Junde Dong’s research while affiliated with Institute of Oceanology and other places

Background Coral reefs experience frequent and severe disturbances that can overwhelm their natural resilience. In such cases, ecological restoration is essential for coral reef recovery. Sexual reproduction has been reported to present the simplest and most cost-effective means for coral reef restoration. However, larval settlement and post-settlement survival represent bottlenecks for coral recruitment in sexual reproduction. While bacteria play a significant role in triggering coral metamorphosis and settlement in many coral species, the underlying molecular mechanisms remain largely unknown. In this study, we employed a transcriptome-level analysis to elucidate the intricate interactions between bacteria and coral larvae that are crucial for the settlement process. Results High Metabacillus indicus strain cB07 inoculation densities resulted in the successful induction of metamorphosis and settlement of coral Pocillopora damicoris larvae. Compared with controls, inoculated coral larvae exhibited a pronounced increase in the abundance of strain cB07 during metamorphosis and settlement, followed by a significant decrease in total lipid contents during the settled stage. The differentially expressed genes (DEGs) during metamorphosis were significantly enriched in amino acid, protein, fatty acid, and glucose related metabolic pathways. In settled coral larvae induced by strain cB07, there was a significant enrichment of DEGs with essential roles in the establishment of a symbiotic relationship between coral larvae and their symbiotic partners. The photosynthetic efficiency of strain cB07 induced primary polyp holobionts was improved compared to those of the negative controls. In addition, coral primary polyps induced by strain cB07 showed significant improvements in energy storage and survival. Conclusions Our findings revealed that strain cB07 can promote coral larval settlement and enhance post-settlement survival and fitness. Manipulating coral sexual reproduction with strain cB07 can overcome the current recruitment bottleneck. This innovative approach holds promise for future coral reef restoration efforts.

In the background of global warming, coral bleaching induced by elevated seawater temperature is the primary cause of coral reef degradation. Coral microbiome engineering using the beneficial microorganisms for corals (BMCs) has become a hot spot in the field of coral reef conservation and restoration. Investigating the potential of alleviating thermal stress by quorum quenching (QQ) bacteria may provide more tools for coral microbial engineering remediation. In this study, QQ bacteria strain Pseudoalteromonas piscicida SCSIO 43740 was screened among 75 coral-derived bacterial strains, and its quorum sensing inhibitor (QSI) compound was isolated and identified as 2,4-di-tert-butylphenol (2,4-DTBP). Then, the thermal stress alleviating potential of QQ bacteria on coral Pocillopora damicornis was tested by a 30-day controlled experiment with three different treatments: control group (Con: 29 °C), high temperature group (HT: 31 °C), and the group of high temperature with QQ bacteria inoculation (HTQQ: 31 °C + QQ bacteria). The results showed that QQ bacteria SCSIO 43740 inoculation can significantly mitigate the loss of symbiotic algae and impairment of photosynthesis efficiency of coral P. damicornis under thermal stress. Significant difference in superoxide dismutase (SOD) and catalase (CAT) enzyme activities between HT and HTQQ was not observed. In addition, QQ bacteria inoculation suppressed the coral microbial community beta-dispersion and improved the stability of microbial co-occurrence network under thermal stress. It was suggested that QQ bacteria inoculation can alleviate coral thermal stress via reshaping microbial interaction and maintain community stability of coral microbiome. This study provided new evidence for the probiotic function of QQ bacteria in corals, which shedding light on the development of new microbiological tools for coral reef conservation.

Thermal stress causes the overproduction and toxic accumulation of reactive oxygen species (ROS), which seems to be correlated with coral bleaching and, ultimately, death. The reduction of ROS concentration within the coral holobiont could minimize the effects of thermal stress and support efforts to reduce coral decline globally. In the current study, we explored the physiological responses of Pocillopora damicornis to ROS-scavenging bacteria inoculation as well as the microbiome restructuring that correlates with P. damicornis’s resilience to thermal stress after probiotic inoculation. Inoculation of corals with ROS-scavenging bacteria enhanced coral health and reduced ROS concentration. Furthermore, the enhanced coral thermal resistance promoted by ROS-scavenging bacteria was also correlated with an overall coral microbiome restructuring. In addition, the complex network relationships between bacteria and Symbiodiniaceae in corals after ROS-scavenging bacteria inoculation contributed to corals’ resilience to high temperatures. Besides, coral heat tolerance bacterial biomarkers, such as Myxococcota, were enriched in corals with added ROS-scavenging bacteria. Collectively, our findings validate the selected ROS-scavenging bacteria as coral probiotics that could help corals resist thermal stress on a short timescale. Additionally, our data contribute to our understanding of the potential interactions between different members of the coral holobiont and the use of probiotics as tools to aid coral restoration efforts.

In the background of global warming, coral bleaching induced by elevated seawater temperature is the primary cause of coral reef degradation. Coral microbiome engineering using the beneficial microorganisms for corals (BMCs) has become a hot spot in the field of coral reef conservation and restoration. Investigating the potential of alleviating thermal stress by quorum quenching (QQ) bacteria may provide more tools for coral microbial engineering remediation. In this study, QQ bacteria strain Pseudoalteromonas piscicida SCSIO 43740 was screened among 75 coral-derived bacterial strains, and its quorum sensing inhibitor (QSI) compound was isolated and identified as 2,4-di-tert-butylphenol (2,4-DTBP). Then, the thermal stress alleviating potential of QQ bacteria on coral Pocillopora damicornis was tested by a 30-day controlled experiment with three different treatments: control group (Con: 29°C), high temperature group (HT: 31°C), and the group of high temperature with QQ bacteria inoculation (HTQQ: 31°C + QQ bacteria). The results showed that QQ bacteria SCSIO 43740 inoculation can significantly mitigate the loss of symbiotic algae and impairment of photosynthesis efficiency of coral P. damicornis under thermal stress. In addition, QQ bacteria inoculation suppressed the coral microbial community beta-dispersion and improved the stability of microbial co-occurrence network under thermal stress. It was suggested that QQ bacteria inoculation can alleviate coral thermal stress via reshaping microbial interaction and maintain community stability of coral microbiome. This study provided new evidence for the probiotic function of QQ bacteria in corals, which shedding light on the development of new microbiological tools for coral reef conservation.