Co-fermentation of carbon sources by Enterobacter aerogenes ATCC 29007 to enhance the production of bioethanol

We investigated the enhancement of bioethanol production in Enterobacter aerogenes ATCC 29007 by co-fermentation of carbon sources such as glycerol, glucose, galactose, sucrose, fructose, xylose, starch, mannitol and citric acid. Biofuel production increases with increasing growth rate of microorganisms; that is why we investigated the optimal growth rate of E. aerogenes ATCC 29007, using mixtures of different carbon sources with glycerol. E. aerogenes ATCC 29007 was incubated in media containing each carbon source and glycerol; growth rate and bioethanol production improved in all cases compared to those in medium containing glycerol alone. The growth rate and bioethanol production were highest with mannitol. Fermentation was carried out at 37 °C for 18 h, pH 7, using 50 mL defined production medium in 100 mL serum bottles at 200 rpm. Bioethanol production under optimized conditions in medium containing 16 g/L mannitol and 20 g/L glycerol increased sixfold (32.10 g/L) than that containing glycerol alone (5.23 g/L) as the carbon source in anaerobic conditions. Similarly, bioethanol production using free cells in continuous co-fermentation also improved (27.28 g/L) when 90.37 % of 16 g/L mannitol and 67.15 % of 20 g/L glycerol were used. Although naturally existing or engineered microorganisms can ferment mixed sugars sequentially, the preferential utilization of glucose to non-glucose sugars often results in lower overall yield and productivity of ethanol. Here, we present new findings in E. aerogenes ATCC 29007 that can be used to improve bioethanol production by simultaneous co-fermentation of glycerol and mannitol.     

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 oxidoreduction potential shift control strategy for high purity propionic acid production by Propionibacterium freudenreichii CCTCC M207015 with glycerol as sole carbon source

The effects of oxidoreduction potential (ORP) regulation on the process of propionic acid production by Propionibacterium freudenreichii CCTCC M207015 have been investigated. Potassium ferricyanide and sodium borohydride were determined as ORP control agents through serum bottle experiment. In batch fermentation, cell growth, propionic acid and by-products distribution were changed with ORP levels in the range of 0–160 mV. Based on these analysis results, an ORP-shift control strategy was proposed: at first 156 h, ORP was controlled at 120 mV to obtain higher cell growth rate and propionic acid formation rate, and then it was shifted to 80 mV after 156 h to maintain the higher propionic acid formation rate. By applying this strategy, the optimal parameters were obtained as follows: the propionic acid concentration 45.99 g L^?1, productivity 0.192 g L^?1 h^?1, the proportion of propionic acid to total organic acids 92.26 % (w/w) and glycerol conversion efficiency 76.65 %. The mechanism of ORP regulation was discussed by the ratio of NADH/NAD⁺, ATP levels, and metabolic flux analysis. The results suggest that it is possible to redistribute energy and metabolic fluxes by the ORP-shift control strategy, and the strategy could provide a simple and efficient tool to realize high purity propionic acid production with glycerol as carbon source.     

Production of biomass, carotenoid and other lipid metabolites by several red yeast strains cultivated on waste glycerol from biofuel production – a comparative screening study

This study was focused on a comparison of growth and production properties of seven red yeast strains of the genus Rhodotorula, Sporobolomyces and Cystofilobasidium cultivated on glycerol substrate. Production of enriched yeast biomas and specific yeast metabolites (carotenoids, ergosterol, lipids) was evaluated on medium with glucose, pure technical glycerol and/or waste glycerol from biofuel production (40 g/L) and mixture of glycerol and glucose (1:3, 1:1, 3:1; C/N ratio 57 in all cultivations). All tested strains were able to utilize glycerol as the only carbon source. Production of biomass on waste glycerol was in most strains higher than in control as well as in medium with pure technical glycerol and reached 15.97–21.76 g/L. Production of carotenoids and ergosterol was better in glucose medium than in medium with glycerol only. Nevertheless, using glycerol medium with addition of glucose, higher yields of total carotenoids, beta-carotene and ergosterol were obtained than in control. The highest yields of total pigments were reached by Sporobolomyces roseus (3.60 mg/g cell dry weight (CDW); glycerol:glucose 1:3), Sporobolomyces salmonicolor (2.85 mg/g CDW; glycerol:glucose 1:3) and Rhodotorula glutinis (2.80 mg/g CDW; glycerol:glucose 3:1) In glucose medium, most tested strains except Cystofilobasidium capitatum (22.6 %) produced neutral lipids in the range of 11–15 %. Production of triacylglycerols in all strains was in 10–30 % better in glycerol medium, in which Rhodotorula aurantiaca and Sporobolomyces shibatanus also reached intracellular triacylglycerol concentrations up to 20 % of biomass. This study has shown that oleaginous red yeasts could have great potential for converting crude glycerol to valuable lipids and carotenoids in respect of efficient bioresources utilization.     

Metabolic flux analysis of Gluconacetobacter xylinus for bacterial cellulose production

Metabolic flux analysis was used to reveal the metabolic distributions in Gluconacetobacter xylinus (CGMCC no. 2955) cultured on different carbon sources. Compared with other sources, glucose, fructose, and glycerol could achieve much higher bacterial cellulose (BC) yields from G. xylinus (CGMCC no. 2955). The glycerol led to the highest BC production with a metabolic yield of 14.7 g/mol C, which was approximately 1.69-fold and 2.38-fold greater than that produced using fructose and glucose medium, respectively. The highest BC productivity from G. xylinus CGMCC 2955 was 5.97 g BC/L (dry weight) when using glycerol as the sole carbon source. Metabolic flux analysis for the central carbon metabolism revealed that about 47.96 % of glycerol was transformed into BC, while only 19.05 % of glucose and 24.78 % of fructose were transformed into BC. Instead, when glucose was used as the sole carbon source, 40.03 % of glucose was turned into the by-product gluconic acid. Compared with BC from glucose and fructose, BC from the glycerol medium showed the highest tensile strength at 83.5 MPa, with thinner fibers and lower porosity. As a main byproduct of biodiesel production, glycerol holds great potential to produce BC with superior mechanical and microstructural characteristics.     

Production of carotenoids and lipids by <Emphasis Type="Italic">Rhodococcus opacus</Emphasis> PD630 in batch and fed-batch culture

Production of carotenoids by Rhodococcus opacus PD630 is reported. A modified mineral salt medium formulated with glycerol as an inexpensive carbon source was used for the fermentation. Ammonium acetate was the nitrogen source. A dry cell mass concentration of nearly 5.4 g/L could be produced in shake flasks with a carotenoid concentration of 0.54 mg/L. In batch culture in a 5 L bioreactor, without pH control, the maximum dry biomass concentration was ~30 % lower than in shake flasks and the carotenoids concentration was 0.09 mg/L. Both the biomass concentration and the carotenoids concentration could be raised using a fed-batch operation with a feed mixture of ammonium acetate and acetic acid. With this strategy, the final biomass concentration was 8.2 g/L and the carotenoids concentration was 0.20 mg/L in a 10-day fermentation. A control of pH proved to be unnecessary for maximizing the production of carotenoids in this fermentation.     

Biosynthesis of 1,3-propanediol from recombinant E. coli by optimization process using pure and crude glycerol as a sole carbon source under two-phase fermentation system

The environmental and nutritional condition for 1,3-propanediol (1,3-PD) production by the novel recombinant E. coli BP41Y3 expressing fusion protein were first optimized using conventional approach. The optimum environmental conditions were: initial pH at 8.0, incubation at 37 °C without shaking and agitation. Among ten nutrient variables, fumarate, (NH₄)₂HPO₄ and peptone were selected to study on their interaction effect using the response surface methodology. The optimum medium contained modified Riesenberg medium (containing pure glycerol as a sole carbon source) supplemented with 63.65 mM fumarate, 3.80 g/L (NH₄)₂HPO₄ and 1.12 g/L peptone, giving the maximum 1,3-PD production of 2.43 g/L. This was 3.5-fold higher than the original medium (0.7 g/L). Two-phase cultivation system was conducted and the effect of pH control (at 6.5, 7.0 and 8.0) was investigated under anaerobic condition by comparing with the no pH control condition. The cultivation system without pH control (initial pH of 8.0) gave the maximum values of 1.65 g/L 1,3-PD, the 1,3-PD production rate of 0.13 g/L h and the yield of 0.31 mol 1,3-PD/mol crude glycerol. Hence, using crude glycerol as a sole carbon source resulted in 32 % lower 1,3-PD production from this recombinant strain that may be due to the presence of various impurities in the crude glycerol of biodiesel plant. In addition, succinic acid was found to be a major product during fermentation by giving the maximum concentration of 11.92 g/L after 24 h anaerobic cultivation.     

Improved n-butanol production by a non-acetone producing Clostridium pasteurianum DSMZ 525 in mixed substrate fermentation

The kinetics of growth, acid and solvent production in batch culture of Clostridium pasteurianum DSMZ 525 were examined in mixed or mono-substrate fermentations. In pH-uncontrolled batch cultures, the addition of butyric acid or glucose significantly enhanced n-butanol production and the ratio of butanol/1,3-propanediol. In pH-controlled batch culture at pH?=?6, butyric acid addition had a negative effect on growth and did not lead to a higher n-butanol productivity. On the other hand, mixed substrate fermentation using glucose and glycerol enhanced the growth and acid production significantly. Glucose limitation in the mixed substrate fermentation led to the reduction or inhibition of the glycerol consumption by the growing bacteria. Therefore, for the optimal growth and n-butanol production by C. pasteurianum, a limitation of either substrate should be avoided. Under optimized batch conditions, n-butanol concentration and maximum productivity achieved were 21 g/L, and 0.96 g/L?×?h, respectively. In comparison, mixed substrate fermentation using biomass hydrolysate and glycerol gave a n-butanol concentration of 17 g/L with a maximum productivity of 1.1 g/L?×?h. In terms of productivity and final n-butanol concentration, the results demonstrated that C. pasteurianum DSMZ 525 is well suitable for n-butanol production from mixed substrates of biomass hydrolysate and glycerol and represents an alternative promising production strain.     

Enhancing Lipid Production from Crude Glycerol by Newly Isolated Oleaginous Yeasts: Strain Selection, Process Optimization, and Fed-Batch Strategy

High lipid-accumulating yeast Trichosporonoides spathulata was newly isolated using crude glycerol as a sole carbon source. After process optimization in a 5-L bioreactor equipped with pH control and aeration system, T. spathulata produced biomass of 11.3 g/L and lipid of 5.01 g/L with a lipid content of 44.3 % using 10 % (w/v) of crude glycerol supplemented only with 0.5 % (w/v) of ammonium sulfate. A one-stage fed-batch feeding with crude glycerol and ammonium sulfate enhanced biomass and lipid production up to 17.3 and 7.25 g/L, respectively, with a lipid content of 41.9 %, while a two-stage fed-batch feeding with only crude glycerol in the second stage led to a lower biomass of 13.8 g/L but a higher lipid production of 7.78 g/L and a higher lipid content of 56.4 %. The fatty acid composition of produced lipid that is similar to plant oil indicates the high potential use of T. spathulata lipid as biodiesel feedstocks.     

Enhanced cellulase production by <Emphasis Type="Italic">Trichoderma harzianum</Emphasis> by cultivation on glycerol followed by induction on cellulosic substrates

The use of glycerol obtained as an intermediate of the biodiesel manufacturing process as carbon source for microbial growth is a potential alternative strategy for the production of enzymes and other high-value bioproducts. This work evaluates the production of cellulase enzymes using glycerol for high cell density growth of Trichoderma harzianum followed by induction with a cellulosic material. Firstly, the influence of the carbon source used in the pre-culture step was investigated in terms of total protein secretion and fungal morphology. Enzymatic productivity was then determined for cultivation strategies using different types and concentrations of carbon source, as well as different feeding procedures (batch and fed-batch). The best strategy for cellulase production was then further studied on a larger scale using a stirred tank bioreactor. The proposed strategy for cellulase production, using glycerol to achieve high cell density growth followed by induction with pretreated sugarcane bagasse, achieved enzymatic activities up to 2.27 ± 0.37 FPU/mL, 106.40 ± 8.87 IU/mL, and 9.04 ± 0.39 IU/mL of cellulase, xylanase, and β-glucosidase, respectively. These values were 2 times higher when compared to the control experiments using glucose instead of glycerol. This novel strategy proved to be a promising approach for improving cellulolytic enzymes production, and could potentially contribute to adding value to biomass within the biofuels sector.     

Production of 2,3-Butanediol from Sucrose by a <Emphasis Type="Italic">Klebsiella</Emphasis> Species

Chemical 2,3-butanediol is an important platform compound possessing diverse industrial applications. So far, it is mainly produced by using petrochemical feedstock which is associated with high cost and adverse environmental impacts. Hence, finding alternative routes (e.g., via fermentation using renewable carbon sources) to produce 2,3-butanediol are urgently needed. In this study, we report a wild-type Klebsiella sp. strain XRM21, which is capable of producing 2,3-butanediol from a wide variety of carbon sources including glucose, sucrose, xylose, and glycerol. Among them, fermentation of sucrose leads to the highest production of 2,3-butanediol. To maximize the production of 2,3-butanediol, fermentation conditions were first optimized for strain XMR21 by using response surface methodology (RSM) in batch reactors. Subsequently, a fed-batch fermentation strategy was designed based on the optimized parameters, where 91.2 g/L of 2,3-butanediol could be produced from substrate sucrose dosing in 100 g/L for three times. Moreover, random mutagenesis of stain XMR21 resulted in a highly productive mutant strain, capable of producing 119.4 and 22.5 g/L of 2,3-butanediol and ethanol under optimized fed-batch fermentation process within 65 h with a total productivity of 2.18 g/L/h, which is comparable to the reported highest 2,3-butanediol concentration produced by previous strains. This study provides a potential strategy to produce industrially important 2,3-butanediol from low-cost sucrose.     

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.     

Batch and fed-batch growth of Pichia pastoris under increased air pressure

Pichia pastoris CBS 2612 behavior under air pressures of 1, 3 and 5 bar in culture media of glycerol (pure and crude) and methanol was studied. Generally, the increase in oxygen transfer rate due to the increase of total pressure improved cellular growth for all carbon sources and for batch and fed-batch processes with different feeding rate strategies. In batch cultures, 1.4-, 1.2-, and 1.5-fold improvement in biomass production was obtained with the increase of air pressure up to 5 bar, using methanol, pure glycerol, and crude glycerol, respectively. The increase of air pressure to 5 bar using exponential feeding rate led to 1.4-fold improvement in biomass yield per glycerol mass consumed, for crude and pure glycerol. The current low cost of crude glycerol from the biodiesel production together with the present results shows the possibility of improving cell mass production of P. pastoris using increased air pressure.     

Production of 1,3-propanediol by <Emphasis Type="Italic">Clostridium butyricum</Emphasis> growing on biodiesel-derived crude glycerol through a non-sterilized fermentation process

The aim of the present study was to investigate the production of 1,3-propanediol (PDO) under non-sterile fermentation conditions by employing the strain Clostridium butyricum VPI 1718. A series of batch cultures were performed by utilizing biodiesel-derived crude glycerol feedstocks of different origins as the sole carbon source, in various initial concentrations. The strain presented similarities in terms of PDO production when cultivated on crude glycerol of various origins, with final concentrations ranging between 11.1 and 11.5 g/L. Moreover, PDO fermentation was successfully concluded regardless of the initial crude glycerol concentration imposed (from 20 to 80 g/L), accompanied by sufficient PDO production yields (0.52–0.55 g per gram of glycerol consumed). During fed-batch operation under non-sterile culture conditions, 67.9 g/L of PDO were finally produced, with a yield of 0.55 g/g. Additionally, the sustainability of the bioprocess during a continuous operation was tested; indeed, the system was able to run at steady state for 16 days, during which PDO effluent level was 13.9 g/L. Furthermore, possible existence of a microbial community inside the chemostat was evaluated by operating a polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE) analysis, and DGGE results revealed the presence of only one band corresponding to that of C. butyricum VPI 1718. Finally, non-sterile continuous cultures were carried out at different dilution rates (D), with inlet glycerol concentration at 80 g/L. Maximum PDO production was achieved at low D values (0.02 h⁻¹) corresponding to 30.1 g/L, while the elaboration of kinetic data from continuous cultures revealed the stability of the bioprocess proposed, with global PDO production yield corresponding to 0.52 g/g.     

Hydrogen production by immobilized Chlorella vulgaris: optimizing pH, carbon source and light

The effects of light, pH and organic carbon sources were investigated on hydrogen production by algae. An optical fiber was examined as an internal light source. The optical fiber rendered prolonged lag time and total time of hydrogen production. The optimal pH to produce hydrogen for Chlorella sp. was 8.0. Glucose, fructose, sucrose and malt extract were compared as organic carbon sources. The optimal dose of each carbon source was 5 g/L for maximum hydrogen yield. Sucrose produced the largest hydrogen volume (1,315 ml/L), while the highest production rate (24 ml/L/h) was observed in the presence of fructose.     

Bioconversion of glycerol to 1,3-propanediol in thin stillage-based media by engineered Lactobacillus panis PM1

Thin stillage (TS) is a waste residue that remains after bioethanol production, and its disposal reflects the high costs of bioethanol production. Thus, the development of cost-effective ways to process TS is a pending issue in bioethanol plants. The aim of this study was to evaluate the utilization of TS for the production of the valuable chemical, 1,3-propanediol (1,3-PDO), by Lactobacillus panis PM1. Different fermentation parameters, including temperature, pH and strains [wild-type and a recombinant strain expressing a NADPH-dependent aldehyde reductase (YqhD) gene] were tested in batch and fed-batch cultivations. The highest 1,3-PDO concentration (12.85 g/L) and yield (0.84 g/g) were achieved by batch fermentation at pH-4.5/30 °C by the YqhD recombinant strain. Furthermore, pH-controlled batch fermentation reduced the total fermentation period, resulting in the maximal 1,3-PDO concentration of 16.23 g/L and yield of 0.72 g/g in TS without an expensive nutrient or nitrogen (e.g., yeast extract, beef extract, and peptone) supplementation. The addition of two trace elements, Mg²⁺ and Mn²⁺, in TS increased 1,3-PDO yield (0.74 g/g) without 3-hydroxypropionaldehyde production, the only intermediate of 1,3-PDO biosynthetic pathway in L. panis PM1. Our results suggest that L. panis PM1 can offer a cost-effective process that utilizes the TS to produce a value-added chemical, 1,3-PDO.     

Pullulan production and physiological characteristics of Aureobasidium pullulans under acid stress

In this study, batch processes of pullulan production by Aureobasidium pullulans CCTCC M 2012259 under different pH environments were evaluated. The pH of the medium decreased quickly to an acid stress condition under batch fermentation without pH control. A higher pullulan production was always obtained with a lower biomass under a given glucose concentration with constant pH control, and vice versa. Based on the nonlinear regression analysis of the results obtained from diverse pH control modes, a constant controlled pH of 3.8 was predicted as an optimum pH for efficient pullulan production using a one-element cubic equation. A maximum pullulan concentration of 26.8 g/L and a minimum biomass of 8.1 g/L were achieved under the optimal pH of 3.8, which were in good agreement with the results predicted by the mathematical model. Further information on the physiological characteristics of A. pullulans CCTCC M 2012259 such as intracellular pH, NADH/NAD⁺, ATP/ADP, and glutathione generation under moderate or severe acidic conditions were investigated, and the results presented more evidence on why pullulan biosynthesized with high efficiency under moderate acid stress (e.g., pH 3.8), which would also help us to better understand the response of the cells to acid stress.     

Mechanistic investigation of ultrasonic enhancement of glycerol bioconversion by immobilized Clostridium pasteurianum on silica support

Glycerol, the principal byproduct of biodiesel production, can be a valuable carbon source for bioconversion into diverse class of compounds. This article attempts to investigate the mechanistic aspects of ultrasound mediated bioconversion of glycerol to ethanol and 1,3‐propanediol (1,3‐PDO) by immobilized Clostridium pasteurianum cells on silica support. Our approach is of coupling experimental results with simulations of cavitation bubble dynamics and enzyme kinetics. In addition, the statistical analysis (ANOVA) of experimental results was also done. The glycerol uptake by cells was not affected by either immobilization or with ultrasonication. Nonetheless, both immobilization and ultrasonication were found to enhance glycerol consumption. The enhancement effect of ultrasound on glycerol consumption was most marked (175%) at the highest glycerol concentration of 25 g/L (271.7 mM). The highest glycerol consumption (32.4 mM) was seen for 10 g/L (108.7 mM) initial glycerol concentration. The immobilization of cells shifted the metabolic pathway almost completely towards 1,3‐PDO. No formation of ethanol was seen with mechanical shaking, while traces of ethanol were detected with ultrasonication. On the basis of analysis of enzyme kinetics parameters, we attribute these results to increased substrate‐enzyme affinity and decreased substrate inhibition for 1,3‐PDO dehydrogenase in presence of ultrasound that resulted in preferential conversion of glycerol into 1,3‐PDO. Biotechnol. Bioeng. 2013; 110: 1637–1645. © 2013 Wiley Periodicals, Inc.     

High-level production of Fc-fused kringle domain in Pichia pastoris

Recently, as a new non-immunoglobulin-based protein scaffold, a human kringle domain was successfully engineered toward biologically functional agonists and antagonists. In this study, the fed-batch cultivation conditions were optimized for enhanced production of an Fc-fused kringle domain (KD548-Fc) in Pichia pastoris. Fed-batch cultivations were performed in 5-l laboratory-scale bioreactors, and in order to find the optimal conditions for high-level production of KD548-Fc, several parameters including the initial carbon source (glycerol) concentration, temperature, and pH were investigated. When cells were cultivated at pH 4.0 and 25 °C with 9.5 % glycerol in the initial medium, the highest production yield (635 mg/l) was achieved with high productivity (7.2 mg/l/h). Furthermore, functional KD548-Fc was successfully purified from the culture broth using a simple purification procedure with high purity and recovery yield.     

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.