Abstract: Virus contaminations of bioreactors can cause considerable losses in the industry and prevention of such contaminations is usually a major concern, especially in continuous cultures and particularly in outdoor/uncovered operations such as ponds or “racing ponds”. Use of transgenic algae/cyanobacteria harboring introgressed virus/phage DNA fragments, cultured in these bioreactors/ponds will provide protection to a range of viruses/phages. Molecular mechanisms such as lysogeny and post transcriptional gene silencing (PTGS) are being exploited to produce protected algae/cyanobacteria with cross protective resistance against various viruses/phage, thus gaining bioreactor stability.