Production of recombinant antibody fragments in Bacillus megaterium

Abstract

Background: Recombinant antibodies are essential reagents for research, diagnostics and therapy. The well established production host Escherichia coli relies on the secretion into the periplasmic space for antibody synthesis. Due to the outer membrane of gram-negative bacteria, only a fraction of this material reaches the medium. Recently, the gram-positive bacterium Bacillus megaterium was shown to efficiently secrete recombinant proteins into the growth medium. Here we evaluated B. megaterium for the recombinant production of antibody fragments.

Results: The lysozyme specific single chain Fv (scFv) fragment D1.3 was successfully produced using B. megaterium. The impact of culture medium composition, gene expression time and culture temperatures on the production of functional scFv protein was systematically analyzed. A production and secretion at 41 degrees C for 24 h using TB medium was optimal for this individual scFv. Interestingly, these parameters were very different to the optimal conditions for the expression of other proteins in B. megaterium. Per L culture supernatant, more than 400 microg of recombinant His6-tagged antibody fragment were purified by one step affinity chromatography. The material produced by B. megaterium showed an increased specific activity compared to material produced in E. coli.

Conclusion: High yields of functional scFv antibody fragments can be produced and secreted into the culture medium by B. megaterium, making this production system a reasonable alternative to E. coli.

Figure 1

Construction of plasmid pEJBmD1.3scFv for the production of scFv antibody fragment D1.3 in B. megaterium. The complete scFv ORF plus the complete promoter region were verified by nucleotide sequencing. Abbreviations: bla: β-lactamase gene for ampicillin resistence; colE1: E. coli origin of plasmid replication; F1 IR: intergenic region of phage f1; gIII: fd phage gene III; His-tag: synthetic tag binding to 6xhistidine; ori: B. megaterium origin of plasmid replication; P_lacZ: promoter of the bacterial lac operon; P_xylA: xylose inducible promoter; RBS: ribosome binding site; repU: a gene essential for plasmid replication in B. megaterium; scFv: single chain fragment variable; SP_lipA: signal peptide sequence of B. megaterium extracellular esterase LipA; SP_pelB: signal peptide sequence of bacterial pectate lyase; strep-tag II: synthetic tag binding to streptactin; terminator: sequence terminating transcription; tet: tetracyclin resistence gene; VH: sequence encoding the variable fragment of the heavy chain; VL: sequence encoding the variable fragment of the light chain chain; xylR: xylose repressor

Figure 2

Impact of the cultivation temperature on the scFv production. Production of functional antibodies was analyzed by antigen binding ELISA of D1.3 scFvs of 50 μL culture supernatant after 24 h production in 100 mL scale. Mean values and standard deviations of data obtained from three different cultures are given. Antigens: 1 μg/well lysozyme or 1 μg/well control protein BSA. The D1.3 antibodies were detected using mAb mouse anti-His and goat anti-mouse IgGHRP (Fab specific).

Figure 3

Impact of different culture media on the production of functional scFvs. A Antigen binding ELISA with 50 μL culture supernatant from 18 h production in 100 mL scale, performed as described in figure 2. Mean values and standard deviations of data obtained from three different cultures are given. B Immunoblot of culture supernatant. Ammonium sulfate precipated scFvs from 1.5 mL supernatant were separated by reducing SDS-PAGE (12 %) and detected using mAb mouse anti-His and goat anti-mouse IgG AP (Fab specific).

Figure 4

Impact of the production time on the yield of functional scFvs (TB medium, 41°C). A Antigen binding ELISA with 50 μL culture supernatant from different time points, performed as described in figure 2 and 3. Mean values and standard deviations of data obtained from three different cultures are given. B Immunoblot of produced scFvs. Ammonium sulphate precipated scFvs from 1 mL supernatant were separated by reducing SDS-PAGE (12 %) and detected as described in figure 3.

Figure 5

Antigen ELISA of purified D1.3 scFv from E. coli or Bacillus megaterium. Antigen: 1 μg/well lysozyme. The detection was performed as described in figure 2-4.