Camp, EF, Kahlke, T, Nitschke, MR, Varkey, D, Fisher, NL, Fujise, L, Goyen, S, Hughes, DJ, Lawson, CA, Ros, M, Woodcock, S, Xiao, K, Leggat, W & Suggett, DJ 2020, 'Revealing changes in the microbiome of Symbiodiniaceae under thermal stress', ENVIRONMENTAL MICROBIOLOGY, vol. 22, no. 4, pp. 1294-1309.View/Download from: Publisher's site
Camp, EF, Suggett, DJ, Pogoreutz, C, Nitschke, MR, Houlbreque, F, Hume, BCC, Gardner, SG, Zampighi, M, Rodolfo-Metalpa, R & Voolstra, CR 2020, 'Corals exhibit distinct patterns of microbial reorganisation to thrive in an extreme inshore environment', CORAL REEFS, vol. 39, no. 3, pp. 701-716.View/Download from: Publisher's site
Nitschke, MR, Craveiro, SC, Brandão, C, Fidalgo, C, Serôdio, J, Calado, AJ & Frommlet, JC 2020, 'Description of Freudenthalidium gen. nov. and Halluxium gen. nov. to Formally Recognize Clades Fr3 and H as Genera in the Family Symbiodiniaceae (Dinophyceae)', Journal of Phycology, vol. 56, no. 4, pp. 923-940.View/Download from: Publisher's site
© 2020 Phycological Society of America The Symbiodiniaceae are a family of marine dinoflagellates known mostly for their endosymbiotic interactions with invertebrates and protists, but facultatively and exclusively free-living life histories in this family are also evident. A recent systematic revision of the Symbiodiniaceae replaced the clade-based nomenclature of seven divergent lineages of "Symbiodinium" sensu lato with one based on formally described genera. The revised taxonomy was not extended to the whole group because type species to describe a new genus for each of the remaining clades and subclades were lacking. In an effort to characterize benthic habitats of symbiodiniaceans in sediments at Heron Island (Great Barrier Reef, Australia), we isolated >100 monoclonal Symbiodiniaceae cultures. Four of these belonged to Symbiodiniaceae 'subclade' Fr3, and three to Clade H, based on nucleotide sequence similarity (ITS2, LSU, cp23S, and mtCOB), representing the first cultures of these taxa. Based on these isolates, we propose two new genera: Freudenthalidium gen. nov. and Halluxium gen. nov., circumscribing Clades Fr3 and H, respectively. Three new species are described: Freudenthalidium heronense, F. endolithicum, and Halluxium pauxillum. Kofoidian tabulations of motile cells confirm previous observations that amphiesmal vesicle arrangements are generally conserved across the family. These descriptions are an important step toward completing the systematic revision of the Symbiodiniaceae. That this contribution was enabled by isolates from an endopsammic habitat highlights the potential of discovering new symbiodiniacean species in the environment, the study of which will lead to a deeper understanding of free-living versus symbiotic life histories in this ecologically important family of dinoflagellates.
Nitschke, MR, Fidalgo, C, Simões, J, Brandão, C, Alves, A, Serôdio, J & Frommlet, JC 2020, 'Symbiolite formation: a powerful in vitro model to untangle the role of bacterial communities in the photosynthesis-induced formation of microbialites', ISME Journal, vol. 14, no. 6, pp. 1533-1546.View/Download from: Publisher's site
© 2020, The Author(s), under exclusive licence to International Society for Microbial Ecology. Microbially induced calcification is an ancient, community-driven mineralisation process that produces different types of microbialites. Symbiolites are photosynthesis-induced microbialites, formed by calcifying co-cultures of dinoflagellates from the family Symbiodiniaceae and bacteria. Symbiolites encase the calcifying community as endolithic cells, pointing at an autoendolithic niche of symbiotic dinoflagellates, and provide a rare opportunity to study the role of bacteria in bacterial–algal calcification, as symbiodiniacean cultures display either distinct symbiolite-producing (SP) or non-symbiolite-producing (NP) phenotypes. Using Illumina sequencing, we found that the bacterial communities of SP and NP cultures differed significantly in the relative abundance of 23 genera, 14 families, and 2 phyla. SP cultures were rich in biofilm digesters from the phylum Planctomycetes and their predicted metagenomes were enriched in orthologs related to biofilm formation. In contrast, NP cultures were dominated by biofilm digesters from the Bacteroidetes, and were inferred as enriched in proteases and nucleases. Functional assays confirmed the potential of co-cultures and bacterial isolates to produce biofilms and point at acidic polysaccharides as key stimulators for mineral precipitation. Hence, bacteria appear to influence symbiolite formation primarily through their biofilm-producing and modifying activity and we anticipate that symbiolite formation, as a low-complexity in vitro model, will significantly advance our understanding of photosynthesis-induced microbial calcification processes.
Goyen, S, Camp, EF, Fujise, L, Lloyd, A, Nitschke, MR, LaJeunensse, T, Kahlke, T, Ralph, PJ & Suggett, D 2019, 'Mass coral bleaching of P. versipora in Sydney Harbour driven by the 2015–2016 heatwave', Coral Reefs, vol. 38, no. 4, pp. 815-830.View/Download from: Publisher's site
© 2019, Springer-Verlag GmbH Germany, part of Springer Nature. High-latitude coral communities are distinct from their tropical counterparts, and how they respond to recent heat wave events that have decimated tropical reefs remains unknown. In Australia, the 2016 El Niño resulted in the largest global mass coral bleaching event to date, reaching as far south as Sydney Harbour (~ 34°S). Coral bleaching was observed for the first time (affecting ca., 60% of all corals) as sea surface temperatures in Sydney Harbour remained > 2 °C above the long-term mean summer maxima, enabling us to examine whether high-latitude corals bleached in a manner described for tropical corals. Responses of the geographically cosmopolitan Plesiastrea versipora and southerly restricted Coscinaraea mcneilli were contrasted across two harbour sites, both in situ and among samples-maintained ex situ in aquaria continually supplied with Sydney Harbour seawater. While both coral taxa hosted the same species of microalgal endosymbiont (Breviolum spp; formerly clade B), only P. versipora bleached both in situ and ex situ via pronounced losses of endosymbiont cells. Both species displayed very different metabolic responses (growth, photosynthesis, respiration and calcification) and bleaching susceptibilities under elevated temperatures. Bacterial microbiome profiling, however, revealed a convergence of bacterial community composition across coral species throughout the bleaching. Corals species found in temperate regions, including the generalist P. versipora, will therefore likely be highly susceptible to future change as heat waves grow in frequency and severity unless their thermal thresholds increase. Our observations provide further evidence that high-latitude systems are susceptible to community reorganisation under climate change.
Goyen, S, Camp, EF, Fujise, L, Lloyd, A, Nitschke, MR, LaJeunesse, TC, Kahlke, T, Ralph, PJ & Suggett, D 2019, 'Mass coral bleaching of P. versipora in Sydney Harbour driven by the 2015-2016 heatwave (vol 38, pg 815, 2019)', CORAL REEFS, vol. 38, no. 4, pp. 877-877.View/Download from: Publisher's site
Fujise, L, Nitschke, MR, Frommlet, JC, Serôdio, J, Woodcock, S, Ralph, PJ & Suggett, DJ 2018, 'Cell Cycle Dynamics of Cultured Coral Endosymbiotic Microalgae (Symbiodinium) Across Different Types (Species) Under Alternate Light and Temperature Conditions', Journal of Eukaryotic Microbiology, vol. 65, pp. 505-517.View/Download from: Publisher's site
Nitschke, MR, Gardner, SG, Goyen, S, Fujise, L, Camp, EF, Ralph, PJ & Suggett, DJ 2018, 'Utility of photochemical traits as diagnostics of thermal tolerance amongst great barrier reef corals', Frontiers in Marine Science, vol. 5, no. FEB.View/Download from: Publisher's site
© 2018 Nitschke, Gardner, Goyen, Fujise, Camp, Ralph and Suggett. Light availability is considered a key factor regulating the thermal sensitivity of reef building corals, where excessive excitation of photosystem II (PSII) further exacerbates pressure on photochemical pathways already compromised by heat stress. Coral symbionts acclimate to changes in light availability (photoacclimation) by continually fine-tuning the photochemical operating efficiency of PSII. However, how this process adjusts throughout the warmest months in naturally heat-tolerant or sensitive species is unknown, and whether this influences the capacity to tolerate transient heat stress is untested. We therefore examined the PSII photophysiology of 10 coral species (with known thermal tolerances) from shallow reef environments at Heron Island (Great Barrier Reef, Australia), in spring (October-November, 2015) vs. summer (February-March, 2016). Corals were maintained in flow-through aquaria and rapid light curve (RLC) protocols using pulse amplitude modulated (PAM) fluorometry captured changes in the PSII photoacclimation strategy, characterized as the minimum saturating irradiance (Ek), and the extent of photochemical ([1-C], operating efficiency) vs. non-photochemical ([1-Q]) energy dissipation. Values of Ekacross species were > 2-fold higher in all coral species in spring, consistent with a climate of higher overall light exposure (i.e., higher PAR from lower cloud cover, rainfall and wind speed) compared with summer. Summer decreases in Ekwere combined with a shift toward preferential photochemical quenching in all species. All coral species were subsequently subjected to thermal stress assays. An equivalent temperature-ramping profile of 1°C increase per day and then maintenance at 32°C was applied in each season. Despite the significant seasonal photoacclimation, the species hierarchy of thermal tolerance [maximum quantum yields of PSII (Fv/Fm), monitored at dawn and dusk] did not shift...
Serôdio, J, Schmidt, W, Frommlet, JC, Christa, G & Nitschke, MR 2018, 'An LED-based multi-actinic illumination system for the high throughput study of photosynthetic light responses', PeerJ, vol. 2018, no. 9.View/Download from: Publisher's site
©2018 Serôdio et al. The responses of photosynthetic organisms to light stress are of interest for both fundamental and applied research. Functional traits related to the photoinhibition, the light-induced loss of photosynthetic efficiency, are particularly interesting as this process is a key limiting factor of photosynthetic productivity in algae and plants. The quantitative characterization of light responses is often time-consuming and calls for cost-effective high throughput approaches that enable the fast screening of multiple samples. Here we present a novel illumination system based on the concept of 'multiactinic imaging' of in vivo chlorophyll fluorescence. The system is based on the combination of an array of individually addressable low power RGBW LEDs and customdesigned well plates, allowing for the independent illumination of 64 samples through the digital manipulation of both exposure duration and light intensity. The illumination system is inexpensive and easily fabricated, based on open source electronics, off-theshelf components, and 3D-printed parts, and is optimized for imaging of chlorophyll fluorescence. The high-throughput potential of the system is illustrated by assessing the functional diversity in light responses of marine macroalgal species, through the fast and simultaneous determination of kinetic parameters characterizing the response to light stress of multiple samples. Although the presented illumination system was primarily designed for the measurement of phenotypic traits related to photosynthetic activity and photoinhibition, it can be potentially used for a number of alternative applications, including the measurement of chloroplast phototaxis and action spectra, or as the basis for microphotobioreactors.
Lohr, KE, Smith, DJ, Suggett, DJ, Nitschke, MR, Dumbrell, AJ, Woodcock, S & Camp, EF 2017, 'Coral Community Structure and Recruitment in Seagrass Meadows', Frontiers in Marine Science, vol. 4, pp. 1-13.View/Download from: Publisher's site
Camp, EF, Nitschke, MR, Rodolfo-Metalpa, R, Houlbreque, F, Gardner, SG, Smith, DJ, Zampighi, M & Suggett, DJ 2017, 'Reef-building corals thrive within hot-acidified and deoxygenated waters.', Scientific reports, vol. 7, no. 1, pp. 2434-2434.View/Download from: Publisher's site
Coral reefs are deteriorating under climate change as oceans continue to warm and acidify and thermal anomalies grow in frequency and intensity. In vitro experiments are widely used to forecast reef-building coral health into the future, but often fail to account for the complex ecological and biogeochemical interactions that govern reefs. Consequently, observations from coral communities under naturally occurring extremes have become central for improved predictions of future reef form and function. Here, we present a semi-enclosed lagoon system in New Caledonia characterised by diel fluctuations of hot-deoxygenated water coupled with tidally driven persistently low pH, relative to neighbouring reefs. Coral communities within the lagoon system exhibited high richness (number of species = 20) and cover (24-35% across lagoon sites). Calcification rates for key species (Acropora formosa, Acropora pulchra, Coelastrea aspera and Porites lutea) for populations from the lagoon were equivalent to, or reduced by ca. 30-40% compared to those from the reef. Enhanced coral respiration, alongside high particulate organic content of the lagoon sediment, suggests acclimatisation to this trio of temperature, oxygen and pH changes through heterotrophic plasticity. This semi-enclosed lagoon therefore provides a novel system to understand coral acclimatisation to complex climatic scenarios and may serve as a reservoir of coral populations already resistant to extreme environmental conditions.
Klein, SG, Pitt, KA, Nitschke, MR, Goyen, S, Welsh, DT, Suggett, DJ & Carroll, AR 2017, 'Symbiodinium mitigate the combined effects of hypoxia and acidification on a noncalcifying cnidarian.', Global Change Biology, vol. 23, no. 9, pp. 3690-3703.View/Download from: Publisher's site
Anthropogenic nutrient inputs enhance microbial respiration within many coastal ecosystems, driving concurrent hypoxia and acidification. During photosynthesis, Symbiodinium spp., the microalgal endosymbionts of cnidarians and other marine phyla, produce O2 and assimilate CO2 and thus potentially mitigate the exposure of the host to these stresses. However, such a role for Symbiodinium remains untested for noncalcifying cnidarians. We therefore contrasted the fitness of symbiotic and aposymbiotic polyps of a model host jellyfish (Cassiopea sp.) under reduced O2 (~2.09 mg/L) and pH (~ 7.63) scenarios in a full-factorial experiment. Host fitness was characterized as asexual reproduction and their ability to regulate internal pH and Symbiodinium performance characterized by maximum photochemical efficiency, chla content and cell density. Acidification alone resulted in 58% more asexual reproduction of symbiotic polyps than aposymbiotic polyps (and enhanced Symbiodinium cell density) suggesting Cassiopea sp. fitness was enhanced by CO2 -stimulated Symbiodinium photosynthetic activity. Indeed, greater CO2 drawdown (elevated pH) was observed within host tissues of symbiotic polyps under acidification regardless of O2 conditions. Hypoxia alone produced 22% fewer polyps than ambient conditions regardless of acidification and symbiont status, suggesting Symbiodinium photosynthetic activity did not mitigate its effects. Combined hypoxia and acidification, however, produced similar numbers of symbiotic polyps compared with aposymbiotic kept under ambient conditions, demonstrating that the presence of Symbiodinium was key for mitigating the combined effects of hypoxia and acidification on asexual reproduction. We hypothesize that this mitigation occurred because of reduced photorespiration under elevated CO2 conditions where increased net O2 production ameliorates oxygen debt. We show that Symbiodinium play an important role in facilitating enhanced fitness of Cassiopea sp. ...
Levin, RA, Suggett, DJ, Nitschke, MR, van Oppen, MJH & Steinberg, PD 2017, 'Expanding the Symbiodinium (Dinophyceae, Suessiales) Toolkit Through Protoplast Technology.', The Journal of Eukaryotic Microbiology, vol. 64, no. 5, pp. 588-597.View/Download from: Publisher's site
Dinoflagellates within the genus Symbiodinium are photosymbionts of many tropical reef invertebrates, including corals, making them central to the health of coral reefs. Symbiodinium have therefore gained significant research attention, though studies have been constrained by technical limitations. In particular, the generation of viable cells with their cell walls removed (termed protoplasts) has enabled a wide range of experimental techniques for bacteria, fungi, plants, and algae such as ultrastructure studies, virus infection studies, patch clamping, genetic transformation, and protoplast fusion. However, previous studies have struggled to remove the cell walls from armored dinoflagellates, potentially due to the internal placement of their cell walls. Here, we produce the first Symbiodinium protoplasts from three genetically and physiologically distinct strains via incubation with cellulase and osmotic agents. Digestion of the cell walls was verified by a lack of Calcofluor White fluorescence signal and by cell swelling in hypotonic culture medium. Fused protoplasts were also observed, motivating future investigation into intra- and inter-specific somatic hybridization of Symbiodinium. Following digestion and transfer to regeneration medium, protoplasts remained photosynthetically active, regrew cell walls, regained motility, and entered exponential growth. Generation of Symbiodinium protoplasts opens exciting, new avenues for researching these crucial symbiotic dinoflagellates, including genetic modification.
Gardner, SG, Raina, J-B, Nitschke, MR, Nielsen, DA, Stat, M, Motti, CA, Ralph, PJ & Petrou, K 2017, 'A multi-trait systems approach reveals a response cascade to bleaching in corals', BMC BIOLOGY, vol. 15.View/Download from: Publisher's site
Nitschke, MR, Davy, SK & Ward, S 2016, 'Horizontal transmission of Symbiodinium cells between adult and juvenile corals is aided by benthic sediment', Coral Reefs, vol. 35, no. 1, pp. 335-344.View/Download from: Publisher's site
© 2015, Springer-Verlag Berlin Heidelberg. Of all reef-building coral species, 80–85 % initially draw their intracellular symbionts (dinoflagellates of the genus Symbiodinium) from the environment. Although Symbiodinium cells are crucial for the growth of corals and the formation of coral reefs, little is known about how corals first encounter free-living Symbiodinium cells. We report how the supply of free-living Symbiodinium cells to the benthos by adult corals can increase the rate of horizontal symbiont acquisition for conspecific recruits. Three species of newly settled aposymbiotic (i.e., symbiont-free) corals were maintained in an open aquarium system containing: sterilized sediment and adult coral fragments combined; adult coral fragments alone; sterilized sediment alone; or seawater at Heron Island, Great Barrier Reef, Australia. In all instances, the combination of an adult coral and sediment resulted in the highest symbiont acquisition rates by juvenile corals (up to five-fold greater than seawater alone). Juvenile corals exposed to individual treatments of adult coral or sediment produced an intermediate acquisition response (<52 % of recruits), and symbiont acquisition from unfiltered seawater was comparatively low (<20 % of recruits). Additionally, benthic free-living Symbiodinium cells reached their highest densities in the adult coral + sediment treatment (up to 1.2 × 104 cells mL−1). Our results suggest that corals seed microhabitats with free-living Symbiodinium cells suitable for many coral species during the process of coral recruitment.
Gibbin, EM, Putnam, HM, Gates, RD, Nitschke, MR & Davy, SK 2015, 'Species-specific differences in thermal tolerance may define susceptibility to intracellular acidosis in reef corals', Marine Biology, vol. 162, no. 3, pp. 717-723.View/Download from: Publisher's site
© 2015, Springer-Verlag Berlin Heidelberg. It is widely acknowledged that temperature stress affects an organism's sensitivity to ocean acidification and vice versa, yet it is not clear how the two are mechanistically linked. Here, we induced thermal stress in two coral species with differing bleaching susceptibilities to measure how a reduction in photosynthetic performance impacts intracellular pH (pHi) regulation in the symbiotic dinoflagellates (Symbiodinium sp.) and their host coral cells. Our hypothesis was that thermally induced photosynthetic dysfunction in the symbiont would prevent the efficient removal of additional CO2, lowering its buffering capacity and thus increasing the host cell's susceptibility to intracellular acidosis. To test this, we exposed Pocillopora damicornis (a thermally sensitive coral) and Montipora capitata (a thermally resilient coral) to four different temperature treatments (23.8, 25.5, 28 and 31 °C) for 1 week. We then isolated intact symbiotic coral endodermal cells, placed them in a live-cell chamber attached to a confocal microscope and bathed them in CO2-acidified seawater (~pH 7.6) for 30 min, before measuring the light-adapted pHi of both the host cell and its symbiont. Cells isolated from P. damicornis were more prone to cellular acidosis (declines in pHi of 11 and 8 % in host and symbiont, respectively, at 31 °C relative to 23.8 °C) than cells isolated from M. capitata (5 and 4 %, respectively). These results highlight the important role of Symbiodinium productivity (in addition to a range of physico-chemical factors such as skeletal morphology and tissue pigmentation) in determining the sensitivity of corals to rising sea surface temperatures and ocean acidification.
Nitschke, MR, Davy, SK, Cribb, TH & Ward, S 2015, 'The effect of elevated temperature and substrate on free-living Symbiodinium cultures', Coral Reefs, vol. 34, no. 1, pp. 161-171.View/Download from: Publisher's site
© 2014, Springer-Verlag Berlin Heidelberg. Elevated temperatures can produce a range of serious, deleterious effects on marine invertebrate—Symbiodinium symbioses. The responses of free-living Symbiodinium to elevated temperature, however, have been little studied, especially in the context of their natural habitat. In this study, we investigated physiological responses of two Symbiodinium cultures to elevated temperature, an exclusively free-living ITS2 clade A (strain HI-0509) and the symbiosis-forming ITS2 type A1 (strain CCMP2467). Free-living Symbiodinium strains have recently been isolated from benthic sediments, and both cultures were therefore grown with or without a microhabitat of carbonate sediment at 25, 28 or 31 °C. Maximum quantum yield of photosystem II (Fv/Fm) and specific growth rate were measured as response variables. In culture, Symbiodinium cells exhibit motility in a helical swimming pattern, and therefore, revolutions per minute (RPM) were also measured with video microscopy. The exclusively free-living clade A was physiologically superior to Symbiodinium A1 across all measured variables and treatment combinations. Fv/Fm remained relatively stable through time (at approximately 0.55) and was not substantially affected by temperature or the presence or the absence of sediment. Populations of the exclusively free-living Symbiodinium A reproduced faster with sediment than without and exhibited high levels of motility across all treatments (surpassing 300 RPM). In contrast, the Fv/Fm of A1 dropped to 0.42 in sediment (relative to cultures without sediment) and exhibited dramatic declines in cell concentration, most severely at 31 °C. A > 50 % reduction in motility was also observed at 31 °C. Even in the absence of sediment, elevated temperature was observed to reduce population growth and cell motility of type A1. We suggest that vital behaviours linked to motility (such as vertical migration and the locating of potential hosts) may become impa...
Starzak, DE, Quinnell, RG, Nitschke, MR & Davy, SK 2014, 'The influence of symbiont type on photosynthetic carbon flux in a model cnidarian-dinoflagellate symbiosis', Marine Biology, vol. 161, no. 3, pp. 711-724.View/Download from: Publisher's site
We measured the relationship between symbiont diversity, nutritional potential, and symbiotic success in the cnidarian-dinoflagellate symbiosis, by infecting aposymbiotic (i.e. symbiont-free) specimens of the model sea anemone Aiptasia sp. with a range of Symbiodinium types. Four cultured heterologous Symbiodinium types (i.e. originally isolated from other host species) were used, plus both cultured and freshly isolated homologous zooxanthellae (i.e. from Aiptasia sp.). Rates of photosynthesis, respiration, and symbiont growth were measured during symbiosis establishment and used to estimate the contribution of the zooxanthellae to the animal's respiratory carbon demands (CZAR). Anemones containing Symbiodinium B1 (both homologous and heterologous) tended to attain higher CZAR values and hence benefit most from their symbiotic partners. This was despite Symbiodinium B1 not achieving the highest cell densities, though it did grow more quickly during the earliest stages of the infection process. Rather, the heterologous Symbiodinium types A1.4, E2, and F5.1 attained the highest densities, with populations of E2 and F5.1 also exhibiting the highest photosynthetic rates. This apparent success was countered, however, by very high rates of symbiosis respiration that ultimately resulted in lower CZAR values. This study highlights the impact of symbiont type on the functionality and autotrophic potential of the symbiosis. Most interestingly, it suggests that certain heterologous symbionts may behave opportunistically, proliferating rapidly but in a manner that is energetically costly to the host. Such negative host-symbiont interactions may contribute to the host-symbiont specificity seen in cnidarian-dinoflagellate symbioses and potentially limit the potential for partner switching as an adaptive mechanism. © 2013 Springer-Verlag Berlin Heidelberg.