Development of a novel Bacillus subtilis cloning system employing its neutral protease as screen marker

Expression of green fluorescent protein in Bacillus brevis under the control of a novel constitutive promoter F1 and insertion mutagenesis of F1 in Escherichia coli DH5alpha

The constitutive expression vector pHY300-F1gfp was constructed to test the function of a promoter, F1, cloned from the rice epiphyte Bacillus brevis strain DX01. The DX01 cells harboring the plasmid pHY300-F1gfp were shown to produce bright green fluorescence. The results were confirmed by Western blot analysis and fluorescence-activated cell sorting. Expression of the F1 promoter was constitutive. To improve the activity of F1, insertion mutagenesis of F1 based on in vitro transposition reaction was performed. Seven mutants with enhanced transcription activity in Escherichia coli DH5alpha were obtained. The enhanced promoters showed similar high activities in B. brevis strain DX01.

Improved shuttle vector for expression of chitinase gene in Bacillus thuringiensis

A 6.96-kbp plasmid vector pBCX was constructed from the plasmid pBC16 (4.4 kbp) and a 2.56-kbp fragment of pBluescript II KS. The bifunctional plasmid pBCX conferred ampicillin and tetracycline resistance in Escherichia coli but only tetracycline resistance in Bacillus thuringiensis. It has unique sites for BamHI, SmaI, PstI, HindIII, SalI, XhoI, DraII, ApaI and KpnI derived from pBluescript II KS and was lost at a low rate in B. thuringiensis subsp. israelensis when cultured in Luria-Bertani broth without antibiotic. The chitinase gene from B. circulans number 4.1 (pCHIB1) was subcloned into the HindIII sites of this vector and designated as pBX43 (9.56 kbp). This plasmid produced three times as much chitinase in B. thuringiensis subsp. israelensis strain c4Q272 as pHYB43, which comprises the commercial shuttle vector pHY300PLK plus the chitinase gene.

Blue/white screening of recombinant plasmids in Gram-positive bacteria by interruption of alkaline phosphatase gene (phoZ) expression

The process of screening bacterial transformants for recombinant plasmids is made more rapid and simple by the use of vectors with visually detectable reporter genes. In such systems, an alteration in colony phenotype occurs when a vector-borne indicator gene is interrupted with exogenous DNA. Although the lacZ system has been used extensively for this purpose in E. coli, analogous systems for use in Gram-positive bacteria remain uncommon. We have developed a Gram-positive cloning vector that utilizes the interruption of an alkaline phosphatase gene, phoZ, to identify recombinant plasmids. To facilitate introduction of foreign DNA, a multiple cloning site (MCS) was inserted distal to the region coding for the putative signal peptide of phoZ. Alkaline phosphatase expressed from the derivative phoZ gene (phoZMCS) retained activity similar to that of the native protein. The phoZMCS was transferred to pJS3, a well-characterized, high-copy number, and broad-host-range plasmid, to produce pDC123. In pDC123, phoZMCS was transcriptionally linked to the chloramphenicol acetyl transferase (cat) gene under the control of the constitutively expressed tetM and cat promoters that drive cat expression in pJS3. S. agalactiae (Group B streptococci, GBS), E. faecalis, S. pyogenes, S. gordonii, and E. coli containing pDC123 displayed a blue colonial phenotype on agar containing 5-bromo-4-chloro-3-indolyl phosphate (X-p), which was readily distinguished from that of colonies containing the parent plasmid pJS3. Introduction of foreign DNA into the MCS of phoZMCS produced a white colonial phenotype in E. coli and GBS on agar containing X-p and allowed discrimination between transformants containing recombinant plasmids versus those maintaining self-annealed or uncut vector. We have used pDC123 to subclone the cpsE gene from the plasmid pCER111, which carries a 9.0-kb fragment of the GBS capsular polysaccharide synthesis locus. The plasmid pDC123 containing cpsE was isolated by direct electroporation into GBS strain A909 with selection of transformants containing recombinant plasmids achieved by 'blue/white' screening, without the use of an intermediate host. This new cloning vector should improve the efficiency of performing recombinant DNA experiments in Gram-positive bacteria.

Expression and secretion of heterologous proteases by Corynebacterium glutamicum

Genes encoding the basic protease of Dichelobacter nodosus (bprV) and the subtilisin of Bacillus subtilis (aprE) were cloned and expressed in Corynebacterium glutamicum. In each case, enzymatically active protein was detected in the supernatants of liquid cultures. While the secretion of subtilisin was directed by its own signal peptide, the natural signal peptide of the bprV basic protease did not facilitate secretion. A hybrid aprE-bprV gene in which the promoter and signal peptide coding sequences of subtilisin replaced those of bprV could be expressed, and basic protease was secreted by C. glutamicum. Expression of these proteases in C. glutamicum provides an opportunity to compare protein secretion from this gram-positive host with that from other gram-positive and gram-negative bacteria.

Bacterial extracellular zinc-containing metalloproteases

Extracellular zinc-containing metalloproteases are widely distributed in the bacterial world. The most extensively studied are those which are associated with pathogenic bacteria or bacteria which have industrial significance. They are found practically wherever they are sought in both gram-negative and gram-positive microorganisms, be they aerobic or anaerobic. This ubiquity in itself implies that these enzymes serve important functions for the organisms which produce them. Because of the importance of zinc to enzymatic activity, it is not surprising that there is a pervasive amino acid sequence homology in the primary structure of this family of enzymes regardless of their source. The evidence suggests that both convergent and divergent evolutionary forces are at work. Within the large family of bacterial zinc-containing metalloendopeptidases, smaller family units are observed, such as thermolysin-like, elastase-like, and Serratia protease-like metalloproteases from various bacterial species. While this review was in the process of construction, a new function for zinc-containing metalloproteases was discovered: the neurotoxins of Clostridium tetani and Clostridium botulinum type B have been shown to be zinc metalloproteases with specificity for synaptobrevin, an integral membrane protein of small synaptic vesicles which is involved in neurotransmission. Additional understanding of the mode of action of proteases which contribute to pathogenicity could lead to the development of inhibitors, such as chelators, surrogate substrates, or antibodies, which could prevent or interrupt the disease process. Further studies of this broad family of metalloproteases will provide important additional insights into the pathogenesis and structure-function relationships of enzymes and will lead to the development of products, including "designer proteins," which might be industrially and/or therapeutically useful.

Use of a gram- signal peptide for protein secretion by gram+ hosts: basic protease of Dichelobacter nodosus is produced and secreted by Bacillus subtilis

The bprV gene, encoding the extracellular basic protease of the Gram- anaerobic bacterium Dichelobacter nodosus, was expressed and the protein secreted in Bacillus subtilis using the novel cloning/expression vector pNC3 [Wu et al., Gene 106 (1991) 103-107]. The pre- and pro-peptides were processed correctly in this heterologous system, and the 127-amino acid C-terminal extension region was also removed. The recombinant gene product was indistinguishable biochemically or immunochemically from the authentic protease and was able to form crystals upon dialysis, as was found for the authentic protease. This is the first example of the direct secretion of a Gram- extracellular enzyme in B. subtilis via its own signal peptide. The fact that this gene can be expressed and its product secreted in both Escherichia coli and B. subtilis provides a unique opportunity to study and compare the similarities and differences in protein secretion between Gram- and Gram+ organisms.