Microalgae Crop Improvement: Tools for Quality Control and Molecular Breeding

Microalgae are cultivated as clonally propagated, rapidly multiplying aqueous crops that require unique approaches for crop improvement. Adoption of seed-banking practices from terrestrial agriculture can help to assure quality control of a cultivated microalgal variety or strain from a master propagule bank through to commercial scale-up. Screening for pathogens at specific stages is recommended for algal biomass intended for use in aquaculture, specifically to protect larval health during larviculture and to exclude entry of human pathogens for a quality food product. Contributions to the improvements of an algal cultivar also can be made by innovation in molecular tools. The identification of inducible promoters, constitutive promoters, and a means to combat transgene silencing in Chlorophytes enables progress in strain improvement using genetic engineering. Seven promoters were assayed to determine the ability to express transgenes in a bioprocess green alga, Marinichlorella. Two viral promoters (Cauliflower Mosaic Virus CaMV 35S and Paramecium bursaria Chlorella virus Vp54), one light-inducible promoter (RbcS2), and four inducible promoters from a different genus of Chlorophyte, Chlamydomonas (Amt1;1, Amt1;2, Rh1, and Nit1), were shown to express transgenes transiently at various levels. For further high-quality, stable gene expression, nesting a transgene in an orientation-dependent manner inside the intergenic spacer region from Chlamydomonas reinhardtii was shown to reduce transgene silencing in nuclear transformed C. reinhardtii.