Synthesis of silver nanoparticles using a biosurfactant produced in low-cost medium as stabilizing agent

BackgroundA biosurfactant produced by Pseudomonas aeruginosa cultivated in a low-cost medium formulated with 2.5% vegetable oil refinery residue and 2.5% corn steep liquor and distilled water was employed to stabilize silver nanoparticles in the liquid phase. The particles were initially synthesized using NaBH₄ as reducing agent in biosurfactant reverse micelles and were extracted from the micellar solution to disperse in heptane.ResultsA silver particle size in the range of 1.13 nm was observed. The UV–vis absorption spectra proposed that silver nanoparticles could be formed in the reverse micelles and relatively stabilized for at least 3 months without passivator addition. The Transmission Electron Microscope (TEM) shows that the silver nanoparticles are of spherical form and relatively uniform.ConclusionsThis process provided a simpler route for nanoparticle synthesis compared to existing systems using whole organisms or partially purified biological extracts, showing that the low-cost biosurfactant can be used for nanoparticle synthesis as a non-toxic and biodegradable stabilizing agent.     

Kinetic study and modeling of biosurfactant production using Bacillus sp.

BackgroundSurfactants are one of the most important raw materials used in various industrial fields as emulsifiers, corrosion inhibitors, foaming agents, detergent products, and so on. However, commercial surfactant production is costly, and its demand is steadily increasing. This study aimed to evaluate the performance of typical strains of Bacillus sp. to produce biosurfactants through fermentation. It also included the investigation of the effect of initial glucose concentration and the carbon to nitrogen ratio.ResultsThe biosurfactant yield was in the range of 1–2.46 g/L at initial glucose concentrations of 10–70 g/L. The optimum fermentation condition was achieved at a carbon to nitrogen ratio of 12.4, with a decrease in surface tension of up to 27 mN/m.ConclusionsFor further development and industrial applications, the modified Gompertz equation is proposed to predict the cell mass and biosurfactant production as a goodness of fit was obtained with this model. The modified Gompertz equation was also extended to enable the excellent prediction of the surface tension.     

Bioconversion of mixed free fatty acids to poly-3-hydroxyalkanoates by Pseudomonas putida BET001 and modeling of its fermentation in shake flasks

BackgroundThe paper reports on the utilization of palm kernel oil (PKO) as a low cost renewable substrate for medium-chain-length poly-3-hydroxyalkanoates (mcl-PHA) production by Pseudomonas putida BET001. Investigation on the effects of selected key variables on growth, mixed free fatty acids consumption and mcl-PHA production by the bacterial culture in the shaken flask system were carried out along with its kinetic modeling.ResultsThe biomass production, fatty acids consumption and mcl-PHA production were found favorable when the strain was cultured in mineral medium at pH 6–7, 28°C, aeration surface-to-volume ratio of 0.4 × 10⁶ m^- 1, 250 rpm agitation rate for 48 h. Mcl-PHA production by this strain showed mixed growth and non-growth associated components as described by Luedeking–Piret kinetic model.ConclusionThe findings of this study provided add to the literature on key variables in for achieving good microbial growth and mcl-PHA production in shake flasks culture. In addition, suitable kinetic model to describe cultivation in this system was also presented.     

Effects of volatile fatty acids in biohydrogen effluent on biohythane production from palm oil mill effluent under thermophilic condition

BackgroundBiohydrogen effluent contains a high concentration of volatile fatty acid (VFA) mainly as butyric, acetic, lactic and propionic acids. The presence of various VFAs (mixture VFAs) and their cooperative effects on two-stage biohythane production need to be further studied. The effect of VFA concentrations in biohydrogen effluent of palm oil mill effluent (POME) on methane yield in methane stage of biohythane production was investigated.ResultsThe methane yield obtained in low VFA loading (0.9 and 1.8 g/L) was 15–20% times greater than that of high VFA loading (3.6 and 4.7 g/L). Butyric acid at high concentrations (8 g/L) has the individual significantly negative effect the methane production process (P < 0.05). Lactic, acetic and butyric acid mixed with propionic acid at a concentration higher than 0.5 g/L has an interaction significantly negative effect on the methanogenesis process (P < 0.05). Inhibition condition had a negative effect on both bacteria and archaea with inhibited on Geobacillus sp., Thermoanaerobacterium thermosaccharolyticum, Methanoculleus thermophilus and Methanothermobacter delfuvii resulting in low methane yield.ConclusionPreventing the high concentration of butyric acid, and propionic acid in the hydrogenic effluent could enhance methane production in two-stage anaerobic digestion for biohythane production.     

Escherichia coli expressing endoglucanase gene from Thai higher termite bacteria for enzymatic and microbial hydrolysis of cellulosic materials

BackgroundEndoglucanase plays a major role in initiating cellulose hydrolysis. Various wild-type strains were searched to produce this enzyme, but mostly low extracellular enzyme activities were obtained. To improve extracellular enzyme production for potential industrial applications, the endoglucanase gene of Bacillus subtilis M015, isolated from Thai higher termite, was expressed in a periplasmic-leaky Escherichia coli. Then, the crude recombinant endoglucanase (EglS) along with a commercial cellulase (Cel) was used for hydrolyzing celluloses and microbial hydrolysis using whole bacterial cells.ResultsE. coli Glu5 expressing endoglucanase at high levels was successfully constructed. It produced EglS (55 kDa) with extracellular activity of 18.56 U/mg total protein at optimal hydrolytic conditions (pH 4.8 and 50°C). EglS was highly stable (over 80% activity retained) at 40–50°C after 100 h. The addition of EglS significantly improved the initial sugar production rates of Cel on the hydrolysis of carboxymethyl cellulose (CMC), microcrystalline cellulose, and corncob about 5.2-, 1.7-, and 4.0-folds, respectively, compared to those with Cel alone. E. coli Glu5 could secrete EglS with high activity in the presence of glucose (1% w/v) and Tween 80 (5% w/v) with low glucose consumption. Microbial hydrolysis of CMC using E. coli Glu5 yielded 26 mg reducing sugar/g CMC at pH 7.0 and 37°C after 48 h.ConclusionsThe recombinant endoglucanase activity improved by 17 times compared with that of the native strain and could greatly enhance the enzymatic hydrolysis of all studied celluloses when combined with a commercial cellulase.     

Effect of nitrogen,carbon sources and agitation speed on acetoin production of Bacillus subtilis SF4-3

BackgroundCurrently, microbial fermentation method has become the research hotspot for acetoin production. In our previous work, an acetoin-producing strain, Bacillus subtilis SF4-3, was isolated from Japanese traditional fermented food natto. However, its conversion of glucose to acetoin was relatively low. In order to achieve a high-efficient accumulation of acetoin in B. subtilis SF4-3, main medium components and fermentation conditions were evaluated in this work.ResultsThe by-products analysis showed that there existed reversible transformation between acetoin and 2,3-butanediol that was strictly responsible for acetoin production in B. subtilis SF4-3. The carbon sources, nitrogen sources and agitation speed were determined to play crucial role in the acetoin production. The optimal media (glucose·H₂O 150 g/L, yeast extract 10 g/L, corn steep dry 5 g/L, urea 2 g/L, K₂HPO₄ 0.5 g/L, MgSO₄ 0.5 g/L) were obtained. Furthermore, the low agitation speed of 300 r/min was found to be beneficial to the reversible transformation of 2,3-butanediol for acetoin production in B. subtilis SF4-3. Eventually, 48.9 g/L of acetoin and 5.5 g/L of 2,3-butanediol were obtained in a 5-L fermenter, and the specific production of acetoin was 39.12% (g/g), which accounted for 79.90% of the theoretical conversion.ConclusionsThe results indicated acetoin production of B. subtilis SF4-3 was closely related to the medium components and dissolved oxygen concentrations. It also provided a method for acetoin production via the reversible transformation of acetoin and 2,3-butanediol.     

Combined strategies for improving production of a thermo-alkali stable laccase in Pichia pastoris

BackgroundLaccases are copper-containing enzymes which have been used as green biocatalysts for many industrial processes. Although bacterial laccases have high stabilities which facilitate their application under harsh conditions, their activities and production yields are usually very low. In this work, we attempt to use a combinatorial strategy, including site-directed mutagenesis, codon and cultivation optimization, for improving the productivity of a thermo-alkali stable bacterial laccase in Pichia pastoris.ResultsA D500G mutant of Bacillus licheniformis LS04 laccase, which was constructed by site-directed mutagenesis, demonstrated 2.1-fold higher activity when expressed in P. pastoris. The D500G variant retained similar catalytic characteristics to the wild-type laccase, and could efficiently decolorize synthetic dyes at alkaline conditions. Various cultivation factors such as medium components, pH and temperature were investigated for their effects on laccase expression. After cultivation optimization, a laccase activity of 347 ± 7 U/L was finally achieved for D500G after 3 d of induction, which was about 9.3 times higher than that of wild-type enzyme. The protein yield under the optimized conditions was about 59 mg/L for D500G.ConclusionsThe productivity of the thermo-alkali stable laccase from B. licheniformis expressed in P. pastoris was significantly improved through the combination of site-directed mutagenesis and optimization of the cultivation process. The mutant enzyme retains good stability under high temperature and alkaline conditions, and is a good candidate for industrial application in dye decolorization.     

Improvement of hydrogen yield of ethanol-producing Escherichia coli recombinants in acidic conditions

BackgroundAn effective single culture with high glycerol consumption and hydrogen and ethanol coproduction yield is still in demand. A locally isolated glycerol-consuming Escherichia coli SS1 was found to produce lower hydrogen levels under optimized ethanol production conditions. Molecular approach was proposed to improve the hydrogen yield of E. coli SS1 while maintaining the ethanol yield, particularly in acidic conditions. Therefore, the effect of an additional copy of the native hydrogenase gene hycE and recombinant clostridial hydrogenase gene hydA on hydrogen production by E. coli SS1 at low pH was investigated.ResultsRecombinant E. coli with an additional copy of hycE or clostridial hydA was used for fermentation using 10 g/L (108.7 mmol/L) of glycerol with an initial pH of 5.8. The recombinant E. coli with hycE and recombinant E. coli with hydA showed 41% and 20% higher hydrogen yield than wild-type SS1 (0.46 ± 0.01 mol/mol glycerol), respectively. The ethanol yield of recombinant E. coli with hycE (0.50 ± 0.02 mol/mol glycerol) was approximately 30% lower than that of wild-type SS1, whereas the ethanol yield of recombinant E. coli with hydA (0.68 ± 0.09 mol/mol glycerol) was comparable to that of wild-type SS1.ConclusionsInsertion of either hycE or hydA can improve the hydrogen yield with an initial pH of 5.8. The recombinant E. coli with hydA could retain ethanol yield despite high hydrogen production, suggesting that clostridial hydA has an advantage over the hycE gene in hydrogen and ethanol coproduction under acidic conditions. This study could serve as a useful guidance for the future development of an effective strain coproducing hydrogen and ethanol.     

Poly(dl-lactide)-degrading enzyme production by immobilized Actinomadura keratinilytica strain T16-1 in a 5-L fermenter under various fermentation processes

BackgroundPoly(dl-lactic acid), or PDLLA, is a biodegradable polymer that can be hydrolyzed by various types of enzymes. The protease produced by Actinomadura keratinilytica strain T16-1 was previously reported to have PDLLA depolymerase activity. However, few studies have reported on PDLLA-degrading enzyme production by bacteria. Therefore, the aims of this study were to determine a suitable immobilization material for PDLLA-degrading enzyme production and optimize PDLLA-degrading enzyme production by using immobilized A. keratinilytica strain T16-1 under various fermentation process conditions in a stirrer fermenter.ResultsAmong the tested immobilization materials, a scrub pad was the best immobilizer, giving an enzyme activity of 30.03 U/mL in a shake-flask scale. The maximum enzyme activity was obtained at aeration 0.25 vvm, agitation 170 rpm, 45°C, and 48 h of cultivation time. Under these conditions, a PDLLA-degrading enzyme production of 766.33 U/mL with 15.97 U/mL·h productivity was observed using batch fermentation in a 5-L stirrer fermenter. Increased enzyme activity and productivity were observed in repeated-batch (942.67 U/mL and 19.64 U/mL·h) and continuous fermentation (796.43 U/mL and 16.58 U/mL·h) at a dilution rate of 0.013/h. Scaled-up production of the enzyme in a 10-L stirrer bioreactor using the optimized conditions showed a maximum enzyme activity of 578.67 U/mL and a productivity of 12.06 U/mL·h.ConclusionsThis research successfully scaled-up the enzyme production to 5 and 10 L in a stirrer fermenter and is helpful for many applications of poly(lactic acid).     

Effects of fermentation conditions on valuable products of ethanolic fungus Mucor indicus

BackgroundMucor indicus is a dimorphic fungus used in the production of ethanol, oil, protein, and glucosamine. It can ferment different pentoses and hexoses; however, the yields of products highly depend on the nutrients and cultivation conditions. In this study, the effects of different morphologic forms, cultivation time and temperature, presence or absence of oxygen, carbon sources, and concentration of nitrogen source on the products of M. indicus were investigated.ResultsThe fungus with all morphologies produced high yields of ethanol, in the range of 0.32–0.43 g/g, on glucose. However, the fungus with filamentous morphology produced higher amounts of oil, protein, phosphate, and glucosamine together with ethanol, compared with other morphologies. A higher amount of oil (0.145 g/g biomass) was produced at 28°C, while the best temperature for protein and glucosamine production was 32 and 37°C, respectively. Although ethanol was produced at a higher yield (0.44 g/g) under anaerobic conditions compared with aerobic conditions (yield of 0.41 g/g), aerobic cultivation resulted in higher yields of protein (0.51 g/g biomass), glucosamine (0.16 g/g alkali insoluble material, AIM), and phosphate (0.11 g/g AIM).ConclusionsIt is not possible to have the maximum amounts of the products simultaneously. The fermentation conditions and composition of culture media determine the product yields. Carbon source type and the addition of nitrogen source are among the most influencing factors on the product yields. Moreover, all measured products were made with higher yields in cultivation on glucose, except glucosamine, which was produced with higher yields on xylose.     

Enhanced alkaline catalase production by Serratia marcescens FZSF01: Enzyme purification,characterization, and recombinant expression

BackgroundCatalase (CAT) is an important enzyme that degrades H₂O₂ into H₂O and O₂. To obtain an efficient catalase, in this study, a new strain of high catalase-producing Serratia marcescens, named FZSF01, was screened and its catalase was purified and characterized.ResultsAfter optimization of fermentation conditions, the yield of catalase produced by this strain was as high as 51,468 U/ml. This catalase was further purified using two steps: DEAE-fast flow and Sephedex-G150. The purified catalase showed a specific activity of 197,575 U/mg with a molecular mass of 58 kDa. This catalase exhibited high activity at 20–70°C and pH 5.0–11.0. Km of the catalase was approximately 68 mM, and Vmax was 1886.8 mol/min mg. This catalase was further identified by LC–MS/MS, and the encoding gene was cloned and expressed in Escherichia coli BL21 (DE3) with a production of 17,267 ± 2037 U/ml.ConclusionsTo our knowledge, these results represent one of the highest fermentation levels reported among current catalase-producing strains. This FZSF01 catalase may be suitable for several industrial applications that comprise exposure to alkaline conditions and under a wide range of temperatures.     

Indole acetic acid and ACC deaminase from endophytic bacteria improves the growth of Solanum lycopersicum

BackgroundEndophytic bacteria are ubiquitous in all plant species contributing in host plant's nutrient uptake and helping the host to improve its growth. Moringa peregrina which is a medicinal plant, growing in arid region of Arabia, was assessed for the presence of endophytic bacterial strains.ResultsPCR amplification and sequencing of 16S rRNA of bacterial endophytes revealed the 5 endophytic bacteria, in which 2 strains were from Sphingomonas sp.; 2 strains from Bacillus sp. and 1 from Methylobacterium genus. Among the endophytic bacterial strains, a strain of Bacillus subtilis LK14 has shown significant prospects in phosphate solubilization (clearing zone of 56.71 mm after 5 d), ACC deaminase (448.3 ± 2.91 nM α-ketobutyrate mg^- 1 h^- 1) and acid phosphatase activity (8.4 ± 1.2 nM mg^- 1 min^- 1). The endophytic bacteria were also assessed for their potential to produce indole-3-acetic acid (IAA). Among isolated strains, the initial spectrophotometry analysis showed significantly higher IAA production by Bacillus subtilis LK14. The diurnal production of IAA was quantified using multiple reactions monitoring method in UPLC/MS–MS. The analysis showed that LK14 produced the highest (8.7 μM) IAA on 14th d of growth. Looking at LK14 potentials, it was applied to Solanum lycopersicum, where it significantly increased the shoot and root biomass and chlorophyll (a and b) contents as compared to control plants.ConclusionThe study concludes that using endophytic bacterial strains can be bio-prospective for plant growth promotion, which might be an ideal strategy for improving growth of crops in marginal lands.     

Characterization of a hyperthermophilic sulphur-oxidizing biofilm produced by archaea isolated from a hot spring

BackgroundSulphur-oxidizing microorganisms are widely used in the biofiltration of total reduced sulphur compounds (odorous and neurotoxic) produced by industries such as the cellulose and petrochemical industries, which include high-temperature process steps. Some hyperthermophilic microorganisms have the capability to oxidize these compounds at high temperatures (> 60°C), and archaea of this group, for example, Sulfolobus metallicus, are commonly used in biofiltration technology.ResultsIn this study, a hyperthermophilic sulphur-oxidizing strain of archaea was isolated from a hot spring (Chillán, Chile) and designated as M1. It was identified as archaea of the genus Sulfolobus (99% homology with S. solfataricus 16S rDNA). Biofilms of this culture grown on polyethylene rings showed an elemental sulphur oxidation rate of 95.15 ± 15.39 mg S l^-1 d^-1, higher than the rate exhibited by the biofilm of the sulphur-oxidizing archaea S. metallicus (56.8 ± 10.91 mg l^-1 d^-1).ConclusionsThe results suggest that the culture M1 is useful for the biofiltration of total reduced sulphur gases at high temperatures and for other biotechnological applications.     

Optimization of Bacillus subtilis cell growth effecting jiean-peptide production in fed batch fermentation using central composite design

BackgroundOptimization of nutrient feeding was developed to improve the growth of Bacillus subtilis in fed batch fermentation to increase the production of jiean-peptide (JAA). A central composite design (CCD) was used to obtain a model describing the relationship between glucose, total nitrogen, and the maximum cell dry weight in the culture broth with fed batch fermentation in a 5 L fermentor.ResultsThe results were analyzed using response surface methodology (RSM), and the optimized values of glucose and total nitrogen concentration were 30.70 g/L and 1.68 g/L in the culture, respectively. The highest cell dry weight was improved to 77.50 g/L in fed batch fermentation, which is 280% higher than the batch fermentation concentration (20.37 g/L). This led to a 44% increase of JAA production in fed batch fermentation as compared to the production of batch fermentation.ConclusionThe results of this work improve the present production of JAA and may be adopted for other objective products' production.     

High-yield production of the human lysozyme by Pichia pastoris SMD1168 using response surface methodology and high-cell-density fermentation

BackgroundLysozyme plays a crucial role in innate immunity with its well-recognized bacteriolytic activity. In this study, the influence of expression parameters (inoculation volume, culture volume, growth time, induction temperature and time, initial pH and methanol concentration) on human lysozyme (HLZ) production in recombinant P. pastoris SMD1168 was investigated through Plackett–Burman (PB) design and response surface methodology (RSM).ResultsIt was revealed that induction temperature, induction time and culture volume had significant influence (P < 0.01) on HLZ expression level, which were elected for further optimization with three-dimensional response surface designs for enhanced HLZ production. The highest lysozyme activity reached 3301 U/mL under optimized conditions (at 23.5°C for 90 h with culture volume of 48 mL) in shake flask, which increased 2.2 fold compared with that achieved with the standard protocol (Invitrogen). When high-cell-density fermentation of the recombinant Pichia pastoris was performed in a 15 L fermenter under optimized conditions, the extracellular lysozyme activity reached 47,680 U/mL. SDS-PAGE analysis of the product demonstrated that HLZ was produced as a single major protein with a molecular weight of approximately 14.7 kDa, consistent with its expected size.ConclusionsThe results indicated that the optimized culture conditions using PB design and RSM significantly enhanced the expression level of HLZ, and the Pichia expression system for HLZ production was successful and industrially promising.     

Improvement of ethanol production from sweet sorghum juice under batch and fed-batch fermentations: Effects of sugar levels,nitrogen supplementation,and feeding regimes

BackgroundFermentation process development has been very important for efficient ethanol production. Improvement of ethanol production efficiency from sweet sorghum juice (SSJ) under normal gravity (NG, 160 g/L of sugar), high gravity (HG, 200 and 240 g/L of sugar) and very high gravity (VHG, 280 and 320 g/L of sugar) conditions by nutrient supplementation and alternative feeding regimes (batch and fed-batch systems) was investigated using a highly ethanol-tolerant strain, Saccharomyces cerevisiae NP01.ResultsIn the batch fermentations without yeast extract, HG fermentation at 200 g/L of sugar showed the highest ethanol concentration (P_E, 90.0 g/L) and ethanol productivity (Q_E, 1.25 g/L·h). With yeast extract supplementation (9 g/L), the ethanol production efficiency increased at all sugar concentrations. The highest P_E (112.5 g/L) and Q_E (1.56 g/L·h) were observed with the VHG fermentation at 280 g/L of sugar. In the fed-batch fermentations, two feeding regimes, i.e., stepwise and continuous feedings, were studied at sugar concentrations of 280 g/L. Continuous feeding gave better results with the highest P_E and Q_E of 112.9 g/L and 2.35 g/L·h, respectively, at a feeding time of 9 h and feeding rate of 40 g sugar/h.ConclusionsIn the batch fermentation, nitrogen supplementation resulted in 4 to 32 g/L increases in ethanol production, depending on the initial sugar level in the SSJ. Under the VHG condition, with sufficient nitrogen, the fed-batch fermentation with continuous feeding resulted in a similar P_E and increased Q_P by 51% compared to those in the batch fermentation.     

Molecular cloning,expression, and immobilization of glutamate decarboxylase from Lactobacillus fermentum YS2

BackgroundGABA (γ-aminobutyric acid) is a four-carbon nonprotein amino acid that has hypotensive, diuretic, and tranquilizing properties. Glutamate decarboxylase (GAD) is the key enzyme to generate GABA. A simple and economical method of preparing and immobilizing GAD would be helpful for GABA production. In this study, the GAD from Lactobacillus fermentum YS2 was expressed under the control of a stress-inducible promoter and was purified and immobilized in a fusion form, and its reusability was investigated.ResultsThe fusion protein CBM-GAD was expressed in Escherichia coli DH5α carrying pCROCB-gadB, which contained promoter P_rpoS, cbm3 (family 3 carbohydrate-binding module from Clostridium thermocellum) coding sequence, the gadB gene from L. fermentum YS2 coding for GAD, and the T7 terminator. After a one-step purification of CBM-GAD using regenerated amorphous cellulose (RAC) as an adsorbent, SDS-PAGE analysis revealed a clear band of 71 kDa; the specific activity of the purified fusion protein CBM-GAD reached 83.6 ± 0.7 U·mg^-1. After adsorption onto RAC, the immobilized GAD with CBM3 tag was repeatedly used for GABA synthesis. The protein-binding capacity of RAC was 174 ± 8 mg·g^-1. The immobilized CBM-GAD could repeatedly catalyze GABA synthesis, and 8% of the initial activities was retained after 10 uses. We tested the conversion of monosodium glutamate to GABA by the immobilized enzyme; the yield reached 5.15 g/L and the productivity reached 3.09 g/L·h.ConclusionsRAC could be used as an adsorbent in one-step purification and immobilization of CBM-GAD, and the immobilized enzyme could be repeatedly used to catalyze the conversion of glutamate to GABA.     

On the fermentative behavior of auxotrophic strains of Saccharomyces cerevisiae

BackgroundThe selection of new yeast strains could lead to improvements in bioethanol production. Here, we have studied the fermentative capacity of different auxotrophic mutants of Saccharomyces cerevisiae, which are routinely used as hosts for the production of heterologous proteins. It has recently been found that these strains exhibit physiological alterations and peculiar sensitivities with respect to the parental prototrophic strains from which they derive. In this work the performance of auxotrophic S. cerevisiae CEN.PK strains was compared to the corresponding prototrophic strain, to S. cerevisiae T5bV, a strain isolated from grape must and to another auxotrophic strain, S. cerevisiae BY4741.ResultsThe results indicate that the fermentative capacity of strains grown in 2% glucose was similar in all the strains tested. However, in 15% initial glucose, the auxotrophic strains exhibited a more than doubled ethanol yield on biomass (10 g g^- 1_dw) compared to the prototrophic strains (less than 5 g g^- 1_dw). Other tests have also evidenced that in medium depletion conditions, ethanol production continues after growth arrest.ConclusionsThe results highlight the capacity of auxotrophic yeast strains to produce ethanol per mass unit, in a higher amount with respect to the prototrophic ones. This leads to potential applications for auxotrophic strains of S. cerevisiae in the production of ethanol in both homogeneous and heterogeneous phases (immobilized systems). The higher ethanol yield on biomass would be advantageous in immobilized cell systems, as a reduced yeast biomass could greatly reduce the mass transfer limitations through the immobilization matrix.     

A novel pH-stable,endoglucanase (JqCel5A) isolated from a salt-lake microorganism,Jonesia quinghaiensis

BackgroundEndoglucanase, one of three type cellulases, can randomly cleave internal β-1,4-linkages in cellulose polymers. Thus, it could be applied in agricultural and industrial processes.ResultsA novel endoglucanase gene (JqCel5A) was cloned from Jonesia quinghaiensis and functionally expressed in Escherichia coli Rosetta (DE3). It contained 1722 bp and encoded a 573-residue polypeptide consisting of a catalytic domain of glycoside hydrolase family 5 (GH5) and a type 2 carbohydrate-binding module (CBM2), together with a predicted molecular mass of 61.79 kD. The purified JqCel5A displayed maximum activity at 55°C and pH 7.0, with 21.7 U/mg, 26.19 U/mg and 4.81 U/mg towards the substrate carboxymethyl cellulose, barley glucan and filter paper, respectively. Interestingly, JqCel5A exhibited high pH stability over a broad pH range of pH (3–11), and had good tolerance to a wide variety of deleterious chemicals including heavy metals and detergent. The catalytic mechanism of JqCel5A was also investigated by site mutagenesis and homology-modeling in this study.ConclusionsIt was believed that these properties might make JqCel5A to be potentially used in the suitable industrial catalytic condition, which has a broad pH fluctuation and/or chemical disturbance.     

The exopolysaccharides biosynthesis by Candida yeast depends on carbon sources

BackgroundThe exopolysaccharides (EPS) produced by yeast exhibit physico-chemical and rheological properties, which are useful in the production of food and in the cosmetic and pharmaceutical industries as well. The effect was investigated of selected carbon sources on the biosynthesis of EPS by Candida famata and Candida guilliermondii strains originally isolated from kefirs.ResultsThe biomass yields were dependent on carbon source (sucrose, maltose, lactose, glycerol, sorbitol) and ranged from 4.13 to 7.15 g/L. The highest biomass yield was reported for C. guilliermondii after cultivation on maltose. The maximum specific productivity of EPS during cultivation on maltose was 0.505 and 0.321 for C. guilliermondii and C. famata, respectively. The highest EPS yield was found for C. guilliermondii strain. The EPS produced under these conditions contained 65.4% and 61.5% carbohydrates, respectively. The specific growth rate (μ) of C. famata in medium containing EPS as a sole carbon source was 0.0068 h^-1 and 0.0138 h^-1 for C. guilliermondii strain.ConclusionsThe most preferred carbon source in the synthesis of EPS for both Candida strains was maltose, wherein C. guilliermondii strain showed the higher yield of EPS biosynthesis. The carbon source affected the chemical composition of the resulting EPS and the contribution of carbohydrate in the precipitated preparation of polymers was higher during supplementation of maltose as compared to sucrose. It was also found that the EPS can be a source of carbon for the producing strains.