Glycerol production by Candida krusei employing NaCl as an osmoregulator in batch and continuous fermentations

Addition of 40 g NaCl l^–1 to a chemically defined medium containing 140 g glucose l^–1 in shake-flask culture improved glycerol production by Candida krusei from 16.5 g l^–1 to 47.7 g l^–1. With 40 g NaCl l^–1 at a dilution rate of 0.065 h^–1, glycerol concentration, glycerol yield (based on glucose consumed), and productivity in a four-stage cascade bioreactor were higher by 240%, 27% and 28%, respectively, than in a single-stage continuous culture system.     

Production of cellulases in batch culture using a mutant strain of Trichoderma reesei growing on soluble carbon source

Trichoderma reesei Rut-C30 is a highly derepressed mutant which synthesised active cellulases in culture media containing glucose and lactose as the only carbon sources. The maximum biomass, filter paper and specific filter paper activities for cell growth on 20 g glucose l^–1 were 20 g dry cell wt l^–1, 1.9 FPU ml^–1 and 4.8 FPU mg^–1 protein respectively, while on 40 g glucose l^–1 were 25 g dry cell wt l^–1, 4.5 FPU ml^–1 and 6.2 FPU mg^–1 protein, respectively. This strain had a higher specific filter paper activity (6.2 FPU mg^–1 protein) than was produced by other T. reesei mutants (3.6 FPU mg^–1 protein).     

Evaluation of the potential of Aspergillus niger species for the bioconversion of L-phenylalanine into 2-phenylethanol

Aspergillus niger was explored, for the first time, for the production of 2-phenylethanol (a rose-like aroma) using L-phenylalanine as precursor. Among the strains screened, A. niger CMICC 298302 was shown to produce, in a culture medium containing 6 g L-phenylalanine l^–1 and 60 g glucose l^–1, 1375 mg 2-phenylethanol l^–1 with a productivity of 153 mg l^–1 day^–1 and a molar yield of 74%. 2-Phenylethanol concentrations of 1 to 2 g l^–1 led to a two-fold and ten-fold decrease, respectively, in the mycelial radial growth rate. However, 2-phenylethanol was synthesized as the sole aromatic product and accumulated in the culture broth.     

Poly(3-hydroxybutyrate) synthesis in fed-batch culture of Ralstonia eutropha with phosphate limitation under different glucose concentrations

Poly(3-hydroxybutyrate) (PHB) was produced by fed-batch cultures of Ralstonia eutropha with phosphate limitation under different glucose concentrations. When glucose was kept at 2.5 g l^–1, cell growth and PHB synthesis were limited due to the shortage of carbon source but a higher PHB content occurred in the cell-growth stage. This shows that a low glucose concentration is favorable for PHB accumulation in R. eutropha. PHB obtained with glucose at 9 g l^–1 is 1.6 times that obtained with 40 g l^–1. When glucose was in the range of 9 to 40 g l^–1, PHB concentration and productivity decreased significantly with the increase of glucose concentration. The highest PHB productivity was obtained with glucose at 9 g l^–1.     

Biological conversion of wood hydrolysate to succinic acid by Anaerobiospirillum succiniciproducens

Anaerobiospirillum succiniciproducens grew on a minimal salts medium containing wood hydrolysate (equivalent to 27 g glucose l^–1) and, when supplemented with 10 g corn steep liquor l^–1 as a complex nitrogen source, succinic acid at 24 g l^–1 was obtained (yield = 88% w/w glucose). This may therefore be an economical method to produce succinic acid.     

Glucose repression of xylitol production in Candida tropicalis mixed-sugar fermentations

Glucose repressed xylose utilization inCandida tropicalis pre-grown on xylose until glucose reached approximately 0–5 g l^–1. In fermentations consisting of xylose (93 g l^–1) and glucose (47 g l^–1), xylitol was produced with a yield of 0.65 g g^–1 and a specific rate of 0.09 g g^–1 h^–1, and high concentrations of ethanol were also produced (25 g l^–1). If the initial glucose was decreased to 8 g l^–1, the xylitol yield (0.79 g g^–1) and specific rate (0.24 g g^–1 h^–1) increased with little ethanol formation (<5 g l^–1). To minimize glucose repression, batch fermentations were performed using an aerobic, glucose growth phase followed by xylitol production. Xylitol was produced under O₂ limited and anaerobic conditions, but the specific production rate was higher under O₂ limited conditions (0.1–0.4 vs. 0.03 g g^–1 h^–1). On-line analysis of the respiratory quotient defined the time of xylose reductase induction.     

Selective production of bikaverin in a fluidized bioreactor with immobilized Gibberella fujikuroi

The best culture medium composition for the production of bikaverin by Gibberella fujikuroi in shake-flasks, i.e. 100 g glucose l^–1; 1 g NH₄Cl l^–1; 2 g rice flour l^–1; 5 g KH₂PO₄ l^–1 and 2.5 g MgSO₄ l^–1, was obtained through a fractional factorial design and then scaled-up to a fluidized bioreactor. The effects of carbon and nitrogen concentrations, inoculum size, aeration, flow rate and bead sizes on batch bikaverin production using immobilized G. fujikuroi in a fluidized bioreactor were determined by an orthogonal experimental design. Concentrations of up to 6.83 g bikaverin l^–1 were obtained when the medium contained 100 g glucose l^–1 and 1 g NH₄Cl l^–1 with an inoculum ratio of 10% v/v, an aeration rate of 3 volumes of air per volume of medium min^–1, and a bead size of 3 mm. Based on dry weight, the bikaverin production was 30–100 times larger than found in submerged culture and approximately three times larger than reported for solid substrate fermentation.     

Fed-batch fermentation of Lactobacillus lactis for hyper-production of l-lactic acid

A fed-batch fermentation of Lactobacillus lactis to produce l-lactic acid was developed in which the residual glucose concentration in the culture was used to control a continuous feeding strategy. Up to 210 g l-lactic acid l^–1 (97% yield) was obtained. The maximal dry cell was 2.7 g l^–1 and the average l-lactic acid productivity was 2.2 g l^–1 h^–1.     

Production of mannitol by a novel strain of Candida magnoliae

A novel microorganism was isolated which is able to produce mannitol when grown in the presence of fructose and glucose as carbon sources. In flask culture in a medium containing 150 g fructose l^–1, it yielded 67 g mannitol l^–1 after 168 h. In fed-batch culture with 3–12% (w/v) fructose, production reached a maximum of 209 g mannitol l^–1 after 200 h, corresponding to an 83% yield and a 1.03 g l^–1 h^–1 productivity. The isolated strain was identified as Candida magnoliae based on identical sequences in the D1/D2 domain of its 26S rDNA and a similar carbon source utilization pattern with C. magnoliae reference strains.     

Impact of carbon and nitrogen nutrition on the quality, yield and composition of blastospores of the bioinsecticidal fungus Paecilomyces fumosoroseus

The impact of growing cultures of Paecilomyces fumosoroseus in liquid media containing four combinations of glucose and casamino acids (8 g l^–1 or 80 g l^–1 glucose, 1.32 g l^–1 or 13.2 g l^–1 casamino acids) was evaluated, based on blastospore production, germination rate, viability after freeze-drying and short-term storage stability. When blastospores were produced using a high casamino acid concentration, blastospore yields and germination rates were significantly higher (13.2–18.5×10⁷ blastospores ml^–1, 50–60% germination after 4 h), compared to cultures grown in media containing lower casamino acid concentrations (0.4–2.3×10⁷ blastospores ml^–1, 10–20% germination after 4 h). Chemical analyses of blastospore composition showed that accelerated blastospore germination may be related to increased proteinaceous reserves rather than to glycogen or lipid accumulation. Tolerance to freeze-drying by blastospores suspended in spent medium was enhanced by a high initial casamino acid concentration in the culture medium (75% survival) and by the residual glucose concentrations in the spent medium. Under the conditions of this study, the storage stability of blastospores of P. fumosoroseus was unaffected by the nutritional condition in which they were produced.     

Transformation of arachidonic acid to 19-hydroxy- and 20-hydroxy-eicosatetraenoic acids using Candida bombicola

Candida bombicola (ATCC 22214) and C. apicola (ATCC 96134), grown on glucose (100 g l^–1) and arachidonic acid (5Z, 8Z, 11Z, 14Z-eicosatetraenoic acid; AA), 1.25 g l^–1, synthesized sophorolipid up to 0.93 g l^–1. Acid hydrolysis of sophorolipid yielded 19-hydroxy-5Z, 8Z, 11Z, 14Z-eicosatetraenoic acid (19-HETE) and 20-hydroxy-5Z, 8Z, 11Z, 14Z-eicosatetraenoic acid (20-HETE) which were identified by TLC and GC-MS; the ratio of synthesis was 73:27, respectively. Conversion of AA by immobilized Candida bombicola, suspended in beads of 2% (w/v) calcium alginate for 96 h, gave an 83% conversion of 1 g AA l^–1 to 19- and 20-HETE. There was no significant loss in the efficiency of the immobilized cells after ten uses.     

Characteristics of mixotrophic growth of Synechocystis sp. in an enclosed photobioreactor

Synechocystis sp. PCC 6803 was grown in a 2.5 l enclosed photobioreactor on medium with or without glucose. The incident light intensities ranged from 1.5 klux to 7 klux. The highest average specific growth rates of mixotrophic culture and photoautotrophic culture were, respectively, 1.3 h^–1 at a light intensity of 7 klux on 3.2 g l^–1 glucose and 0.3 h^–1 at both light intensities of 5 klux and 7 klux. The highest cell density 2.5 g l ^–1 was obtained at both of light intensities 5 klux and 7 klux on 3.2 g glucose l^–1. Glucose consumption decreased with decreasing light intensity. The energy yields of mixotrophic cultures were 4 to 6 times higher than that of photoautotrophic cultures. Light favored mixotrophic growth of Synechocystis sp. PCC 6803, especially at higher light intensities (5–7 klux).     

Fungal biotransformation of p-coumaric acid into caffeic acid by Pycnoporus cinnabarinus: an alternative for producing a strong natural antioxidant

Fungal biotransformation of p-coumaric acid into caffeic acid, potentially a strong antioxidant, was evidenced in Pycnoporus cinnabarinus cultures grown with high feeding of p-coumaric acid. Preliminary experiments showed no toxicity of both p-coumaric and caffeic acids at concentrations ranging from 0 to 500 mg l^–1. Feeding 450 mg p-coumaric acid l^–1 into P. cinnabarinus cultures grown on 20 g l^–1 glucose medium resulted in the production of 257 mg caffeic acid l^–1with a molar yield of 21%.     

L-Sorbose production in a continuous fermenter with and without cell recycle

The kinetics of continuous l-sorbose fermentation using Acetobacter suboxydans with and without cell recycle (100%) were investigated at dilution rates (D) of 0.05, 0.10, 0.15 and 0.3 h^–1. The biomass and sorbose concentrations for continuous fermentation without recycle increased as the dilution rate was increased from 0.05 to 0.10 h^–1. A maximum biomass concentration of 8.44 g l^–1 and sorbose concentration of 176.90 g l^–1 were obtained at D=0.10 h^–1. The specific rate of sorbose production and volumetric sorbose productivity at this dilution rate were 2.09 g g^–1 h^–1 and 17.69 g l^–1 h^–1. However, on further increasing the dilution rate to 0.3 h^–1, both biomass and sorbose concentrations decreased to 2.93 and 73.20 g l^–1 respectively, mainly due to washout of the reactor contents. However, the specific rate of sorbose formation and volumetric sorbose productivity at this dilution rate increased to 7.49 g g^–1 h^–1 and 21.96 g l^–1 h^–1 respectively. Continuous fermentation with 100% cell recycle served to further enhance the concentration of biomass and sorbose to 28.27 and 184.32 g l^–1 respectively (in the reactor at a dilution rate of 0.05 h^–1). Even though, there was a decline in the biomass and sorbose concentrations to 6.8 and 83.40 g l^–1 at a dilution rate of 0.3 h^–1, the specific rates of sorbose formation and volumetric sorbose productivity increased to 3.67 g g^–1h^–1 and 25.02 g l^–1 h^–1.     

Culture conditions of tannase production by Lactobacillus plantarum

Lactobacillus plantarum produced an extracellular tannase after 24 h growth on minimal medium of amino acids containing 2 g tannic acid l^–1. Enzyme production (6 U ml^–1) was optimal at 37 °C and pH 6 with 2 g glucose l^–1 and 7 g tannic acid l^–1 in absence of O₂.     

Enhanced shear protection and increased production of an anti-tumor polysaccharide by Agaricus blazei in xanthan-supplemented cultures

Xanthan supplementation provided shear protection and stimulated polysaccharide production by Agaricus blazei. In xanthan-free cultures, the optimal cell yield, 0.63 g biomass g^–1 glucose, and product yield, 0.19 g polysaccharide g^–1 glucose, were, respectively, when the critical impeller tip speed was 50.3 cm s^–1 and 100.5 cm s^–1. Furthermore, the critical impeller tip speed of cell yield shifted from 50.3 cm s^–1 to 100.5 cm s^–1 with the supplementation of 1 g xanthan l^–1. Maximum specific product yield, namely 0.74 g polysaccharide g^–1 biomass, was achieved with inlet air supply of 3% O₂ and impeller tip speed of 100.5 cm s^–1.     

Heterotrophic glucose uptake and respiration in Lake Kinneret

The turnover times of glucose, averaged for 0–10 m in the upper waters of Lake Kinneret and measured by the addition of single or multiple concentrations of substrate, ranged from 23 to 188 hours and 1 to 87 hours respectively. Potential uptake rates (estimated as V_max) ranged from 0.095 to 1.94 µg glucose l^–1h^–1, while measured uptake rates varied from 0.09 to 1.1 µg glucose l^–1h^–1. Concentrations of dissolved carbohydrates and glucose averaged 0.71 mg glucose equivalents l^–1 and 39 µg glucose l^–1 respectively. No evident relationships between glucose cycling and any fractions of dissolved organic matter, phytoplankton biomass or primary productivity were found. Turnover times were generally most rapid immediately after the decline of the spring Peridinium bloom. The respiration percentage of incorporated glucose ranged from 25% to 61% with highest values during the summer months. Respiration may be influenced by the nature of the indigenous bacterial population as well as by temperature. Daily heterotrophic glucose carbon uptake was about 9% of the photosynthetic incorporation and could provide a bacterial yield of about 7 × 10⁴ ml^–1d^–1.     

2-Propanol degradation by Sulfolobus solfataricus

Sulfolobus solfataricus used 2-propanol and 2-propanone (acetone) when grown in static cultures at 78 °C with or without glucose at 10 g l^–1. The presence of 3.92 g 2-propanol l^–1 in both cases inhibited growth. However, acetone accumulation following 2-propanol depletion suggested that 2-propanol was co-metabolized via the acetone metabolic pathway. Glucose at 10 g l^–1 increased 2-propanol and acetone utilization from 0.93 g l^–1 to 1.77 g l^–1 and from 0.11 g l^–1 to 1.62 g l^–1, respectively. Without glucose, immobilized S. solfataricus cells increased the 2-propanol removal rate to 0.035 g l^–1 h^–1, compared to 0.0012 g l^–1 h^–1 by its suspended counterpart. The results suggest the establishment of an immobilized reactor configuration is preferential for the treatment of high temperature solvent waste streams by this acidothermophilic Crenarchaeon.     

Poly-3-hydroxybutyrate (P3HB) production by bacteria from xylose,glucose and sugarcane bagasse hydrolysate

Fifty-five bacterial strains isolated from soil were screened for efficient poly-3-hydroxybutyrate (P3HB) biosynthesis from xylose. Three strains were also evaluated for the utilization of bagasse hydrolysate after different detoxification steps. The results showed that activated charcoal treatment is pivotal to the production of a hydrolysate easy to assimilate. Burkholderia cepacia IPT 048 and B. sacchari IPT 101 were selected for bioreactor studies, in which higher polymer contents and yields from the carbon source were observed with bagasse hydrolysate, compared with the use of analytical grade carbon sources. Polymer contents and yields, respectively, reached 62% and 0.39 g g^–1 with strain IPT 101 and 53% and 0.29 g g^–1 with strain IPT 048. A higher polymer content and yield from the carbon source was observed under P limitation, compared with N limitation, for strain IPT 101. IPT 048 showed similar performances in the presence of either growth-limiting nutrient. In high-cell-density cultures using xylose plus glucose under P limitation, both strains reached about 60 g l^–1 dry biomass, containing 60% P3HB. Polymer productivity and yield from this carbon source reached 0.47 g l^–1 h^–1 and 0.22 g g^–1, respectively.     

Production of a hypoglycemic, extracellular polysaccharide from the submerged culture of the mushroom, Phellinus linteus

Mycelial growth and extracellular polysaccharide production of Phellinus linteus were optimal at pH 5 and 25 °C. Maximum biomass production (14.2 g l^–1) was after 15 d of cultivation, whereas, extracellular polysaccharide was maximal (3.5 g l^–1) after 21 d. The hypoglycemic effect of the polysaccharide, investigated in streptozotocin-induced diabetic rats, decreased plasma glucose, total cholesterol and triacylglycerol concentrations by 49%, 32%, and 28%, respectively, and aspartate aminotransferase activity by 20%. The results indicate the potential of this polysaccharide to prevent hyperglycemia in diabetic patients.