Synthesis and regulation of D-xylanase from Cellulomonas flavigena wild type and a mutant

The xylanolytic system from Cellulomonas flavigena was enhanced by adding cellulose to the growth medium. The Solka floc:xylan (60:40 w/w) mixture induced xylanase synthesis by more than 3-fold over that induced by growing C. flavigena, wild type and its mutant PN-120 on pure xylan. The hydrolysis pattern of sugar cane bagasse and xylan indicated the presence of debranching endo-;-xylanase activity.     

Induction of xylanases by sugar cane bagasse at different cell densities of Cellulomonas flavigena

The effect of cell density on xylanolytic activity and productivity of Cellulomonas flavigena was evaluated under two different culturing conditions: fed-batch culture with discontinuous feed of sugar cane bagasse (SCB; condition 1) and glycerol fed-batch culture followed by addition of SBC as xylanases inducer (condition 2). The enzymatic profile of xylanases was similar in both systems, regardless of the initial cell density at time of induction. However, the xylanolytic activity changed with initial cell density at the time of induction (condition 2). The maximum volumetric xylanase activity increased with increased initial cell density from 4 to 34 g l⁻¹ but decreased above this value. The largest total volumetric xylanase productivity under condition 2 (1.3 IU ml⁻¹ h⁻¹) was significantly greater compared to condition 1 (maximum 0.6 IU ml⁻¹ h⁻¹). Consequently, induction of xylanase activity by SCB after growing of C. flavigena on glycerol at intermediate cell density can be a feasible alternative to improve activity and productivity of xylanolytic enzymes.     

Isolation of a high-specific-growth-rate mutant of Cellulomonas flavigena on sugar cane bagasse

By treatment of a wild-type strain of Cellulomonas flavigena with N-methyl-N'-nitro-N-nitrosoguanidine at 150 g/ml, mutants PN-7 and PN-10 were obtained, which produce 1.38 and 1.5 times more carboxymethylcellulase than the wild strain when cultured in a batch system with sugar cane bagasse as the sole carbon source. These mutants also exhibited higher specific growth rates compared to the wild strain. From a second mutagenesis of mutant PN-10, mutant PN-120 was obtained in continuous culture. This mutant was able to use a larger portion of sugar cane bagasse than did the wild-type and therefore its biomass yield was also higher. The mutant showed a specific growth rate on sugar cane bagasse threefold higher than the wild strain.     

Evaluation of inert and organic carriers for <Emphasis Type="Italic">Verticillium lecanii</Emphasis> spore production in solid-state fermentation

Growth and sporulation of Verticillium lecanii on inert and organic carriers (sugar-cane bagasse, corncob, rice straw, polyurethane foam and activated carbon) in a solid-state fermentation process was studied. Sugar-cane bagasse and polyurethane foam produced 10¹⁰ spores g⁻¹ dry carrier whereas corncob, rice straw, and activated carbon yielded, respectively 8 × 10⁹, 4 × 10⁹, and 3 × 10⁸ spores g⁻¹. Chitinase activity of the conidia was in the following order: sugar-cane bagasse (3.3 U mg⁻¹) > wheat bran (3.0 U mg⁻¹) > polyurethane foam (2.7 U mg⁻¹). There was no significant difference (2.5–2.7 U mg⁻¹) in the proteinase activity among the conidia from the three cultures. Scanning electron microscopy shows that aerial mycelium freely penetrated into the internal area of polyurethane foam. Sugar-cane bagasse provided enough area for vegetative hyphae to attach. Of the carriers analyzed, polyurethane foams and sugar-cane bagasse were the best carriers for V. lecanii growth and spore production.     

γ-ray induced mutagenesis ofCellulomonas biazotea for improved production of cellulases

A rifampin-resistant mutant ofCellulomonas biazotea secreted elevated levels of cellulasesin vivo. The cellulase production in the mutant was not inhibited in the presence of 5% glucose, cellobiose or glycerol in the solid medium. The mutant exhibited approximately two- to three-fold enhanced product yields and productivity of cellular β-glucosidase over the wild parent in shake-flask culture studies when grown on either cellulosic or lignocellulosic substrates. Extracellular production of filter paper cellulase (FPase) and endo-glucanase (CMCase) were also significantly (p≤0.05) altered. During growth of the mutant on α-cellulose, the maximum volumetric productivities for CMCase, FPase and β-glucosidase were 52, 23.3, and 15.2 IUL⁻¹ h⁻¹,i.e 118, 121, and 229% their respective values for the parental strain. Some enzyme properties of the mutant cellulases were altered. Mutant-derived cellulases produced higher yields of glucose arising by degradation of bagasse, wheat straw, and α-cellulose (1.53-, 1.57-, and 1.75-fold, respectively).     

β-Methyl-xyloside: positive effect on xylanase induction in Cellulomonas flavigena

Synthesis of extracellular xylanase in Cellulomonas flavigena is induced in the presence of xylan and sugarcane bagasse as substrates. The essential factors for efficient production of xylanase are the appropriate medium composition and an inducing substrate. The increase in xylanase production levels in C. flavigena were tested with a number of carbon sources and different culture conditions. Xylose, arabinose, glycerol and glucose did not induce xylanase production in this microorganism. β-Methyl-xyloside (β-mx), a structural analog of xylobiose, also did not induce xylanase when used as the sole carbon source, but when xylan or sugar cane bagasse was supplemented with β-mx, extracellular xylanase production increased by 25 or 46%, respectively. The response of C. flavigena to xylan plus β-mx was accompanied by a significant accumulation of reducing sugar, an effect not observed with the combination sugarcane bagasse plus β-mx as substrate. To our knowledge, this is the first report on the effect of β-mx on the induction of xylanase in C. flavigena.     

Solid state bioreactor production of transglutaminase by Amazonian Bacillus circulans BL32 strain

In this work, we investigated the production of transglutaminase (TGase) by an Amazonian isolated strain of Bacillus circulans by solid-state cultivation (SSC). Several agro-industrial residues, such as untreated corn grits, milled brewers rice, industrial fibrous soy residue, soy hull, and malt bagasse, were used as substrates for microbial growth and enzyme production. Growth on industrial fibrous soy residue, which is rich in protein and hemicellulose, produced the highest TGase activity (0.74 U g⁻¹ of dried substrate after 48 h of incubation). A 2³ central composite design was applied to determine the optimal conditions of aeration, cultivation temperature and inoculum cell concentration to TGase production. The best culture conditions were determined as being 0.6 L air min⁻¹, 33 °C and 10 log ₁₀ CFU g⁻¹ of dried substrate, respectively. Under the proposed optimized conditions, the model predicted an enzyme production of 1.16 U g⁻¹ of dried substrate, closely matching the experimental activity of 1.25 U g⁻¹. Results presented in this work point to the use of this newly isolated B. circulans strain as a potential alternative of microbial source for TGase production by SSC, using inexpensive culture media.     

Lignocellulose-degrading enzyme production by white-rot <Emphasis Type="Italic">Basidiomycetes</Emphasis> isolated from the forests of Georgia

The production of lignocellulolytic enzymes by eleven basidiomycetes species isolated from two ecosystems of Georgia was investigated for the first time under submerged (SF) and solid-state fermentation (SSF) of lignocellulosic by-products. Notable intergeneric and intrageneric differences were revealed with regard to the extent of hydrolase and oxidase activity. Several fungi produced laccase along with hydrolases in parallel with growth during the trophophase, showing that the synthesis of this enzyme is not connected with secondary metabolism. The lignocellulosic substrate type had the greatest impact on enzyme secretion. Some of the substrates significantly stimulated lignocellulolytic enzyme synthesis without supplementation of the culture medium with specific inducers. Exceptionally high carboxymethyl cellulase (CMCase, 122 U ml⁻¹) and xylanase (195 U ml⁻¹) activities were revealed in SF of mandarin peelings by Pseudotremella gibbosa IBB 22 and of residue after ethanol production (REP) by Fomes fomentarius IBB 38, respectively. The SSF of REP by T. pubescens IBB 11 ensured the highest level of laccase activity (24,690 U l⁻¹), whereas the SSF of wheat bran and SF of mandarin peels provided the highest manganese peroxidase activity (570–620 U l⁻¹) of Trichaptum biforme IBB 117. Moreover, the variation of lignocellulosic growth substrate provides an opportunity to obtain enzyme preparations containing different ratios of individual enzymes.     

β-Galactosidase production by the psychrotolerant yeast Guehomyces pullulans 17-1 isolated from sea sediment in Antarctica and lactose hydrolysis

A psychrotolerant yeast Guehomyces pullulans 17-1 was isolated from sea sediment in Antarctica. It was found that it could yield both extracellular and cell-bound β-galactosidase. After optimization of the medium and cultivation conditions, it was found that the yeast strain produced over 17.2 U mL⁻¹ of β-galactosidase activity within 120 h at the flask level while the yeast strain produced over 25.3 U mL⁻¹ of β-galactosidase activity within 144 h during the 2-L fermentation. This is the highest β-galactosidase activity produced by the wild type yeast strains reported so far. However, the optimal pH and temperature for the crude β-galactosidase were 4.0 and 50 °C, respectively. Lactose could be converted into glucose and galactose and a large amount of reducing sugar could be released from milk under catalysis of the yeast culture.     

Enantioselective biocatalytic hydrolysis of (<Emphasis Type="Italic">R</Emphasis>,<Emphasis Type="Italic">S</Emphasis>)-mandelonitrile for production of (<Emphasis Type="Italic">R</Emphasis>)-(−)-mandelic acid by a newly isolated mutant strain

(R)-(−)-Mandelic acid (R-MA) is an important intermediate with broad uses. Recently, R-MA production using nitrilase has been gaining more and more attention due to its higher productivity and enantioselectivity. In this work, a new bacterium WT10, which exhibited favorable nitrilase activity and excellent enantioselectivity for production of R-MA by enantioselective biocatalytic hydrolysis of (R,S)-mandelonitrile, was isolated and identified as a strain of Alcaligenes faecalis. In order to improve its nitrilase activity for industrial application, the wild-type strain WT10 was further subjected to mutagenesis using a combined LiCl–ultraviolet irradiation and low energy N⁺ ion beams implantation technique. A valuable mutant strain A. faecalis ZJUTB10 was obtained. The nitrilase specific activity of the mutant strain was greatly improved up to 350.8 U g⁻¹, in comparison with wild-type strain WT10 of 53.09 U g⁻¹. The reaction conditions for R-MA production by mutant strain A. faecalis ZJUTB10 were also optimized. Nitrilase activity in mutant strain showed a broad pH optimum at pH 7.7–8.5. The optimal temperature was 35°C. The highest production rate reached 9.3 mmol h⁻¹ g⁻¹. The results showed that mutant strain A. faecalis ZJUTB10 was a new candidate for efficient R-MA production from (R,S)-mandelonitrile and could potentially be used in industrial production.     

Regulation of cellulases and xylanases from a derepressed mutant of Cellulomonas flavigena growing on sugar-cane bagasse in continuous culture

When the wild type Cellulomonas flavigena was grown on glycerol, xylose or cellobiose, it produced basal levels of carboxymethyl-cellulase (CMCase), filter-paperase (FPase) and xylanase activities. By comparison, a catabolic derepressed mutant strain of the same organism produced markedly higher levels of these enzymes when grown on the same carbon sources. Sugar-cane bagasse induced both the wild type and the mutant strain to produce three- to eight-time higher levels of FPase and xylanase than was observed with xylose or cellobiose. Continuous culture was used to determine the minimal cellobiose or glucose concentrations that repress the enzyme synthesis in both strains. 2.5 g l(-1) glucose repressed FPase and xylanases from wild type, while 1.6 times more glucose was needed to repress the same activities in the PN-120 strain. In the same way, twofold more cellobiose was needed to reduce by 75% the CMCase and xylanase activities in the mutant compared to the wild type. The FPase in the presence of 4 g l(-1) cellobiose did not change in the same strain. Therefore, its derepressed and feedback resistant characters of PN-120 mutant are evident. On the other hand, isoelectrofocused crude extracts of mutant and wild strains induced by sugar-cane bagasse, did not show differences in protein patterns, however, the Schiffs staining was more intense in the PN-120 than in the wild strain. These results point out that the mutational treatment did not apparently change the extracellular proteins from mutant PN-120 and this could affect their regulation sites, since derepressed and feed-back resistant enzymes may be produced.     

Cholesterol assimilation and biotransformation by Lactobacillus helveticus

Lactobacillus helveticus, grown at 37°C in MRS medium supplemented with 3 mM cholesterol, assimilated all the cholesterol in 42 h having 68 U mg⁻¹ of intracellular cholesterol oxidase activity. The strain transformed 1 g cholesterol to 0.05 g of androsta-1, 4-diene-3, 17-dione and 0.04 g of androst-4-ene-3, 17 dione within 48 h at 37°C with extracellular cholesterol oxidase activity at 12 U mg⁻¹ and intracellular oxidase at 0.5 U mg⁻¹.     

Enhanced fructooligosaccharides and inulinase production by a <Emphasis Type="Italic">Xanthomonas campestris</Emphasis> pv. <Emphasis Type="Italic">phaseoli</Emphasis> KM 24 mutant

Xanthomonas campestris pv phaseoli produced an extracellular endoinulinase (9.24 ± 0.03 U mL⁻¹) in an optimized medium comprising of 3% sucrose and 2.5% tryptone. X. campestris pv. phaseoli was further subjected to ethylmethanesulfonate mutagenesis and the resulting mutant, X. campestris pv. phaseoli KM 24 demonstrated inulinase production of 22.09 ± 0.03 U mL⁻¹ after 18 h, which was 2.4-fold higher than that of the wild type. Inulinase production by this mutant was scaled up using sucrose as a carbon source in a 5-L fermenter yielding maximum volumetric (21,865 U L⁻¹ h⁻¹) and specific (119,025 U g⁻¹ h⁻¹) productivities of inulinase after 18 h with an inulinase/invertase ratio of 2.6. A maximum FOS production of 11.9 g L⁻¹ h⁻¹ and specific productivity of 72 g g⁻¹ h⁻¹ FOS from inulin were observed in a fermenter, when the mutant was grown on medium containing 3% inulin and 2.5% tryptone. The detection of mono- and oligosaccharides in inulin hydrolysates by TLC analysis indicated the presence of an endoinulinase. This mutant has potential for large-scale production of inulinase and fructooligosaccharides.     

Curdlan-like exopolysaccharide production by <Emphasis Type="Italic">Cellulomonas flavigena</Emphasis> UNP3 during growth on hydrocarbon substrates

Cellulomonas flavigena UNP3, a natural isolate from vegetable oil contaminated soil sample has been studied for growth associated exopolysaccharide (EPS) production during growth on glucose, groundnut oil and naphthalene. The EPS showed matrix formation surrounding the cells during scanning electron microscopy. Cell surface hydrophobicity and emulsifying activity studies confirmed the role of EPS as bioemulsifier. Emulsifying activity was found to increase with time (0.2 U/mg for 10 min to 0.27 U/mg for 30 min). Emulsification index, E₂₄ value increased with the increase in EPS concentration. Degradation of polyaromatic hydrocarbons was confirmed using gas chromatography analysis. FTIR analysis showed presence of characteristic absorbance at 895.10 cm⁻¹ for β-configuration of glucan. NMR studies also revealed EPS produced by C. flavigena UNP3 as a linear β-1, 3-d-glucan, and a curdlan like polysaccharide.     

Optimization of fermentation conditions for production of xylanase by a newly isolated strain,Penicillium thiersii ZH-19

The objective of this study was to maximize production of xylanase by a newly isolated strain Penicillium thiersii ZH-19. Response surface methodology was employed to study the effects of significant factors such as pH, temperature, xylan concentration, and cultivation time, on the production of xylanase by Penicillium thiersii ZH-19. The optimal fermentation parameters for enhanced xylanase production were found to be pH 7.72, temperature 24.8°C, xylan 13.2 g l⁻¹ and the fermentation time 125.8 h. The model predicted a xylanase activity of 75.24 U ml⁻¹. Verification of the optimization showed that the maximum xylanase production reached 73.50 U mL⁻¹ in the flask experiments and 80.23 U mL⁻¹ in the scale of 15-L fermenter under the optimal condition.     

Cellulase production from agricultural residues by recombinant fusant strain of a fungal endophyte of the marine sponge Latrunculia corticata for production of ethanol

Several fungal endophytes of the Egyptian marine sponge Latrunculia corticata were isolated, including strains Trichoderma sp. Merv6, Penicillium sp. Merv2 and Aspergillus sp. Merv70. These fungi exhibited high cellulase activity using different lignocellulosic substrates in solid state fermentations (SSF). By applying mutagenesis and intergeneric protoplast fusion, we have obtained a recombinant strain (Tahrir-25) that overproduced cellulases (exo-β-1,4-glucanase, endo-β-1,4-glucanase and β-1,4-glucosidase) that facilitated complete cellulolysis of agricultural residues. The process parameters for cellulase production by strain Tahrir-25 were optimized in SSF. The highest cellulase recovery from fermentation slurries was achieved with 0.2% Tween 80 as leaching agent. Enzyme production was optimized under the following conditions: initial moisture content of 60% (v/w), inoculum size of 10⁶ spores ml⁻¹, average substrate particle size of 1.0 mm, mixture of sugarcane bagasse and corncob (2:1) as the carbon source supplemented with carboxymethyl cellulose (CMC) and corn steep solids, fermentation time of 7 days, medium pH of 5.5 at 30°C. These optimized conditions yielded 450, 191, and 225 units/gram dry substrate (U gds⁻¹) of carboxylmethyl cellulase, filter-paperase (FPase), and β-glucosidase, respectively. Subsequent fermentation by the yeast, Saccharomyces cerevisiae NRC2, using lignocellulose hydrolysates obtained from the optimized cellulase process produced the highest amount of ethanol (58 g l⁻¹). This study has revealed the potential of exploiting marine fungi for cost-effective production of cellulases for second generation bioethanol processes.     

Strain improvement of <Emphasis Type="Italic">Trichoderma reesei</Emphasis> Rut C-30 for increased cellulase production

The strain of Trichoderma reesei Rut C-30 was subjected to mutation after treatment with N-methyl-N′-nitro-N-nitrosoguanidine (NG) for 6 h followed by UV irradiation for 15 min. Successive mutants showed enhanced cellulase production, clear hydrolysis zone and rapid growth on Avicel-containing plate. Particularly, the mutant NU-6 showed approximately two-fold increases in activity of both FPA and CMCase in shake flask culture when grown on basal medium containing peptone (1%) and wheat bran (1%). The enzyme production was further optimized using eight different media. When a mixture of lactose and yeast cream was used as cellulase inducer, the mutant NU-6 yielded the highest enzyme and cell production with a FPase activity of 6.2 U ml⁻¹, a CMCase activity of 54.2 U ml⁻¹, a β-glucosidase activity of 0.39 U ml⁻¹, and a fungal biomass of 12.6 mg ml⁻¹. It deserved noting that the mutant NU-6 also secreted large amounts of xylanases (291.3 U ml⁻¹). These results suggested that NU-6 should be an attractive producer for both cellulose and xylanase production.     

Ethanol and xylitol production from glucose and xylose at high temperature by <Emphasis Type="Italic">Kluyveromyces</Emphasis> sp. IIPE453

A yeast strain Kluyveromyces sp. IIPE453 (MTCC 5314), isolated from soil samples collected from dumping sites of crushed sugarcane bagasse in Sugar Mill, showed growth and fermentation efficiency at high temperatures ranging from 45°C to 50°C. The yeast strain was able to use a wide range of substrates, such as glucose, xylose, mannose, galactose, arabinose, sucrose, and cellobiose, either for growth or fermentation to ethanol. The strain also showed xylitol production from xylose. In batch fermentation, the strain showed maximum ethanol concentration of 82 ± 0.5 g l⁻¹ (10.4% v/v) on initial glucose concentration of 200 g l⁻¹, and ethanol concentration of 1.75 ± 0.05 g l⁻¹ as well as xylitol concentration of 11.5 ± 0.4 g l⁻¹ on initial xylose concentration of 20 g l⁻¹ at 50°C. The strain was capable of simultaneously using glucose and xylose in a mixture of glucose concentration of 75 g l⁻¹ and xylose concentration of 25 g l⁻¹, achieving maximum ethanol concentration of 38 ± 0.5 g l⁻¹ and xylitol concentration of 14.5 ± 0.2 g l⁻¹ in batch fermentation. High stability of the strain was observed in a continuous fermentation by feeding the mixture of glucose concentration of 75 g l⁻¹ and xylose concentration of 25 g l⁻¹ by recycling the cells, achieving maximum ethanol concentration of 30.8 ± 6.2 g l⁻¹ and xylitol concentration of 7.35 ± 3.3 g l⁻¹ with ethanol productivity of 3.1 ± 0.6 g l⁻¹ h⁻¹ and xylitol productivity of 0.75 ± 0.35 g l⁻¹ h⁻¹, respectively.     

Production and activities of chitinases and hydrophobins from Lecanicillium lecanii

The production of chitinases and hydrophobins from Lecanicillium lecanii was influenced by the cultivation method and type of carbon source. Crude enzyme obtained from solid-substrate culture presented activities of exochitinases (32 and 51 kDa), endochitinases (26 kDa), β-N-acetylhexosaminidases (61, 80, 96 and 111 kDa). Additionally, submerged cultures produced exochitinases (32 and 45 kDa), endochitinases (10 and 26 kDa) and β-N-acetylhexosaminidases (61, 96 and 111 kDa). β-N-acetylhexosaminidases activity determined in solid-substrate culture with added chitin was ca. threefold (7.58 ± 0.57 U mg⁻¹) higher than submerged culture (2.73 + 0.57 U mg⁻¹). Similarly, hydrophobins displayed higher activities in solid-substrate culture (627.3 ± 2 μg protein mL⁻¹) than the submerged one (57.4 ± 4.7 μg protein mL⁻¹). Molecular weight of hydrophobins produced in solid-substrate culture was 7.6 kDa and they displayed surface activity on Teflon.     

Isolation of a Hyperxylanolytic Cellulomonas Flavigena Mutant Growing on Continuous Culture on Sugar Cane Bagasse

Mutant M9-82 from Cellulomonas flavigena PN-120 was obtained by combined treatment of NTG and EMS. Xylanase activity of this mutant strain growing on batch culture, was 33.5 IU/ml, 2.7 times higher than its parent strain. When mutant M9-82 was grown on continuous culture at a dilution rate of 0.05 h^-1, xylanolytic activity increased to 45 IU/ml.