Comparative genome analysis and global methylation patterns for epigenetic study in the brackish water flea...

The brackish water flea Diaphanosoma celebensis is a crucial organism in brackish and estuarine ecosystems, acting as a key trophic link between primary producers and higher trophic levels. Its small size, short life cycle, and high reproductive capacity make it an ideal model for studying ecological responses to environmental stressors, especially in polluted environments. This study provides a chromosome-level genome assembly of D. celebensis, consisting of 22 chromosomes with an N50 of 4,113,329 base pairs and 95.1 % completeness, achieved by combining de novo assembly with Hi-C data from D. dubium. Whole-genome bisulfite sequencing (WGBS) revealed distinct DNA methylation patterns, with exons showing higher methylation than introns and intergenic regions. A detailed analysis identified four gene clusters based on methylation levels. Cluster δ (highly methylated), enriched for pathways related to protein processing, ribosomal activity, and ubiquitin-mediated proteolysis, suggests a regulatory mechanism for stress adaptation in D. celebensis. In contrast, cluster α (hypo methylated), associated with transcription regulation and neural functions, highlights genes involved in cellular processes that may respond dynamically to environmental changes. Functional gene comparisons indicated significant differences in pathways related to ion transport and ubiquitination, emphasizing the unique adaptations of D. celebensis to its brackish environment. These findings provide a deeper understanding of the species' genomic and epigenetic regulation, offering valuable insights for future studies on its adaptation to environmental pollutants.