Challenges in enzymatic hydrolysis and fermentation of pretreated Arundo donax revealed by a comparison between SHF and SSF

The perennial herbaceous crop Arundo donax is a potential feedstock for second-generation bioethanol production. In the present work, two different process options were investigated for the conversion of two differently steam-pretreated batches of A. donax. The pretreated raw material was converted to ethanol with a xylose-consuming Saccharomyces cerevisiae strain, VTT C-10880, by applying either separate hydrolysis and fermentation (SHF) or simultaneous saccharification and fermentation (SSF). The highest overall ethanol yield and final ethanol concentration were achieved using SHF (0.27 g g^?1 and 20.6 g L^?1 compared to 0.24 g g^?1 and 19.0 g L^?1 when SSF was used). The performance of both SHF and SSF was improved by complementing the cellulolytic enzymes with hemicellulases. The higher amount of acetic acid in one of the batches was shown to strongly affect xylose consumption in the fermentation. Only half of the xylose was consumed when batch 1 (high acetic acid) was fermented, compared to that 94% of the xylose was consumed in fermentation of batch 2 (lower acetic acid). Furthermore, the high amount of xylooligomers present in the pretreated materials considerably inhibited the enzymatic hydrolysis. Both the formation of xylooligomers and acetic acid thus need to be considered in the pretreatment process in order to achieve efficient conversion of A. donax to ethanol.     

Continuous production of selenomethionine-enriched Chlorella sorokiniana biomass in a photobioreactor

This article describes the enrichment of the fresh-water green microalga Chlorella sorokiniana in selenomethionine (SeMet). The microalga was cultivated in a 2.2 L glass-vessel photobioreactor, in a culture medium supplemented with selenate (SeO₄^2?) concentrations ranging from 5 to 50 mg L^?1. Although selenate exposure lowered culture viability, C. sorokiniana grew well at all tested selenate concentrations, however cultures supplemented with 50 mg L^?1 selenate did not remain stable at steady state. A suitable selenate concentration in fresh culture medium for continuous operation was determined, which allowed stable long-term cultivation at steady state and maximal SeMet productivity. In order to do that, the effect of dilution rate on biomass productivity, viability and SeMet content of C. sorokiniana at several selenate concentrations were determined in the photobioreactor. A maximal SeMet productivity of 21 μg L^?1 day^?1 was obtained with 40 mg L^?1 selenate in the culture medium. Then a continuous cultivation process at several dilution rates was performed at 40 mg L^?1 selenate obtaining a maximum of 246 μg L^?1 day^?1 SeMet at a low dilution rate of 0.49 day^?1, calculated on total daily effluent volume. This paper describes for the first time an efficient long-term continuous cultivation of C. sorokiniana for the production of biomass enriched in the high value amino acid SeMet, at laboratory scale.     

Production of yeast chitin–glucan complex from biodiesel industry byproduct

Crude glycerol from the biodiesel industry was used as carbon source for high cell density fed-batch cultivation of Pichia pastoris aiming at producing a chitin–glucan complex (CGC). More than 100 g L^?1 biomass was obtained in less than 48 h. The yield of biomass on a glycerol basis was 0.55 g g^?1 during the batch phase and 0.63 g g^?1 during the fed-batch phase. The chitin–glucan complex was recovered from the yeast cell wall by hot alkaline extraction. CGC content in the cell wall was found to be relatively constant throughout the cultivation (18–26%) with a volumetric productivity of 1.28 g L^?1 h^?1 at the end of the fed-batch phase. The molar ratio of chitin:β-glucan in the extracted biopolymer was 16:84, close to other CGC extracted from Aspergillus biomass. The extracted polymer was characterized by Differential Scanning Calorimetry (DCS) and solid-state Nuclear Magnetic Resonance (NMR) spectroscopy and compared with commercial biopolymers, namely, crab shell chitin and/or chitosan, algal β-glucan (laminarin) and fungal chitin–glucan complex (kiOsmetine).     

Improved β-carotene production of Rhodotorula glutinis in fermented radish brine by continuous cultivation

Fermentation kinetics of growth and β-carotene production by Rhodotorula glutinis DM28 in batch and continuous cultures using fermented radish brine, a waste generated from fermented vegetable industry, as a cultivation medium were investigated. The suitable brine concentration for β-carotene production by R. glutinis DM28 was 30 g l^?1. Its growth and β-carotene production obtained by batch culture in shake flasks were 2.2 g l^?1 and 87 μg l^?1, respectively, while, in a bioreactor were 2.6 g l^?1 and 186 μg l^?1, respectively. Furthermore, its maximum growth rate and β-carotene productivity in continuous culture obtained at the dilution rate of 0.24 h^?1 were 0.3 g l^?1 h^?1 and 19 μg l^?1 h^?1, respectively, which were significantly higher than those in the batch. Therefore, improved growth rate and β-carotene productivity of R. glutinis in fermented radish brine could be accomplished by continuous cultivation.     

Poly(3-hydroxybutyrate) production by Cupriavidus necator using waste glycerol

Polyhydroxyalkanoates (PHAs) have been recognized as good substitutes for the non-biodegradable petrochemically produced polymers. However, their high (real or estimated) current production cost limits their industrial applications. This work exploits two strategies to enhance PHAs substitution potential: the increase in PHA volumetric productivity in high density cultures and the use of waste glycerol (GRP), a by-product from the biodiesel industry, as primary carbon source for cell growth and polymer synthesis. Cupriavidus necator DSM 545 was used to accumulate poly(3-hydroxybutyrate) (P(3HB)) from GRP and from commercial glycerol (PG) as control substrate. On PG, productivities between 0.6 g_PHB L^?1 h^?1 and 1.5 g_PHB L^?1 h^?1 were attained. The maximum cell DW was 82.5 g_DW L^?1, the P(3HB) content being 62%. When GRP was used, 68.8 g_DW L^?1 with a P(3HB) accumulation of 38% resulting in a final productivity of 0.84 g_PHB L^?1 h^?1 was obtained. By decreasing the biomass concentration at which accumulation was triggered, a productivity of 1.1 g_PHB L^?1 h^?1 (50% P(3HB), w/w) was attained using GRP. P(3HB) molecular weights (M_w) ranged from 7.9 × 10⁵ to 9.6 × 10⁵ Da.     

Inulin hydrolysis and citric acid production from inulin using the surface-engineered Yarrowia lipolytica displaying inulinase

The INU1 gene encoding exo-inulinase cloned from Kluyveromyces marxianus CBS 6556 was ligated into the surface display plasmid and expressed in the cells of the marine-derived yeast Yarrowia lipolytica which can produce citric acid. The expressed inulinase was immobilized on the yeast cells. The activity of the immobilized inulinase with 6 × His tag was found to be 22.6 U mg^?1 of cell dry weight after cell growth for 96 h. The optimal pH and temperature of the displayed inulinase were 4.5 and 50 °C, respectively and the inulinase was stable in the pH range of 3–8 and in the temperature range of 0–50 °C. During the inulin hydrolysis, the optimal inulin concentration was 12.0% and the optimal amount of added inulinase was 181.6 U g^?1 of inulin. Under such conditions, over 77.9% of inulin was hydrolyzed within 10 h and the hydrolysate contained main monosaccharides and disaccharides, and minor trisaccharides. During the citric acid production in the flask level, the recombinant yeast could produce 77.9 g L^?1 citric acid and 5.3 g L^?1 iso-citric acid from inulin while 68.9 g L^?1 of citric acid and 4.1 g L^?1 iso-citric acid in the fermented medium were attained within 312 h of the 2-L fermentation, respectively.     

New integrated bioprocess for the continuous production,extraction and purification of lipopeptides produced by Bacillus subtilis in membrane bioreactor

Recently, a bubbleless membrane bioreactor (BMBR) has been successfully developed for biosurfactant production by Bacillus subtilis [1]. In this study, for the first time, continuous culture were carried out for the production of surfactin in a BMBR, both with or without a coupled microfiltration membrane. Results from continuous culture showed that a significant part of biomass was immobilized onto the air/liquid membrane contactor. Immobilized biomass activity onto the air/liquid membrane contactor was monitored using a respirometric analysis. Kinetics of growth, surfactin and primary metabolites production were investigated. Planktonic biomass, immobilized biomass and surfactin production and productivity obtained in batch culture (3 L) of 1.5 days of culture were 4.5 g DW, 1.3 g DW, 1.8 g and 17.4 mg L^?1 h^?1, respectively. In continuous culture without total cell recycling (TCR), the planktonic biomass was leached, but immobilized biomass reached a steady state at an estimated 6.6 g DW. 11.5 g of surfactin was produced after 3 days of culture, this gave an average surfactin productivity of 54.7 mg L^?1 h^?1 for the continuous culture, which presented a surfactin productivity of 30 mg L^?1 h^?1 at the steady state. TCR was then investigated for the continuous production, extraction and purification of surfactin using a coupled ultrafiltration step. In continuous culture with TCR at a dilution rate of 0.1 h^?1, planktonic biomass, immobilized biomass, surfactin production and productivity reached 7.5 g DW, 5.5 g DW, 7.1 g and 41.6 mg L^?1 h^?1 respectively, after 2 days of culture. After this time, biomass and surfactin productions stopped. Increasing dilution rate to 0.2 h^?1 led to the resumption of biomass and surfactin production and these values reached 11.1 g DW, 10.5 g DW, 7.9 g and 110.1 mg L^?1 h^?1, respectively, after 3 days of culture. This study has therefore shown that with this new integrated bioprocess, it was possible to continuously extract and purify several grams of biosurfactant, with purity up to 95%.     

Influence on dithiolopyrrolone antibiotic production by organic acids in Saccharothrix algeriensis NRRL B-24137

The influence of organic acids on growth and dithiolopyrrolone antibiotic production by Saccharothrix algeriensis NRRL B-24137 was studied. The production of dithiolopyrrolones depends upon the nature and concentration of the organic acids in the culture medium. Study of the nature of organic acids showed that the most effective organic acids for thiolutin specific production were maleic, 4-hydroxybenzoic, benzentetracarboxylic, pantothenic, pivalic and pyruvic acids (which yielded almost five-fold over the starting medium) and pimelic acid (more than three-fold). 4-Bromobenzoic acid showed the best production of senecioyl-pyrrothine (59 mg g⁻¹ DCW). Tiglic acid showed the best production of tigloyl-pyrrothine (22 mg g⁻¹ DCW). The highest yield of isobutyryl-pyrrothine (7.6 mg g⁻¹ DCW) was observed in the presence of crotonic acid. Sorbic acid yielded the best production of butanoyl-pyrrothine (26 mg g⁻¹ DCW). Methacrylic, butyric, pyruvic and 4-bromobenzoic acids also exhibited the best production of butanoyl-pyrrothine (27–11-fold).Study of organic acid concentration showed that among the selected organic acids, pimelic acid yielded the highest specific production of thiolutin (91 mg g⁻¹ DCW) at 7.5 mM; and senecioyl-pyrrothine (11 mg g⁻¹ DCW), tigloyl-pyrrothine (9 mg g⁻¹ DCW) and butanoyl-pyrrothine (3.5 mg g⁻¹ DCW) at 5 mM. Pyruvic acid at 1.25 mM enhanced the production of senecioyl-pyrrothine (4.3 mg g⁻¹ DCW). The maximum production of tigloyl-pyrrothine (18.6 mg g⁻¹ DCW) was observed in the presence of tiglic acid at 2.5 mM. Maximum production of isobutyryl-pyrrothine was observed in the presence of 7.5 mM tiglic acid. In addition, methacrylic acid (at 5 mM) and butyric acid (at 2.5 mM) enhanced the production of butanoyl-pyrrothine (26 and 20 times, respectively).The above results can be employed in the optimisation of the culture medium for the production of dithiolopyrrolone in higher quantities.     

Continuous succinic acid production by Actinobacillus succinogenes in a biofilm reactor: Steady-state metabolic flux variation

Continuous anaerobic fermentations were performed in a novel external-recycle, biofilm reactor using d-glucose and CO₂ as carbon substrates. Succinic acid (SA) yields were found to be an increasing function of glucose consumption with the succinic acid to acetic acid ratio increasing from 2.4 g g⁻¹ at a glucose consumption of 10 g L⁻¹, to 5.7 g g⁻¹ at a glucose consumption of 50 g L⁻¹. The formic acid to acetic acid ratio decreased from an equimolar value (0.77 g g⁻¹) at a glucose consumption of 10 g L⁻¹ to a value close to zero at 50 g L⁻¹. The highest SA yield on glucose and highest SA titre obtained were 0.91 g g⁻¹ and 48.5 g L⁻¹ respectively. Metabolic flux analysis based on the established C₃ and C₄ metabolic pathways of Actinobacillus succinogenes revealed that the increase in the succinate to acetate ratio could not be attributed to the decrease in formic acid and that an additional source of NADH was present. The fraction of unaccounted NADH increased with glucose consumption, suggesting that additional reducing power is present in the medium or is provided by the activation of an alternative metabolic pathway.     

d- and l-lactic acid production from fresh sweet potato through simultaneous saccharification and fermentation

The aim of this study was to develop a bioprocess for l- and d-lactic acid production from raw sweet potato through simultaneous saccharification and fermentation by Lactobacillus paracasei and Lactobacillus coryniformis, respectively. The effects of enzyme and nitrogen source concentrations as well as of the ratio of raw material to medium were investigated. At dried material concentrations of 136.36–219.51 g L⁻¹, yields of 90.13–91.17% (w/w) and productivities of 3.41–3.83 g L⁻¹ h⁻¹ were obtained with lactic acid concentrations as high as 198.32 g L⁻¹ for l-lactic acid production. In addition, d-lactic acid was produced with yields of 90.11–84.92% (w/w) and productivities of 2.55–3.11 g L⁻¹ h⁻¹ with a maximum concentration of 186.40 g L⁻¹ at the same concentrations of dried material. The simple and efficient process described in this study will benefit the tuber and root-based lactic acid industries without requiring alterations in plant equipment.     

Culture parameters affecting xylitol production by Debaryomyces hansenii immobilized in alginate beads

Yeast immobilization offers operational advantages such as high cell concentration, and some drawbacks related to cell leaking and restricted mass transfer inside particles. The influence of bead size, chitosan, bead charge, volume of liquid media, and the use of corncob hydrolyzates and vinasses as culture medium were analyzed on xylitol production by Debaryomyces hansenii immobilized in alginate beads. The results showed a profuse growth of free cells, accounting 75–95% of total biomass, but electron micrographs revealed the generation of a dense biofilm with hyphal morphology at the bead surface and a very low intraparticular growth. Xylitol production was not affected by the size of particle; however chitosan had a negative effect. The use of corn cob as carbon source and twofold diluted vinasses as economic nutrients incremented xylitol concentration to 13.7 g L^?1 (Y_P/S = 0.56 g g^?1; Q_P = 0.29 g L^?1 h^?1). The best conditions corresponded to high bead charges and intermediate liquid volumes (44 g Na-alginate and 110 mL liquid medium). These results showed the feasibility of employing these cheap substrates, reflected the importance of the microaerobical conditions, and pointed to the favorable effect of cell immobilization on the metabolism of xylitol production.     

The relationship between the volatile fatty acids supply and the nitrogen retention in growing sheep nourished by total intragastric infusions

Twelve four-month old Suffolk × Small-tail-Han male sheep (live weight 21–26 kg), fitted with rumen and abomasum fistulas and nourished by total intragastric infusions, were used to study the relationship between the volatile fatty acids (VFA) supply and the nitrogen (N) retention in sheep. The animals were randomly divided into four groups and four levels of mixed VFA energy (the molar proportion of acetic acid, propionic acid and butyric acid was 65:25:10), i.e. 333, 378, 423 and 468 kJ kg^?1 W^0.75 d^?1, were infused into the rumen, as treatments I, II, III and IV, respectively. The results showed that the N retention was significantly increased (P < 0.05) with the VFA infusion level. Significant regression relationship was found between the VFA supply (x, g d^?1) and the N retention (y, mg d^?1): y = 2.75x ? 403, r² = 0.86, n = 12, P < 0.01. It was concluded that to get efficient utilization of dietary N and high N retention in sheep, it is necessary to supply enough dietary energy.     

Methanol vapor biofiltration coupled with continuous production of recombinant endochitinase Ech42 by Pichia Pastoris

Methanol biofiltration using methylotrophic microorganisms has been previously reported by various authors. In a previous study, a modified strain of Pichia pastoris was tested for the ability to produce endochitinase (Ech42) when coupled with methanol vapor biodegradation in batch tests. The next challenge was to validate the process in a continuous system. Thus, in the present study, a biofilter packed with perlite and inoculated with P. pastoris transformed with the plasmid pPIC-ech42 was used for methanol vapor biofiltration and the continuous production of recombinant endochitinase (Ech42) for 60 days. The maximum elimination capacity (EC) of methanol obtained was 1320 g m^?3 h^?1 at a loading rate of 1465 g m^?3 h^?1. The extracellular protein production rate in the leachate was 2360 μg h^?1 with a chitinase enzymatic activity of 123 U L^?1. The protein content on the biofilm samples was negligible, indicating the effectiveness of the overall process and of P. pastoris to excrete proteins. The carbon balance indicated that 81% of the consumed methanol was mineralized and 5.8% was incorporated into biomass. The results of this study and the economic balance underscore the promising application of linking methanol vapor biofiltration to the continuous production of recombinant proteins.     

Bench-scale fermentation of Trichoderma viride on wastewater sludge: Rheology,lytic enzymes and biocontrol activity

Conidiation and lytic enzyme production by Trichoderma viride at different solids concentration of pre-treated municipal wastewater sludge was examined in a 15-L fermenter. The maximum conidia concentration (5.94 × 10⁷ CFU mL⁻¹ at 96 h) was obtained at 30 g L⁻¹ suspended solids. The maximum lytic enzyme activities were achieved around 12–30 h of fermentation. Bioassay against a fungal phytopathogen, Fusarium sp. showed maximum activity in the sample drawn around 96 h of fermentation at 30 g L⁻¹ suspended solids concentration. Entomotoxicity against spruce budworm larvae showed maximum value ≈17290 SBU μL⁻¹ at 30 g L⁻¹ suspended solids concentration at the end of fermentation (96 h). Plant bioassay showed dual action of T. viride, i.e., disease prevention and growth promotion. The rheological analyses of fermentation sludges showed the pseudoplastic behaviour. In order to maintain required dissolved oxygen concentration ≥30%, the agitation and aeration requirements significantly increased at 35 g L⁻¹ compared to 30 and 25 g L⁻¹. The oxygen uptake rate and volumetric oxygen mass transfer coefficient, k_La at 35 g L⁻¹ did not increase in comparison to 30 g L⁻¹ due to rheological complexity of the broth during fermentation. Thus, the successful fermentation operation of the biocontrol fungus T. viride is a rational indication of its potential for mass-scale production for agriculture and forest sector as a biocontrol agent.     

Improvement of (R)-carbonyl reductase-mediated biosynthesis of (R)-1-phenyl-1,2-ethanediol by a novel dual-cosubstrate-coupled system for NADH recycling

An NAD(H)-dependent (R)-carbonyl reductase (RCR) from Candida parapsilosis catalyzes the asymmetric reduction of 2-hydroxyacetophenone (2-HAP) to (R)-1-phenyl-1,2-ethanediol ((R)-PED), which is a valuable chiral building block in the pharmaceutical and fine chemical industries. Biosynthesis efficiency of (R)-PED was considerably improved by a novel dual-cosubstrate-coupled system. By simultaneously employing isopropanol (10%, v v^?1) and glycerol (8%, v v^?1) as sacrificial cosubstrates, the (R)-PED product had an excellent optical purity of >99.9% and a conversion of 85.5%, which were nearly 2- and 11-fold higher than those without adding cosubstrate, respectively. Besides, the productivity was dramatically enhanced from 0.02 g L^?1 h^?1 to 5 g L^?1 h^?1, and the maximum acceptable concentration of 2-HAP was elevated to 10 g L^?1. Isopropanol was directly oxidized by RCR in the formation of NADH, while glycerol was metabolized by cellular enzymes to release NADH. Moreover, glycerol prevented cells from losing viability and alleviated the toxicity of isopropanol and acetone for cells. Interestingly, there was a cooperative interaction between isopropanol and glycerol for the improvement of biosynthesis efficiency of (R)-PED.     

Galactose-limited fed-batch cultivation of Escherichia coli for the production of lacto-N-tetraose

Lacto-N-tetraose (Gal(β1-3)GlcNAc(β1-3)Gal(β1-4)Glc) is one of the most abundant oligosaccharide structures in human milk. We recently described the synthesis of lacto-N-tetraose by a whole-cell biotransformation with recombinant Escherichia coli cells. However, only about 5% of the lactose was converted into lacto-N-tetraose by this approach. The major product obtained was the intermediate lacto-N-triose II (GlcNAc(β1-3)Gal(β1-4)Glc).In order to improve the bioconversion of lactose to lacto-N-tetraose, we have investigated the influence of the carbon source on the formation of lacto-N-tetraose and on the intracellular availability of the glycosyltransferase substrates, UDP-N-acetylglucosamine and UDP-galactose. By growth of the recombinant E. coli cells on D-galactose, the yield of lacto-N-tetraose (810.8 mg L⁻¹ culture) was 3.6-times higher compared to cultivation on D-glucose.Using fed-batch cultivation with galactose as sole energy and carbon source, a large-scale synthesis of lacto-N-tetraose was demonstrated. During the 26 h feeding phase the growth rate (μ = 0.05) was maintained by an exponential galactose feed. In total, 16 g L⁻¹ lactose were fed and resulted in final yields of 12.72 ± 0.21 g L⁻¹ lacto-N-tetraose and 13.70 ± 0.10 g L⁻¹ lacto-N-triose II. In total, 173 g of lacto-N-tetraose were produced with a space-time yield of 0.37 g L⁻¹ h⁻¹.     

Repeated fed-batch cultivation of Arthrospira (Spirulina) platensis using urea as nitrogen source

Arthrospira (Spirulina) platensis (Nordstedt) Gomont was autotrophically cultivated for biomass production in repeated fed-batch process using urea as nitrogen source, with the aim of making large-scale production easier, increasing cell productivity and then reducing the production costs. It was investigated the influence of the ratio of renewed volume to total volume (R), the urea feeding time (t_f) and the number of successive repeated fed-batch cycles on the maximum cell concentration (X_m), cell productivity (P_x), nitrogen-to-cell conversion yield (Y_x/n), maximum specific growth rate (μ_m) and protein content of dry biomass. The experimental results demonstrated that R = 0.80 and t_f = 6 d were the best cultivation conditions, being able to simultaneously ensure, throughout the three fed-batch cycles, the highest average values of three of the five responses (X_m = 2101 ± 113 mg L^?1, P_x = 219 ± 13 mg L^?1 d^?1 and Y_x/n = 10.3 ± 0.8 g g^?1).     

Production of specific-molecular-weight hyaluronan by metabolically engineered Bacillus subtilis 168

Low-molecular-weight hyaluronan (LMW-HA) has attracted much attention because of its many potential applications. Here, we efficiently produced specific LMW-HAs from sucrose in Bacillus subtilis. By coexpressing the identified committed genes (tuaD, gtaB, glmU, glmM, and glmS) and downregulating the glycolytic pathway, HA production was significantly increased from 1.01 g L⁻¹ to 3.16 g L⁻¹, with a molecular weight range of 1.40×10⁶–1.83×10⁶ Da. When leech hyaluronidase was actively expressed after N-terminal engineering (1.62×10⁶ U mL⁻¹), the production of HA was substantially increased from 5.96 g L⁻¹ to 19.38 g L⁻¹. The level of hyaluronidase was rationally regulated with a ribosome-binding site engineering strategy, allowing the production of LMW-HAs with a molecular weight range of 2.20×10³–1.42×10⁶ Da. Our results confirm that this strategy for the controllable expression of hyaluronidase, together with the optimization of the HA synthetic pathway, effectively produces specific LMW-HAs, and could also be used to produce other LMW polysaccharides.     

Fermentative production of succinic acid from straw hydrolysate by Actinobacillus succinogenes

In this work, straw hydrolysates were used to produce succinic acid by Actinobacillus succinogenes CGMCC1593 for the first time. Results indicated that both glucose and xylose in the straw hydrolysates were utilized in succinic acid production, and the hydrolysates of corn straw was better than that of rice or wheat straw in anaerobic fermentation of succinic acid. However, cell growth and succinic acid production were inhibited when the initial concentration of sugar, which was from corn straw hydrolysate (CSH), was higher than 60 g l^?1. In batch fermentation, 45.5 g l^?1 succinic acid concentration and 80.7% yield were attained after 48 h incubation with 58 g l^?1 of initial sugar from corn straw hydrolysate in a 5-l stirred bioreactor. While in fed-batch fermentation, concentration of succinic acid achieved 53.2 g l^?1 at a rate of 1.21 g l^?1 h^?1 after 44 h of fermentation. Our work suggested that corn straw could be utilized for the economical production of succinic acid by A. succinogenes.     

Production of surfactin by Bacillus pumilus UFPEDA 448 in solid-state fermentation using a medium based on okara with sugarcane bagasse as a bulking agent

We studied the production of surfactin by Bacillus pumilus UFPEDA 448 in solid-state fermentation (SSF), using a medium based on okara with the addition of sugarcane bagasse as a bulking agent. The optimum proportions of okara and sugarcane bagasse were 50% each, by mass. Due to the relatively high production of proteases during SSF, pre-hydrolysis of the okara with a protease did not improve surfactin levels. The optimum temperature for surfactin production was 37 °C, with the incubation temperature affecting the ratios of the various surfactin homologues produced. Cultivation in column bioreactors with forced aeration under optimized conditions gave a surfactin level of 809 mg L^?1 of impregnating solution, which corresponds to 3.3 g kg-dry-solids^?1. This is the highest surfactin level that has been produced to date in SSF with a non-recombinant microorganism. The peak O₂ uptake rate was 20 mmol min^?1 kg-initial-dry-solids^?1, corresponding to metabolic waste heat production rate of 182 W kg-initial-dry-solids^?1. The tensioactive properties of the surfactin were similar to those reported in the literature for surfactin produced by submerged fermentation. These results suggest that it might be feasible to use SSF to produce surfactin but at large scale special attention will need to be given to heat removal.