Background: Mycoplasma (M.) bovis is a major etiological agent of bovine respiratory disease, which is the most economically costly disease of cattle worldwide. Cattle disease surveillance on M. bovis is increasingly using gene-based techniques, such as multilocus sequence typing (MLST), or genome-based techniques such as core genome MLST that both require only partial genomic data. However, accurate up-to-date surveillance also demands complete, circular genomes that can be used as reference to track the evolution of the different lineages. Yet, in France, two of the main subtypes currently circulating still have no representing genome in public databases. Here, to address this gap, we provide and compare three new complete M. bovis genomes obtained from recent clinical isolates that represent major subtypes circulating in France and Europe. Results: Genomes were obtained using a hybrid assembly strategy (Illumina and Nanopore) with fine-tuning of settings and inputs used in the Unicycler assembly pipeline, such as size selection of reads and quality trimming of the FASTQ files. The main characteristics and synteny of the genomes were compared. The three genomes mainly differed by their content in terms of mobile genetic elements, i.e. integrative conjugative elements (ICE) and insertion sequences (IS), a feature that impacts their structure. For instance, strain L15527, representing subtype3 (st3), harbours an exceptionally high number of ICEs, which results in a bigger-sized genome than all those previously described and could be associated with the propensity of st3 to gain and fix mutations through chromosomal transfer mechanisms. In contrast, strain F9160, of st1, is very close to the PG45 type strain isolated in 1961 in the USA, and harbours a huge number of IS. These features may be associated with an evolution towards a host-restricted state or in a “closed” host or environment reservoir until a recent re-emergence. Conclusions: Whole-genome comparison of the three French M. bovis subtypes provides valuable resources for future studies combining epidemiology, phylogenetic data, and phylodynamic methods.

The marine pennate diatom Haslea ostrearia has long been known for its characteristic blue pigment marennine, which is responsible for the greening of invertebrate gills, a natural phenomenon of great importance for the oyster industry. For two centuries, this taxon was considered unique; however, the recent description of a new blue Haslea species revealed unsuspected biodiversity. Marennine-like pigments are natural blue dyes that display various biological activities—e.g., antibacterial, antioxidant and antiproliferative—with a great potential for applications in the food, feed, cosmetic and health industries. Regarding fundamental prospects, researchers use model organisms as standards to study cellular and physiological processes in other organisms, and there is a growing and crucial need for more, new and unconventional model organisms to better correspond to the diversity of the tree of life. The present work, thus, advocates for establishing H. ostrearia as a new model organism by presenting its pros and cons—i.e., the interesting aspects of this peculiar diatom (representative of benthic-epiphytic phytoplankton, with original behavior and chemodiversity, controlled sexual reproduction, fundamental and applied-oriented importance, reference genome, and transcriptome will soon be available); it will also present the difficulties encountered before this becomes a reality as it is for other diatom models (the genetics of the species in its infancy, the transformation feasibility to be explored, the routine methods needed to cryopreserve strains of interest).

Identification of regulatory regions within genomes is a key challenge for understanding the influence of functional traits on species evolution. Development of whole-genome sequencing programs in the early 2000s has been associated with the rise of comparative genomics as a powerful tool for predicting functional regions in genomes, using structural characteristics of DNA sequences. Conserved Noncoding Elements (CNEs, i.e . untranslated sequences highly similar across divergent species) were early identified as candidate regulatory regions in metazoans, plants, and fungi. CNEs have been repeatedly discriminated from mutational cold-spots, but only few studies have assessed their functional relevance at a genome-wide scale. In the present study, we used a whole-genome alignment of 27 insect species to build a coherent mapping of CNEs in the genome of Drosophila melanogaster . We then exploited polymorphism data from 48 European populations of D. melanogaster to estimate levels of nucleotide diversity and adaptive evolution in CNEs. We show here that about 35% of D. melanogaster autosomes fall into conserved noncoding regions that exhibit reduced genetic diversity and undergo purifying selection. In addition, we report six insertions of Transposable Elements (TEs) in the genome of D. melanogaster showing high levels of conservation across Drosophila species. Half of these insertions are located in untranslated transcribed regions (UTRs) of genes involved in developmental pathways and thus represent potential relics of ancient TE domestication events.

Circadian rhythms in gene expression are coincident with 24 hr dynamics in the recruitment of the core-clock transcription factor heterodimer CLOCK-BMAL1 to chromatin. In the liver, circadian chromatin is characterized by rhythmic histone modifications and the deposition of histone variant H2A.Z. However, other histone variants and remodelers that work in conjunction with CLOCK-BMAL1 on variant chromatin remain poorly understood. Here, we reveal that H3.3 variant histone deposition peaks during the daytime in liver chromatin and that CLOCK-BMAL1 is recruited to H3.3 nucleosomes. Moreover, H3.3:CLOCK-BMAL1 associates with PBAF and BRG1/cBAF complexes - members of the SWI/SNF remodeler family - only during the active phase of the circadian cycle. In clock-disrupted Per1 ^−/− ; Per2 ^−/− livers, we observe a depletion in ARID2, the central cog in the molecular assembly of the PBAF complex, accompanied by an increase in H3.3 incorporation. Remarkably, a disassembly of PBAF complex and the concurrent reduction in BRG1 triggers a remodeler reorganization in Per knockout livers, where BRM/cBAF now targets BMAL1 at readily-accessible genomic sites. An abundance of fragile, acetylated H3.3 nucleosomes and a remodeler reorganization provide a mechanistic basis for BMAL1 activity in the absence of PER-mediated negative feedback.

The first completed, circular mitochondrial genome and the first draft, linear chloroplastic genome of the blue diatom Haslea ostrearia (Simonsen 1974, Naviculaceae, Bacillariophyceae) were assembled from Illumina and PacBio sequencing. The mitochondrial genome was composed of 38,696 bases and contained 64 genes, including 31 protein-coding genes (CDS), 2 ribosomal RNA (rRNA) genes and 23 transfer RNA (tRNA) genes. For the chloroplast, the genome was composed of 130,200 bases with 169 genes (131 CDS, 6 rRNA genes, 31 tRNA genes, and 1 transfer messenger RNA gene). Phylogenetic trees, using the maximum-likehood method and partial genes currently available for Haslea ostrearia and other diatom species, suggested the proximity of all the Haslea ostrearia strains/isolates and the possibility of using these genomes as future references.

Background: The pigment produced by Haslea ostrearia, the marennine, is of an important medical and economic interest. Unfortunately this microalgae is complex to grow under axenic conditions, and H. ostrearia probably needs its own bacterial procession to survive. Consequently, this important bacterial presence greatly complicates any study of its ecological, physiological and genomic content. We have therefore tested a first approach of a protocol to control the bacterial concentration without killing the microalgae, by growing four H. ostrearia NCC 532 cultures under two culture conditions: two with and two without antibiotic treatment. We also sought a first bacterial identification method by 16S sequencing adapted to the bacterial community of H. ostrearia. Results: The V3V4 16S region allowed precise identification of bacteria present in H. ostrearia culture. Also, an antibiotic treatment was found necessary to stabilize the bacterial population of the cultures before the DNA extraction. Conclusions: These first results will allow the testing of other antibiotic treatments specific to these bacteria, as well as a wider study of other H. ostreariaisolates to determine the essential bacterial community of this microalga.