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Human placental lactogen (hPL) is a peptidic hormone that belongs to the short list of growth factors that could treat type-1 diabetes through pancreatic islet transplantation. Placental lactogen has the capacity to improve islet survival and function before or after transplantation. In this study, transgenic tobacco plants were used as a novel expression system for the production of recombinant hPL protein (rhPL). The expression vector pNEKhPL2 containing hPL cDNA was introduced into tobacco plants; the transcriptional activity was confirmed by real-time PCR, and the rhPL levels reached 1% of the total soluble protein (TSP) content in plants cultivated in the greenhouse. In vitro bioassays using the rat insulinoma (INS-1) cell line showed that recombinant protein was able to induce cell proliferation and activate the JAK-2/STAT-5 signal transduction pathway, demonstrating that plant cells can produce the biologically active hPL protein. To further characterize the plant expression system for hPL production, we analyzed the stability of the protein during the life cycle of tobacco plants as well as the transmission of the transgenic trait to the progeny. The recombinant protein was stably accumulated in young leaves, reaching the maximum level in the first month (6.51 μg/g of fresh weight), but showing a decreasing trend of 26% from the initial sampling time until the end of plant's life cycle. The progeny of the selected pNEKhPL2 plant showed in vitro expression levels of up to 1.1% of TSP. Our results therefore indicate that transgenic plants are a suitable expression system for hPL production.

Biomachining has become a promising alternative to micromachining metal pieces, as it is considered more environmentally friendly than their physical and chemical machining counterparts. In this research work, two strategies that contribute to the development of this innovative technology and could promote its industrial implementation were investigated: preservation of biomachining microorganisms (Acidithiobacillus ferrooxidans) for their further use, and making valuable use of the liquid residue obtained following the biomachining process. Regarding the preservation method, freeze‐drying, freezing, and drying were tested to preserve biomachining bacteria, and the effect of different cryoprotectants, storage times, and temperatures was studied. Freezing at –80°C in Eppendorf cryovials using betaine as a cryoprotective agent reported the highest bacteria survival rate (40% of cell recovery) among the studied processes. The treatment of the liquid residue in two successive stages led to the precipitation of most of the total dissolved iron and divalent copper (99.9%). The by‐products obtained (iron and copper hydroxide) could be reused in several industrial applications, thereby enhancing the environmentally friendly nature of the biomachining process.

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