Genome Sequence of Kordia sp. Strain SMS9 Identified in a Non-Axenic Culture of the Diatom Skeletonema marinoi

Genome characteristics of Kordia antarctica IMCC3317T and comparative genome analysis of the genus Kordia

The genus Kordia is one of many genera affiliated with the family Flavobacteriaceae of the phylum Bacteroidetes, well known for its degradation of high molecular weight organic matters. The genus Kordia currently comprises eight species, type strains of which have been isolated from a diverse range of marine environments. As of this report, four genome sequences have been submitted for cultured strains of Kordia, but none are complete nor have they been analyzed comprehensively. In this study, we report the complete genome of Kordia antarctica IMCC3317^T, isolated from coastal seawater off the Antarctic Peninsula. The complete genome of IMCC3317^T consists of a single circular chromosome with 5.5 Mbp and a 33.2 mol% of G+C DNA content. The IMCC3317^T genome showed features typical of chemoheterotrophic marine bacteria and similar to other Kordia genomes, such as complete gene sets for the Embden–Meyerhof–Parnas glycolysis pathway, tricarboxylic acid cycle and oxidative phosphorylation. The genome also encoded many carbohydrate-active enzymes, some of which were clustered into approximately seven polysaccharide utilization loci, thereby demonstrating the potential for polysaccharide utilization. Finally, a nosZ gene encoding nitrous oxide reductase, an enzyme that catalyzes the reduction of N₂O to N₂ gas, was also unique to the IMCC3317^T genome.

Metabolic Engineering Strategies in Diatoms Reveal Unique Phenotypes and Genetic Configurations With Implications for Algal Genetics and Synthetic Biology

Diatoms are photosynthetic microeukaryotes that dominate phytoplankton populations and have increasing applicability in biotechnology. Uncovering their complex biology and elevating strains to commercial standards depends heavily on robust genetic engineering tools. However, engineering microalgal genomes predominantly relies on random integration of transgenes into nuclear DNA, often resulting in detrimental “position-effects” such as transgene silencing, integration into transcriptionally-inactive regions, and endogenous sequence disruption. With the recent development of extrachromosomal transgene expression via independent episomes, it is timely to investigate both strategies at the phenotypic and genomic level. Here, we engineered the model diatom Phaeodactylum tricornutum to produce the high-value heterologous monoterpenoid geraniol, which, besides applications as fragrance and insect repellent, is a key intermediate of high-value pharmaceuticals. Using high-throughput phenotyping we confirmed the suitability of episomes for synthetic biology applications and identified superior geraniol-yielding strains following random integration. We used third generation long-read sequencing technology to generate a complete analysis of all transgene integration events including their genomic locations and arrangements associated with high-performing strains at a genome-wide scale with subchromosomal detail, never before reported in any microalga. This revealed very large, highly concatenated insertion islands, offering profound implications on diatom functional genetics and next generation genome editing technologies, and is key for developing more precise genome engineering approaches in diatoms, including possible genomic safe harbour locations to support high transgene expression for targeted integration approaches. Furthermore, we have demonstrated that exogenous DNA is not integrated inadvertently into the nuclear genome of extrachromosomal-expression clones, an important characterisation of this novel engineering approach that paves the road to synthetic biology applications.

Ecological and functional capabilities of an uncultured Kordia sp

Cultivable bacteria represent only a fraction of the diversity in microbial communities. However, the official procedures for classification and characterization of a novel prokaryotic species still rely on isolates. Nevertheless, due to single cell genomics, it is possible to retrieve genomes from environmental samples by sequencing them individually, and to assign specific genes to a specific taxon, regardless of their ability to grow in culture. In this study, a complete description was performed for uncultured Kordia sp. TARA_039_SRF, a proposed novel species within the genus Kordia, using culture-independent techniques. The type material was a high-quality draft genome (94.97% complete, 4.65% gene redundancy) co-assembled using ten nearly identical single amplified genomes (SAGs) from surface seawater in the North Indian Ocean during the Tara Oceans Expedition. The assembly process was optimized to obtain the best possible assembly metrics and a less fragmented genome. The closest relative of the species was Kordia periserrulae, which shared 97.56% similarity of the 16S rRNA gene, 75% orthologs and 89.13% average nucleotide identity. The functional potential of the proposed novel species included proteorhodopsin, the ability to incorporate nitrate, cytochrome oxidases with high affinity for oxygen, and CAZymes that were unique features within the genus. Its abundance at different depths and size fractions was also evaluated together with its functional annotation, revealing that its putative ecological niche could be particles of phytoplanktonic origin. It could putatively attach to these particles and consume them while sinking to the deeper and oxygen depleted layers of the North Indian Ocean.