Engineered nanoceria alleviates thermally induced oxidative stress in free-living Breviolum minutum (Symbiodiniaceae, formerly Clade B)

Abstract

The breakdown of symbiotic mutualism between cnidarian hosts and dinoflagellate algae partners (i.e., bleaching) has been linked to an immune-like response pathway brought on by a nitro-oxidative burst, a symptom of thermal stress. Stress induced by reactive oxygen species (ROS)/reactive nitrogen species is a problem common to aerobic systems. In this study, we tested the antioxidant effects of engineered poly(acrylic acid)-coated cerium dioxide nanoparticles (CeO2, nanoceria) on free-living Symbiodiniaceae (Breviolum minutum), a dinoflagellate alga that forms symbiotic relationships with reef-building corals and anemones. Results show that poly(acrylic acid)-coated CeO2 with hydrodynamic diameters of ~4 nm are internalized by B. minutum in under 30 min and subsequently localized in the cytosol. Nanoceria exposure does not inhibit cell growth over time, with the treated cultures showing a similar growth trend over the 25-day exposure. Aerobic activity and thermal stress when held at 34°C for 1 h (+6°C above control) led to increased intracellular ROS concentration with time. A clear ROS scavenging effect of the nanoceria was observed, with a 5-fold decrease in intracellular ROS levels during thermal stress. The nitric oxide (NO) concentration decreased by ~17% with thermal stress, suggesting the rapid involvement of NO scavenging enzymes or proteins within 1 h of stress onset. The presence of nanoceria did not appear to influence NO concentration. Furthermore, aposymbiotic anemones (Exaiptasia diaphana, ex Aiptasia pallida) were successfully infected with nanoceria-loaded B. minutum, demonstrating that inoculation could serve as a delivery method. The ability of nanoceria to be taken up by Symbiodiniaceae and reduce ROS production could be leveraged as a potential mitigation strategy to reduce coral bleaching.

Comparing the Role of ROS and RNS in the Thermal Stress Response of Two Cnidarian Models, Exaiptasia diaphana and Galaxea fascicularis

“…The observed differences may be due to the sample's genetic identity, different light levels used, or the different symbiodiniacean communities harbored. However, a recent study also found a significant decrease in RNS of thermally stressed symbiodiniaceans (Breviolum minutum) [70]. A possible scenario for not being able to detect an increase but a decrease in RNS in this study could be that it may have instantly reacted with OH − to form ONOO − .…”

Nanotechnology for coral reef conservation, restoration and rehabilitation

“…and antioxidant drugs increased survival of aposymbiotic coral larvae exposed to thermal stress 6 . Moreover, engineered nanoceria (cerium dioxide nanoparticles coated with poly(acrylic acid), PAA-CeO2) delivered intracellularly to free-living symbiotic algae typically associated with reef-building corals reduced the concentration of ROS when cultures were exposed to thermal stress 7 . Antioxidant treatments could be coupled with "stress-training", i.e.…”

“…Now, with the recent kick-off of the Climate Change National Nanotechnology Challenge (January 2023, https://www.nano.gov/nano4EARTH), coral reef research could leverage these exciting developments towards new coral-specific diagnostic tools, rapid testing, high-resolution health monitoring, coral nanomedicines/ pharmacology, novel bio-nano-fabrication and, more generally, to improve the coral research toolkit. We suggest that combining the known beneficial effects of ROS scavenging with lipid-based supplements or liposome encapsulation is a viable way forward to protect corals during periods of stress 6,7,14,15 . Likewise, the encapsulation of coral probiotic and antibiotic treatments 16.17 in highly modular, target-specific nanocarriers is an important development that will reduce the severity of coral disease outbreaks.…”