Optimization of newly isolated Bacillus cereus α-amylase production using orange peels and crab shells and application in wastewater treatment.

A newly isolated amylolytic strain was identified as Bacillus cereus spH1 based on 16S and 16-23S gene sequencing (Accession numbers OP811441.1 and OP819558, respectively), optimization strategies, using one variable at time (OVAT) and Plackett-Burman design, were employed to improve the alpha-amylase (α-amylase) production. Condition inferred revealed that the optimal physical parameters for maximum enzyme production were 30 °C, pH 7.5, and 12 h of incubation, using tryptone, malt extract, orange (Citrus sinensis) peels, crab (Portunus segnis) shells, calcium, and sodium chloride (NaCl) as culture medium. The full factorial design (FFD) model was observed to possess a predicted R2 and adjusted R2 values of 0.9788 and 0.9862, respectively, and it can effectively predict the response variables (p = 0). Following such efforts, α-amylase activity was increased 141.6-folds, ranging from 0.06 to 8.5 U/mL. The ideal temperature and pH for the crude enzyme activity were 65 °C and 7.5, respectively. The enzyme exhibited significant stability, with residual activity over 90% at 55 °C. The maltose was the only product generated during the starch hydrolysis. Moreover, the Bacillus cereus spH1 strain and its α-amylase were used in the treatment of effluents from the pasta industry. Germination index percentages of 143% and 139% were achieved when using the treated effluent with α-amylase and the strain, respectively. This work proposes the valorization of agro-industrial residues to improve enzyme production and to develop a green and sustainable approach that holds great promise for environmental and economic challenges.

High-Molecular-Weight Xylanase from B. pumilus US570 Strain: Purification, Characterization and Application in Banana and Orange Peels Hydrolysis and Breadmaking.

New xylanase (XylUS570) was purified from the Bacillus pumilus US570 strain. It has a molecular mass of about 232 kDa. This is the first report on the highest molecular weight monomeric xylanase produced by bacteria. The optimum pH and temperature recorded for enzyme activity were 7 and 55 °C, respectively with a half-life time of 10 min at 60 °C. At 37 °C, the enzyme retains more than 50% of its activity at a pH ranging from 6 to 9.5 for 24 h. The XylUS570 exhibited a high activity on xylan, but no activity was detected for cellulosic substrates. The Vmax and Km values exhibited by the purified enzyme on beechwood xylan were 37.05 U mL-1 and 4.189 mg mL-1, respectively. The XylUS570 was used in banana and orange peels hydrolysis and showed potential efficiency to liberate reducing sugars. It could be a good candidate for bio-ethanol production from fruit waste. The purified enzyme was used also as an additive in breadmaking. A decrease in water absorption, an increase in dough rising and improvements in volume and specific volume of the bread were recorded.

Expression of a Copper Activated Xylanase in Yeast: Location of the His-Tag in the Protein Significantly Affects the Enzymatic Properties.

A copper activated xylanase produced by E. coli BL21 was expressed in Pichia pastoris using the pGAPZαB expression vector. Two recombinant GH11 xylanase forms were obtained (N-His-rXAn11 and N-C-His-rXAn11). The findings revealed that the two recombinant xylanases displayed different behaviors toward the copper. In the presence of 3-mM Cu2+, the relative activity of the N-His-rXAn11 was enhanced by about 52%. However, the xylanase activity of the N- and C-terminal tagged one (N-C-His-rXAn11) was strongly inhibited by copper. In the presence of 3-mM Cu2+, the N-His-rXAn11 revealed to be thermostable at 60 °C with a half-life of 10 min. However, the N-C-His-rXAn11 was noted to be unstable since it was inactivated after 15 min of incubation at 55 °C. 3D models of the two recombinant forms showed that the created copper site in the N-His-rXAn11 was loosed in the C-terminal tagged protein. The C-terminal tag could trigger some structural changes with a notable displacement of secondary structures leading to great hindrance of the active site due to high fluctuations and probably new interactions among the N- and C-terminal amino acids.

Enzyme Storage and Recycling: Nanoassemblies of α-Amylase and Xylanase Immobilized on Biomimetic Magnetic Nanoparticles.

Immobilization of enzymes has been extensively required in a wide variety of industrial applications as a way to ensure functionality and the potential of enzyme recycling after use. In particular, enzyme immobilization on magnetic nanoparticles (MNPs) could offer reusability by means of magnetic recovery and concentration, along with increased stability and robust activity of the enzyme under different physicochemical conditions. In the present work, microbial α-amylase (AmyKS) and xylanase (XAn11) were both immobilized on different types of MNPs [MamC-mediated biomimetic MNPs (BMNPs) and inorganic MNPs] by using two different strategies (electrostatic interaction and covalent bond). AmyKS immobilization was successful using electrostatic interaction with BMNPs. Instead, the best strategy to immobilize XAn11 was using MNPs through the hetero-crosslinker 1-ethyl-3-(3-dimethylaminopropyl) carbodiimide (EDC) and N-hydroxysuccinimide (NHS). The immobilization protocols were optimized by varying glutaraldehyde (GA) concentration, enzyme quantity, and reaction time. Under optimal conditions, 92% of AmyKS and 87% of XAn11 were immobilized on BMNPs and MNPs-E/N, respectively (here referred as AmyKS-BMNPs and XAn11-MNPs nanoassemblies). The results show that the immobilization of the enzymes did not extensively alter their functionality and increased enzyme stability compared to that of the free enzyme upon storage at 4 and 20 °C. Interestingly, the immobilized amylase and xylanase were reused for 15 and 8 cycles, respectively, without significant loss of activity upon magnetic recovery of the nanoassemblies. The results suggest the great potential of these nanoassemblies in bioindustry applications.

Biochemical characterization and structural insights into the high substrate affinity of a dimeric and Ca2+ independent Bacillus subtilis α-amylase.

An extracellular amylase (AmyKS) produced by a newly isolated Bacillus subtilis strain US572 was purified and characterized. AmyKS showed maximal activity at pH 6 and 60°C with a half-life of 10 min at 70°C. It is a Ca2+ independent enzyme and able to hydrolyze soluble starch into oligosaccharides consisting mainly of maltose and maltotriose. When compared to the studied α-amylases, AmyKS presents a high affinity toward soluble starch with a Km value of 0.252 mg ml-1 . Coupled with the size-exclusion chromatography data, MALDI-TOF/MS analysis indicated that the purified amylase is a dimer with a molecular mass of 136,938.18 Da. It is an unusual feature of a non-maltogenic α-amylase. A 3D model and a dimeric model of AmyKS were generated showing the presence of an additional domain suspected to be involved in the dimerization process. This dimer arrangement could explain the high substrate affinity and catalytic efficiency of this enzyme.

Aspergillus oryzae S2 AmyA amylase expression in Pichia pastoris: production, purification and novel properties.

A synthetic cDNA-AmyA gene was cloned and successfully expressed in Pichia pastoris as a His-tagged enzyme under the methanol inducible AOX1 promoter. High level of extracellular amylase production of 72 U/mL was obtained after a 72 h induction by methanol. As expected, the recombinant strain produced only the AmyA isoform since the host is a protease deficient strain. Besides, the purified r-AmyA showed a molecular mass of 54 kDa, the same pH optimum equal to 5.6 but a higher thermoactivity of 60 °C against 50 °C for the native enzyme. Unlike AmyA which maintained 50% of its activity after a 10-min incubation at 60 °C, r-AmyA reached 45 min. The higher thermoactivity and thermostability could be related to the N-glycosylation. The r-AmyA activity was enhanced by 46% and 45% respectively in the presence of 4 mM Fe2+ and Mg2+ ions. This enzyme was more efficient in bread-making since such ions were reported to have a positive impact on the nutriment quality and the rheological characteristics of the wheat flour dough. The thermoactivity/thermostability as well as the iron and magnesium activations could also be ascribed to the presence of an additional C-terminal loop containing the His tag.

A trimeric and thermostable lichenase from B. pumilus US570 strain: Biochemical and molecular characterization.

New ß-1,3;1,4-glucanase (GluUS570) was purified from a newly isolated Bacillus pumilus US570 strain. The enzyme was active in a wide range of pH and temperature and displayed a great thermostability with a half-life of 30min at 80°C. The enzyme was demonstrated to be a lichenase since it was only active toward glucan containing ß-1,3;1,4- linkages. The analysis of the enzyme in native and denaturing conditions suggests that it has a trimeric form (75kDa). This is the first report on the purification and characterization of a bacterial lichenase with a trimeric structure. ß-1,3;1,4-glucanase encoding gene was amplified, cloned and sequenced showing an open reading frame of 732bp encoding 243 amino acids. The GluUS570 enzyme showed 97% homology with glucanase from Bacillus lichenoformis. The 3D model of GluUS570 in trimeric form was generated and showed that a region named R2 was involved in the oligomerization of the enzyme.

Biochemical characterization of a detergent-stable serine alkaline protease from Caldicoprobacter guelmensis.

Caldicoprobacter guelmensis isolated from the hydrothermal hot spring of Guelma (Algeria) produced high amounts of extracellular thermostable serine alkaline protease (called SAPCG) (23,000U/mL). The latter was purified by ammonium sulphate precipitation, UNO Q-6 FPLC and Zorbex PSM 300 HPLC, and submitted to biochemical characterization assays. Matrix assisted laser desorption ionization-time of flight mass spectrometry (MALDI-TOF/MS) analysis revealed that the purified enzyme was a monomer, with a molecular mass of 55,824.19Da. The 19 N-terminal residue sequence of SAPCG showed high homology with those of microbial proteases. The enzyme was completely inhibited by phenylmethanesulfonyl fluoride (PMSF) and diiodopropyl fluorophosphates (DFP), which suggested its belonging to the serine protease family. It showed optimum protease activity at pH 10 and 70°C with casein as a substrate. The thermoactivity and thermostability of SAPCG were enhanced in the presence of 2mM Ca(2+). Its half-life times at 80 and 90°C were 180 and 60min, respectively. Interestingly, the SAPCG protease exhibited significant compatibility with iSiS and Persil, and wash performance analysis revealed that it could remove blood-stains effectively. Overall, SAPCG displayed a number of attractive properties that make it a promising candidate for future applications as an additive in detergent formulations.

Expression of an Aspergillus niger xylanase in yeast: Application in breadmaking and in vitro digestion.

The cDNA of the ß-1,4-endoxylanase of Aspergillus niger US368 was cloned and expressed in Pichia pastoris under the constitutive GAP promoter. The maximum activity obtained was 41 U mL(-1), which was about 3-fold higher than that obtained with the native species. The purified enzyme showed a specific activity of 910 U mg(-1) and a molecular mass of 24 kDa. It had an optimal activity at pH 4 and 50 °C, stable in a wide range of pH and in the presence of some detergents and organic solvents. r-XAn11-His6 (recombinant xylanase) was used as an additive in breadmaking. A decrease in water absorption, an increase in dough rising and improvements in volume and specific volume of the bread were recorded. The r-XAn11-His6 was also used in in vitro digestion of barley and wheat bran leading to a decrease of the viscosities and an increase of the reducing sugars and total sugars contents.

Improvement of Trichoderma reesei xylanase II thermal stability by serine to threonine surface mutations.

Three simple mutants, S80T, S146T, and S149T, and a double mutant, S80T-S149T, were constructed and expressed in Escherichia coli to replace Serine on the surface of the Trichoderma reesei xylanase protein with Threonine residues. While the Wild-type (WT) xylanase showed a half-life time (t1/2) of 20 min at 55 °C, the double mutant was more thermostable exhibiting a t1/2 value of 37 min, followed by the S80T and S149T mutants whose t1/2 values were 25 and 23 min, respectively. At 55 °C, the S146T mutant showed a decrease in thermostability with a t1/2 value of 3 min. While the WT enzyme retained only 32% of residual activity after incubation for 5 min at 60°C, the S80T, S149T, and the S80T-S149T mutant enzymes retained 45%, 41%, and 60%, respectively. Molecular modeling attributed the increase in the thermostability of the S80T and S149T mutants to a new hydrogen bond formation and a packing effect, respectively.

Expression of A. niger US368 xylanase in E. coli: purification, characterization and copper activation.

The XAn11 cDNA was cloned in pET-28a(+) and the recombinant plasmid was transformed in Escherichia coli. The His-tagged r-XAn11 was purified using Ni-NTA affinity and anion exchange chromatography. The enzyme showed a specific activity of 415.1 U mg(-1) and a molecular mass of 25 kDa. It had an optimal activity at pH 5 and 50°C. It was stable in a wide range of pH and in the presence of some detergents and organic solvents. In the presence of 3mM Cu2+, the relative activity of the His-tagged r-XAn11 was enhanced by 54%. This is the first work reporting that copper is a strong activator for xylanase activity making this enzyme very attractive for future industrial applications. Molecular modeling suggests that the contact region between the catalytic site and the N-terminal His-tag fusion peptide could be responsible for the different behavior of the native and recombinant enzyme toward copper.

Overexpression and biochemical characterization of a thermostable phytase from Bacillus subtilis US417 in Pichia pastoris.

The overexpression of the native gene encoding the thermostable Bacillus subtilis US417 phytase using Pichia pastoris system is described. The phytase gene, in which the sequence encoding the signal peptide was replaced by that of the α-factor of Saccharomyces cerevisiae, was placed under the control of the methanol-inducible promoter of the alcohol oxidase 1 gene and expressed in Pichia pastoris. Small-scale expression experiments and activity assays were used to screen positive colonies. A recombinant strain was selected and produces 43 and 227 U/mL of phytase activity in shake flasks and in high-cell-density fermentation, respectively. The purified phytase was glycosylated protein and varied in size (50-65 kDa). It has a molecular mass of 43 kDa when it was deglycosylated. The purified r-PHY maintains 100% of its activity after 10 min incubation at 75 °C and pH 7.5. This thermostable phytase, which is also active over broad pH ranges, may be useful as feed additives, since it can resist the temperature used in the feed-pelleting process.

Purification and biochemical characterization of a novel thermostable lichenase from Aspergillus niger US368.

New ß-1,3;1,4-glucanase was purified from Aspergillus niger US368. The pure glucanase has a molecular mass of about 32 kDa. The N-terminal sequence of the purified enzyme (A-G-T-N-P-P-I-G-V) was determined. The optimum pH and temperature recorded for enzyme activity were 5 and 60 °C, respectively. It also displayed marked thermostability with a half-life of 30 min at 70 °C. At 37 °C, the enzyme showed 100% stability from pH 3 to 10. The Km and Vmax values exhibited by the enzyme on barley ß-glucan were 0.62 mg ml(-1) and 34.46 U ml(-1), respectively. The enzyme is a retaining-one and was only active toward glucan containing ß-1,3;1,4-linkages. The production of ß-glucanase with barley flour as the sole carbon source was optimized. This is the first report on the purification and characterization of a ß-1,3;1,4-glucanase from A. niger. This lichenase could be considered as a candidate for future application particularly in the animal feed industry.

Identification of salt stress-induced transcripts in potato leaves by cDNA-AFLP.

Potato (Solanum tuberosum L.) is highly sensitive to salt stress, which is one of the most important factors limiting plant cultivation. The investigation of plant response to high salinity was envisaged in this report using cDNA-amplified fragment length polymorphism (AFLP). This technique was applied to salt- stressed and control potato plants (cv. Nicola). The expression profiles showed approx 5000 bands. Of these, 154 were upregulated and 120 were repressed by salt stress. In this study we have only considered cDNA fragments that seem to be originated from salt-induced mRNA. Eighteen fragments were then reamplified, cloned, and sequenced. Sequence comparison of these cDNA, identified in response to salt stress in potato, revealed that some of them present homologies with proteins in other species that are involved in cell wall structure and turnover such as proline-rich proteins and beta-galactosidase. A number of identified clones encoded putative stress response proteins such as NADP-dependant glyceraldehyde dehydrogenase and wound-induced protein. In addition, some of them encode proteins related to hypersensitive response against pathogens such as putative late blight and nematode as well as putative pathogenesis-related proteins. These cDNA seem to be differentially expressed in the presence of salt stress as shown by Northern blot or reverse Northern hybridization experiments.