Crystal structure of the GH-46 subclass III chitosanase from Bacillus circulans MH-K1 in complex with chitotetraose

BACKGROUND

Chitosanases (EC 3.2.1.132) hydrolyze chitosan which is a polymer of glucosamine (GlcN) linked by β - 1,4 bonds, and show cleavage specificity against partially acetylated chitosan containing N-acetylglucosamine (GlcNAc) residues. Chitosanases' structural underpinnings for cleavage specificity and the conformational switch from open to closed structures are still a mystery.

METHODS

The GH-46 subclass III chitosanase from Bacillus circulans MH-K1 (MH-K1 chitosanase), which also catalyzes the hydrolysis of GlcN-GlcNAc bonds in addition to GlcN-GlcN, has had its chitotetraose [(GlcN)4]-complexed crystal structure solved at 1.35 Å resolution.

RESULTS

The MH-K1 chitosanase's (GlcN)4-bound structure has numerous structural similarities to other GH-46 chitosanases in terms of substrate binding and catalytic processes. However, subsite -1, which is absolutely specific for GlcN, seems to characterize the structure of a subclass III chitosanase due to its distinctive length and angle of a flexible loop. According to a comparison of the (GlcN)4-bound and apo-form structures, the particular binding of a GlcN residue at subsite -2 through Asp77 causes the backbone helix to kink, which causes the upper- and lower-domains to approach closely when binding a substrate.

CONCLUSIONS

Although GH-46 chitosanases vary in the finer details of the subsites defining cleavage specificity, they share similar structural characteristics in substrate-binding, catalytic processes, and potentially in conformational change.

GENERAL SIGNIFICANCE

The precise binding of a GlcN residue to the -2 subsite is essential for the conformational shift that occurs in all GH-46 chitosanases, as shown by the crystal structures of the apo- and substrate-bound forms of MH-K1 chitosanase.

Metabolomic Analysis of Fermented Tibetan Tea Using Bacillus circulans and Their Biological Activity on Mice via the Intestine-Hepatic Axis

The use of Bacillus circulans as the sole starter provides better process control compared to natural fermentation. However, the chemical composition of fermented Tibetan tea by B. circulans and its regulatory effects on the intestine-liver axis has not been reported. For this purpose, a high-resolution liquid chromatography tandem mass spectrometry metabolomics approach was performed. The effects of fermented Tibetan tea on the intestine-liver axis of mice were also evaluated. Untargeted metabolomics analysis showed that the contents of catechin derivatives, flavonoids, phenolic acids, and terpenoids increased by 0.3, 2.38, 2.65, and 3.36%, respectively, compared with those before fermentation. Furthermore, 16S ribosomal RNA sequence analysis revealed that the relative abundance of Lactobacillus spp. in the intestine increased after consumption of fermented tea. Additionally, based on histological and quantitative PCR analyses, fermented Tibetan tea also improved intestinal development and intestinal barrier function in mouse, while increasing the antioxidant capacity of mouse liver. Thus, fermented Tibetan tea could provide beneficial health effects through the intestine-liver axis. These findings have facilitated the study of the chemical composition of Tibetan tea and provided theoretical support for its use as a natural beverage with intestinal probiotic functions.

Safety evaluation of the food enzyme β-galactosidase from the non-genetically modified Neobacillus sp. strain AE-LT

The food enzyme β‐galactosidase (EC 3.2.1.23) is produced with the non‐genetically modified Neobacillus sp. strain AE‐LT by Amano Enzyme Inc. The strain is not cytotoxic and does not harbour any known virulence factor or antimicrobial resistance gene. The presence of viable cells of the production strain in the food enzyme could not be excluded, but the likelihood of this being a hazard is considered low. The food enzyme is intended to be used for lactose hydrolysis in milk processing and the manufacture of galacto‐oligosaccharides (GOS). The dietary exposure to the food enzyme–total organic solids (TOS) was estimated to be up to 2.971 mg TOS/kg body weight (bw) per day in European populations. Genotoxicity tests did not raise a safety concern. The systemic toxicity was assessed by means of a repeated dose 90‐day oral toxicity study in rats. The Panel identified a no observed adverse effect level of 1,223 mg TOS/kg bw per day, the highest dose tested, which when compared with the estimated dietary exposure, results in a margin of exposure of at least 412. A search for similarity of the amino acid sequence of the food enzyme to known allergens was made and no match was found. The Panel considered that, under the intended conditions of use, the risk of allergic reactions by dietary exposure cannot be excluded, but the likelihood for this to occur is low. Based on the data provided, the Panel concluded that this food enzyme does not give rise to safety concerns under the intended conditions of use.

β-galactosidase GALA from Bacillus circulans with high transgalactosylation activity

β-galactosidase catalyzes lactose hydrolysis and transfers reactions to produce prebiotics such as galacto-oligosaccharides (GOS) with potential applications in the food industry and pharmaceuticals. However, there is still a need for improved transgalactosylation activity of β-galactosidases and reaction conditions of GOS production in order to maximize GOS output and reduce production costs. In this study, a β-galactosidase gene, galA, from Bacillus circulans was expressed in Pichia pastoris, which not only hydrolyzed lactose but also had strong transgalactosylation activity to produce GOS. Response surface methodology was adopted to investigate the effects of temperature, enzyme concentration, pH, initial lactose concentration, and reaction time on the production of GOS and optimize the reaction conditions for GOS. The optimal pH for the enzyme was 6.0 and remained stable under neutral and basic conditions. Meanwhile, GALA showed most activity at 50°C and retained considerable activity at a lower temperature 30–40°C, indicating this enzyme could work under mild conditions. The enzyme concentration and temperature were found to be the critical parameters affecting the transgalactosylation activity. Response surface methodology showed that the optimal enzyme concentration, initial lactose concentration, temperature, pH, and reaction time were 3.03 U/mL, 500 g/L, 30°C, 5.08, and 4 h, respectively. Under such conditions, the maximum yield of GOS was 252.8 g/L, accounting for approximately 50.56% of the total sugar. This yield can be considered relatively high compared to those obtained from other sources of β-galactosidases, implying a great potential for GALA in the industrial production and application of GOS.

Lemierre's syndrome by Bacillus circulans, Fusobacterium nucleatum and Staphylococcus aureus with involvement of the internal and external jugular vein

Introduction

Lemierre's syndrome refers to the septic thrombophlebitis of the internal jugular vein, secondary to a pharyngeal infection. Although it mainly affects the internal jugular vein, isolated cases have been described of involvement of the external jugular vein. The main etiological agent is Fusobacterium necrophorum.

Case report

A 27-year-old male, previously healthy, presented with a 7-day history of sore throat and fever. He was diagnosed with Lemierre's syndrome, coinfection by Bacillus circulans, F. nucleatum and Staphylococcus aureus with an atypical presentation due to the involvement of the external jugular vein and the internal jugular vein.

Conclusions

As far as we are aware, we present the first case of Lemierre's syndrome with these characteristics.

Composition analysis and oral administered effects on dextran sulfate sodium-induced colitis of galactooligosaccharides bioconverted by Bacillus circulans

Galactooligosaccharides have been known to have many health benefits as prebiotic ingredients. In this study, we examined the anti-inflammatory activity of the galactooligosaccharide, NeoGOS-P70 (Korean commercial product), in a dextran sodium sulfate-induced colitis model. Next, we performed compositional characterization of NeoGOS-P70, which confirmed that it was a 77.4% high-purity GOS products, including a large amount of 4'-galactosyllactose. Further experiments in DSS-induced colitis model showed that oral administration of NeoGOS-P70 could significantly improve DSS-induced colitis symptoms, such as weight loss, reduction in colon shortening, and suppression of inflammatory mediators, including interleukin-6, tumor necrosis factor-α, and myeloperoxidase secretion from colon of ulcerative colitis mice. Histological analysis of mucin expression in colon tissue revealed the protective effects of NeoGOS-P70. These results suggest the potential of the novel GOS, NeoGOS-P70, as an anti-ulcerative colitis agent that could regulate inflammatory responses.

First report of spondylodiscitis caused by Bacillus circulans in an immunocompetent patient: Clinical case and review of the literature

Bacillus circulans is mainly considered an opportunistic pathogen in immunocompromised patients. However, many different infections have been described in the literature: bacteremia, abscesses, meningitis, endophthalmitis, and wound infections. We observed a spondylodiscitis caused by Bacillus circulans in an immunocompetent patient. To date, this is the first case reported in literature. Vertebral osteomyelitis represents for clinicians a challenging infection to manage and treat, because of its insidious and indolent course. The diagnosis is frequently difficult and can often be delayed for several months and initially be misdiagnosed and mismanaged. For this reason, the clinical case was described and all published cases of infection caused by Bacillus circulans were reviewed.

Bacillus circulans GN03 Alters the Microbiota, Promotes Cotton Seedling Growth and Disease Resistance, and Increases the Expression of Phytohormone Synthesis and Disease Resistance-Related Genes

Plant growth-promoting bacteria (PGPB) are components of the plant rhizosphere that promote plant growth and/or inhibit pathogen activity. To explore the cotton seedlings response to Bacillus circulans GN03 with high efficiency of plant growth promotion and disease resistance, a pot experiment was carried out, in which inoculations levels of GN03 were set at 10⁴ and 10⁸ cfu^⋅mL^-1. The results showed that GN03 inoculation remarkably enhanced growth promotion as well as disease resistance of cotton seedlings. GN03 inoculation altered the microbiota in and around the plant roots, led to a significant accumulation of growth-related hormones (indole acetic acid, gibberellic acid, and brassinosteroid) and disease resistance-related hormones (salicylic acid and jasmonic acid) in cotton seedlings, as determined with ELISA, up-regulated the expression of phytohormone synthesis-related genes (EDS1, AOC1, BES1, and GA20ox), auxin transporter gene (Aux1), and disease-resistance genes (NPR1 and PR1). Comparative genomic analyses was performed between GN03 and four similar species, with regards to phenotype, biochemical characteristics, and gene function. This study provides valuable information for applying the PGPB alternative, GN03, as a plant growth and disease-resistance promoting fertilizer.

Update of the list of QPS-recommended biological agents intentionally added to food or feed as notified to EFSA 13: suitability of taxonomic units notified to EFSA until September 2020

The qualified presumption of safety (QPS) approach was developed to provide a regularly updated generic pre-evaluation of the safety of biological agents, intended for addition to food or feed, to support the work of EFSA's Scientific Panels. It is based on an assessment of published data for each agent, with respect to its taxonomic identity, the body of knowledge, safety concerns and antimicrobial resistance. Safety concerns identified for a taxonomic unit (TU) are, where possible, confirmed at strain or product level, and reflected by 'qualifications'. In the period covered by this statement, no new information was found that would change the status of previously recommended QPS TUs. Of the 36 microorganisms notified to EFSA between April and September 2020, 33 were excluded; seven filamentous fungi (including Aureobasidium pullulans based on recent taxonomic insights), one Clostridium butyricum, one Enterococcus faecium, three Escherichia coli, one Streptomyces spp. and 20 TUs that had been previously evaluated. Three TUs were evaluated; Methylorubrum extorquens and Mycobacterium aurum for the first time and Bacillus circulans was re-assessed because an update was requested in relation to a new mandate. M. extorquens and M. aurum are not recommended for QPS status due to the lack of a body of knowledge in relation to use in the food or feed chain and M. aurum, due to uncertainty concerning its pathogenicity potential. B. circulans was recommended for QPS status with the qualifications for 'production purposes only' and 'absence of cytotoxic activity'.

High Galacto-Oligosaccharide Production and a Structural Model for Transgalactosylation of β-Galactosidase II from Bacillus circulans

The transgalactosylase activity of β-galactosidase produces galacto-oligosaccharides (GOSs) with prebiotic effects similar to those of major oligosaccharides in human milk. β-Galactosidases from Bacillus circulans ATCC 31382 are important enzymes in industrial-scale GOS production. Here, we show the high GOS yield of β-galactosidase II from B. circulans (β-Gal-II, Lactazyme-B), compared to other commercial enzymes. We also determine the crystal structure of the five conserved domains of β-Gal-II in an apo-form and complexed with galactose and an acceptor sugar, showing the heterogeneous mode of transgalactosylation by the enzyme. Truncation studies of the five conserved domains reveal that all five domains are essential for enzyme catalysis, while some truncated constructs were still expressed as soluble proteins. Structural comparison of β-Gal-II with other β-galactosidase homologues suggests that the GOS linkage preference of the enzyme might be quite different from other enzymes. The structural information on β-Gal-II might provide molecular insights into the transgalactosylation process of the β-galactosidases in GOS production.

Mitigation of Copper Stress in Maize by Inoculation with Paenibacillus polymyxa and Bacillus circulans

Copper (Cu) is a micronutrient that assumes a principal role in plant growth and development. However, its excess concentration in soil is imperiling crop productivity. Inoculation with different bacterial strains in cereals could modify growth traits, photosynthetic effectiveness, and generation of strong antioxidant defense systems to make them more tolerant of Cu stress. Therefore, a pot study was designed to test plant growth-promoting rhizobacteria (PGPR) including Paenibacillus polymyxa and Bacillus circulans to Cu exposed maize (Zea mays L.) plants. Increasing Cu (100 to 500 µM of CuSO₄) concentration decreased growth traits, photosynthetic pigments, soluble sugars, phosphorous (P) and potassium (K) contents, and the activity of catalase (CAT) but increased proline and malondialdehyde (MDA) content, the activity of peroxidase (POD) and Cu ions at root and shoot level. Moreover, the bacterial treatment also modulated the antioxidant capability in stress-free plants. Nevertheless, inoculation with P. polymyxa and B. circulans alleviated Cu-induced growth, photosynthetic pigments and mineral nutrient (P and K) on one hand and regulating the pools of osmolytes and antioxidant enzymes, whilst simultaneously reducing MDA and Cu root and shoot contents. These improved activities of antioxidant enzymes and the regulation of osmolytes content elicited by the blend of bacterial inoculation would have retained the ability of maize plants to confer resilience to Cu stress. This study further affirms that the application of two specific bacterial strains to maize plants proved very effective to ameliorate the Cu toxicity.

Ultrasound-assisted improvements in biocatalytic activity and production of organic-solvent stable protease from Bacillus circulans MTCC 7942

This study reports the ultrasound-assisted improvements in biocatalytic activity and production of protease from organic solvent-tolerant, alkaliphilic Bacillus circulans MTCC 7942. The strain withstands 10min ultrasound treatment (33kHz); this treatment promotes the growth of bacterium. The protease production was improved by 1.5-fold on multiple ultrasound treatment at 0, 6, 12h intervals. Although the substrate casein remains unaffected by ultrasound treatment (33kHz, 10min); the treatment had boosted the enzyme activity of purified protease. Also, the ultrasound treated purified protease showed enhancement in enzyme activity in presence of n-dodecane, n-octane, n-hexadecane, n-decane, xylene, butanol, toluene, pyridine and chloroform.

The structure of RbmB from Streptomyces ribosidificus, an aminotransferase involved in the biosynthesis of ribostamycin

Aminoglycoside antibiotics represent a classical group of antimicrobials first discovered in the 1940s. Due to their ototoxic and nephrotoxic side effects, they are typically only used against Gram negative bacteria which have become resistant to other therapeutics. One family of aminoglycosides includes such compounds as butirosin, ribostamycin, neomycin, and kanamycin, amongst others. The common theme in these antibiotics is that they are constructed around a chemically stable aminocyclitol unit referred to as 2-deoxystreptamine (2-DOS). Four enzymes are required for the in vivo production of 2-DOS. Here, we report the structure of RbmB from Streptomyces ribosidificus, which is a pyridoxal 5'-phosphate dependent enzyme that catalyzes two of the required steps in 2-DOS formation by functioning on distinct substrates. For this analysis, the structure of the external aldimine form of RbmB with 2-DOS was determined to 2.1 Å resolution. In addition, the structure of a similar enzyme, BtrR from Bacillus circulans, was also determined to 2.1 Å resolution in the same external aldimine form. These two structures represent the first detailed molecular descriptions of the active sites for those aminotransferases involved in 2-DOS production. Given the fact that the 2-DOS unit is widespread amongst aminoglycoside antibiotics, the data presented herein provide new molecular insight into the biosynthesis of these sugar-based drugs.

Simultaneous decolorization of sulfonated azo dyes and reduction of hexavalent chromium under high salt condition by a newly isolated salt-tolerant strain Bacillus circulans BWL1061

The co-existence of dyes, Cr(VI) and high concentration of salt in dyeing wastewater causes serious and complex environmental problems. In this study, a salt-tolerant strain Bacillus circulans BWL1061 was reported to simultaneously remove 50mg/L methyl orange and 50mg/L Cr(VI) under the anaerobic condition with 60g/L NaCl. During the decolorization process, the Cr(VI) reduction occurred preferentially over the dye decolorization due to the dominate utilization of electron by Cr(VI). The analysis of enzyme activities suggested that azoreductase, NADH-DCIP reductase, and laccase were associated with decolorization of methyl orange. A possible degradation pathway was proposed based on the metabolites analysis. The decolorization of methyl orange is involved in the symmetric cleavage of azo bond, which formed N,N-dimethyl p-phenylenediamine and 4-amino sulfonic acid, or the asymmetric cleavage of azo bond, which formed 4-(dimethylamino) phenol and 4-diazenylbenzene sulfonic acid. Phytotoxicity assays showed that strain BWL1061 could decrease the toxicity of methyl orange to Triticum aestivum, Pogostemon cablin and Isatis indigotica Fort during the decolorization process. In this study, Bacillus circulans is reported for the first time that could simultaneously remove azo dyes and Cr (VI) under high salt condition.

[Activation of biosynthesis of guanyl-specific ribonuclease secreted by Bacillus circulans under salt stress]

The gene transcription of guanyl-specific ribonucleases (RNases), which provide available phosphate to cells of Bacillus, is controlled by the signal transduction system PhoP-PhoR. However, the biosynthesis of B. circulans RNase does not depend on the signal-transduction regulatory proteins of Pho regulon. It has been found that raising the salt molar concentration in culture medium increases the level of extracellular guanyl-specific ribonuclease Bci synthesized by B. circulans. Sequences homologous to the binding sites of the regulatory protein DegU were found in RNase Bci promoter. The functioning of the DegS-DegU signal transduction system is stimulated by a high salt concentration. Using a strain of B. subtilis that is defective in the DegU regulatory protein, we have shown that the DegS-DegU system participates in the regulation of RNase Bci expression under salt stress.

Detergent-compatible, organic solvent-tolerant alkaline protease from Bacillus circulans MTCC 7942: Purification and characterization

Proteases are now recognized as the most indispensable industrial biocatalyst owing to their diverse microbial sources and innovative applications. In the present investigation, a thermostable, organic solvent-tolerant, alkaline serine protease from Bacillus circulans MTCC 7942, was purified and characterized. The protease was purified to 37-fold by a three-step purification scheme with 39% recovery. The optimum pH and temperature for protease was 10 and 60 °C, respectively. The apparent molecular mass of the purified enzyme was 43 kD as revealed by sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE). The Km and Vmax values using casein-substrate were 3.1 mg/mL and 1.8 µmol/min, respectively. The protease remained stable in the presence of organic solvents with higher (>3.2) log P value (cyclohexane, n-octane, n-hexadecane, n-decane, and n-dodecane), as compared to organic solvents with lower (<3.2) log P value (acetone, butanol, benzene, chloroform, toluene). Remarkably, the protease showed profound stability even in the presence of organic solvents with less log P values (glycerol, dimethyl sulfate [DMSO], p-xylene), indicating the possibility of nonaqueous enzymatic applications. Also, protease activity was improved in the presence of metal ions (Ca(2+), Mg(2+), Mn(2+)); enhanced by biosurfactants; hardly affected by bleaching agents, oxidizing agents, and chemical surfactants; and stable in commercial detergents. In addition, a protease-detergent formulation effectively washed out egg and blood stains as compared to detergent alone. The protease was suitable for various commercial applications like processing of gelatinous film and as a compatible additive to detergent formulation with its operative utility in hard water.

Characterization of mannanase from Bacillus circulans NT 6.7 and its application in mannooligosaccharides preparation as prebiotic

This study focused on the characterization of mannanase from Bacillus circulans NT 6.7 for mannooligosaccharides (MOS) production. The enzyme from B. circulans NT 6.7 was produced using defatted copra meal as a carbon source. The mannanase was purified by ultrafiltration and column chromatography of Q-Sepharose. The purified protein (M1) was a dimeric protein with a 40 kDa subunit. The purified M1 exhibited optimum pH and temperature at pH 6.0 and 60 °C, respectively. It was activated by Mn(2+,) Mg(2+,) and Cu(2+), and as inhibited by EDTA (45-65 %). The purified enzyme exhibited high specificity to beta-mannan: konjac (glucomannan), locust bean gum (galactomannan), ivory nut (mannan), guar gum (galactomannan) and defatted copra meal (galactomannan). The defatted copra meal could be hydrolyzed by purified M1 into mannooligosaccharides which promoted beneficial bacteria, especially Lactobacillus group, and inhibited pathogenic bacteria; Shigella dysenteria DMST 1511, Staphylococcus aureus TISTR 029, and Salmonella enterica serovar Enteritidis DMST 17368. Therefore, the mannanase from B. circulans NT 6.7 would be a novel source of enzymes for the mannooligosaccharides production as prebiotics.

Continuous production of cyclodextrins in an ultrafiltration membrane reactor, catalyzed by cyclodextrin glycosyltransferase from Bacillus circulans DF 9R

Cyclodextrins (CDs) are cyclic oligosaccharides of wide industrial application, whose synthesis is catalyzed by Cyclodextrin glycosyltransferase (CGTase) from starch. Here, CDs were produced using CGTase from Bacillus circulans DF 9R in continuous process and an ultrafiltration membrane reactor. The batch process was conducted as a control. This method allowed increasing the yield from 40 to 55.6% and the productivity from 26.1 to 99.5 mg of CD per unit of enzyme. The method also allowed obtaining a high-purity product. The flow rate remained at 50% of its initial value after 24 h of process, improving the results described in the literature for starch hydrolysis processes. CGTase remained active throughout the process, which could be explained by the protective effect of the substrate and reaction products on CGTase stability. In addition, batch processes were developed using starches from different sources. We concluded that any of the starches studied could be used as substrate for CD production with similar yields and product specificity.

Biochemical characterization of mutants in the active site residues of the β-galactosidase enzyme of Bacillus circulans ATCC 31382

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Active site characteristics of the β-galactosidase enzyme of Bacillus circulans ATCC 31382.

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Residues essential for catalysis were identified by structure-based alignments.

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Mutational analysis identified two catalytic glutamate amino acid residues.

The Bacillus circulans ATCC 31382 β-galactosidase (BgaD) is a retaining-type glycosidase of glycoside hydrolase family 2 (GH2). Its commercial enzyme preparation, Biolacta N5, is used for commercial-scale production of galacto-oligosaccharides (GOS). The BgaD active site and catalytic amino acid residues have not been studied. Using bioinformatic routines we identified two putative catalytic glutamates and two highly conserved active site histidines. The site-directed mutants E447N, E532Q, and H345F, H379F had lost (almost) all catalytic activity. This confirmed their essential role in catalysis, as general acid/base catalyst (E447) and nucleophile (E532), and as transition state stabilizers (H345, H379), respectively.

β-galactosidase stability at high substrate concentrations

Enzymatic synthesis of galacto-oligosaccharides is usually performed at high initial substrate concentrations since higher yields are obtained. We report here on the stability of β-galactosidase from Bacillus circulans at 25, 40, and 60°C in buffer, and in systems with initially 5.0 and 30% (w/w) lactose. In buffer, the half-life time was 220 h and 13 h at 25 and 40°C, respectively, whereas the enzyme was completely inactivated after two hours at 60°C. In systems with 5.0 and 30% (w/w) lactose, a mechanistic model was used to correct the oNPG converting activity for the presence of lactose, glucose, galactose, and oligosaccharides in the activity assay. Without correction, the stability at 5.0% (w/w) lactose was overestimated, while the stability at 30% (w/w) lactose was underestimated. The inactivation constant k d was strongly dependent on temperature in buffer, whereas only a slight increase in k d was found with temperature at high substrate concentrations. The enzyme stability was found to increase strongly with the initial substrate concentrations. The inactivation energy E a appeared to be lower at high initial substrate concentrations.

Crystallization and preliminary X-ray crystallographic analysis of cycloisomaltooligosaccharide glucanotransferase from Bacillus circulans T-3040

Bacillus circulans T-3040 cycloisomaltooligosaccharide glucanotransferase (BcCITase) catalyses an intramolecular transglucosylation reaction and produces cycloisomaltooligosaccharides from dextran. BcCITase was overexpressed in Escherichia coli in two different forms and crystallized by the sitting-drop vapour-diffusion method. The crystal of BcCITase bearing an N-terminal His₆ tag diffracted to a resolution of 2.3 Å and belonged to space group P3₁21, containing a single molecule in the asymmetric unit. The crystal of BcCITase bearing a C-terminal His6 tag diffracted to a resolution of 1.9 Å and belonged to space group P2₁2₁2₁, containing two molecules in the asymmetric unit.

Molecular Cloning and Nucleotide Sequence of the Gene for an Alkaline Protease from Bacillus circulans MTCC 7906

Bacillus circulans MTCC 7906, an extracellular alkaline protease producer was genetically characterized. B. circulans genomic DNA was isolated, oligonucleotide primers specific to alkaline protease gene of B. circulans were designed and its PCR amplification was done. The purified PCR product and pTrcHisA vector were subjected to restriction digestion with NcoI and HindIII and transformed into Escherichia coli DH5-α competent cells. The recombinant expression of alkaline protease gene studied by inducible expression and analysis by SDS-PAGE, established that the alkaline protease protein had an estimated molecular size of 46 kDa. Gene sequencing of the insert from selected recombinant clone showed it to be a 1329 bp gene encoding a protein of 442 amino acids. The sequence was blasted and aligned with known alkaline protease genes for comparison with their nucleotide and amino acid sequences. This identified major matches with three closely related subsp. of B. subtilis (B. subtilis subsp. subtilis strain 168, B. subtilis BSn5 and B. subtilis subsp. spizizenii strain W23). The insert also showed a number of substitutions (mutations) with other sp. of Bacillus which established that alkaline protease of B. circulans MTCC 7906 is a novel gene. The phylogenetic analysis of alkaline protease gene and its predicted amino acid sequences also validated that alkaline protease gene is a novel gene and the same has been accessioned in GenBank with accession number JN645176.1.

An alkaline protease from Bacillus circulans BM15, newly isolated from a mangrove station: characterization and application in laundry detergent formulations

An investigation on the properties of an alkaline protease secreted by Bacillus circulans BM15 strain isolated from a mangrove sediment sample was carried out in order to characterize the enzyme and to test its potency as a detergent additive. The protease was purified to apparent homogeneity by ammonium sulphate precipitation and was a 30-kDa protease as shown by SDS-PAGE and its proteolytic activity was detected by casein zymography. It had optimum activity at pH 7, was stable at alkaline pH range (7 to 11), had optimum temperature of activity 40°C and was stable up to a temperature of 55°C after incubation for one hour. Hg(2+), Zn(2+), Co(2+), and Cu(2+)completely inhibited the enzyme activity, while Ca(2+), Mg(2+), K(+) and Fe(3+) were enhancing the same. The serine protease inhibitor PMSF and metal chelator EDTA inhibited the activity of this protease while the classic metalloprotease inhibitor 1, 10 phenanthroline did not show inhibition. The enzyme was stable in SDS, Triton-X-100 and H(2) O(2) as well as in various commercial detergents after incubation for one hour. The extracellular production of the enzyme, the pH and temperature stability and stability in presence of oxidants, surfactants and commercial detergents suggest its possible use as a detergent additive.