Development of Methylobacterium extorquens as a recombinant protein production system and the expression of the heterologous cry1Aa gene from Bacillus thuringiensis

Methylobacterium extorquens ATCC55366 is an interesting candidate for large-scale production of recombinant proteins. Development and optimization of this recombinant expression system were done using the green fluorescent protein (GFP) gene cloned into expression vectors (pRK310 and pCM110) as model systems. Selection of efficient GFP-expressing clones, long-term production stability without selection in flasks, effects of selection, oxygen and methanol supplies, were studied during fed-batch fermentations in a 20-l bioreactor. Sequential batch-culture cultivations in shake flasks showed that specific GFP production was constant in the presence of tetracycline. However, the GFP production decreased in the absence of this selective pressure. In fed-batch fermentations of recombinant M. extorquens ATCC 55366 (pMxaF-GFP), overall GFP yields (≈70 mg/g; GFP/cell dry weight) were not affected by the presence or absence of tetracycline, nor by oxygen and methanol concentration oscillations. The cry1Aa gene from Bacillus thuringiensis kurstaki NRD-12 was cloned in pCM110 and then transformed into M. extorquens. Heterologous expression of the cry1Aa gene in M. extorquens AM1 and ATCC 55366 was detected by immunoblot analyses. This study suggests that M. extorquens can be used as a valuable expression system for intracellular recombinant protein production.