Biology subjects

Brekhman, V.

Publications and source records attributed to Brekhman, V..

4 recordsLinked to original sources

bioRxiv2024

Jellyfish blooms Through the Microbial Lens: Temporal Changes, Cross-Species and Jellyfish-Water Comparisons

In this study, we explore the dynamics of bacterial communities associated with Rhopilema nomadica blooms, the predominant jellyfish in the Eastern Mediterranean Sea. We collected over 120 samples from more than 30 individuals across five major bloom events, capturing both lesser-studied winter blooms and the peaks and declines of summer blooms. Our analysis revealed significant microbial shifts-increases in Endozoicomonas and unclassified Rickettsiales were significantly more abundance during late summer blooms, while Tenacibaculum dominated in winter. Additionally, we examined microbial patterns within specific tissues--bell, gonads, tentacles, and gastrovascular system--to assess variations across these different niches. This revealed high relative abundance of specific taxa tailored to different tissue-Bacteroides was predominantly found in the bell, Simkaniaceae in the gonads, and Endozoicomonas in the tentacles. Further expanding our research, we compared the top taxa of R. nomadica with those of nine other jellyfish species from different locations. Interestingly, while no universal core microbiome was found, several taxa, including Endozoicomonas, Mycoplasma, and Spiroplasma, were common across different species, suggesting their potential ecological roles across jellyfish. Lastly, our study of potential bacterial transmission modes revealed that key bacteria associated with R. nomadica are exclusively found near bloom areas, and are absent from remote seawater, highlighting potential localized transmission dynamics between jellyfish and their immediate marine environment. Our study marks the first exploration of microbial dynamics within R. nomadica, while also broadening the understanding of other jellyfish microbial communities and setting the stage for future studies to delve deeper into their complex interactions. IMPORTANCEJellyfish blooms, like those of Rhopilema nomadica in the Eastern Mediterranean, impact marine ecosystems and human industries. Understanding the complex relationships between jellyfish and their microbiomes is important, as these interactions may influence bloom formation and decline. Our study explores microbiome variations across different stages of R. nomadica blooms, identifies common bacteria among jellyfish from various locations, and examines potential transmission modes of the main jellyfish-associated bacteria. Microbial communities vary significantly between bloom stages and jellyfish tissues, becoming less diverse towards the end of the bloom. Although no universal core microbiome was discovered, taxa such as Endozoicomonas, Mycoplasma, and Spiroplasma are prevalent across various jellyfish, suggesting significant ecological roles. Finally, our findings indicate that key bacteria associated with R. nomadica predominantly reside near bloom areas and are absent from distant seawater, highlighting localized transmission mode. This study enhances our understanding of jellyfish-associated microbial communities and their role in bloom dynamics.

microbiology↗

bioRxiv2022

Selecting 16S rRNA primers for microbiome analysis in a host-microbe system: the case of the jellyfish Rhopilema nomadica

Amplicon sequencing of the 16S rRNA gene is extensively used to characterize bacterial communities, including those living in association with eukaryotic hosts. Deciding which region of the 16S rRNA gene to analyze and selecting the appropriate PCR primers remained a major decision when initiating any new microbiome study. Here, we compared three commonly used primers targeting different hypervariable regions of the 16S rRNA gene, V1V2, V3V4, and V4V5, using the jellyfish Rhopilema nomadica as a model. Although all primers exhibit a similar pattern in bacterial community composition, the performance of the V3V4 primer set was superior to V1V2 and V4V5. The V1V2 primers misclassified bacteria from the Bacilli class and exhibited low classification resolution for Rickettsiales, which represent the second most abundant 16S rRNA gene sequence in all the primers. The V4V5 primer set detected almost the same community composition as the V3V4, but the ability of these primers to also amplify eukaryotic 18S rRNA gene may hinder bacterial community observations. However, after overcoming the challenges possessed by each one of those primers, we found that all three of them show very similar bacterial community dynamics and composition. Nevertheless, based on our results, we propose that the V3V4 primer set is the most suitable for studying jellyfish-associated bacterial communities. Our results suggest that, at least for jellyfish samples, it may be feasible to directly compare microbial community estimates from different studies, each using different primers but otherwise similar experimental protocols. More generally, we recommend specifically testing different primers as a prelude to large-scale 16S rRNA gene amplicon analyses, especially of previously unstudied host-microbe associations.

microbiology↗

bioRxiv2021

Cellular pathways during spawning induction in the starlet sea anemone Nematostella vectensis

In cnidarians, long-term ecological success relies on sexual reproduction. The sea anemone Nematostella vectensis, which has emerged as an important model organism for developmental studies, can be induced for spawning by temperature elevation and light exposure. To uncover molecular mechanisms and pathways underlying spawning, we characterized the transcriptome of Nematostella females before and during spawning induction. We identified an array of processes involving numerous receptors, circadian clock components, cytoskeleton, and extracellular transcripts that are upregulated upon spawning induction. Concurrently, processes related to the cell cycle, fatty acid metabolism, and other housekeeping functions are downregulated. Real-time qPCR revealed that light exposure has a minor effect on expression levels of most examined transcripts, implying that temperature change is a stronger inducer for spawning in Nematostella. Our findings reveal the mechanisms that may enable the mesenteries to serve as a gonad-like tissue for the developing oocytes and expand our understanding of sexual reproduction in cnidarians. Summary statementAnalysis of transcriptional changes during spawning induction in Nematostella vectensis, revealed upregulation of processes related to signal perception and cytoskeleton rearrangement and downregulation of fatty acid metabolism and housekeeping processes.

ecology↗

bioRxiv2019

Signaling via GABAB receptors regulates early development and neurogenesis in the basal metazoan Nematostella vectensis

The metabotropic gamma-amino-butyric acid B receptor (GABABR) is a G protein-coupled receptor that mediates neuronal inhibition by the neurotransmitter GABA. Here, we identified putative GABAB receptors and signaling modulators in the basal sea anemone Nematostella vectensis. Activation of GABABR signaling reversibly arrests planula-to-polyp transformation during early development and affects the neurogenic program. We identified four Nematostella GABABR homologs that have the conserved 3D extracellular domains and residues needed for binding of GABA and the GABABR agonist baclofen. Transcriptomic analysis, combined with spatial analysis of baclofen-treated planulae, revealed that baclofen down-regulated pro-neural factors such as NvSoxB(2), NvNeuroD1 and NvElav1. Baclofen also inhibited neuron development and extended neurites, resulting in an under-developed and less organized nervous system. Our results shed light on cnidarian development and suggest an evolutionarily conserved function for GABABR in regulation of neurogenesis, highlighting Nematostella as a new model system to study GABABR signaling.

molecular biology↗