Biology subjects

Bollati, E.

Publications and source records attributed to Bollati, E..

4 recordsLinked to original sources

bioRxiv2026

From Coral Color to Tissue Heating: How Host Pigments Redirect Light Within the Tissue

Coral host pigments strongly modify the internal light environment of corals, yet their influence on heat dissipation in coral tissue remains poorly understood. Here, we combined scalar irradiance and temperature microsensor measurements with mechanistic multiphysics modelling to quantify how chromoproteins (CPs) and fluorescent proteins (FPs) regulate light propagation and tissue heating in corals. Measurement-informed simulations of coupled radiative and heat transfer showed that high host pigment concentrations increase broadband scattering while strongly absorbing light within their characteristic spectral bands, reducing light penetration into deeper tissue layers and producing localized energy deposition. Under high symbiont densities, tissue heating was governed by absorption by both symbionts and host pigments, whereas in bleached corals, host pigments became the dominant source of heat generation. Heat generated by CP absorption was concentrated within the epidermis, while symbiont absorption caused deeper heating within the gastrodermis. Unlike CPs, FPs additionally redistributed a fraction of the absorbed photons through lower energy fluorescence emission, increasing scalar irradiance at longer wavelengths and shifting energy deposition deeper into the tissue, thereby enhancing subsurface heating relative to the corresponding non-fluorescent CP scenario. In the model, this pathway changes scalar irradiance and predicted energy deposition relative to the same FP parameterization with fluorescence disabled. The magnitude of this effect varied with FP concentration, spatial organization (granular or diffuse), and symbiont density. Model outputs were supported by surface light and temperature microsensor measurements across sampled coral phenotypes and symbiont densities. Together, our results demonstrate distinct modeled optical pathways for CPs and FPs that regulate not only light propagation but also the spatial distribution of heat generation within coral tissues. By balancing light attenuation, spectral redistribution, and heat generation, host pigmentation is thus likely to influence photoacclimation, bleaching susceptibility, and recovery of the coral-algal symbiosis.

biophysics↗

bioRxiv2025

Chemical Microenvironment of the Coral Gastrovascular Cavity and Its Associated Bacterial Diversity

Coral gastrovascular cavities (GVCs) host diverse microorganisms and, as semi-closed compartments, are characterized by elevated nutrient concentrations and pronounced diel fluctuations in oxygen (O2) and pH. However, their broader chemical microenvironment and associated microbial activities remain poorly understood. Here, we provide direct evidence for active anaerobic metabolism in the GVC by measuring hydrogen (H2), nitric oxide (NO), and nitrous oxide (N2O) production, indicative of microbial fermentation, nitrogen fixation and denitrification. Changes in GVC H2 concentrations after feeding suggest that feeding modulates substrate availability, which in turn influences microbial activity in this compartment. In bleached corals, the GVC remained consistently hypoxic and acidic, and anaerobic metabolic processes persisted across the diel cycle. These patterns suggest a shift in energy and nutrient cycling pathways within the bleached coral holobiont. Together, our findings identify the GVC as a dynamic site of microbial activity that may play an important role in holobiont carbon and nitrogen cycling, with potential implications for nutrient balance and coral resilience.

ecology↗

bioRxiv2024

Microscale sampling of the coral gastric cavity reveals a gut-like microbial community

Animal guts contain numerous microbes, which are critical for nutrient assimilation and pathogen defence. While corals and other Cnidaria lack a true differentiated gut, they possess gastrovascular cavities (GVCs), semi-enclosed compartments where vital processes such as digestion, reproduction and symbiotic exchanges take place. The microbiome harboured in GVCs is therefore likely key to holobiont fitness, but remains severely understudied due to challenges of working in these small compartments. Here, we developed minimally invasive methodologies to sample the GVC of coral polyps and characterise the microbial communities harboured within. We used glass capillaries, low dead volume microneedles, or nylon microswabs to sample the gastric microbiome of individual polyps from six species of corals, then applied low-input DNA extraction to characterise the microbial communities from these microliter volume samples. Microsensor measurements of GVCs revealed anoxic or hypoxic micro-niches, which persist even under prolonged illumination with saturating irradiance. These niches harboured microbial communities enriched in putatively microaerophilic or facultatively anaerobic taxa, such as Epsilonproteobacteria. Some core taxa found in the GVC of Lobophyllia hemprichii from the Great Barrier Reef were also detected in conspecific colonies held in aquaria, indicating that these associations are unlikely to be transient. Our findings suggest that the coral GVC is chemically and microbiologically similar to the gut of higher Metazoa. Given the importance of gut microbiomes in mediating animal health, harnessing the coral "gut microbiome" may foster novel active interventions aimed at increasing the resilience of coral reefs to the climate crisis.

microbiology↗

bioRxiv2021

Green fluorescent protein-like pigments optimize the internal light environment in symbiotic reef building corals

Pigments homologous to the Green Fluorescent Protein (GFP) have been proposed to fine-tune the internal light microclimate of corals, facilitating photoacclimation of photosynthetic coral symbionts (Symbiodiniaceae) to life in different reef habitats and environmental conditions. However, direct measurements of the in vivo light conditions inside the coral tissue supporting this conclusion are lacking. Here, we quantified the intra-tissue spectral light environment of corals expressing GFP-like proteins from widely different light regimes. We focus on (1) photoconvertible red fluorescent proteins (pcRFPs), thought to enhance photosynthesis in mesophotic habitats via wavelength conversion, and (2) chromoproteins (CPs), which provide photoprotection to the symbionts in shallow water via light absorption. Optical microsensor measurements indicated that both pigment groups strongly alter the coral tissue light environment. Estimates derived from light spectra measured in pcRFP-containing corals showed that fluorescence emission can contribute to >50% of orange-red light available to the photosynthetic symbionts at mesophotic depths. We further show that upregulation of pink CPs in shallow-water corals during bleaching leads to a reduction of orange light by 10-20% compared to low-CP tissue. Thus, screening by CPs has an important role in mitigating the light-enhancing effect of coral tissue scattering during bleaching. Our results provide the first experimental quantification of the importance of GFP-like proteins in fine-tuning the light microclimate of corals during photoacclimation.

ecology↗