Enzyme production by genetically engineeredStreptomyces strains: Influence of culture conditions

Fed-batch production of thermomonospora fusca endoglucanase by recombinant streptomyces lividans

The factors affecting the production of a Thermomonospora fusca endoglucanase by a recombinant Streptomyces lividans strain were studied in a fermentor with glucose addition controlled by a pH-stat. The recombinant plasmid was stable for 35 generations with constant endoglucanase productivity. Glucose and peptone were used as the carbon and nitrogen sources. Addition of Tween-80 increased endoglucanase production twofold. A significant decrease in endoglucanase production was observed at low aeration. During fed-batch cultivation, pulse feeding (6 g/L) of a glucose-ammonium sulfate solution was optimal for endoglucanase production. With higher concentrations of glucose (15 g/L), a significant amount of organic acid, including acetic acid, was produced, which inhibited cell growth and endoglucanase production. Under optimum conditions, 1.7 U/mL of endoglucanase were produced. Copyright 1998 John Wiley & Sons, Inc.

Cloning and heterologous expression of the gene for BLIP-II, a beta-lactamase-inhibitory protein from Streptomyces exfoliatus SMF19

A beta-lactamase-inhibitory protein (BLIP-II) was purified from the culture filtrate of Streptomyces exfoliatus SMF 19 and its N-terminal amino acid sequence was determined. A clone containing the gene encoding BLIP-II (bliB) was selected from a cosmid library by colony hybridization using an oligonucleotide probe based on the N-terminal amino acid sequence of BLIP-II. The bliB gene was isolated and sequenced. Analysis of the nucleotide sequence revealed that the gene consists of 1116 bp and encodes a mature protein of 332 amino acids preceded by a 40 amino acid signal sequence. bliB, expressed under the control of the T7 promoter in Escherichia coli, was accumulated in an inactive form in inclusion bodies, but beta-lactamase-inhibitory activity was recovered after refolding. In addition, bliB was heterologously expressed in Streptomyces lividans TK24 using the melC1 promoter. The BLIP-II protein produced in recombinant strains of S. lividans was secreted into the culture supernatant in a biologically active form.

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.

Review of the Streptomyces lividans/vector pIJ702 system for gene cloning

Interest in the biology of the Streptomyces and application of these soil bacteria to production of commercial antibiotics and enzymes has stimulated the development of efficient cloning techniques and a variety of streptomycete plasmid and phage vectors. Streptomyces lividans is routinely employed as a host for gene cloning, largely because this species recognizes a large number of promoters and appears to lack a restriction system. Vector pIJ702 was constructed from a variant of a larger autonomous plasmid and is often used as a cloning vehicle in conjunction with S. lividans. The host range of vector pIJ702 extends beyond Streptomyces spp., and its high copy number has been exploited for the overproduction of cloned gene products. This combination of host and vector has been used successfully to investigate antibiotic biosynthesis, gene structure and expression, and to map various Streptomyces mutants.

Transcriptional analysis of the DD-peptidase/penicillin-binding protein-encoding dac gene of Streptomyces R61: use of the promoter and signal sequences in a secretion vector

The promoter region of the gene encoding the extracellular DD-peptidase/penicillin-binding protein of Streptomyces R61 has been identified by in vivo promoter probing and S1 mapping. A secretion vector, pDML116, was constructed by inserting into the multicopy Streptomyces plasmid pIJ702, a 247 bp DNA sequence that contained the transcriptional, translational and secretory signals and the 12 amino acid N-terminal region-encoding sequence of the mature Streptomyces DD-peptidase/penicillin-binding protein. Insertion, downstream of this 247 bp segment, of the Streptomyces R61 DD-peptidase-encoding gene or the Escherichia coli R-TEM beta-lactamase-encoding gene yielded plasmids pDML120 and pDML128, respectively, which allowed expression and secretion of the relevant enzymes by Streptomyces lividans. The maximal secretion levels obtained were 42 mg protein/ml for the autologous Streptomyces DD-peptidase and 0.9 mg protein/ml for the heterologous E. coli beta-lactamase.