HKU study reveals the hidden fight within corals
Researchers from the School of Biological Sciences and Swire Institute of Marine Science at The University of Hong Kong are working to understand how the coral symbiosis may respond to global warming through changes in their microbiome, specifically their symbiotic algae. Using a newly developed method they revealed , which may be a determining factor in the sucthe metabolic function of algae changes in response to competition with other speciescess or failure of certain host-symbiont combinations. The research, published in The ISME Journal, used single-celled algae (dinoflagellates) which were isolated from reef-building corals to understand how hotter ocean temperatures might influence their ability to compete against each other within their coral host. The work builds on decades of research which has honed in on certain types of algal species which confer heat resistance to their host. Why these heat-tolerant species are not more widespread has remained a mystery, until now. “We know that the ability of corals to withstand warming oceans is related to their microbiome. You could say we are asking the same types of questions as a physician: Can we manipulate the host microbiome to improve coral health? Our paper demonstrates that the efficacy of probiotic treatments or assisted evolution might depend on how these microbes interact with each other” explains postdoctoral fellow Dr Shelby McIlroy who co-led the study with PhD student Jane Wong. The experiments were conducted at two temperatures; a heated treatment to simulate a coral bleaching event and an unheated control. The researchers found that the heat-tolerant algae were poor competitors at both temperatures and adopted a “shelter-in-place” strategy by storing more fats and carbohydrates to persist through times of stress. At normal temperatures, the thermally sensitive species grew similarly whether the other species was present or not. However, with warming competition triggered a marked increase in resource consumption, essentially restricting the availability of growth resources to its competitors. What the researchers suggest is that thermally tolerant algae have failed to become more widespread because they are outcompeted in most scenarios and simply the “last-man standing” under conditions unsuitable for other species. The researchers combined three established methods - Fluorescent In-Situ Hybridization (FISH), Flow Cytometry (Flow), and Stable Isotope Analysis (SIA) - to differentiate two species of algae from one another that were grown together in a mixed culture. After introducing isotopically labeled nutrients, the team allowed the cells to assimilate carbon and nitrogen prior to separating them for isotope analysis. In this way they could see if one species was obtaining more resources for growth and reproduction than the other - evidence of competition. They called the method FFS. “FFS is an exciting marriage of established methods. We applied it to an interesting question related to corals, but it can be adapted for any microbial community - such as the human gut. In doing so we can begin to assign metabolic functions to certain bacteria which are known to be present and may express certain genes but whose actual function remains unknown.” said Dr David Baker, Associate Professor of School of Biological Sciences and Swire Institute of Marine Science who supervised the study. This research was funded by the Research Grants Council Hong Kong General Research. About the journal paper Citation: McIlroy S.E., Wong J.C.Y., Baker D.M. (2020). Competitive traits of coral symbionts may alter the structure and function of the microbiome. ISME J. https://doi.org/10.1038/s41396-020-0697-0
Revisiting energy flow in photosynthetic plant cells
By developing innovative methods to visualize energy changes in subcellular compartments in live plants, the team of Dr Boon Leong LIM, Associate Professor of the School of Biological Sciences of The University of Hong Kong, after showing how chloroplasts optimizes its energy efficiency 2 years ago, recently solved a controversial question in photosynthesis: what is the source of NADH (Reduced Nicotinamide adenine dinucleotide) for mitochondria to generate ATP (Adenosine triphosphate)? The results were just published in the journal Nature Communications. Photosynthesis utilizes light as an energy source for plant chloroplasts to synthesize carbohydrates from water and CO2 molecules. ATPplays an important role in this process, as it promotes plant growth and supply energy for various cellular activities. It had been a general belief that mature plant chloroplasts can import ATP from cytosol since 1969, but it was shown to be untrue by Dr Lim and his team in 2018 (Note 1), through introducing a novel ATP sensor in the subcellular compartments of a C3 model plant, Arabidopsis thaliana. This finding has revised our understanding on chloroplast bioenergetics during daytime and nighttime and how mature chloroplasts optimize energy efficiency. Another unresolved problem in photo-energy is that the source of NADH as a fuel for mitochondria (the major ATP synthesizing organelle in cells) to produce ATP during photosynthesis is unclear. Some researchers suggested that excess reducing equivalents carried by surplus NADPH (Reduced Nicotinamide adenine dinucleotide phosphate) can be exported to the cytosol in the form of malate, which can then enter mitochondria through the malate-OAA shuttle, and converted into OAA and NADH in the mitochondrial matrix. On the other hand, some researchers proposed that during photorespiration glycine decarboxylase generates a large amount of NADH in mitochondria for ATP production and surplus reducing equivalents carried by NADH is exported by the mitochondrial malate-OAA shuttle to the cytosol. In the above two pathways, the directions of the malate-OAA shuttle across the mitochondrial membrane during photosynthesis are opposite to each other and therefore this issue had been a matter of debate. To study this problem, Dr Lim’s group introduced two novel sensors that measure real-time dynamic changes in NADPH levels and NADH/NAD+ ratios (this ratio reflects the reduction/oxidation status of the cellular compartments) in Arabidopsis thaliana. The conventional detection methods require extraction and purification of plant metabolites and determination by chemical methods. These methods have a few drawbacks: in planta measurement and real-time dynamic measurement not feasible; incapable of measurement the energy molecules in different cell types or different subcellular compartments. “Our novel technique solves all of the problems above. By employing these energy sensors, we found that photorespiration supplies a large amount of NADH to mitochondria during photosynthesis, which exceeds the NADH-dissipating capacity of the mitochondria. Consequently, the surplus NADH must be exported from the mitochondria to the cytosol through the mitochondrial malate-OAA shuttle. (see figure)”, said Ms Sheyli Lim, a PhD student and the first author of a manuscript published in Nature Communications. “Solving this question allows us to understand more about the energy flow between chloroplasts and mitochondria during photosynthesis, which could help us to booth the efficiency of photosynthesis in the future”. “We are the first group to introduce these three novel energy sensors in plants. They will have wide applications in researches regarding plant bioenergetics. Now we are employing them to study bioenergetics of guard cells, pollen tube growth and C4 plants with international collaborators,” said Dr Lim. “It is a great satisfaction to revisit and clarify some general believes in my field. I wish our findings can eventually help humans to boost agriculture production,’ he added. Note 1: press release (Oct 2018): https://www.hku.hk/press/press-releases/detail/c_18582.html The paper is published in Nature Communications and can be accessed here: https://www.nature.com/articles/s41467-020-17056-0 7-day-old seedlings with NADPH sensor in plastids
HKU-codeveloped automated laser-scanning ‘hunter drone’ seeks out fossils, minerals and biological targets
Science fiction has machine-intelligent hunter drones and they have now become science fact with a new HKU-codeveloped autonomous ‘hunter drone’ that seeks out targets at night using a scanning laser (Figure 1). This technique - Laser-Stimulated Fluorescence (LSF) - was codeveloped at HKU and has been highly successful in palaeontology, making fossil bones glow and revealing otherwise invisible details like skin and cartilage (note 1). The application of LSF to an aerial system is possible because of the laser’s ability to project over great distances with little loss in power. HKU Research Assistant Professor Dr Michael Pittman (Vertebrate Palaeontology Laboratory, Division of Earth & Planetary Science and Department of Earth Sciences) and his colleague Thomas G Kaye of the Foundation for Scientific Advancement made this a reality by developing a fully autonomous LSF drone system. “Nicknamed ‘Laser Raptor’, this system is designed to more efficiently seek out fossils exposed on the surface in the field”, said Dr Pittman. Loaded with pre-programmed flight paths during the day, this prototype was launched at night in the badlands of Arizona and Wyoming, USA to search for fossils (Figure 1). Laser Raptor flies rapidly to search locations using its on-board navigation and then descends and maintains an altitude of 4 metres above ground so it can ‘mow the lawn’ in search of glowing targets as small as a thumbnail. After each “mission” is complete, a video of the laser scan is processed to find hot spots that are investigated the next day (Figure 2), leading to the recovery of new fossil specimens (Figure 3). Fluorescence is extremely sensitive to differences in mineral composition. Although Laser Raptor was designed to locate fossils, it is ready to seek out a whole range of fluorescent targets including minerals e.g. to study rare and unusual geology or in search of mining materials like gemstones, certain organisms like scorpions, shellfish and cyanobacteria, and even archaeological artefacts and structures. Asked about future plans, Thomas Kaye replied, “As members of HKU’s Laboratory of Space Research, Dr Pittman and I are currently working to develop LSF applications for the study of geologic landscapes beyond Earth.” Note 1 press release (March 2017): https://www.hku.hk/press/press-releases/detail/15989.html The paper is published in Methods in Ecology and Evolution and can be accessed here: https://besjournals.onlinelibrary.wiley.com/doi/full/10.1111/2041-210X.13402 Please visit the video at here. Figure 2. Hot spot on laser ‘scan strip’ produced by the Laser Raptor drone system is ~2cm wide fragment of a fossil mammal tooth. Image Credit: Thomas G Kaye & Michael Pittman. Figure 3. ~2cm wide fragment of a fossil mammal tooth found using the Laser Raptor drone system. The tooth belongs to a brontothere which lived in ancient Wyoming, USA ~35 million years ago. Scale is 5mm. Image Credit: Thomas G Kaye & Michael Pittman.