Production of succinic acid and lactic acid by Corynebacterium crenatum under anaerobic conditions

A new succinic acid and lactic acid production bioprocess by Corynebacterium crenatum was investigated in mineral medium under anaerobic conditions. Corynebacterium crenatum cells with sustained acid production ability and high acid volumetric productivity harvested from the glutamic acid fermentation broth were used to produce succinic acid and lactic acid. Compared with the first cycle, succinic acid production in the third cycle increased 120% and reached 43.4 g/L in 10 h during cell-recycling repeated fermentations. The volumetric productivities of succinic acid and lactic acid could maintain above 4.2 g/(L·h) and 3.1 g/(L·h), respectively, for at least 100 h. Moreover, wheat bran hydrolysates could be used for succinic acid and lactic acid production by the recycled C. crenatum cells. The final succinic acid concentration reached 43.6 g/L with a volumetric productivity of 4.36 g/(L·h); at the same time, 32 g/L lactic acid was produced.     

Enhancing polyhydroxybutyrate production from high cell density fed-batch fermentation of Bacillus megaterium BA-019

This study demonstrated the improved polyhydroxybutyrate (PHB) production via high cell density cultivation of Bacillus megaterium BA-019 with balanced initial total sugar concentration and carbon to nitrogen (C/N) weight ratio. In the 10 L stirred fermentor operated at 30 °C, pH 7.0, 600 rpm, and 1.0 vvm air, with the initial total sugar concentration of 60 g/L and urea at the C/N weight ratio of 10:1, 32.48 g/L cell biomass with the corresponding PHB weight content of 26.94 % and volumetric productivity of 0.73 g/L h were obtained from batch cultivation. Continuing cultivation by intermittent feeding of the sugarcane molasses along with urea at the C/N weight ratio of 12.5:1 gave much improved biomass and PHB production (90.71 g/L biomass with 45.84 % PHB content and 1.73 g/L h PHB productivity). Similar biomass and PHB yields were obtained in the 90 L stirred fermentor when using the impeller tip speed as the scale-up criterion.     

Optimization of enzymatic hydrolysis and ethanol fermentation from AFEX-treated rice straw

An abundant agricultural residue, rice straw (RS) was pretreated using ammonia fiber expansion (AFEX) process with less than 3% sugar loss. Along with commercial cellulase (Spezyme® CP) at 15 filter paper unit/g of glucan, the addition of Multifect® Xylanase at 2.67 mg protein/g glucan and Multifect® Pectinase at 3.65 mg protein/g glucan was optimized to greatly increase sugar conversion of AFEX-treated RS. During enzymatic hydrolysis even at 6% glucan loading (equivalent to 17.8% solid loading), about 80.6% of glucan and 89.6% of xylan conversions (including monomeric and oligomeric sugars) were achieved. However, oligomeric glucose and xylose accounted for 12.3% of the total glucose and 37.0% of the total xylose, respectively. Comparison among the three ethanologenic strains revealed Saccharomyces cerevisiae 424A(LNH-ST) to be a promising candidate for RS hydrolysate with maximum ethanol metabolic yield of 95.3% and ethanol volumetric productivity of 0.26 g/L/h. The final concentration of ethanol at 37.0 g/L was obtained by S. cerevisiae 424A(LNH-ST) even with low cell density inoculum. A biorefinery combining AFEX pretreatment with S. cerevisiae 424A(LNH-ST) in separate hydrolysis and fermentation could achieve 175.6 g EtOH/kg untreated rice straw at low initial cell density (0.28 g dw/L) without washing pretreated biomass, detoxification, or nutrient supplementation.     

Improvement of mannitol production by Lactobacillus brevis mutant 3-A5 based on dual-stage pH control and fed-batch fermentations

Lactobacillus brevis 3-A5 was isolated and expected to produce mannitol efficiently by regulating pH in batch and fed-batch fermentations. In 48 h batch fermentations with free and constant pH, the optimal pH for cell growth and mannitol production in the first 24 h of incubation was 5.5, whereas that for mannitol production in the second 24 h of incubation was 4.5. To achieve high cell density and mannitol yield simultaneously, a dual-stage pH control strategy was proposed based on the kinetic analysis of mannitol production. The pH value was controlled at 5.5 for the first 12 h of fermentation and subsequently shifted to 4.5 until the fermentation was completed. Under dual-stage pH control fermentation, a 103 g/L yield of mannitol with a volumetric production rate of 3.7 g/L/h was achieved after 28 h. The dual-stage pH control fed-batch fermentation strategy was further developed to improve mannitol yield, wherein the yield increased by 109 % to 215 g/L after 98 h of fermentation. This value is the highest yield of mannitol ever reported using L. brevis.     

An integrated process for the production of 1,3-propanediol,lactate and 3-hydroxypropionic acid by an engineered Lactobacillus reuteri

The process economy of food grade 1,3-propanediol (1,3-PD) production by GRAS organisms like Lactobacillus reuteri (L. reuteri), is negatively impacted by the low yield and use of expensive feedstocks. In order to improve the process economy, we have developed a multiproduct process involving the production of three commercially important chemicals, namely, 1,3-PD, lactate and 3-Hydroxypropionic acid (3-HP), by engineered L. reuteri. The maximum 1,3-PD and lactate titer of 41 g/L and 31 g/L, with a volumetric productivity of 1.69 g/L/h and 0.67 g/L/h were achieved, respectively. The maximum 3-HP titer of 5.2 g/L with a volumetric productivity of 1.3 g/L/h, was obtained by biotransformation using cells recovered from the repeated fed-batch process. The volumetric productivity of 1,3-PD obtained in this study is the highest ever reported for this organism. Further cost reduction can be achieved by using waste feedstocks like milk whey, biomass hydrolysate, and crude glycerol.     

Utilization of by-products derived from bioethanol production process for cost-effective production of lactic acid

The by-products of bioethanol production such as thin stillage (TS) and condensed distillers solubles (CDS) were used as a potential nitrogen source for economical production of lactic acid. The effect of those by-products and their concentrations on lactic acid fermentation were investigated using Lactobacillus paracasei CHB2121. Approximately, 6.7 g/L of yeast extract at a carbon source to nitrogen source ratio of 15 was required to produce 90 g/L of lactic acid in the medium containing 100 g/L of glucose. Batch fermentation of TS medium resulted in 90 g/L of lactic acid after 48 h, and the medium containing 10 % CDS resulted in 95 g/L of lactic acid after 44 h. Therefore, TS and CDS could be considered as potential alternative fermentation medium for the economical production of lactic acid. Furthermore, lactic acid fermentation was performed using only cassava and CDS for commercial production of lactic acid. The volumetric productivity of lactic acid [2.94 g/(L·h)] was 37 % higher than the productivity obtained from the medium with glucose and CDS.     

Stimulation of acetoin production in metabolically engineered <Emphasis Type="Italic">Lactococcus lactis</Emphasis> by increasing ATP demand

Having a sufficient supply of energy, usually in the form of ATP, is essential for all living organisms. In this study, however, we demonstrate that it can be beneficial to reduce ATP availability when the objective is microbial production. By introducing the ATP hydrolyzing F₁-ATPase into a Lactococcus lactis strain engineered into producing acetoin, we show that production titer and yield both can be increased. At high F₁-ATPase expression level, the acetoin production yield could be increased by 10 %; however, because of the negative effect that the F₁-ATPase had on biomass yield and growth, this increase was at the cost of volumetric productivity. By lowering the expression level of the F₁-ATPase, both the volumetric productivity and the final yield could be increased by 5 % compared to the reference strain not overexpressing the F₁-ATPase, and in batch fermentation, it was possible to convert 176 mM (32 g/L) of glucose into 146.5 mM (12.9 g/L) acetoin with a yield of 83 % of the theoretical maximum. To further demonstrate the potential of the cell factory developed, we complemented it with the lactose plasmid pLP712, which allowed for growth and acetoin production from a dairy waste stream, deproteinized whey. Using this cheap and renewable feedstock, efficient acetoin production with a titer of 157 mM (14 g/L) acetoin was accomplished.     

Effect of Mg, Si, and Sr on growth and antioxidant activity of the marine microalga Tetraselmis suecica

Efforts to increase the productivity of microalgal cultures have been focused on the improvement of photobioreactors, but little attention has been paid to the nutritional requirements of microalgae in order to improve culture media formulation. In this study, the main goal was obtaining a high productivity for Tetraselmis suecica (Chlorophyta) in semicontinuous culture by adding magnesium (Mg), silicon (Si), and strontium (Sr) at concentrations from 0.01 to 10 mM; at the time, the effect on steady-state cell density, biochemical composition, and antioxidant activity of T. suecica was evaluated. Because productivity is higher in high-density cultures, the work was focused many times to cell density. Mg (3 mM) and Sr (0.1 mM) added separately reached the highest steady-state cell density (7.0?×?10⁶?±?0.4 cells mL^?1) in comparison to control (4.2?±?0.1 cells mL^?1), but simultaneous addition had a synergic effect, achieving 8.7?×?10⁶?±?0.6 cells mL^?1. Silicon (3 mM) significantly affected the steady-state cell density, reaching 6.0?±?0.3 cells mL^?1 and increased the cell ash-free dry weight, reaching 127?±?7.9 pg cell^?1 in comparison to control (102.7?±?5.0 pg cell^?1), resulting in an ash-free dry weight productivity of 0.75?±?0.07 g?L^?1 day^?1. The highest fatty acids content and antioxidant activity, measured by 2, 2-diphenyl-1-picrylhydrazyl (DPPH) method were obtained with Sr 10 mM. Sr treatments showed a high correlation (R ²?=?0.98) between DPPH inhibition and polyphenolic content, explaining its high antioxidant activity. Therefore, the addition of Mg, Si, and Sr to culture medium of T. suecica is recommended to achieve high steady-state cell density in semicontinuous cultures.     

Ethanol production from galactose by a newly isolated Saccharomyces cerevisiae KL17

A wild-type yeast strain with a good galactose-utilization efficiency was newly isolated from the soil, and identified and named Saccharomyces cerevisiae KL17 by 18s RNA sequencing. Its performance of producing ethanol from galactose was investigated in flask cultures with media containing various combination and concentrations of galactose and glucose. When the initial galactose concentration was 20 g/L, it showed 2.2 g/L/h of substrate consumption rate and 0.63 g/L/h of ethanol productivity. Although they were about 70 % of those with glucose, such performance of S. cerevisiae KL17 with galactose was considered to be quite high compared with other strains reported to date. Its additional merit was that its galactose metabolism was not repressed by the existence of glucose. Its capability of ethanol production under a high ethanol concentration was demonstrated by fed-batch fermentation in a bioreactor. A high ethanol productivity of 3.03 g/L/h was obtained with an ethanol concentration and yield of 95 and 0.39 g/L, respectively, when the cells were pre-cultured on glucose. When the cells were pre-cultured on galactose instead of glucose, fermentation time could be reduced significantly, resulting in an improved ethanol productivity of 3.46 g/L/h. The inhibitory effects of two major impurities in a crude galactose solution obtained from acid hydrolysis of galactan were assessed. Only 5-Hydroxymethylfurfural (5-HMF) significantly inhibited ethanol fermentation, while levulinic acid (LA) was benign in the range up to 10 g/L.     

Enhanced isopropanol and <Emphasis Type="Italic">n</Emphasis>-butanol production by supplying exogenous acetic acid via co-culturing two clostridium strains from cassava bagasse hydrolysate

The focus of this study was to produce isopropanol and butanol (IB) from dilute sulfuric acid treated cassava bagasse hydrolysate (SACBH), and improve IB production by co-culturing Clostridium beijerinckii (C. beijerinckii) with Clostridium tyrobutyricum (C. tyrobutyricum) in an immobilized-cell fermentation system. Concentrated SACBH could be converted to solvents efficiently by immobilized pure culture of C. beijerinckii. Considerable solvent concentrations of 6.19 g/L isopropanol and 12.32 g/L butanol were obtained from batch fermentation, and the total solvent yield and volumetric productivity were 0.42 g/g and 0.30 g/L/h, respectively. Furthermore, the concentrations of isopropanol and butanol increased to 7.63 and 13.26 g/L, respectively, under the immobilized co-culture conditions when concentrated SACBH was used as the carbon source. The concentrations of isopropanol and butanol from the immobilized co-culture fermentation were, respectively, 42.62 and 25.45 % higher than the production resulting from pure culture fermentation. The total solvent yield and volumetric productivity increased to 0.51 g/g and 0.44 g/L/h when co-culture conditions were utilized. Our results indicated that SACBH could be used as an economically favorable carbon source or substrate for IB production using immobilized fermentation. Additionally, IB production could be significantly improved by co-culture immobilization, which provides extracellular acetic acid to C. beijerinckii from C. tyrobutyricum. This study provided a technically feasible and cost-efficient way for IB production using cassava bagasse, which may be suitable for industrial solvent production.     

Long-term outdoor growth and lipid productivity of Tetraselmis suecica, Dunaliella tertiolecta and Chlorella sp (Chlorophyta) in bag photobioreactors

There has been considerable interest on cultivation of green microalgae (Chlorophyta) as a source of lipid that can alternatively be converted to biodiesel. The ideal microalga characteristics are that it must grow well even under high cell density and under varying outdoor environmental conditions and be able to have a high biomass productivity and contain a high oil content (~25–30 %). The main advantage of Chlorophyta is that their fatty acid profile is suitable for biodiesel conversion. Tetraselmis suecica CS-187 and Chlorella sp. were grown semi-continuously in bag photobioreactors (120 L, W?×?L?=?40?×?380 cm) over a period of 11 months in Melbourne, Victoria, Australia. Monthly biomass productivity of T. suecica CS-187 and Chlorella sp. was strongly correlated to available solar irradiance. The total dry weight productivity of T. suecica and Chlorella sp. was 110 and 140 mg L^?1 d^?1, respectively, with minimum 25 % lipid content for both strains. Both strains were able to tolerate a wide range of shear produced by mixing. Operating cultures at lower cell density resulted in increasing specific growth rates of T. suecica and Chlorella sp. but did not affect their overall biomass productivity. On the other hand, self shading sets the upper limit of operational maximum cell density. Several attempts in cultivating Dunaliella tertiolecta CS-175 under the same climatic conditions were unsuccessful.     

Cloning,deletion, and overexpression of a glucose oxidase gene in <Emphasis Type="Italic">Aureobasidium</Emphasis> sp. P6 for Ca<Superscript>2+</Superscript>-gluconic acid overproduction

This study aimed to overexpress a glucose oxidase gene (GOD1) in Aureobasidium sp. P6 to achieve Ca²⁺-gluconic acid (GA) overproduction. The GOD1 gene was cloned, deleted, and overexpressed. A protein deduced from the GOD1 gene of Aureobasidium sp. P6 strain had 1824 bp that encoded a protein with 606 amino acids, with a conserved NADB-ROSSMAN domain and a GMC-oxred domain. Deleting the GOD1 gene made the disruptant GOK1 completely lose the ability to produce GA and GOD1 activity, whereas overexpressing the GOD1 gene rendered the transformant GOEX8 to produce considerably more Ca²⁺-GA (160.5?±?5.6 g/L) and higher GOD1 activity (1438.6?±?73.2 U/mg of protein) than its parent P6 strain (118.7?±?4.3 g/L of Ca²⁺-GA and 1100.0?±?23.6 U/mg of GOD1 protein). During a 10-L fermentation, the transformant GOEX8 grown in the medium containing 160.0 g/L of glucose produced 186.8?±?6.0 g/L of Ca²⁺-GA, the yield was 1.2 g/g of glucose, and the volumetric productivity was 1.7 g/L/h. Most of the produced GOD1 were located in the yeast cell wall. The purified product was identified to be a GA. The transformant GOEX8 overexpressing the GOD1 gene could produce considerably more Ca²⁺-GA (186.8?±?6.0 g/L) than its wild-type strain P6.     

Investigation of continuous-batch mode of two-stage culture of Nannochloropsis sp. for lipid production

Microalgal lipid induction through nitrogen stress often suffers from a contradiction between biomass productivity and lipid content, i.e., either high biomass productivity with low lipid content or vice versa. A two-stage nitrogen-replete and nitrogen-deplete (NR–ND) culture was suggested to be an option to attain high lipid productivity. In this study, the effects of culture conditions and modes on biomass productivity and lipid productivity of Nannochloropsis sp. in the two stages were comprehensively investigated. The optimal culture conditions for the two stages, aiming to high biomass productivity and lipid productivity respectively, were consistent, i.e., CO₂ content in aeration (1 %), phosphorus concentration in medium (181 μmol/L), incident light intensity (150 μE/(m²s)), temperature (25 °C). Different culture modes of the two stages were compared. The overall lipid productivity of the two-stage continuous-batch mode achieved 0.123 g/(L day), which was 60.3, 48.2, 34.9 and 13.5 % higher than that of single nitrogen-replete batch, single nitrogen-limited batch, continuous nitrogen-replete culture and two-stage batch–batch culture, respectively, and also higher than most reported values. This contribution provides fundamental data for the two-stage NR–ND cultivation process design of Nannochloropsis sp.     

Pilot-scale production of fuel ethanol from concentrated food waste hydrolysates using Saccharomyces cerevisiae H058

The aim of this study was to develop a bioprocess to produce ethanol from food waste at laboratory, semipilot and pilot scales. Laboratory tests demonstrated that ethanol fermentation with reducing sugar concentration of 200 g/L, inoculum size of 2 % (Initial cell number was 2 × 10⁶ CFU/mL) and addition of YEP (3 g/L of yeast extract and 5 g/L of peptone) was the best choice. The maximum ethanol concentration in laboratory scale (93.86 ± 1.15 g/L) was in satisfactory with semipilot scale (93.79 ± 1.11 g/L), but lower than that (96.46 ± 1.12 g/L) of pilot-scale. Similar ethanol yield and volumetric ethanol productivity of 0.47 ± 0.02 g/g, 1.56 ± 0.03 g/L/h and 0.47 ± 0.03 g/g, 1.56 ± 0.03 g/L/h after 60 h of fermentation in laboratory and semipilot fermentors, respectively, however, both were lower than that (0.48 ± 0.02 g/g, 1.79 ± 0.03 g/L/h) of pilot reactor. In addition, simple models were developed to predict the fermentation kinetics during the scale-up process and they were successfully applied to simulate experimental results.     

Step-up/step-down perfusion approach for increased mAb 520C9 production by a hybridoma cell line

The hybridoma cell line, HB-8696, produces a monoclonal antibody, 520C9 (mouse IgG₁) that recognizes the breast cancer oncoprotein, c-erbB2. The effect of perfusion rate (volume of fresh feed/working volume of reactor/day) on cell growth and mAb production was investigated but perfusion at a constant rate and at an arbitrarily increased rate could not maintain exponential cell growth or a higher specific mAb production rate. An optimum step-up/step-down perfusion strategy is therefore proposed for maintaining a steady state production phase at high cell density for ten days. The optimum step-up perfusion could achieve fast cell growth by avoiding any nutrient limited condition and the following optimum step-down perfusion could potentially maintain high live cell density and reduced product dilution as well. The maximum viable cell achieved under optimum perfusion strategy was 2.3 × 10⁷ cells/ml which was 19-fold higher than in optimum batch culture. The mAb yield and volumetric productivity were significantly improved to 52 and 50 mg/l day compared to 25 and 3.8 mg/l day in optimum batch, respectively, and could be maintained for up to ten days.     

Adventitious root culture of <Emphasis Type="Italic">Polygonum multiflorum</Emphasis> for phenolic compounds and its pilot-scale production in 500 L-tank

Polygonum multiflorum Thunb. is an important medicinal plant that synthesizes an array of phenolic compounds. Its roots are used in a variety of pharmacological and cosmetic formulations, notably as hair dye. In the present study, the inoculum density (3–15 g/L) and culture period (1–7 weeks) were optimized in a 3 L bioreactor. High root biomass (14.18 g/L dry weight (DW)) was recorded with an inoculum of 7 g/L (p?≤?0.05), which is consistent with the results for 5 and 10 g/L. However, significantly higher yield of bioactive compounds (53.87 mg/g DW total phenolics and 27.96 mg/g DW total flavonoids) with high free radical scavenging activity was obtained in root samples from 5 g/L inoculum density. A 4 week culture period was sufficient for optimum root growth and metabolite production. The optimized conditions were used for large-scale (5 and 20 L) and pilot-scale (500 L) studies. Considering that the continuous aeration of root cultures may lead to oxidative stress, antioxidant enzyme activity and lipid peroxidation also were studied. The results revealed high catalase (CAT) and guaiacol peroxidase (G-POD) activities, and low malondialdehyde (MDA) production, with increasing culture scale (20 and 500 L), which may indicate low-level oxidative damage to the cultures. An optimal yield of 4.01 kg dry root biomass with 287.12 mg/L of total phenolic productivity was achieved in a 500 L pilot-scale bioreactor. This work can pave the way for commercial production of biomass and secondary metabolites at the industrial level, and meet the rising demand for natural ingredients, especially in the pharmaceutical and cosmetic industries.     

Conversion of acid hydrolysate of oil palm empty fruit bunch to L-lactic acid by newly isolated Bacillus coagulans JI12

Cost-effective conversion of lignocellulose hydrolysate to optically pure lactic acid is commercially attractive but very challenging. Bacillus coagulans JI12 was isolated from natural environment and used to produce L-lactic acid (optical purity?>?99.5 %) from lignocellulose sugars and acid hydrolysate of oil palm empty fruit bunch (EFB) at 50 °C and pH 6.0 without sterilization of the medium. In fed-batch fermentation with 85 g/L initial xylose and 55 g/L xylose added after 7.5 h, 137.5 g/L lactic acid was produced with a yield of 98 % and a productivity of 4.4 g/L?h. In batch fermentation of a sugar mixture containing 8.5 % xylose, 1 % glucose, and 1 % L-arabinose, the lactic acid yield and productivity reached 98 % and 4.8 g/L?h, respectively. When EFB hydrolysate was used, 59.2 g/L of lactic acid was produced within 9.5 h at a yield of 97 % and a productivity of 6.2 g/L?h, which are the highest among those ever reported from lignocellulose hydrolysates. These results indicate that B. coagulans JI12 is a promising strain for industrial production of L-lactic acid from lignocellulose hydrolysate.     

Production of 3-hydroxypropionic acid from glycerol by acid tolerant Escherichia coli

The biological production of 3-hydroxypropionic acid (3-HP) has attracted significant attention because of its industrial importance. The low titer, yield and productivity, all of which are related directly or indirectly to the toxicity of 3-HP, have limited the commercial production of 3-HP. The aim of this study was to identify and select a 3-HP tolerant Escherichia coli strain among nine strains reported to produce various organic acids efficiently at high titer. When transformed with heterologous glycerol dehydratase, reactivase and aldehyde dehydrogenase, all nine E. coli strains produced 3-HP from glycerol but the level of 3-HP production, protein expression and activities of the important enzymes differed significantly according to the strain. Two E. coli strains, W3110 and W, showed higher levels of growth than the others in the presence of 25 g/L 3-HP. In the glycerol fed-batch bioreactor experiments, the recombinant E. coli W produced a high level of 3-HP at 460 ± 10 mM (41.5 ± 1.1 g/L) in 48 h with a yield of 31 % and a productivity of 0.86 ± 0.05 g/L h. In contrast, the recombinant E. coli W3110 produced only 180 ± 8.5 mM 3-HP (15.3 ± 0.8 g/L) in 48 h with a yield and productivity of 26 % and 0.36 ± 0.02 g/L h, respectively. This shows that the tolerance to and the production of 3-HP differ significantly among the well-known, similar strains of E. coli. The titer and productivity obtained with E. coli W were the highest reported thus far for the biological production of 3-HP from glycerol by E. coli.     

Simultaneous single-cell protein production and COD removal with characterization of residual protein and intermediate metabolites during whey fermentation by K. marxianus

Cheese whey fermentation with Kluyveromyces marxianus was carried out at 40 °C and pH 3.5 to examine simultaneous single-cell protein production and chemical oxygen demand (COD) removal, determine the fate of soluble whey protein and characterize intermediate metabolites. After 36 h of batch fermentation, the biomass concentration increased from 2.0 to 6.0 g/L with 55 % COD reduction (including protein), whereas soluble whey protein concentration decreased from 5.6 to 4.1 g/L. It was confirmed through electrophoresis (SDS-PAGE) that the fermented whey protein was different from native whey protein. HPLC and GC–MS analysis revealed a change in composition of organic compounds post-fermentation. High inoculum concentration in batch fermentation resulted in an increase in biomass concentration from 10.3 to 15.9 g/L with 80 % COD reduction (including protein) within 36 h with residual protein concentration of 4.5 g/L. In third batch fermentation, the biomass concentration increased from 7.3 to 12.4 g/L with 71 % of COD removal and residual protein concentration of 4.3 g/L after 22 h. After 22 h, the batch process was shifted to a continuous process with cell recycle, and the steady state was achieved after another 60 h with biomass yield of 0.19 g biomass/g lactose and productivity of 0.26 g/L h. COD removal efficiency was 78–79 % with residual protein concentration of 3.8–4.2 g/L. The aerobic continuous fermentation process with cell recycle could be applied to single-cell protein production with substantial COD removal at low pH and high temperature from cheese whey.     

High cell density cultivation of a novel Aurantiochytrium sp. strain TC 20 in a fed-batch system using glycerol to produce feedstock for biodiesel and omega-3 oils

A recently isolated Australian Aurantiochytrium sp. strain TC 20 was investigated using small-scale (2 L) bioreactors for the potential of co-producing biodiesel and high-value omega-3 long-chain polyunsaturated fatty acids. Higher initial glucose concentration (100 g/L compared to 40 g/L) did not result in markedly different biomass (48 g/L) or fatty acid (12–14 g/L) yields by 69 h. This comparison suggests factors other than carbon source were limiting biomass production. The effect of both glucose and glycerol as carbon sources for Aurantiochytrium sp. strain TC 20 was evaluated in a fed-batch process. Both glucose and glycerol resulted in similar biomass yields (57 and 56 g/L, respectively) by 69 h. The agro-industrial waste from biodiesel production—glycerol—is a suitable carbon source for Aurantiochytrium sp. strain TC 20. Approximately half the fatty acids from Aurantiochytrium sp. strain TC 20 are suitable for development of sustainable, low emission sources of transportation fuels and bioproducts. To further improve biomass and oil production, fortification of the feed with additional nutrients (nitrogen sources, trace metals and vitamins) improved the biomass yield from 56 g/L (34 % total fatty acids) to 71 g/L (52 % total fatty acids, cell dry weight) at 69 h; these yields are to our knowledge around 70 % of the biomass yields achieved, however, in less than half of the time by other researchers using glycerol and markedly greater than achieved using other industrial wastes. The fast growth and suitable fatty acid profile of this newly isolated Aurantiochytrium sp. strain TC 20 highlights the potential of co-producing the drop-in biodiesel and high value omega-3 oils.