Bacillus brevis, a host bacterium for efficient extracellular production of useful proteins

Heterologous Expression of the Marine-Derived Quorum Quenching Enzyme MomL Can Expand the Antibacterial Spectrum of Bacillus brevis

Quorum sensing (QS) is closely associated with the production of multiple virulence factors in bacterial pathogens. N-acyl homoserine lactones (AHLs) are important QS signal molecules that modulate the virulence of gram-negative pathogenic bacteria. Enzymatic degradation of AHLs to interrupt QS, termed quorum quenching (QQ), has been considered a novel strategy for reduction of pathogenicity and prevention of bacterial disease. However, the low expression levels of QQ proteins in the original host bacteria has affected the applications of these proteins. Previously, we identified a novel marine QQ enzyme, named MomL, with high activity and promising biocontrol function. In this study, we linked the target fragment momL to pNCMO2, which provided a basis for the first heterologous expression of MomL in the antifungal and anti-gram-positive-bacteria biocontrol strain Bacillus brevis, and obtaining the recombinant strain named BbMomL. The QQ activity of BbMomL was confirmed using a series of bioassays. BbMomL could not only degrade the exogenous signal molecule C6-HSL, but also the AHL signal molecules produced by the gram-negative pathogens Pectobacterium carotovorum subsp. carotovorum (Pcc) and Pseudomonas aeruginosa PAO1. In addition, BbMomL significantly reduced the secretion of pathogenic factors and the pathogenicity of Pcc and P. aeruginosa PAO1. We tested the biocontrol function of BbMomL for prevention of plant diseases in vitro. The result indicates that BbMomL has a broad antibacterial spectrum. Compared with wild-type B. brevis, BbMomL not only inhibited fungi and gram-positive bacterial pathogens but also considerably inhibited gram-negative bacterial pathogens. Moreover, the Bacillus brevis expression system has good application prospects and is an ideal host for expression and secretion of foreign proteins.

Efficient soluble expression of secreted matrix metalloproteinase 26 in Brevibacillus choshinensis

Matrix metalloproteinase 26 (MMP-26) is a novel member of the matrix metalloproteinase family with minimal domain constitution and unknown physiological function. The three-dimensional (3D) structure of the enzyme also remains to be deciphered. Previous studies show that MMP-26 may be expressed in Escherichia coli (E. coli) as inclusion bodies and re-natured with catalytic activity. However, the low re-naturation rate of this method limits its usage in structural studies. In this paper, we tried to clone, express and purify the pro form and catalytic form of MMP-26 (ProMMP-26 and CatMMP-26) in several widely used expression vectors and express the recombinant MMP-26 proteins in E. coli cells. These constructs resulted in insoluble expressions or soluble expressions of MMP-26 with little catalytic activity. We then used Brevibacillus choshinensis (B. choshinensis) as the host system for the soluble and active expression of MMP-26. The enzyme was secreted in soluble form in the supernatant of cell culture medium and purified via a two-step purification process that included Ni(2+) affinity chromatography followed by gel filtration. The yields of purified ProMMP-26 and CatMMP-26 were 12 and 18mg/L, respectively, with high purity and homogeneity. Both ProMMP-26 and CatMMP-26 showed gelatin zymography activity and the purified CatMMP-26 had high enzymatic activity against DQ-gelatin substrate. The large-scale soluble and active protein production for future structural studies of MMP-26 is thus feasible using the B. choshinensis host system.

Expression and purification of canine granulocyte colony-stimulating factor (cG-CSF)

Canine granulocyte colony-stimulating factor (cG-CSF) with modification of cysteine at position 17 to serine was expressed in Brevibacillus choshinensis HPD31. cG-CSF secreted into the culture medium was purified by ammonium sulfate precipitation and consecutive column chromatography, using butyl sepharose and DEAE sepharose. Biological activity of the recombinant cG-CSF was 8.0 x 10(6) U/mg protein, as determined by its stimulatory effect on NFS-60 cell proliferation. Purified cG-CSF was subcutaneously administered once a day for two successive days to dogs (1, 5, 25, or 125 microg). Neutrophil count increased the following day in all dogs except those administered the lowest dose (1 microg). No severe side effects were observed in dogs after administration of cG-CSF.

S-layer nanoglycobiology of bacteria

Cell surface layers (S-layers) are common structures of the bacterial cell envelope with a lattice-like appearance that are formed by a self-assembly process. Frequently, the constituting S-layer proteins are modified with covalently linked glycan chains facing the extracellular environment. S-layer glycoproteins from organisms of the Bacillaceae family possess long, O-glycosidically linked glycans that are composed of a great variety of sugar constituents. The observed variations already exceed the display found in eukaryotic glycoproteins. Recent investigations of the S-layer protein glycosylation process at the molecular level, which has lagged behind the structural studies due to the lack of suitable molecular tools, indicated that the S-layer glycoprotein glycan biosynthesis pathway utilizes different modules of the well-known biosynthesis routes of lipopolysaccharide O-antigens. The genetic information for S-layer glycan biosynthesis is usually present in S-layer glycosylation (slg) gene clusters acting in concert with housekeeping genes. To account for the nanometer-scale cell surface display feature of bacterial S-layer glycosylation, we have coined the neologism 'nanoglycobiology'. It includes structural and biochemical aspects of S-layer glycans as well as molecular data on the machinery underlying the glycosylation event. A key aspect for the full potency of S-layer nanoglycobiology is the unique self-assembly feature of the S-layer protein matrix. Being aware that in many cases the glycan structures associated with a protein are the key to protein function, S-layer protein glycosylation will add a new and valuable component to an 'S-layer based molecular construction kit'. In our long-term research strategy, S-layer nanoglycobiology shall converge with other functional glycosylation systems to produce 'functional' S-layer neoglycoproteins for diverse applications in the fields of nanobiotechnology and vaccine technology. Recent advances in the field of S-layer nanoglycobiology have made our overall strategy a tangible aim of the near future.

Secretion of human epidermal growth factor by Corynebacterium glutamicum

AIMS

To examine the secretion of human epidermal growth factor (hEGF) by Corynebacterium glutamicum.

METHODS AND RESULTS

We recently showed that a novel protein-secretion system in C. glutamicum could produce Streptomyces mobaraensis transglutaminase. In the present study, the industrially important protein hEGF was secreted into the culture medium in a fully active form by C. glutamicum and accumulated at a rate of up to 156 mg l(-1) day(-1).

CONCLUSIONS

These results demonstrated that the hEGF protein could be secreted in an active form by C. glutamicum.

SIGNIFICANCE AND IMPACT OF THE STUDY

Our data confirmed that the pharmaceutically important human protein hEGF could be efficiently secreted in an active form by the C. glutamicum protein-expression system. Moreover, we demonstrated that this bacterium has potential as a host for the industrial-scale production of human proteins.

Expression and purification of thioredoxin (TrxA) and thioredoxin reductase (TrxB) from Brevibacillus choshinensis

Brevibacillus choshinensis (formerly Bacillus brevis) is a protein-hyperproducing bacterium and has been used for commercial protein production. Here, we cloned thioredoxin (trxA) and thioredoxin reductase (trxB) genes from B. choshinensis, and expressed the gene products in Escherichia coli with an amino-terminal hexa-His-tag for purification and characterization. His-TrxA and His-TrxB were purified to homogeneity with one-step Ni-NTA affinity column chromatography, and the two recombinant proteins showed identical specific activity with or without removal of the amino-terminal His-tag, indicating that the extrasequence containing the hexa-His-tag did not affect their enzymatic activities. The E. coli expression system used here resulted in a 40-fold increase in production of His-TrxB protein compared to the level of native TrxB produced in non-recombinant B. choshinensis cells. TrxA and TrxB proteins with carboxy-terminal His-tag (TrxA-His and TrxB-His) were successfully expressed in B. choshinensis and were purified by Ni-NTA column chromatography. Co-expression of TrxA-His with recombinant human epidermal growth factor (hEGF) in B. choshinensis promoted the extracellular production of hEGF by up to about 200%.

Bacillus subtilis as a tool for vaccine development: from antigen factories to delivery vectors

Bacillus subtilis and some of its close relatives have a long history of industrial and biotechnological applications. Search for antigen expression systems based on recombinant B. subtilis strains sounds attractive both by the extensive genetic knowledge and the lack of an outer membrane, which simplify the secretion and purification of heterologous proteins. More recently, genetically modified B. subtilis spores have been described as indestructible delivery vehicles for vaccine antigens. Nonetheless both production and delivery of antigens by B. subtilis strains face some inherent obstacles, as unstable gene expression and reduced immunogenicity that, otherwise, can be overcome by already available gene technology approaches. In the present review we present the status of B. subtilis-based vaccine research, either as protein factories or delivery vectors, and discuss some alternatives for a better use of genetically modified strains.

Cloning and expression of the ccdA-associated thiol-disulfide oxidoreductase (catA) gene from Brevibacillus choshinensis: stimulation of human epidermal growth factor production

Brevibacillus choshinensis (Bacillus brevis) is a protein-hyperproducing bacterium with a useful host-vector system for the production of recombinant proteins. Here, we cloned the ccdA-catA (cmacr;cdA āssociated thioredoxin-like tmacr;hiol-disulfide oxidoreductase) locus of B. choshinensis HPD31-S5. CatA protein (molecular weight, 19664) contains a thioredoxin-like motif, Cys-Gly-Pro-Cys. It was successfully expressed in B. choshinensis extracellularly ( approximately 100 microg x ml(-1) culture) using the secretion vector pNCMO2, and in Escherichia coli intracellularly ( approximately 350 microg x ml(-1) culture) with an amino-terminal His-tag. Both recombinant proteins showed thiol-disulfide oxidoreductase activity. Incubation of non-native human epidermal growth factor (hEGF) containing incorrect disulfide bonds with B. choshinensis cells secreting CatA protein resulted in the stimulation of the conversion of non-native hEGF to the native form. Furthermore, co-expression of CatA protein with recombinant hEGF in the B. choshinensis production system increased the yield of native hEGF.

Secretion of active-form Streptoverticillium mobaraense transglutaminase by Corynebacterium glutamicum: processing of the pro-transglutaminase by a cosecreted subtilisin-Like protease from Streptomyces albogriseolus

The transglutaminase secreted by Streptoverticillium mobaraense is a useful enzyme in the food industry. A fragment of transglutaminase was secreted by Corynebacterium glutamicum when it was coupled on a plasmid to the promoter and signal peptide of a cell surface protein from C. glutamicum. We analyzed the signal peptide and the pro-domain of the transglutaminase gene and found that the signal peptide consists of 31 amino acid residues and the pro-domain consists of 45 residues. When the pro-domain of the transglutaminase was used, the pro-transglutaminase was secreted efficiently by C. glutamicum but had no enzymatic activity. However, when the plasmid carrying the S. mobaraense transglutaminase also encoded SAM-P45, a subtilisin-like serine protease derived from Streptomyces albogriseolus, the peptide bond to the C side of 41-Ser of the pro-transglutaminase was hydrolyzed, and the pro-transglutaminase was converted to an active form. Our findings suggest that C. glutamicum has potential as a host for industrial-scale protein production.

Mucosal immunoadjuvant activity of the low toxic recombinant Escherichia coli heat-labile enterotoxin produced by Bacillus brevis for the bacterial subunit or component vaccine in pigs and cattle

A gene encoding the mature Escherichia coli heat-labile enterotoxin (LT) lacking the nick site in the A subunit by deleting tripeptides was introduced in a vector pNH301 and expressed extracellularly as mutant molecule of holotoxin at high levels in Bacilus brevis HPD31-S5 of the host bacterium. The mucosal adjuvant activities of the produced mutant LT (mLT) preparation were studied in pigs and cattle. Intranasal immunization of pigs with the recombinant subunit vaccine of Erysipelothrix rhusiopathiae or the component vaccine of Bordetella bronchiseptica mixed with the mLT resulted in a substantial enhancement of both mucosal and serum-specific antibody levels. The immunized pigs were also protected when challenge-exposed intradermally with a highly virulent E. rhusiopathiae strain or challenge-exposed intranasally with a highly virulent strain of B. bronchiseptica. The mLT intranasally administered with recombinant intimin (an outer membrane adhesin) of E. coli O157:H7 also induced an elevation of IgA-specific antibody in the nasal secretion and saliva of calves as well as an elevation of IgG1-specific antibody level against the intimin in the sera and colostrum of cows. The three kinds tested protein antigens were poorly immunogenic when antigen administered intranasally alone. The mLT intranasally administered at a higher effective dose did not induce local adverse reactions or diarrhea in pigs and cattle. The present study demonstrates that the recombinant mLT produced using the B. brevis expression system might represent promising immunoadjuvants for the potential application of intranasal vaccines directed against infectious diseases in pigs and cattle.

Human interleukin-1 receptor antagonist: large-scale expression in Bacillus brevis 47-5Q

Interleukin-1 receptor antagonist (IL-1RA) has been used as a tool to study the biologic activity of IL-1 and as a possible therapeutic substance for inflammatory disease. To perform in vivo study, however, large quantities of IL-1RA are required. Bacillus brevis strains secrete large amounts of protein but little protease into the medium. Using B. brevis 47-5Q, we developed a large-scale expression system of human IL-1RA (HuIL-1RA). The bacteria secreted HuIL-1RA into the culture medium at very high levels, approximately 200 mg/L. The protein was isolated in one-step purification with monoclonal antibody (mAb) against HuIL-1RA. The IL-1RA molecule was determined to be functionally active by the inhibiting assay of HuIL-1-induced cell proliferation in a mouse T cell line, D10N4M.

Molecular cloning of the dnaK locus, and purification and characterization of a DnaK protein from Bacillus brevis HPD31

Using part of the dnaK gene from Bacillus subtilis as a probe, a 4. 4-kbp SacI-BglII fragment of chromosomal DNA of Bacillus brevis, a protein-hypersecreting bacterium, was cloned. Nucleotide sequencing revealed 3 open reading frames in the order of grpE-dnaK-dnaJ homologues. We purified DnaK protein to homogeneity from B. brevis HPD31 harboring a multi-copy dnaK expression plasmid. Purified DnaK showed ATPase activity which was synergistically stimulated 14-fold by the addition of glutathione S-transferase-DnaJ and glutathione S-transferase-GrpE fusion proteins. DnaK hydrolyzed not only ATP but also CTP, UTP, and GTP at about 40% of the efficiency of ATP. The specific activity of DnaK-ATPase was 7.25x10-3 unit/mg protein (the turnover number against ATP was 0.47 min-1) under our assay conditions. The DnaK dimers dissociated into monomers on addition of ATP, GTP, CTP, UTP and ATPgammaS, but not ADP or AMP. DnaK formed a stable complex with permanently unfolded carboxymethylated alpha-lactalbumin but not with native alpha-lactalbumin, and this complex was dissociated by addition of ATP/Mg. Formation of this complex was inhibited in the presence of inorganic phosphate.

The efficient production of human epidermal growth factor by Bacillus brevis

A system has been developed for the efficient production of heterologous proteins using Bacillus brevis as a host that secretes large amounts of cell wall protein into the medium. The promoter region and signal peptide-encoding region of the cell wall protein gene were used to construct an expression-secretion vector. Bacterial proteins such as amylases can be produced in large amounts by this system (1 g/l or more), but mammalian proteins such as human alpha-amylase are produced at a low level (one or two orders of magnitude less than for bacterial proteins). The highly efficient secretion of human epidermal growth factor (h-EGF, more than 1 g/l) was obtained with B. brevis HPD31 as the host and plasmid pHY481, derived from B. brevis 481, as the vector. Recombinant hEGF was purified easily from the culture supernatant by two steps. Purified hEGF had the identical NH2-terminal amino acid sequence and COOH-terminal amino acid sequence with those of the authentic hEGF, and it was fully active in biological assays. This recombinant hEGF has been shown to be successful for biological wool harvesting (CSIRO, Australia). These results, in combination with previous results, indicate that foreign proteins of diverse origins can be produced efficiently as functional proteins in B. brevis.

Heterologous expression and site-directed mutagenesis studies on the activation mechanism and the roles of the basic residues in the prosegment of aspergillopepsinogen I

To study the structure/function relationship of the prosegment of aspartic proteinase, a putative proform of aspergillopepsin I (or proteinase B) from Aspergillus niger var. macrosporus was expressed by Escherichia coli, refolded in vitro, and purified. The conversion of the purified proenzyme (aspergillopepsinogen I, proproteinase B) into the active mature form occurred at pH < or = 4.5 and was completely inhibited by pepstatin A, a specific inhibitor for aspartic proteinase, suggesting autoprocessing. The N-terminus of this mature form was Glu67 (numbering in preproform), which was different from the N-terminal Ser70 of native proteinase B although there was no significant difference in enzymatic activity. During the conversion, two intermediates were observed on SDS/PAGE, indicating a stepwise mechanism. The Lys56-Phe57 sequence seems to be a counterpart of the Lys-Tyr pair highly conserved in the prosequences of aspartic proteinases. When the mutant proenzyme (K56N), in which Lys56 was replaced with Asn by site-directed mutagenesis, was allowed to refold under various conditions, no significant potential activity could be obtained. Proproteinase B was also expressed by Bacillus brevis HPD31. This system required no in vitro refolding to obtain potentially active proenzyme, which was secreted into the culture medium (30-120 mg/l) and had the same properties with that obtained by the E. coli system. The K56N mutant prepared by this system also had no potential activity, and was rapidly digested by incubation with native proteinase B, suggesting that the mutant did not fold correctly. On the other hand, the K56R mutant (Lys56-Arg) was potentially active. These results indicated that Lys56 is essential for the folding through electrostatic interaction with the catalytic Asp residues in the active site although it may be replaced with Arg. In the presence of a low concentration of pepstatin A, an incompletely processed form with N-terminal Ser53 was obtained. Further, the R52Q (Arg52-->Glin) mutant showed no processing but was converted to the active mature form by incubation with the native enzyme. Therefore, the cleavage between Arg52 and Ser53 is considered to be the initial and essential step of the autoactivation. The R26Q, K27Q, R36Q, K40Q, R42Q, and K66Q mutants were also potentially active. The K66Q mutant was processed to a form with N-terminal Ala55.

Dynamics in oxygen-induced changes in S-layer protein synthesis from Bacillus stearothermophilus PV72 and the S-layer-deficient variant T5 in continuous culture and studies of the cell wall composition

Stable synthesis of the hexagonally ordered (p6) S-layer protein from the wild-type strain of Bacillus stearothermophilus PV72 could be achieved in continuous culture on complex medium only under oxygen-limited conditions when glucose was used as the sole carbon source. Depending on the adaptation of the wild-type strain to low oxygen supply, the dynamics in oxygen-induced changes in S-layer protein synthesis was different when the rate of aeration was increased to a level that allowed dissimilation of amino acids. If oxygen supply was increased at the beginning of continuous culture, synthesis of the p6 S-layer protein from the wild-type strain (encoded by the sbsA gene) was immediately stopped and replaced by that of a new type of S-layer protein (encoded by the sbsB gene) which assembled into an oblique (p2) lattice. In cells adapted to a prolonged low oxygen supply, first, low-level p2 S-layer protein synthesis and second, synchronous synthesis of comparable amounts of both types of S-layer proteins could be induced by stepwise increasing the rate of aeration. The time course of changes in S-layer protein synthesis was followed up by immunogold labelling of whole cells. Synthesis of the p2 S-layer protein could also be induced in the p6-deficient variant T5. Hybridization data obtained by applying the radiolabelled N-terminal and C-terminal sbsA fragments and the N-terminal sbsB fragment to the genomic DNA of all the three organisms indicated that changes in S-layer protein synthesis were accompanied by chromosomal rearrangement. Chemical analysis of peptidoglycan-containing sacculi and extraction and recrystallization experiments revealed that at least for the wild-type strain, a cell wall polymer consisting of N-acetylglucosamine and glucose is responsible for binding of the p6 S-layer protein to the rigid cell wall layer.

Cloning and characterization of the gene for a protein thiol-disulfide oxidoreductase in Bacillus brevis

The gene (bdb) for protein thiol-disulfide oxidoreductase cloned from Bacillus brevis was found to encode a polypeptide consisting of 117 amino acid residues with a signal peptide of 27 residues. Bdb contains a well-conserved motif, Cys-X-X-Cys, which functions as the active center of disulfide oxidoreductases such as DsbA, protein disulfide isomerase, and thioredoxin. The deduced amino acid sequence showed significant homology with those of several bacterial thioredoxins. The bdb gene complemented the Escherichia coli dsbA mutation, restoring motility by means of flagellar and alkaline phosphatase activity. The Bdb protein overproduced in B. brevis was enzymatically active in both reduction and oxidization of disulfide bonds in vitro. Immunoblotting indicated that Bdb could function at the periphery of the cell.

Expression and secretion of malarial parasite beta-tubulin in Bacillus brevis

Microtubule inhibitors are active against the human malarial parasite Plasmodium falciparum, but whether these drugs actually interact with parasite tubulins is not known. It has not previously been possible to produce mg quantities of isolated, soluble tubulin subunits for drug-binding experiments. A cDNA encoding P falciparum beta-tubulin was expressed and the protein secreted in Bacillus brevis. With the addition of EGTA to the culture medium, which increases shedding of proteins from the cell surface, up to 2 mg/l recombinant beta-tubulin was obtained in supernatants. It is not clear why B brevis is able to secrete this normally cytoplasmic protein, but the secretion levels of recombinant proteins may be related to the net charge of the first few residues of the mature polypeptide.

Direct high-level secretion into the culture medium of tuna growth hormone in biologically active form by Bacillus brevis

The characteristic features of the Bacillus brevis system developed by us are very high productivity of heterologous proteins and very low extracellular proteinase activity. However, the production level of eucaryotic proteins with this system was generally one or two orders of magnitude lower than that of bacterial proteins. Therefore, we have explored methods for increasing the production efficiency as to animal proteins. Signal peptide modification was found to be very effective for high-level secretion of tuna growth hormone (tGH). Modification of the signal peptide with higher basicity in the amino terminal region and higher hydrophobicity in the middle region brought about a ten-fold increase in tGH production. Further elevation of the tGH yield to 240 mg/l was achieved by using a low proteinase mutant and a stable plasmid, and by culturing B. brevis under optimal conditions with the addition of some chemicals. Thus, biologically active tGH can be efficiently produced directly in the medium with this B. brevis system.

Production of human protein disulfide isomerase by Bacillus brevis

Human protein disulfide isomerase (PDI; EC 5.3.4.1) was expressed and secreted into the culture medium using Bacillus brevis as host and pNU200 which codes the promoter and signal sequence of major cell wall protein of B. brevis as vector. The accumulation of recombinant human PDI (rhPDI) reached about 5 mg l-1 in the late exponential phase of the bacterial growth. The purified rhPDI was found to be exactly processed at the carboxyl terminus of the signal sequence. It was as active as natural PDI derived from human placenta as determined by its ability to reactivate scrambled ribonuclease that was a fully oxidized mixture containing randomly formed disulfide bonds. The activity was significantly accelerated in the presence of dithiothreitol or a mixture of reduced and oxidized glutathione. These indicate that the characteristics of rhPDI are similar to those reported for mammalian PDI and that it can be used for refolding inactive proteins having incorrect disulfide bonds.

Very efficient extracellular production of cholera toxin B subunit using Bacillus brevis

We have constructed a very efficient synthesis and secretion system for cholera toxin B subunit (CTB) of Vibrio cholerae 569B using Bacillus-brevis. The constructed expression-secretion vector has the multiple promoters and the signal peptide coding region of the mwp gene, a structural gene for one of the major cell wall proteins of B. brevis strain 47, directly followed by the gene encoding the mature CTB. A large amount of mature CTB (1.4 g per liter of culture) was secreted into the medium. It had the same amino terminal amino acid sequence as that of authentic CTB and was fully active in GM1 ganglioside binding assay.

Protein secretion in Bacillus species

Bacilli secrete numerous proteins into the environment. Many of the secretory proteins, their export signals, and their processing steps during secretion have been characterized in detail. In contrast, the molecular mechanisms of protein secretion have been relatively poorly characterized. However, several components of the protein secretion machinery have been identified and cloned recently, which is likely to lead to rapid expansion of the knowledge of the protein secretion mechanism in Bacillus species. Comparison of the presently known export components of Bacillus species with those of Escherichia coli suggests that the mechanism of protein translocation across the cytoplasmic membrane is conserved among gram-negative and gram-positive bacteria differences are found in steps preceding and following the translocation process. Many of the secretory proteins of bacilli are produced industrially, but several problems have been encountered in the production of Bacillus heterologous secretory proteins. In the final section we discuss these problems and point out some possibilities to overcome them.

Production of a fungal protein, Taka-amylase A, by protein-producing Bacillus brevis HPD31

An expression-secretion vector, pMK300, was constructed to express the Aspergillus oryzae Taka-amylase A (Taa) cDNA. The promoter and signal peptide regions of the HWP (a major cell wall protein of Bacillus brevis HPD31) gene on pMK300 were efficiently utilized in B. brevis HPD31 and a large amount of Taa (22 mg/l) was secreted into the medium. The HWP signal peptide utilized for secretion of Taa was correctly processed during the protein transport across the membrane. The enzymatic properties of Taa produced by B. brevis HPD31 were the same as those of the Aspergillus oryzae Taa in several respects; specific activity, thermal and pH stabilities, and temperature and pH optima. These results, in combination with previous results, indicate that B. brevis HPD31 could be used to produce extracellularly foreign proteins of diverse origins as functional proteins.

Cloning, characterization, and inactivation of the Bacillus brevis lon gene

A gene of Bacillus brevis HPD31 analogous to the Escherichia coli lon gene has been cloned and characterized. The cloned gene (B. brevis lon gene) encodes a polypeptide of 779 amino acids with a molecular weight of 87,400 which resembles E. coli protease La, the lon gene product. Fifty-two percent of the amino acid residues of the two polypeptides were identical. The ATP-binding sequences found in E. coli protease La were highly conserved. The promoter of the B. brevis lon gene resembled that recognized by the major RNA polymerase of Bacillus subtilis and did not contain sequences homologous to the E. coli heat shock promoters. The B. brevis lon gene was inactivated by insertion of the neomycin resistance gene. A mutant B. brevis carrying the inactivated lon gene showed diminished ability for the degradation of abnormal polypeptides synthesized in the presence of puromycin.

Characterization of an extracellular protease inhibitor of Bacillus brevis HPD31 and nucleotide sequence of the corresponding gene

A novel proteinaceous protease inhibitor was isolated from the culture supernatant of Bacillus brevis HPD31. The protease inhibitor of B. brevis (designated BbrPI) was produced extracellularly in multiple forms having at least three different molecular weights. One of them, BbrPI-a, was purified to near homogeneity and only showed inhibitory activity toward serine proteases, such as trypsin, chymotrypsin, and subtilisin. BbrPI was presumed to form a trypsin-inhibitor complex in a molar ratio of 1:1. The inhibitor was found to be heat resistant at neutral and acidic pHs. The gene coding for BbrPI was cloned into Escherichia coli, and its nucleotide sequence was determined. The sequence suggested that BbrPI is produced with a signal peptide of 24 amino acid residues. The amino acid sequence of the protein deduced from the DNA sequence contained the amino acid sequences of amino termini of the inhibitors, a, b, and c, and their putative precursor determined chemically. The molecular weight of the precursor was about 33,000, and the molecular weights of inhibitors a, b, and c were about 22,000, 23,500, and 24,000, respectively. It is presumed that the secreted precursor protein, which is probably inactive, is cleaved by protease into several active protease inhibitor molecules. BbrPI shows no significant homology to the protease inhibitors described previously and is unique in not having any cysteine residues in its molecule.

Characteristics of batch culture of a recombinant bacillus brevis excreting a foreign esterase

The productivity of extracellular enzyme was evaluated in batch culture using a protein hyperexcreting host, Bacillus brevis HPD31(5) harboring pHSC131, which carried a gene (est) encoding esterase activity from Bacillus stearother mophilus. Optimum temperature and pH for the bacterial growth and the production of extracellular esterase were found to be 35 degrees C and pH 6.5, by using the standard medium (GPY) containing neomycin as a selective pressure, Under the cultivation condition employed, cell growth reached 5 g dry cell weight/L, while the extracellular esterase activity amounted to 4.5 U/mL. Most (79%-92%) of the esterase produced was excreted into the medium. pHSC131 was stably retained in the host cell during cultivation in the presence of neomycin. However, in the absence of neomycin, the plasmid was completely lost from the host after 12-h cultivation accompanied by decreases in both esterase activity and production of total extracellular protein. The copy number of the plasmid was estimated to be approximately 7 throughout the cultivation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of the excreted proteins showed the presence of a protein having an apparent molecular weight of 32,000, which equals to the value predicted from the DNA sequence of the est gene.