Advances in time course extracellular production of human pre-miR-29b from Rhodovulum sulfidophilum

The present study reports the successful production of human pre-miR-29b both intra-and extracellularly in the marine phototrophic bacterium Rhodovulum sulfidophilum using recombinant RNA technology. In a first stage, the optimal transformation conditions (0.025 mu g of plasmid DNA, with a heat-shock of 2 min at 35 degrees C) were established, in order to transfer the pre-miR-29b encoding plasmid to R. sulfidophilum host. Furthermore, the extracellular recovery of this RNA product from the culture medium was greatly improved, achieving quantities that are compatible with the majority of applications, namely for in vitro or in vivo studies. Using this system, the extracellular human pre-miR-29b concentration was approximately 182 mu g/L, after 40 h of bacterial growth, and the total intracellular pre-miR-29b was of about 358 mu g/L, at 32 h. At the end of the fermentation, it was verified that almost 87 % of cells were viable, indicating that cell lysis is minimized and that the extracellular medium is not highly contaminated with the host intracellular ribonucleases (RNases) and endotoxins, which is a critical parameter to guarantee the microRNA (miRNA) integrity. These findings demonstrate that pre-miRNAs can be produced by recombinant RNA technology, offering novel clues for the production of natural pre-miRNA agents for functional studies and RNA interference (RNAi)-based therapeutics.