Biology subjects

Luter, H. M.

Publications and source records attributed to Luter, H. M..

5 recordsLinked to original sources

bioRxiv2026

Thermal stress disrupts microbial symbiosis and host activity in the model sponge Ianthella basta

Climate change is threatening coral reef ecosystems around the world, causing significant declines in reef organisms, including sponges. The health of sponges is intimately linked to their symbiosis with microorganisms, yet little is known about their integrated response to ocean warming. Here, we present a comprehensive view of the effect of elevated sea surface temperatures (SST) on the model sponge Ianthella basta. I. basta individuals were exposed to temperatures up to 32 {degrees}C, 2-3 {degrees}C above the mean annual maxima. Host gene expression profiles showed an initial response to heat stress after 2 days, and a decreased expression of genes involved in maintaining tissue integrity, pumping capacity, vitamin transport, and stable symbioses after 4 to 8 days. Congruently, heat stressed samples started to show tissue regression and a reduced abundance of the dominant symbionts after 4 days. A significant loss of the symbionts occurred after 8 days, together with a reduction in microbially driven nitrogen cycling and amino-acid transport and an introduction of opportunistic microbes, which could lead to nutrient imbalance and further destabilisation of the holobiont. Together, this work provides important insights into the avenues through which future SST can impact host-microbe interactions in coral reef sponges.

microbiology↗

bioRxiv2025

Branched-chain amino acid assimilation promotes mixotrophy of ammonia-oxidizing archaeal sponge symbionts

Ammonia-oxidizing archaea (AOA) frequently form symbiotic associations with marine sponges. While free-living AOA are generally considered metabolically constrained chemolithoautotrophs, sponge-associated AOA encode for a branched-chain amino acid (BCAA) transporter, suggesting mixotrophic potential. Here, we test the unusual mixotrophic lifestyle of sponge-associated AOA by tracing the assimilation of 13C- and 15N-labeled BCAA in the sponge holobiont Ianthella basta. We demonstrate that BCAA degradation fuels ammonia oxidation and quantify BCAA uptake at the single-cell level by combining stable isotope probing, catalyzed reporter deposition fluorescence in situ hybridization, and nanoscale secondary ion mass spectrometry. Our results reveal that sponge-associated AOA are mixotrophic, assimilating BCAA as an additional carbon and nitrogen source. This metabolic adaptation may modulate BCAA availability in the holobiont, potentially regulating the hosts mTOR pathway. Collectively, our study reveals a novel nutritional interaction in sponge holobionts and challenges the perception of constrained metabolic capacities of AOA.

microbiology↗

bioRxiv2025

Unravelling the influence of light on inshore coral and sponge recruits and their substrate communities

Recruitment of progeny to coral reef populations involves complex ecological interactions, influenced by environmental factors such as altered underwater light conditions associated with poor water quality. Here, we exposed newly settled corals (Acropora millepora and Acropora cf. tenuis), the sponge (Phyllospongia foliascens), and their substrate communities to various light intensities and spectral profiles relevant to turbid inshore reefs. Coral and sponge recruit survivorship and growth generally exhibited an inverted U-shaped response to light intensity, suggesting environmental optima at lower light levels, while the influence of light spectra remained less clear within environmentally realistic treatment combinations. Crustose coralline algae cover similarly peaked at lower light levels, whereas turf algae increased with higher light conditions. Competitive interactions between the substrate communities and the recruits, along with photophysiological responses, were also assessed. Our results suggest that altered light characteristics associated with turbidity may not be as detrimental to coral and sponge recruits as other sediment-related stressors.

ecology↗

bioRxiv2023

Novel nitrifying symbiont lineages are vertically inherited and widespread in marine sponges

Ammonia-oxidising archaea and nitrite-oxidising bacteria are common members of marine sponge microbiomes. They derive energy for carbon fixation and growth from nitrification - the oxidation of ammonia to nitrite and further to nitrate - and are proposed to play essential roles in the carbon and nitrogen cycling of sponge holobionts. In this study, we characterise two novel nitrifying symbiont lineages, Ca. Nitrosokoinonia and Ca. Nitrosymbion in the marine sponge Coscinoderma matthewsi using a combination of molecular tools, single-cell imaging techniques, and physiological rate measurements. Both represent a new genus in the ammonia-oxidising archaeal class Nitrososphaeria and the nitrite-oxidising bacterial order Nitrospirales, respectively. Furthermore, we show that larvae of this viviparous sponge are densely colonised by representatives of Ca. Nitrosokoinonia and Ca. Nitrosymbion indicating vertical transmission. In adults, the representatives of both symbiont genera are located extracellularly in the mesohyl. Comparative metagenome analyses and physiological data suggest that ammonia-oxidising archaeal symbionts of the genus Ca. Nitrosokoinonia strongly rely on endogenously produced nitrogenous compounds (i.e., ammonium, urea, nitriles/cyanides, and creatinine) rather than on exogenous ammonium sources taken up by the sponge. Additionally, the nitrite-oxidising bacterial symbionts Ca. Nitrosymbion may reciprocally support the ammonia-oxidisers with ammonia via the utilisation of sponge-derived urea and cyanate. Interestingly, comparative analyses of published environmental 16S rRNA amplicon data revealed that Ca. Nitrosokoinonia and Ca. Nitrosymbion are widely distributed and predominantly associated with marine sponges and corals, suggesting a broad relevance of our findings.

microbiology↗

bioRxiv2020

Impacts of water quality on Acropora coral settlement: The relative importance of substrate quality and light

Coral larval settlement patterns are influenced by a vast array of factors; however, the relative roles of individual factors are rarely tested in isolation, leading to confusion about which are most crucial for settlement. For example, direct effects of light environment are often cited as a major determinate of settlement patterns, yet this has not been demonstrated under environmentally realistic lighting regimes in the absence of confounding factors. Here we apply programmable multispectral lights to create realistic light spectra, while removing correlating (but not obvious) factors that are common in laboratory settlement experiments. Using two common species of Acropora - key framework builders of the Great Barrier Reef - we find little evidence that light intensity or changes in the spectral profile play a substantial role in larval settlement under most environmentally realistic settings but can under more extreme or artificial settings. We alternatively hypothesise and provide evidence that chronic conditions of light and recent sediment exposures that impact benthic substrates (e.g., crustose coralline algae) preceding settlement have a greater impact, with up to 74% decrease in settlement observed on substrates with prior exposure and poor water quality conditions. Management of water quality conditions that impact the quality of benthic-settlement substrates therefore should present a priority area of focus for improving coral recruitment.

ecology↗