Virus-like particles used to control HABs

Harmful algal blooms (HABs) can cause mass mortality of fish and other aquatic organisms through the depletion of oxygen from the water, the contamination of the surrounding air, blockage of gills and production of toxins and reactive oxygen species. HABs are becoming a global issue with recurrent cases along many coastal areas. Many of the commonly used techniques to control HABs (e.g. ozonation, chlorination, ultrasonic treatment, etc.) have limited success and also have the capacity to disrupt marine ecosystems. Safer biological strategies for mitigating HABs have been proposed that utilise marine bacteria, algal viruses, protozoa and macrophytes. Kang et al., (2015) set out to investigate the potential use of virus-like particles (VLPs) to deliver algicidal compounds directly to harmful algae.

The toxic dinoflagellate Heterocapsa circularisquama is widely spread along the Chinese coast from Japan to Hong Kong and causes severe die-off of cultured clams, mussels, razor shells and oysters. The capsid protein of HcRNAV34, a single stranded RNA virus that infects and lyses H. circularisquama, produced from Escherichia coli  was self-assembled into VLPs  in vitro and employed as a carrier for the potent algicidal compound thiazolidinedione 49 (TD49). The self-assembled VLPs were significantly smaller than the authentic HcRNAV34 capsid reflecting the various morphological forms a virion may adopt during maturation. However, despite this difference in size, the TD49-HcRNAV34 VLP showed the same host specificity as the native particles. The TD49-encapsidated VLPs showed a more potent target-specific algicidal effect than TD49 alone by increasing TD49 local concentrations near the target cells. In contrast, encapsulated TD49 protected non-host cells at low concentrations (0.5μM) even after 72h. Interestingly, at 5.0μM the VLP lost their protective effect for non-host cells by 72h and resulted in higher growth inhibition rates that free TD49. One of the possible explanations for this is the protection of TD49 by VLP from degradation, hence prolonging its otherwise short half-life.

VLPs have some major advantages for the delivery of algicidal compounds to harmful algae such as high target specificity and thus protection of non-target species, the use of a naturally occurring biodegradable protein and stabilisation of the algicidal compound from degradation in sea water. However, the stabilisation of the algicidal compounds could also be considered a disadvantage as it can increase the effect on non-target species once the VLPs have degraded as it makes the algicidal compounds linger around for longer. More work needs to be done on the production and stability of VLPs as HABs can be comprised of more than one strain and different types of VLPs would need to be deployed. It would also be interesting to test the efficiency of other algicidal compounds while encapsulated in VLPs and see whether the findings of this paper apply to other compounds as well.

Kang, B. S., Eom, C. Y., Kim, W., Ju, S. Y., Ryu, J., Han, G. H., ... & Kim, S. W. (2015). Construction of target‐specific virus‐like particles for the delivery of algicidal compounds to harmful algae. Environmental microbiology, 17(4), 1463-1474

http://onlinelibrary.wiley.com/doi/10.1111/1462-2920.12650/abstract?deniedAccessCustomisedMessage=&userIsAuthenticated=false