Micro-bioplastic impact on gut microbiome, cephalic transcription and cognitive function in the aquatic invertebrate Daphnia magna

The role of the gut microbiome-brain axis on contaminant effects in invertebrates is limited by our poor knowledge of gut microbiome neurological regulatory pathways. This study investigates the influence of microplastics on the gut microbiome composition and assess subsequent alterations in the cephalic transcriptome, feeding patterns, and overall behaviour of the organism. D. magna individuals were exposed to low and high levels of bioplastic particles and kaolin natural particles and under starving conditions. Feeding and behavioral effects were assessed using previously well-established assays. Changes in gut microbiome composition, cephalic transcription and their functional interpretation were studied by 16S rRNA gene sequencing and cephalic D magna RNA high-throughput sequencing, respectively, and using appropriate bioinformatic pipelines. Only exposures to high concentrations of bioplastic microparticles inhibited feeding and impacted behavioural responses in D. magna, resembling effects observed under starvation. Microbiome analysis revealed shifts in taxonomic composition and functional profiles across the tested microplastic concentrations, which become more notable at higher ones. Functional changes in the gut microbiome indicated that bioplastics at high concentrations altered to a greater extent short-chain fatty acid biosynthesis and tryptophan and L-glutamate metabolism pathways than at low concentrations. Transcriptomic analyses revealed that microplastics up-regulated neurological pathways, cell turnover, and differentiation. In summary exposure to microplastics resulted in gut dysbiosis and increased biosynthesis of short-chain fatty acid signalling pathways in the gut, altered neurological pathways in the cephalic transcriptome and disrupted behavioural responses, altogether supporting the role of the microbiota-gut-brain crosstalk on neurological disorders.