Cloning and characterization of a gene of Streptomyces griseus that increases production of extracellular enzymes in several species of Streptomyces

Substrate analysis and molecular cloning of the extracellular alkaline phosphatase of Streptomyces griseus

Streptomyces species secrete large amounts of alkaline phosphatase (AP) enzymes that have not been characterized so far. An AP has been purified to homogeneity from cultures of Streptomyces griseus IMRU 3570. The enzyme has a monomer size of 62 kDa and is processed in the culture to a 33 kDa protein as shown by immunoblotting. The enzyme was purified by ammonium sulfate precipitation, CM-Sephadex cationic exchange, chromatofocusing and HPLC Sphaerogel 3000SW filtration. The pure enzyme uses a variety of organic phosphorylated compounds as substrates. The N-terminal end of the mature protein was found to be RLREDPFTLGVASGDPHP. The gene phoA has been cloned using as probe an oligomer based on the N-terminal sequence of the S. griseus AP. phoA encodes a protein of 62678 Da with low homology to the AP of Escherichia coli. The phoA gene was found to be homologous to three alkaline-phosphatase-encoding genes previously identified in the Streptomyces coelicolor genome. On the basis of the optimal pH, substrate specificity and differences in amino acid sequence of motifs defining the active centre of APs, the S. griseus AP uses a wide range of organic phosphate substrates and is different from the phosphatases of Gram-negative bacteria.

Multiple paralogous genes related to the Streptomyces coelicolor developmental regulatory gene whiB are present in Streptomyces and other actinomycetes

The whiB sporulation gene of Streptomyces coelicolor was shown [Davis, N. K. & Chater, K. F. (1992). Mol Gen Genet 232, 351-358] to encode a small, cysteine-rich putative transcription factor unlike any that had been described previously. The large database of DNA sequences of mycobacteria (like Streptomyces, members of the Actinomycetales) has revealed a family of genes encoding proteins related to WhiB. Mycobacterium tuberculosis contains at least six such genes (whiB homologues in mycobacteria: whmA-F) and a likely seventh, whmG. Using conserved features of Whm proteins, a PCR-based approach led to the discovery that S. coelicolor A3(2) contains several similar genes. Cloning and sequencing of these whiB-like (wbI) genes revealed likely orthologues of four of the whm genes of M. tuberculosis. In all, S. coelicolor contains at least five wbI genes in addition to whiB itself. All five were shown by RT-PCR to be transcribed. A Southern blotting survey using each wbI gene as a probe showed that nearly all of a series of representatives of ten actinomycete genera (including morphologically simple organisms) contain close homologues of several wbI genes, suggesting that the ancient progenitor of all these organisms already contained a family of such genes, which have not been found in any other organisms.

Characterization of the secA gene of Streptomyces lividans encoding a protein translocase which complements and Escherichia coli mutant defective in the ATPase activity of SecA

The secA gene of Streptomyces lividans was cloned using as probe a 57-mer oligonucleotide based on conserved sequences of the Escherichia coli secA and the Bacillus subtilis div genes. It encodes a protein of 946 amino acids (aa) with a deduced M(r) of 106,079, with high similarity to all known SecA proteins. All the previously described conserved motifs of SecA proteins were conserved in the S. lividans protein. The secA gene of S. lividans restored sensitivity to sodium azide in E. coli SecA4 (AzR) a mutant with an azide-resistant (ATPase defective) SecA protein. However, it did not complement the temperature-sensitive mutation in E. coli MM52 (SecAts) (a conditional lethal mutant defective in protein translocation) allowing only poor growth at the nonpermissive temperature. secA homologous sequences were present in 11 different species of Streptomyces and Nocardia.

Construction of new cloning vectors for Brevibacterium lactofermentum

Two plasmid cloning vectors (pULMJ55 and pULMJ95) were constructed for Brevibacterium lactofermentum using the origin of replication of the endogenous plasmid pBL1. Plasmid pULMJ55 is a replacement vector with transcriptional terminators from the B. lactofermentum trp operon flanking the BglII cloning sites. Religation of the BglII digested vector without insert creates a 376 bp perfect palindrome that is not tolerated in B. lactofermentum, giving positive selection for recombinant plasmids with inserts. Plasmid pULMJ95 contains the promoter-less alpha-amylase gene from Streptomyces griseus downstream of the trp terminator and is particularly suitable for the detection of promoters which are activated late during the growth phase. alpha-Amylase is secreted and its activity can be detected using simple plate tests.

Production and secretion of proteins by streptomycetes

Streptomycetes produce a large number of extracellular enzymes as part of their saprophytic mode of life. Their ability to synthesize enzymes as products of their primary metabolism could lead to the production of many proteins of industrial importance. The development of high-yielding expression systems for both homologous and heterologous gene products is of considerable interest. In this article, we review the current knowledge on the various factors that affect the production and secretion of proteins by streptomycetes and try to evaluate the suitability of these bacteria for the large-scale production of proteins of industrial importance.

Effect of growth rate and cultivation environments on cloned gene stability and the cloned gene product formation in Streptomyces lividans

The growth rate and environmental effects on the stability of recombinant plasmid, pDML6 containing beta-lactamase gene, and the cloned gene product formation in Streptomyces lividans were studied. A maximum production rate of the cloned gene product was obtained at a specific growth rate 0.106 h-1 in glucose-limited chemostat cultivations without genetic selection pressure. Optimum environmental conditions for the recombinant plasmid stability and maximum formation rates of the cloned gene product were determined using continuous cultivations at the optimum specific growth rate. The fractions of plasmid harboring mycelium in prolonged cultivation up to 50 generations were varied from 77 to 95%. The recombinant plasmid was stably maintained in the host cells grown in different temperatures (24 to 36 degrees C) and pH (6.0 to 8.5). The formation of the cloned gene product was optimum at pH 7.0 and 27 degrees C, at which the maximum enzyme production rate was 0.82 kU g-1 h-1. Continuous cultivations varying the dissolved oxygen tension (10 to 80% air saturation) showed that the plasmids were maintained stably and the specific enzyme production rates were increased with increasing dissolved oxygen levels.

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.

Cloning, characterization, and expression in Streptomyces lividans 66 of an extracellular lipase-encoding gene from Streptomyces sp. M11

A gene encoding an extracellular lipase from Streptomyces sp. M11 was cloned in the high-copy-number vector pIJ486, using S. lividans 66 as host. A 28-kDa protein was secreted by S. lividans carrying pB13, which harbors a 6-kb insert, and identified as the product of the cloned gene. Comparison of the N-terminal amino acid (aa) sequence of the purified extracellular lipase with the nucleotide (nt) sequence of the lip gene revealed the presence of a 48 aa long signal peptide. The nucleotide sequence also revealed the presence of a motif, Gly-His-Ser-Met-Gly, similar to the one found surrounding the active-site Ser in other lipases. The gene is most likely monocistronic. Subcloning experiments indicated that another gene might be required for high-level expression, since subcloning of the structural gene alone resulted in diminished extracellular lipase activity. The lipase gene promoter was identified by S1 mapping experiments, and found to be similar to other Streptomyces vegetative promoters.

A metalloprotease gene from Streptomyces coelicolor 'Müller' and its transcriptional activator, a member of the LysR family

A metalloprotease gene (mprA) and its regulatory gene (mprR) from Streptomyces coelicolor 'Müller' DSM3030 were isolated and their DNA sequences determined. The protease secreted by the heterologous host Streptomyces lividans was characterized biochemically as a metalloprotease with a M(r) of 20,000, which is in good agreement with data derived from DNA sequence analysis. The mprA gene is transcribed divergently from mprR, the deduced protein of which displays homology to prokaryotic transcriptional regulators of the LysR family. The regulatory protein (MprR) was shown to bind to the intergenic region between mprR and mprA. It was found to activate transcription of mprA in S. lividans and also in Escherichia coli.

Streptomyces: a host for heterologous gene expression

Streptomyces species offer many potential advantages as hosts for the expression and secretion of eukaryotic gene products. In this review we discuss the expression and localization signals that have been used to direct heterologous gene expression and the applications of these signals. Finally, we discuss future strategies aimed at increasing the capacity of this host for the high level production of biologically active eukaryotic gene products.

Analysis of the promoter region of saf, a Streptomyces griseus gene that increases production of extracellular enzymes

The product of the saf gene of Streptomyces griseus ATCC10137 mediated an increase in the production of several extracellular enzymes and retarded the formation of pigments and spores in Streptomyces [Daza et al., Mol. Gen. Genet. 222 (1990) 384-392]. A promoter upstream from saf was identified by subcloning a DNA fragment in the promoter probe pIJ486. Using the Escherichia coli-Brevibacterium lactofermentum promoter-probe shuttle vector, pULMJ51, we determined that the saf promoter region is also active in E. coli. The transcription start points (tsp) of the saf promoter in Streptomyces and E. coli have been determined using high-resolution S1 mapping. The tsp are at the same position in both microorganisms. Expression from the saf promoter region was negatively regulated by phosphate in Streptomyces, but not in E. coli. The amplification of the saf promoter lacking the saf coding region did not increase the production of extracellular enzymes and did not reduce sporulation or pigmentation in Streptomyces (i.e., it does not titrate out a putative repressor of the genes encoding extracellular enzymes). Several structural features of the saf promoter region and saf mRNA are studied in relation to the regulation of the saf gene expression.

Effects of replacement of promoters and modification of the leader peptide region of the amy gene of Streptomyces griseus on synthesis and secretion of alpha-amylase by Streptomyces lividans

Five different mutations were introduced into the leader peptide region of the alpha-amylase gene of Streptomyces griseus IMRU 3570. A mutation which increased the positive charge of the N-terminal region of the leader peptide enhanced the secretion of alpha-amylase by two- to threefold. Replacement of the native promoter of the amylase gene by the promoter of the Tn5 neo gene or by the promoter of the saf gene resulted in a 16-fold increase in alpha-amylase secretion. The enhanced secretion of alpha-amylase obtained by using the most efficient promoters was due to a correlated increase in the amount of transcript formed. The translation and secretion processes in S. lividans are not a bottleneck for enzyme secretion even at very high transcription rates, since stimulation of transcription of the alpha-amylase gene results in a proportionate increase in secretion of the enzyme.

Characterization, expression in Streptomyces lividans, and processing of the amylase of Streptomyces griseus IMRU 3570: two different amylases are derived from the same gene by an intracellular processing mechanism

Extracellular amylase in Streptomyces lividans was undetectable in starch-supplemented medium. However, S. lividans produced fivefold-higher levels of amylase than Streptomyces griseus IMRU 3570 when transformed with the S. griseus amy gene. Two major proteins of 57 and 50 kDa with amylase activity accumulated in the culture broths of the donor S. griseus and S. lividans transformed with the amy gene. Both proteins were also present in protoplast lysates in the same relative proportion; they gave a positive reaction with antibodies against the 57-kDa amylase. They did not differ in substrate specificity or enzyme kinetics. The two amylases were purified to homogeneity by a two-step procedure. Both proteins showed the same amino-terminal sequence of amino acids, suggesting that both proteins are derived from the same gene. The deduced signal peptide has 28 amino acids with two positively charged arginines near the amino-terminal end. When an internal NcoI fragment was removed from the amy gene, the resulting S. lividans transformants did not synthesize any of the two amylase proteins and showed no reaction in immunoblotting. Formation of the 50-kDa protein was observed when pure 57-kDa amylase was treated with supernatants of protoplast lysates but not when it was treated with membrane preparations, indicating that the native 57-kDa amylase could be processed intracellularly.

Cloning, characterization and expression of an alpha-amylase gene from Streptomyces griseus IMRU3570

A gene, amy, encoding an alpha-amylase, was cloned on a 4.8 kb Sau3A fragment from the DNA of Streptomyces griseus IMRU3570. The gene was localized to a 2.27 kb fragment by subcloning and deletion mapping experiments. The gene contained an open reading frame (ORF) of 1698 nucleotides that encoded a protein of 566 amino acids with a deduced Mr of 59713 Da. Dot-blot analysis revealed that the copy number of the transcript in S. lividans transformed with the amy gene was 2.8-fold higher than in the donor S. griseus strain in good agreement with the proportionally higher secretion of amylase in S. lividans. A transcription initiation site was found approximately 64 bp upstream from the ATG translation start codon. The promoter of the amy gene was subcloned on a 290 bp HindIII--EcoRI fragment. Expression of a neomycin resistance gene from the amy promoter was negatively regulated by glucose. A 219 nucleotide fragment extending from the single BstEII site to the end of the amy gene was dispensable since active alpha-amylase was secreted after deletion of this region and coupling of a TGA translation stop codon.