Aquaculture industries, and in particular the farming of fish and crustaceans, are major contributors to the economy of many countries and an increasingly important component in global food supply. However, the severe impact of aquatic microbial diseases on production performance remains a challenge to these industries. This article considers the potential applications of microalgal technology in the control of such diseases. At the simplest level, microalgae offer health-promoting benefits as a nutritional supplement in feed meal because of their digestibility and high content of proteins, lipids and essential nutrients. Furthermore, some microalgal species possess natural anti-microbial compounds or contain biomolecules that can serve as immunostimulants. In addition, emerging genetic engineering technologies in microalgae offer the possibility of producing ‘functional feed additives’ in which novel and specific bioactives, such as fish growth hormones, anti-bacterials, subunit vaccines, and virus-targeted interfering RNAs, are components of the algal supplement. The evaluation of such technologies for farm applications is an important step in the future development of sustainable aquaculture.

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RNA interference (RNAi) is an effective way of combating shrimp viruses by using sequence-specific double-stranded (dsRNA) designed to knock down key viral genes. The aim of this study was to use microalgae expressing antiviral dsRNA as a sustainable feed supplement for shrimp offering viral protection. In this proof of concept, we engineered the chloroplast genome of the green microalga Chlamydomonas reinhardtii for the expression of a dsRNA cassette targeting a shrimp yellow head viral gene. We used a previously described chloroplast transformation approach that allows for the generation of stable, marker-free C. reinhardtii transformants without the supplementation of antibiotics. The generated dsRNA-expressing microalgal strain was then used in a shrimp feeding trial to evaluate the efficiency of the algal RNAi-based vaccine against the virus. Shrimps treated with dsRNA-expressed algal cells prior to YHV infection had 50% survival at 8 day-post infection (dpi), whereas 84.1% mortality was observed in control groups exposed to the YHV virus. RT-PCR using viral specific primers revealed a lower infection rate in dsRNA-expressing algae treated shrimp (55.6 ± 11.1%) compared to control groups (88.9 ± 11.1% and 100.0 ± 0.0%, respectively). Our results are promising for using microalgae as a novel, sustainable alternative as a nutritious, anti-viral protective feedstock in shrimp aquaculture.

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Arbuscular mycorrhizal fungi have been reported to enhance the growth of many crop plants. This study examines the effect of Funneliformis mosseae, a type of arbuscular mycorrhizal fungus (AMF), on the growth of butterhead lettuce in organic cultivation. Lettuces were inoculated with 50 spores of F. mosseae to determine their physiological and biochemical characters compared to uninoculated lettuces in an abandoned field. After 60 days of growth, the AMF-inoculated plants had significantly more leaves (on average, 19.4) and greater leaf fresh weight (on average, 30.4 g) than for the no-AMF treatment which had 15.8 leaves with a total weight of 14.5 g. Net photosynthesis and the chlorophyll a content were higher in the AMF-inoculated plants than in the control plants. The rhizosphere soil of 60-day-old AMF-inoculated butterhead lettuce showed higher organic matter, available phosphorus content, and exchangeable potassium content. The plants in the AMF treatment showed higher total nitrogen, phosphorus, and potassium contents in leaf and root tissues than the control plants. Antioxidant capacity was analysed by quantifying catalase and ascorbate peroxidase activities, ascorbic acid content, and carotenoid content. All of these parameters tended to be higher in the AMF treatment than in the control. The diphenylpicrylhydrazyl radical scavenging activity in AMF-inoculated plants (54%) was twice that in the control plants (24%). These results demonstrate that applying AMF is a cost-effective way to enhance the growth of organically farmed butterhead lettuce.

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