Biology subjects

Raina, J.-B.

Publications and source records attributed to Raina, J.-B..

7 recordsLinked to original sources

bioRxiv2026

Widespread attraction of marine bacteria to the macroalgae-derived polysaccharide fucoidan

Fucoidan is the second most abundant polysaccharide in brown macroalgae, contributing up to 50% of the dissolved organic matter released daily from these algae into the ocean, substantially influencing the marine carbon cycle. Due to its complex chemical structure, fucoidan is highly resistant to microbial degradation and accumulates on the surface of macroalgae, where it contributes to regulating their microbiome. Here, we used a range of microfluidic assays to quantify the chemotactic and physiological responses of marine bacteria to fucoidan. Our results reveal that all the strains tested (14 out of 14) are attracted to fucoidan produced by two different species of brown macroalgae. Attraction occurred only at high fucoidan concentrations (0.1 to 1 mg/mL), such as those expected in the immediate vicinity of algal surfaces, whereas low concentrations elicited no response or modest chemorepulsion. Although fucoidan did not support bacterial growth under our experimental conditions, it did not impair the utilization of other carbon sources. Together, these findings suggest that fucoidan gradients can act as chemical cues guiding marine bacteria toward the nutrient-rich microenvironment of macroalgal surfaces, pointing to a potential ecological role of fucoidan in shaping macroalgal microbiota, bacterial behavior, and ultimately carbon cycling in the ocean.

microbiology↗

bioRxiv2026

Early origin of sugar sensing in jawed vertebrates

Sweet taste guides animals to consume carbohydrate-rich foods, and many different vertebrate groups, from fish to mammals, rely on sugar-rich fruits or nectar produced by flowering plants (angiosperms). Although the genes encoding T1R2-T1R3, the receptor pair that mammals use to sense sugars, exist in the genomes of many vertebrates, their functions are unclear--and whether sugar sensing arose once early in vertebrate evolution or independently in different lineages after angiosperms evolved is currently unknown. Here, we combined ancestral reconstruction and receptor functional profiling to examine the evolutionary history of T1R taste receptors--including recently-described non-canonical receptors--across all major vertebrate clades. Our results pinpoint the origin of sugar sensing to before the emergence of angiosperms and uncover a myriad of alternative T1R-based sugar-sensing mechanisms, suggesting multiple independent T1R trajectories and revealing uncharted sensory diversity across vertebrates.

evolutionary biology↗

bioRxiv2026

Vitamin B6 Catabolites Act as Interkingdom Signals Within the Marine Microbiome

More than half of all net primary productivity in the oceans is exchanged and recycled among marine microbial communities, through a network of complex interactions that fuel the global carbon cycle and control oceanic biogeochemistry1,2. Cryptic chemical signals control these interactions, thereby governing interspecies metabolite exchanges and structuring the ocean microbiome3. Here, we show that vitamin B6 catabolites--molecules long assumed to be inert byproducts of metabolism--in fact serve as potent, bidirectional, and widely distributed chemical signals that structure metabolite exchanges between marine eukaryotic phytoplankton and bacteria. We demonstrate that a ubiquitous diatom and its bacterial symbiont exchange five intermediates and catabolites in the glycerophospholipid and vitamin B6 metabolic pathways, previously not implicated in interspecies interactions. Acting in combination, these signals induce broad transcriptional responses that prime each organism to anticipate metabolic input from its partner and enter a symbiotic-like state, despite having no measurable effect on growth. We further identify and biochemically validate the enzymes biosynthesizing two of these signals: diatom-derived 4-pyridoxolactone and bacterially-derived 4-pyridoxate--a catabolite long regarded as bacterial waste4. Genes encoding these enzymes are globally distributed and co-expressed across diverse sunlit ocean microbial communities, indicating that vitamin B6-mediated communication is widespread in the ocean. Together, these findings reveal an unexpected signaling role for vitamin B6 and demonstrate that canonical metabolic byproducts can function as information-rich signals structuring interkingdom interactions in the oceans.

microbiology↗

bioRxiv2025

Synergy in viral-bacterial coinfection expedites algal bloom demise

Algal blooms are hotspots for diverse microbial interactions affecting bloom dynamics. Viral infections often regulate the demise of these blooms, recycling >25% of oceanic fixed carbon. Although these blooms collapse synchronously, only 10-30% of algal cells show active viral infection, suggesting additional mortality agents. Using microbial communities from natural coccolithophore blooms, we discovered that bacteria significantly enhanced virus-mediated algal mortality. We quantified this interaction using two novel metrics: the Synergy Index (SI) measuring viral-bacterial interaction strength, and the Benefit Index (BI) assessing changes in bacterial fitness. We identified Alteromonas bacteria as drivers of viral-bacterial coinfection with consistently high SI and BI. In natural communities, Alteromonas exhibited chemoattraction towards infected algal cells, leading to their enrichment in bloom demise particles. This viral-bacterial synergy represents a previously unrecognized mortality agent controlling bloom termination, modulating the balance between the carbon-recycling viral shunt and the carbon-exporting viral shuttle pathways, likely influencing global carbon cycling.

microbiology↗

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↗

bioRxiv2022

Molecular insights into the Darwin paradox of coral reefs from the sea anemone Aiptasia

Symbiotic cnidarians such as corals and anemones form highly productive and biodiverse coral-reef ecosystems in nutrient-poor ocean environments, a phenomenon known as Darwins Paradox. Resolving this paradox requires elucidating the molecular bases of efficient nutrient distribution and recycling in the cnidarian-dinoflagellate symbiosis. Using the sea anemone Aiptasia, we show that during symbiosis, the increased availability of glucose and the presence of the algae jointly induce the coordinated upregulation and re-localization of glucose and ammonium transporters. These molecular responses are critical to support symbiont functioning and organism-wide nitrogen assimilation through GS/GOGAT-mediated amino-acid biosynthesis. Our results reveal crucial aspects of the molecular mechanisms underlying nitrogen conservation and recycling in these organisms that allow them to thrive in the nitrogen-poor ocean environments. One-sentence summaryWhole-organism nitrogen assimilation fueled by glucose from symbiotic algae enables corals to flourish in oligotrophic waters.

molecular biology↗

bioRxiv2017

Aiptasia as a model to study metabolic diversity and specificity in cnidarian-dinoflagellate symbioses

The symbiosis between cnidarian hosts and microalgae of the genus Symbiodinium provides the foundation of coral reefs in oligotrophic waters. Understanding the nutrient-exchange between these partners is key to identifying the fundamental mechanisms behind this symbiosis. However, deciphering the individual role of host and algal partners in the uptake and cycling of nutrients has proven difficult, given the endosymbiotic nature of this relationship. In this study, we highlight the advantages of the emerging model system Aiptasia to investigate the metabolic diversity and specificity of cnidarian - dinoflagellate symbiosis. For this, we combined traditional measurements with nano-scale secondary ion mass spectrometry (NanoSIMS) and stable isotope labeling to investigate carbon and nitrogen cycling both at the organismal scale and the cellular scale. Our results suggest that the individual nutrient assimilation by hosts and symbionts depends on the identity of their respective symbiotic partner. Further,{delta} 13C enrichment patterns revealed that alterations in carbon fixation rates only affected carbon assimilation in the cnidarian host but not the algal symbiont, suggesting a selfish character of this symbiotic association. Based on our findings, we identify new venues for future research regarding the role and regulation of nutrient exchange in the cnidarian - dinoflagellate symbiosis. In this context, the model system approach outlined in this study constitutes a powerful tool set to address these questions.

physiology↗