in the fermentation media. Endopolysaccharides (IPs) were considerably high with a yield on the produced dry cell weight (YIPs/X) (=40.9% w/w) when 85 g/L of glycerol was utilized as the starting material. The fermentation efficiency was further improved when the optimal carbon to nitrogen (C/N) ratio was applied. More specifically, arabitol production was maximized (reaching 56.5 g/L) at a C/N ratio of 158 moles/moles while yield and productivity were also enhanced with respective values of 0.48 g arabitol/g consumed glycerol and 0.112 g/L.h. The increase in C/N ratios led to a decrease in cell dry weight (DCW) concentrations, which is rationally associated with decreased nitrogen availability in the growth medium. YIPs/X values were remarkably high (23.1–26.1% w/w) at the end of each fermentation with the highest concentration in absolute values of 7.3 g/L achieved at the lowest C/N ratio employed (i.e., 79 moles/moles). This study demonstrated the efficient arabitol production along with other value-added metabolites, such as IPs and cellular lipids, implementing biotechnology and renewable resources and thus contributing to the development of circular economy technologies.

The Oxygen Paradigm—Quantitative Impact of High Concentrations of Dissolved Oxygen on Kinetics and Large-Scale Production of Arthrospira platensis

The cultivation of Arthrospira platensis in tubular photobioreactors (tPBRs) presents a promising approach for the commercial production of nutraceuticals and food products as it can achieve high productivity and effective process control. In closed photobioreactors, however, high amounts of photosynthetically produced oxygen can accumulate. So far, there has been a wide range of discussion on how dissolved oxygen concentrations (DOCs) affect bioprocess kinetics, and the subject has mainly been assessed empirically. In this study, we used photorespirometry to quantify the impact of DOCs on the growth kinetics and phycocyanin content of the widely cultivated cyanobacterium A. platensis. The photorespirometric routine revealed that the illumination intensity and cell dry weight concentration are important interconnected process parameters behind the impact that DOCs have on the bioprocess kinetics. Unfavorable process conditions such as low biomass concentrations or high illumination intensities yielded significant growth inhibition and reduced the phycocyanin content of A. platensis by up to 35%. In order to predict the biomass productivity of the large-scale cultivation of A. platensis in tPBRs, a simple process model was extended to include photoautotrophic oxygen production and accumulation in the tPBR to evaluate the performance of two configurations of a 5000 L tPBR.

Cole-Cole modeling of real-time capacitance data for estimation of cell physiological properties in recombinant Escherichia coli cultivation.

Real-time estimation of physiological properties of the cell during recombinant protein production would ensure enhanced process monitoring. In this study, we explored the application of dielectric spectroscopy to track the fed-batch phase of recombinant Escherichia coli cultivation for estimating the physiological properties, namely, cell diameter and viable cell concentration (VCC). The scanning capacitance data from the dielectric spectroscopy were pre-processed using moving average. Later, it was modeled through a nonlinear theoretical Cole-Cole model and further solved using a global evolutionary genetic algorithm (GA). The parameters obtained from the GA were further applied for the estimation of the aforementioned physiological properties. The offline cell diameter and cell viability data were obtained from particle size analyzer and flow cytometry measurements to validate the Cole-Cole model. The offline VCC was calculated from the cell viability % from flow cytometry data and dry cell weight concentration. The Cole-Cole model predicted the cell diameter and VCC with an error of 1.03% and 7.72%, respectively. The proposed approach can enable the operator to take real-time process decisions to achieve desired productivity and product quality.

Application of In-Situ and Soft-Sensors for Estimation of Recombinant P. pastoris GS115 Biomass Concentration: A Case Analysis of HBcAg (Mut+) and HBsAg (MutS) Production Processes under Varying Conditions.

Microbial biomass concentration is a key bioprocess parameter, estimated using various labor, operator and process cross-sensitive techniques, analyzed in a broad context and therefore the subject of correct interpretation. In this paper, the authors present the results of P. pastoris cell density estimation based on off-line (optical density, wet/dry cell weight concentration), in-situ (turbidity, permittivity), and soft-sensor (off-gas O2/CO2, alkali consumption) techniques. Cultivations were performed in a 5 L oxygen-enriched stirred tank bioreactor. The experimental plan determined varying aeration rates/levels, glycerol or methanol substrates, residual methanol levels, and temperature. In total, results from 13 up to 150 g (dry cell weight)/L cultivation runs were analyzed. Linear and exponential correlation models were identified for the turbidity sensor signal and dry cell weight concentration (DCW). Evaluated linear correlation between permittivity and DCW in the glycerol consumption phase (<60 g/L) and medium (for Mut+ strain) to significant (for MutS strain) linearity decline for methanol consumption phase. DCW and permittivity-based biomass estimates used for soft-sensor parameters identification. Dataset consisting from 4 Mut+ strain cultivation experiments used for estimation quality (expressed in NRMSE) comparison for turbidity-based (8%), permittivity-based (11%), O2 uptake-based (10%), CO2 production-based (13%), and alkali consumption-based (8%) biomass estimates. Additionally, the authors present a novel solution (algorithm) for uncommon in-situ turbidity and permittivity sensor signal shift (caused by the intensive stirrer rate change and antifoam agent addition) on-line identification and minimization. The sensor signal filtering method leads to about 5-fold and 2-fold minimized biomass estimate drifts for turbidity- and permittivity-based biomass estimates, respectively.

Contact-free infrared OD measurement for online monitoring of parallel stirred-tank bioreactors up to high cell densities

Miniaturized stirred-tank bioreactor systems provide a scalable platform for high-throughput bioprocess development. Online measurement of process variables is a major demand to enable efficient process monitoring and control in parallel operated bioreactors. One miniaturized laser light source and two photodiodes were placed around a cylindrical disposable bioreactor made of polystyrene for individual and contact-free measurement of optical density (OD). One photodiode was positioned at an angle of 28° to the laser for measuring the scattered light, a second photodiode was positioned face to face with the laser for measuring the transmitted light. Miniaturized lasers with wavelengths of 650 nm (orange), 780 nm (NIR) and 850 nm (IR) were evaluated. The best results were achieved with a laser emitting at 850 nm. Both signals (scattered and transmitted light) were influenced by the stirrer speed (usually constant) and the microorganisms under study. After individual calibration, online OD monitoring of pH-controlled fed-batch processes was successfully shown with Escherichia coli, Corynebacterium glutamicum, and Trichosporon oleaginosus. Online OD measurements based on the transmitted light signals showed low standard deviation at low cell densities, whereas scattered light signals were more accurate at higher cell densities. Correlations were reliable up to cell dry weight concentrations of 46 g L−1 in stirred-tank bioreactors on a milliliter scale.

Assessment of Fatty Acids Profile and Omega-3 Polyunsaturated Fatty Acid Production by the Oleaginous Marine Thraustochytrid Aurantiochytrium sp. T66 Cultivated on Volatile Fatty Acids

Thraustochytrids are considered natural producers of omega-3 fatty acids as they can synthesize up to 70% docosahexaenoic acids (DHA) of total lipids. However, commercial and sustainable production of microbial DHA is limited by elevated cost of carbon substrates for thraustochytrids cultivation. This problem can be addressed by utilizing low-cost renewable substrates. In the present study, growth, lipid accumulation and fatty acid profiles of the marine thraustochytrid Aurantiochytrium sp. T66 (ATCC-PRA-276) cultivated on volatile fatty acids (C1, formic acid; C2, acetic acid; C3, propionic acid; C4, butyric acid; C5, valeric acid and C6, caproic acid) and glucose as control were evaluated for the first time. This strain showed an inability to utilize C3, C5 and C6 as a substrate when provided at >2 g/L, while efficiently utilizing C2 and C4 up to 40 g/L. The highest cell dry weight (12.35 g/L) and total lipid concentration (6.59 g/L) were attained when this strain was cultivated on 40 g/L of butyric acid, followed by cultivation on glucose (11.87 g/L and 5.34 g/L, respectively) and acetic acid (8.70 g/L and 3.43 g/L, respectively). With 40 g/L butyric acid, the maximum docosahexaenoic acid content was 2.81 g/L, corresponding to 42.63% w/w of total lipids and a yield of 0.23 g/gcell dry weight (CDW). This marine oleaginous microorganism showed an elevated potential for polyunsaturated fatty acids production at higher acetic and butyric acid concentrations than previously reported. Moreover, fluorescence microscopy revealed that growth on butyric acid caused cell size to increase to 45 µm, one of the largest values reported for oleaginous microorganisms, as well as the presence of numerous tiny lipid droplets.

Using of Some Agro-industrial Wastes for Improving Carotenoids Production from Yeast Rhodotorula glutinis 32 and Bacteria Erwinia uredovora DSMZ 30080

Some agro-industrial wastes such as clarified cane molasses, high test molasses, sweet whey, potato starch and corn steep liquor were tested as carbon sources or nitrogen source for growth and carotenoid accumulation using bacteria Erwinia uredovora DSMZ 30080 and yeast Rhodotorula glutinis number 32. Erlenmeyer flasks containing 100 ml of production media, the flasks were inoculated with 1 ml of standard inoculum and incubated at 150 rpm for 4 days at 30°C. Samples were collected periodical every 24h, cell dry weight and carotenoids concentration were determined. Sweet whey and highest molasses gave the highest growth being 2.85 and 7.34 gl-1, respectively and scored the same layout on carotenoids conc. which reach the peak during stationary phase (72 h of fermentation). Using of high test molasses and sweet whey as carotenoid production media were incremented carotenoid conc. about 1.7 and 2 fold (with respect to reference media). Increasing high test molasses conc. to give 5% initial sugar led to up great growth, carotenoids conc., productivity, yield and Yc/x from Rhodo. glutinis 32 to be 7.31 gl-1, 2.67 mgl-1, 0.037 mgl-1h-1, 0.067% and 0.365, respectively. Furthermore, using corn steep liquor (30%) as nitrogen sources augmented carotenoids concentration about 3.8 and 4fold for incomplete and complete production media using Rhodo. glutinis32. Also, a negligible effect on growth was observed with dark incubation with both strains which dropped about 75 and 48% with regard to control for E. uredovora DSMZ 30080 and Rhod. glutinis 32, respectively, whereas, carotenoids conc. was increased about 21% for E. uredovora DSMZ 30080 in dark condition.

Enzymatic hydrolysis of cassava stems for butanol production of isolated Clostridium sp.

This research focused on the hydrolysis of cassava stems (CS) and subsequent utilization as a carbon source for the cultivation of isolated Clostridium sp. To yield the highest amount of reducing sugars (RS), the studies on the pretreatment with sodium hydroxide (NaOH) and the hydrolysis with cellulases, amylases, and mixed enzymes were carried out. Afterwards, the hydrolysate was utilized for the cultivation of isolated Clostridium sp. Experimental results revealed that CS after 1.0 M NaOH pretreatment at 121 °C for 15 min and cellulase hydrolysis (Accellerase® 1500, 2500 CMC U/g CS) obtained 10.94 ± 0.29 g/L RS concentration. Hydrolysis of CS with amylases (Termamyl® 120, 1.2 U/g CS and AMG 300L™ 3.5 U/g CS) provided 34.85 ± 0.75 g/L RS and the maximum RS amount of 47.90 ± 0.39 g/L was obtained from the hydrolysis with mixed enzymes (Termamyl® 120, 1.2 U/g CS, AMG 300L™ 3.5 U/g CS followed by Accellerase® 1500, 2500 CMC U/g CS). From the cultivation of Clostridium sp. G10 using CS hydrolysate, the highest dry cell weight concentration of 1.28 ± 0.07 g/L was obtained with 11.68 ± 0.31 g/L butanol. It could be concluded that CS hydrolysate was comparable with glucose for utilization as a carbon source for butanol production.

Sustainable biorefinery concept for biofuel production through holistic volarization of food waste

The aim of this study was to utilize the whole food waste in two stages. In the first stage, the carbohydrate and protein fractions of food waste recovered after enzymatic hydrolysis was used to cultivate heterotrophic microalgae, resulting in biomass yield of 0.346 ± 0.09 g/gsugars and lipid yield of 0.216 ± 0.06 g/gsugars. In the second stage, oil (14.15% w/w) was extracted from food waste after hydrolysis and converted to biodiesel by a two-step transesterification reaction that generated 135.8 g/kgfood waste of fatty acid methyl esters and 13.8 g/kgfood waste of crude glycerol. Finally, crude glycerol obtained from both processes was used at 20 g/L to cultivate heterotrophic microalgae, resulting in a cell dry weight and total lipid concentration of 6.23 g/L and 2.91 g/L, respectively. A total 248.21 g of fatty acid methyl esters were obtained from the 1 kg of food waste through this integrated process.

Reversible retrofitting of a stirred-tank bioreactor for gas-lift operation to perform synthesis gas fermentation studies

A retrofit approach enables the non-invasive and reversible modification of a commercially available stirred-tank bioreactor into a gas-lift bioreactor within a few minutes. The gas-lift bioreactor configuration was characterised using a non-coalescent medium at working volume-specific volumetric gas flow rates of up to 20 L L−1 h−1, showing mean gas bubble diameters of up to 0.57 mm, volumetric power inputs of up to 23 W m-3, gas-liquid mass transfer coefficients of up to 153 h−1 (CO) and up to 122 h−1 (H2), mixing times (θ90) of down to 0.5 min and gas hold-ups of up to 1.2%. A comparison of autotrophic batch processes with Clostridium aceticum and Clostridium carboxidivorans in the stirred-tank (2.0 L) and the retrofitted gas-lift bioreactor (2.5 L) at identical operating conditions showed differences in the cell dry weight and product concentrations (acetate, ethanol, butyrate, 1-butanol, hexanoate, 1-hexanol) due to gas-liquid mass transfer limitations caused by the reduced power input in the gas-lift bioreactor. CO limitation was demonstrated by a myoglobin-protein assay for CO measurement in the liquid phase. The simple retrofitting of a stirred-tank bioreactor for gas-lift operation thus provided comparative data on process performances of acetogenic bacteria that convert synthesis gas in gas-lift and stirred-tank bioreactors on a lab-scale.

Macroalgal biomass subcritical hydrolysates for the production of polyhydroxyalkanoate (PHA) by Haloferax mediterranei

Non-conventional carbon sources, such as macroalgae, are sustainable alternatives for large-scale production of biopolymers. The present study examined macroalgae-derived carbohydrates, as carbon sources for the production of polyhydroxyalkanoates (PHAs) by Haloferax mediterranei. Simulants of the hydrolysates of seven different macroalgal biomasses were prepared and the PHA production was studied. A maximum biomass concentration with maximum PHA content was detected in medium prepared from green macroalgae. The highest cell dry weight and PHA concentrations were 3.8 ± 0.2 g·L−1 and 2.2 ± 0.12 g·L−1 respectively when Haloferax mediterranei was grown in 25% (w/w) of Ulva sp. hydrolysate, at 42 °C temperature and initial pH of 7.2. Poly(3-hydroxy-butyrate-co-3-hydroxyvalerate was the major PHA constituent. The present study demonstrated that Ulva sp. is a promising feedstock for PHA production.

Transcriptome and gene expression analysis of docosahexaenoic acid producer Schizochytrium sp. under different oxygen supply conditions

BackgroundSchizochytrium sp. is a promising strain for the production of docosahexaenoic acid (DHA)-rich oil and biodiesel, and has been widely used in the food additive and bioenergy industries. Oxygen is a particularly important environmental factor for cell growth and DHA synthesis. In general, higher oxygen supply favors lipid accumulation, but could lead to a reduction of the DHA percentage in total fatty acids in Schizochytrium sp. To tackle this problem, it is essential to understand the mechanisms regulating the response of Schizochytrium sp. to oxygen. In this study, we aimed to explore the acclimatization of this DHA producer to different oxygen supply conditions by examining the transcriptome changes.ResultsTwo different fermentation processes, namely normal oxygen supply condition (shift agitation speeds from 400 rpm to 300 rpm) and high oxygen supply condition (constant agitation speeds: 400 rpm), were designed to study how the fermentation characteristics of Schizochytrium sp. HX-308 were affected by different oxygen supply conditions. The results indicated that high oxygen supply condition resulted in 49% and 37.5% improvement in the maximum cell dry weight (CDW) and total lipid concentration, respectively. However, the DHA percentage in total fatty acids decreased to 35%, which was 31.4% lower than that produced by normal oxygen supply condition. Moreover, transcriptome analysis was performed to explore the effect of the oxygen supply condition on genetic expression and metabolism. The results showed that glycolysis and pentose phosphate pathway metabolism-associated genes (hexokinase, phosphofructokinase, fructose-bisphosphate aldolase, glucose-6-phosphate dehydrogenase, and 6-phosphogluconate dehydrogenase) were substantially upregulated in response to high oxygen supply, resulting in more NADPH was available for Schizochytrium. Specially, high oxygen supply condition also led to genes (Δ6 desaturase, Δ12 desaturase, FAS, ORFA, ORFB, and ORFC) involved in fatty acid biosynthesis upregulation. In addition, a transcriptional upregulation of catalase (CAT) became apparent under high oxygen supply condition, while superoxide dismutase (SOD) and ascorbate peroxidase (APX) were found to be down-regulated.ConclusionsThis study is the first to investigate the differences of gene expression at different levels of oxygen availability in the DHA producer Schizochytrium. The results of transcriptome analyses indicated that high oxygen supply condition resulting in more NADPH and acetyl-CoA production for cell growth and lipid synthesis in Schizochytrium. Δ12 desaturase and ORFC showed higher expression levels at high oxygen supply condition, which might be the key regulators for enhancing fatty acid biosynthesis in the future. These results enrich the current knowledge regarding genetic expression and provide important information to enhance DHA production in Schizochytrium sp.

Carbon monoxide conversion with Clostridium aceticum.

Carbon monoxide concentrations in syngas are often high, but tolerance toward CO varies a lot between homoacetogenic bacteria. Analysis of the autotrophic potential revealed that the first isolated acetogenic bacterium Clostridium aceticum was able to use CO as sole carbon and energy source for chemolithoautotrophic carbon fixation but simultaneously showed little tolerance to high CO concentrations. Not yet reported, autotrophic ethanol production by C. aceticum was discovered with CO as a substrate in batch processes. Growth rates estimated in batch processes at varying CO partial pressures were used to identify the CO inhibition kinetics of C. aceticum, using a substrate inhibition model. C. aceticum shows a strong CO inhibition with an optimum CO partial pressure of only 5.4 mbar in the gas phase at cell dry weight concentrations of up to 0.5 g·L -1 . At optimum conditions, growth and acetate formation rates were estimated to be 0.24 hr -1 and 0.52 g·g -1 ·hr -1 , respectively. Syngas fermentation at high partial pressures of up to 280 mbar CO in the inlet gas phase was enabled by applying a continuously operated stirred-tank bioreactor with submerged membranes with total cell retention. Around 70% CO conversion was achieved continuously in the membrane bioreactor with strongly CO inhibited C. aceticum resulting in space-time yields of up to 0.85 g·L -1 ·hr -1 acetate.

Combinatorial pretreatment and fermentation optimization enabled a record yield on lignin bioconversion

BackgroundLignin valorization has recently been considered to be an essential process for sustainable and cost-effective biorefineries. Lignin represents a potential new feedstock for value-added products. Oleaginous bacteria such as Rhodococcus opacus can produce intracellular lipids from biodegradation of aromatic substrates. These lipids can be used for biofuel production, which can potentially replace petroleum-derived chemicals. However, the low reactivity of lignin produced from pretreatment and the underdeveloped fermentation technology hindered lignin bioconversion to lipids. In this study, combinatorial pretreatment with an optimized fermentation strategy was evaluated to improve lignin valorization into lipids using R. opacus PD630.ResultsAs opposed to single pretreatment, combinatorial pretreatment produced a 12.8–75.6% higher lipid concentration in fermentation using lignin as the carbon source. Gas chromatography–mass spectrometry analysis showed that combinatorial pretreatment released more aromatic monomers, which could be more readily utilized by lignin-degrading strains. Three detoxification strategies were used to remove potential inhibitors produced from pretreatment. After heating detoxification of the lignin stream, the lipid concentration further increased by 2.9–9.7%. Different fermentation strategies were evaluated in scale-up lipid fermentation using a 2.0-l fermenter. With laccase treatment of the lignin stream produced from combinatorial pretreatment, the highest cell dry weight and lipid concentration were 10.1 and 1.83 g/l, respectively, in fed-batch fermentation, with a total soluble substrate concentration of 40 g/l. The improvement of the lipid fermentation performance may have resulted from lignin depolymerization by the combinatorial pretreatment and laccase treatment, reduced inhibition effects by fed-batch fermentation, adequate oxygen supply, and an accurate pH control in the fermenter.ConclusionsOverall, these results demonstrate that combinatorial pretreatment, together with fermentation optimization, favorably improves lipid production using lignin as the carbon source. Combinatorial pretreatment integrated with fed-batch fermentation was an effective strategy to improve the bioconversion of lignin into lipids, thus facilitating lignin valorization in biorefineries.

High concentrations of biotechnologically produced astaxanthin by lowering pH in a Phaffia rhodozyma bioprocess

Astaxanthin additions to animal diets predominantly serve as colorization aid to satisfy consumer expectations and desire for a consistent product with familiar coloration, e.g. the characteristic pink colorization of the flesh of species being produced by aquaculture. The heterobasidiomycetous yeast Phaffia rhodozyma (Xanthophyllomyces dendrorhous) can be used as natural feed source of astaxanthin. However, currently, the majority of astaxanthin used for the feed market is produced by chemical synthesis. We present a further step in direction of a competitive production of natural astaxanthin in an optimized bioprocess with non-genetically modified Phaffia rhodozyma. After medium optimization AXJ-20, a mutant strain of P. rhodozyma wild-type strain ATCC 96594, was able to grow to a cell dry weight concentration of over 114 g per kg of culture broth in a fed-batch process. In this bioprocess, where pH was lowered from 5.5 to 3.5 during the maturation phase, AXJ-20 produced the highest value reported for astaxanthin production with P. rhodozyma up to now: 0.7 g astaxanthin per kg of culture broth with a space-time-yield of 3.3 mg astaxanthin per kg of culture broth per hour. Lowering the pH during the bioprocess and increasing trace element and vitamin concentrations prevented loss of cell dry weight concentration in the maturation phase and proved to be critical for astaxanthin concentration and purity.

Acid pretreatment and enzymatic saccharification of brown seaweed for polyhydroxybutyrate (PHB) production using Cupriavidus necator

The brown seaweed Sargassum sp. was used as a feedstock to produce polyhydroxybutyarte (PHB) using Cupriavidus necator PTCC 1615. In order to release monomeric sugars, dilute acid hydrolysis of Sargassum sp. biomass was followed by enzymatic saccharification. In addition, the effect of different nitrogen sources was evaluated for PHB production. The fermentation of hydrolysate with the ammonium sulfate as selected nitrogen source resulted PHB yield of 0.54±0.01g/g reducing sugar. Then, NaCl was used as external stress factor which was added to the media. Addition of 8g/L NaCl had a positive impact on high PHB yield of 0.74±0.01g/g reducing sugar. Increasing trend of NaCl concentration to 16g/L was found to inhibit the production of PHB. Based on obtained results using 20g/L of reducing sugar, at desired condition the highest cell dry weight and PHB concentrations were 5.36±0.22 and 3.93±0.24g/L, respectively. The findings of this study reveal that Sargassum sp. is a promising feedstock for biopolymer production. The characteristics of produced PHB were analyzed by FTIR, differential scanning calorimetry and 1H NMR.