This week was off to a rough start with Hurricane Beryl flooding much of our neighborhood and leading to power outages throughout the Woodlands area. We had power and so we accommodated several affected family friends for the week, which is the reason this blog post is delayed. On Wednesday, I was unable to conduct any lab work because my mentor’s car was flooded in the storm, preventing him from coming in. Consequently, my efforts on Thursday and Friday were redirected towards an in-depth review of the relevant literature and research papers related to my field, allowing me to deepen my understanding of the topic. This blog post will focus on the learnings attained from the various papers I read.

Wednesday

Citation for Paper 1: Marzonie, M., Nitschke, M. R., Bay, L., Bourne, D. G., Harrison, H. B. (2024). Symbiodiniaceae diversity varies by host and environment across thermally distinct reefs. Molecular Ecology.

Information from Paper 1: The study focuses on the diversity of Symbiodiniaceae, a group of endosymbiotic dinoflagellates, which play a vital role in determining the thermal tolerance of corals across different regions and environments. In my project for this REU, we are studying how dinoRNAVs, an RNA virus, impact Symbiodiniaceae and potentially influence the occurrence of coral bleaching. While the individual effects of host genetics, environmental factors, and thermal disturbances on symbiont communities are well-documented, their combined effects remain less understood, prompting the need for the research in the paper. This research was conducted across a 1300 km stretch in Australia’s Coral Sea Marine Park, aiming to identify the interactive effects of host genetics, environment, and thermal disturbances on Symbiodiniaceae communities. The study involved identifying Symbiodiniaceae to the species level in three coral species: Acropora cf humilis, Pocillopora verrucosa, and Pocillopora meandrina, using genetic markers ITS2 and psbAncr for the symbionts and DArT-seq for the coral hosts. The findings revealed that the genus Cladocopium was predominant among the samples, with specific affiliations: Acropora cf humilis with C3k, Pocillopora verrucosa with C. pacificum, and Pocillopora meandrina with C. latusorum. Multivariate analyses showed that the symbiont communities in Acropora were strongly influenced by local environmental conditions and thermal disturbances, whereas in Pocillopora species, host genetic structure played a more significant role. Among the Pocillopora species, the combined effects of environment and host genetics explained more variation in symbiont communities for P. meandrina compared to P. verrucosa. The study also observed that the bleaching event in 2020 had varying impacts on symbiont communities, aligning with patterns seen in P. verrucosa and A. cf humilis, but not in P. meandrina.

Citation for Paper 2: Benites, F. L., Stephens, T. G., Bhattacharya, D. (2022). Multiple waves of viral invasions in Symbiodiniaceae algal genomes. Virus Evolution, 8(2).

Information from Paper 2: Dinoflagellates from the family Symbiodiniaceae are marine organisms that use sunlight to produce energy and form symbiotic relationships with various hosts, including corals. They havelarge and unique genomes characterized by frequent gene duplications, the expansion of gene families with unknown functions, and significant retroposition events, which are processes where genetic elements are copied and inserted into new locations within the genome. Despite the extensive study of their genomes, the role and extent of horizontal gene transfer (HGT) in the evolution of Symbiodiniaceae are not well understood. In some related species, such as Fugacium kawagutii and Brevioloum minutum, a small percentage of their genes are believed to have originated from prokaryotes through HGT events. Higher levels of HGT have been observed in other dinoflagellates, often associated with significant genomic changes, such as the acquisition of viral nucleoproteins that may play a role in chromatin regulation. All sequenced dinoflagellate genomes contain a family of viral-acquired nucleoproteins known as dinoflagellate-viral nucleoproteins (DVNPs), which are thought to have originated from a large DNA algal virus and may help regulate chromosome structure. The acquisition of the DVNP gene family is linked to massive genomic expansion in dinoflagellates and may have provided immunity against infections by similar viruses. Symbiodiniaceae isolated from corals are known to be actively infected by various viral groups, including giant DNA viruses and single-stranded RNA viruses, which may have implications for coral health (not well understood at the moment). There is evidence suggesting that some viral infections in Symbiodiniaceae are latent, meaning the viruses can persist in the host without causing immediate symptoms, and may become active under stress conditions. My work at Rice focuses on determining the impact of dinoRNAVs, single-stranded RNA viruses, on coral colony health.

Thursday

Citation for Paper 3: Chen, B., Wei, Y., Liang, Y., Yu, X., Liao, Z., Qin, Z., Xu, L., Bao, Z. (2024). The microbiome dynamics and interaction of endosymbiotic Symbiodiniaceae and fungi are associated with thermal bleaching susceptibility of coral holobionts. Applied and Environmental Microbiology.

Information from Paper 3: The study focuses on understanding how the interactions between Symbiodiniaceae and fungi within the coral microbiome affect the coral’s susceptibility to thermal bleaching. The research found that heat-tolerant sub-clades of Symbiodiniaceae, specifically the C3u sub-clade and Durusdinium, dominate the coral communities in high-risk thermal bleaching areas. These heat-tolerant Symbiodiniaceae are believed to contribute to the coral’s ability to withstand higher temperatures, potentially reducing bleaching events. Unlike Symbiodiniaceae, the fungal community associated with corals did not have core amplicon sequence variants, indicating high variability among different coral species. The study found a significant positive correlation between fungal richness, the abundance of animal-plant pathogens, and the percentage of coral thermal bleaching, suggesting that higher fungal diversity and pathogen presence increase bleaching susceptibility. Each coral species exhibited a complex Symbiodiniaceae-fungi interaction network (SFIN), driven by the dominant Symbiodiniaceae sub-clades. Corals with low thermal bleaching susceptibility had SFINs characterized by low complexity and high betweenness centrality, indicating a more resilient and less parasitized microbial network. The study highlights that the extra heat tolerance observed in corals from Huangyan Island may be linked to the high abundance of heat-tolerant Symbiodiniaceae and a resilient microbial network. The findings suggest that managing fungal diversity and pathogen abundance could be crucial in mitigating coral bleaching and promoting coral health under thermal stress.

Citation for Paper 4: Springer, K., Kunzmann, A. (2023). Symbiodiniaceae in and ex hospite have differential physiological responses under different heat stress scenarios. Marine Biology Research, 1-13.

Information from Paper 4: The study focuses on the increasing frequency of cnidarian bleaching, which is the breakdown of the symbiosis between cnidarian hosts and their endosymbiotic dinoflagellates, often due to extreme seawater temperatures linked to various human activities, with seawater warming being a significant factor. The primary aim of the research is to understand whether the thermal tolerance of dinoflagellate symbionts differs when they are inside their host (in hospite) compared to when they are free-living (ex hospite). The study measured the maximum quantum yield of photosystem II (Fv/Fm) and symbiont cell density in seven different cnidarian species and five cultures of isolated endosymbionts. These were subjected to three different temperature conditions: 26°C (control), 30°C, and 34°C for a duration of 21 days. Isolated dinoflagellate cells showed a significant susceptibility to elevated temperatures of 30°C, which was evident from a decrease in their photochemical efficiency and cell density. Additionally, there was a progressive disintegration of cellular structures and loss of pigmentation in all but two cultures during the first week of exposure. The study found that bleaching of coral holobionts at 30°C could be explained by a reduced density of algae cells in the host tissue, with this effect being particularly noticeable in soft corals. Exposure to 34°C resulted in drastic bleaching of stony coral species, anemones, and jellyfish, and even led to the death of soft corals. This indicates that higher temperatures have severe impacts on the symbiotic relationship and the survival of these organisms.

Friday

Citation for Paper 5: Mashini, A. (2022). The Impact of Symbiont Diversity on Cellular Integration and Function in the Cnidarian-Dinoflagellate Symbiosis. Open Access Te Herenga Waka-Victoria University of Wellington. Thesis. https://doi.org/10.26686/wgtn.18739247.

Information from Paper 5: Coral health is closely linked to their symbiotic relationship with phototrophic dinoflagellates from the family Symbiodiniaceae. This symbiotic relationship is crucial for coral survival, but it is threatened by elevated temperatures, which can disrupt the symbiosis and lead to coral bleaching, a phenomenon that is becoming more frequent and severe due to climate change. The primary aim of the research was to understand the cellular processes involved in hosting native versus non-native symbionts in the model symbiotic cnidarian Exaiptasia pallida, commonly known as Aiptasia. The study sought to assess the potential for establishing novel symbiotic partnerships by using a multidisciplinary approach, including proteomics and quantitative immunocytochemistry, with a focus on inter-partner nutritional exchange. A new method for characterizing the proteome of Symbiodiniaceae was developed and used to compare the molecular and metabolic pathways underlying successful symbiosis. The proteome of Breviolum minutum, the native symbiont of Aiptasia, was analyzed under different nutritional conditions, revealing distinct proteomes related to immunosuppression, metabolic integration, and oxidative stress in the symbiotic state. The study further characterized the proteome of B. minutum during host colonization and compared it to the proteome of a non-native symbiont, Durusdinium trenchii, which is thermally tolerant but opportunistic. The proteome of D. trenchii showed a lower abundance of photosynthetic proteins and an upregulation of parasite-like immunosuppression mechanisms, indicating a lesser degree of integration with the host compared to B. minutum. Specific immunofluorescent antibodies were designed to localize and quantify host nutrient transporters in Aiptasia colonized with either native or non-native symbionts. The study found different transporter localization patterns in hosts harboring non-native symbionts, suggesting disrupted nutritional flux and a lesser degree of host-symbiont integration. The findings suggest that the cellular integration necessary for a functional symbiosis with efficient nutritional exchange is not easily replicated with non-native symbionts, which may reduce the likelihood of corals adapting to climate change by changing their symbiont population.

This week primarily involved reading papers and familiarizing myself with literature. Next week will focus more on actual lab work.