Chiu, Y.-F. | Search bioRxiv

bioRxiv2025

Comparative genomic analysis of a novel heat-tolerant and euryhaline strain of unicellular marine cyanobacterium Cyanobacterium sp. DS4 from a high-temperature lagoon

BackgroundCyanobacteria have diversified through their long evolutionary history and occupy a wide range of environments on Earth. To advance our understanding of their adaption mechanisms in extreme environments, we performed stress tolerance characterizations, whole genome sequencing, and comparative genomic analyses of a novel heat-tolerant and euryhaline strain of the unicellular cyanobacterium Cyanobacterium sp. Dongsha4 (DS4). This strain was isolated from a lagoon on Dongsha Island in the South China Sea, a habitat with fluctuations in temperature, salinity, light intensity, and nutrient supply. ResultsDS4 cells can tolerate long-term high-temperature up to 50 and salinity from 0 to 6.6 %, which is similar to the results previously obtained for Cyanobacterium aponinum. In contrast, most mesophilic cyanobacteria cannot survive under these extreme conditions. Based on the 16S rRNA gene phylogeny, DS4 is most closely related to Cyanobacterium sp. NBRC 102756 isolated from Iwojima Island, Japan, and Cyanobacterium sp. MCCB114 isolated from Vypeen Island, India. For comparison with strains that have genomic information available, DS4 is most similar to Cyanobacterium aponinum strain PCC 10605 (PCC10605), sharing 81.7% of the genomic segments and 92.9% average nucleotide identity (ANI). Gene content comparisons identified multiple distinct features of DS4. Unlike related strains, DS4 possesses the genes necessary for nitrogen fixation. Other notable genes include those involved in photosynthesis, central metabolisms, cyanobacterial starch metabolisms, stress tolerances, and biosynthesis of novel secondary metabolites. ConclusionsThese findings promote our understanding of the physiology, ecology, evolution, and stress tolerance mechanisms of cyanobacteria. The information is valuable for future functional studies and biotechnology applications of heat-tolerant and euryhaline marine cyanobacteria.

genomics↗

bioRxiv2023

A shift in the host web occupancy of dew-drop spiders associated with genetic divergence in the Southwest Pacific

AimWe assessed the population genetic structure of the kleptoparasitic spider Argyrodes bonadea across the Southwestern Pacific islands. Our focus is on assessing the impact of overseas distances and, in particular, the Kerama gap, as potential drivers of genetic differentiation. We found that the spider kleptoparasites switch to a specific host species is associated with significant genetic variation at fine scales, whereas the same species adoption of a generalist host strategy has likely facilitated its broad dispersal, colonization, and recent range expansion across the southwestern Pacific, and is associated with a lack of geographically- structured genetic variation in these latter, subsequently-colonized landmasses. LocationSouthwestern Pacific Islands TaxonArgyrodes bonadea MethodsWe used mitochondrial Cytochrome Oxidase 1 (CO1) gene sequences, and Restriction Site-associated DNA Sequencing (RAD-seq) for our analyses. ResultsTwo strongly supported lineages, an Amami-Okinawa Lineage (AOL) and an Austral-Asia Lineage (AAL) correspond to two separate clades, roughly divided by the Kerama Gap, in phylogenetic trees estimated here. However, species delimitation led to the interpretation of only a single species present. The AOL exhibits complex, geographically-structured host web spider species specificity, wherein the Amami population utilizes Cyrtophora, but AOL samples in Okinawa associates exclusively with Nephila--and yet all broadly distributed AAL populations show no evidence of host web spider species specificity. Main conclusionThe population boundary between AOL and AAL likely results from local adaptation to novel hosts--instead of isolation by the Kerama Gap--following long-distance dispersal and range expansion. Our results suggest kleptoparasitic spiders have the capacity to overcome permanent deep-sea barriers and colonize distant landmasses. Whereas peripheral populations (AOL) demonstrate the capacity for specialization to a single host, which may have contributed to genetic differentiation and isolation, the broadly-distributed AAL persists and has successfully expanded its geographical range as a host generalist, which may contribute to ongoing gene flow inferred in this study.

evolutionary biology↗