The high complexity of eukaryotic organisms enabled their evolutionary success, driven by the diversification of their proteomes. Various mechanisms contributed to this process. Alternative splicing had the largest known impact among these mechanisms. Earlier, we hypothesized that along with alternative splicing, a different but conceptually similar mechanism creates novel versions of existing proteins in all eukaryotes. However, this mechanism operates at the level of translation, where amino acid sequence novelty arises through multiple programmed ribosomal frameshifting events occurring within the same transcript. This mechanism, which is termed mosaic translation, is very difficult to demonstrate even with the most up-to-date molecular tools. Thus, it remained unnoticed so far. Using a subset of mass spectrometry proteomic data from various organs of the model plant Medicago truncatula, we took the first step toward experimental validation of this hypothesis. Our original in silico approach resulted in the discovery of two candidates for mosaic proteins (homologs of EF1α and RuBisCo) and 154 candidates for chimeric peptides. Chimeric peptides and polypeptides are produced in the course of one ribosomal frameshifting event and may correspond to parts of mosaic proteins. In addition, our analysis reveals the possibility of translation of chimeric peptides from five ribosomal RNA transcripts, ten long non-coding RNA transcripts, and one transfer RNA transcript. These findings are novel and will form the basis for future experimental validation. We also present multiple lines of indirect evidence supporting the validity of our in silico data.

The diatom Haslea ostrearia produces a blue-green pigment known as marennine, which exhibits remarkable antimicrobial, anti-viral, antiproliferative, allelopathic, and antioxidant properties. Despite the potential for marennine production, there is still a lack of understanding surrounding its chemical structure, biosynthetic pathway, genes, and enzymes. This study is the inaugural attempt to identify potential transcripts that may encode enzymes involved in marennine biosynthesis. Bioinformatics analysis comparing the transcriptomes of Haslea strains revealed transcripts coding for enzymes and proteins specific to blue H. ostrearia. Functional annotation and enrichment analysis provided insights into these transcripts’ role in marennine production. It was secondary metabolite biosynthesis (Q), signal transduction (T), transcription (K), post-translational modifications (O), extracellular structures (W), and defense mechanisms (V) that had the most significant amounts of COGs. Notably, eight transporters, one transcription factor, and 38 enzymes putatively related to marennine production were identified. These findings provide a promising avenue for further research into the genetic and molecular mechanisms underlying the biosynthesis of this pigment.

How many different proteins can be produced from a single spliced transcript? Genome annotation projects overlook the coding potential of reading frames other than that of the reference open reading frames (refORFs). Recently, alternative open reading frames (altORFs) and their translational products, alternative proteins, have been shown to carry out important functions in various organisms. AltORFs overlapping refORFs or other altORFs in a different reading frame may be involved in one fundamental mechanism so far overlooked. A few years ago, it was proposed that altORFs may act as building blocks for chimeric (mosaic) polypeptides, which are produced via multiple ribosomal frameshifting events from a single mature transcript. We adopt terminology from that earlier discussion and call this mechanism mosaic translation. This way of extracting and combining genetic information may significantly increase proteome diversity. Thus, we hypothesize that this mechanism may have contributed to the flexibility and adaptability of organisms to a variety of environmental conditions. Specialized ribosomes acting as sensors probably played a central role in this process. Importantly, mosaic translation may be the main source of protein diversity in genomes that lack alternative splicing. The idea of mosaic translation is a testable hypothesis, although its direct demonstration is challenging. Should mosaic translation occur, we would currently highly underestimate the complexity of translation mechanisms and thus the proteome.

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).

Background: Marine actinobacteria are a potential resource for natural products; their secondary bioactive metabolites have shown several biological activities. Most of the isolated and identified actinobacteria in Algeria were usually explored from caves, Saharan soil or palm groves. The marine ecosystem is poorly explored and documented. Methods: Five Streptomyces strains producing bioactive compounds were isolated from Rachgoun Island located in Western Algeria and characterised phenotypically and genotypically using microbiological and 16S rRNA sequencing methods, respectively. The crude extract of the most representative strain “Streptomyces sp. strain SM2.4” and its seven active fractions were characterised by GC/MS analysis. Results: Streptomyces sp. strain SM2.4 revealed the strongest activity against the Gram-positive bacteria Staphylococcus aureus and Bacillus subtilis, the fungus Aspergillus niger and was inactive against Gram-negative bacteria. : GC/MS analysis of the methylated crude extract of Streptomyces sp. strain SM2.4 revealed the presence of 11 major compounds, including fatty acids methyl ester (12-methyltridecanoic acid methyl ester, 9-hexadecenoic acid methyl ester, hexadecanoic acid methyl ester, 14-methylhexadecanoic acid methyl ester and 16-methylheptadecanoic acid methyl ester), 2,4-di-tert-butylphenol, (4S,4aS,8aR)-4,8a-dimethyloctahydro-4a(2H)-naphthalenol (geosmin), 2,4-dimethylbenzaldehyde, 3,4-difluorobenzaldehyde, dimethylfuran-2,4-dicarboxylate and pyrrolo(1,2-a)pyrazine-1,4-dione, hexahydro-3-(2-methylpropyl)-. Partial purification of the crude extract by Thin-layer chromatography provided seven active fractions, which were tested by radial diffusion assay. GC/MS analysis of the active TLC-fractions revealed the presence of a mixture of active compounds from which 2- (bromomethyl)-2-(2-methylphenyl)-1,3-dioxolane was found to be a new 1,3 dioxolane derivative. Furthermore, 3,4-dimethylbenzamide and pyrido[2,3-d] pyridazine-1,4-dione, hexahydro- 3-(2-methylpropyl)-, were extracted for the first time from a natural source. Conclusion: Our study reveals that marine Streptomyces sp. strain SM2.4 has an interesting antimicrobial potential due to its panel of bioactive compounds.