Transgenic Microalgae Expressing Double-Stranded RNA as Potential Feed Supplements for Controlling White Spot Syndrome in Shrimp Aquaculture.

Viral infection of farmed fish and shellfish represents a major issue within the aquaculture industry. One potential control strategy involves RNA interference of viral gene expression through the oral delivery of specific double-stranded RNA (dsRNA). In previous work, we have shown that recombinant dsRNA can be produced in the chloroplast of the edible microalga Chlamydomonas reinhardtii and used to control disease in shrimp. Here, we report a significant improvement in antiviral dsRNA production and its use to protect shrimp against white spot syndrome virus (WSSV). A new strategy for dsRNA synthesis was developed that uses two convergent copies of the endogenous rrnS promoter to drive high-level transcription of both strands of the WSSV gene element in the chloroplast. Quantitative RT-PCR indicated that ~119 ng dsRNA was produced per liter of culture of the transgenic microalga. This represents an ~10-fold increase in dsRNA relative to our previous report. The engineered alga was assessed for its ability to prevent WSSV infection when fed to shrimp larvae prior to a challenge with the virus. The survival of shrimp given feed supplemented with dried alga containing the dsRNA was significantly enhanced (~69% survival) relative to a negative control (<10% survival). The findings suggest that this new dsRNA production platform could be employed as a low-cost, low-tech control method for aquaculture.

Human Intrinsic Factor Expression for Bioavailable Vitamin B12 Enrichment in Microalgae.

Dietary supplements and functional foods are becoming increasingly popular complements to regular diets. A recurring ingredient is the essential cofactor vitamin B12 (B12). Microalgae are making their way into the dietary supplement and functional food market but do not produce B12, and their B12 content is very variable. In this study, the suitability of using the human B12-binding protein intrinsic factor (IF) to enrich bioavailable B12 using microalgae was tested. The IF protein was successfully expressed from the nuclear genome of the model microalga Chlamydomonasreinhardtii and the addition of an N-terminal ARS2 signal peptide resulted in efficient IF secretion to the medium. Co-abundance of B12 and the secreted IF suggests the algal produced IF protein is functional and B12-binding. Utilizing IF expression could be an efficient tool to generate B12-enriched microalgae in a controlled manner that is suitable for vegetarians and, potentially, more bioavailable for humans.