Biology subjects

Coskun, O. K.

Publications and source records attributed to Coskun, O. K..

3 recordsLinked to original sources

bioRxiv2020

Genome evolution in bacteria isolated from million-year-old subseafloor sediments

Beneath the seafloor, microbial life subsists in isolation from the surface world under persistent energy limitation. The nature and extent of genomic evolution in subseafloor microbes has been unknown. Here we show that the genomes of Thalassospira bacterial populations cultured from million-year-old subseafloor sediments evolve by point mutation, with a relatively low rate of homologous recombination and a high frequency of pseudogenes. Ratios of synonymous to non-synonymous mutation rates correlate with the accumulation of pseudogenes, consistent with a dominant role for genetic drift in the subseafloor strains, but not in type strains of Thalassospira isolated from the surface world. Our findings demonstrate that the long term physical isolation of these bacteria, in the absence of recombination, has resulted in clonal populations that evolve consistent with Mullers Ratchet, whereby reduced access to novel genetic material from neighbors has resulted in fixation of new mutations that accumulate in genomes over millions of years. Significance statementThe nature and extent of genomic evolution in subseafloor microbial populations subsisting for millions of years below the seafloor is unknown. Subseafloor populations have ultra-slow metabolic rates that are hypothesized to restrict reproduction and, consequently, the spread of new traits. Our findings demonstrate that genomes of cultivated bacterial strains from the genus Thalassospira isolated from million-year-old abyssal sediment exhibit greatly reduced levels of homologous recombination, elevated numbers of pseudogenes, and genome-wide evidence of relaxed purifying selection. These substitutions and pseudogenes are fixed into the population, suggesting the genome evolution of these bacteria has been dominated by genetic drift, whereby under long-term physical isolation in small population sizes, and in the absence of homologous recombination, newly acquired mutations accumulate in the genomes of clonal populations over millions of years.

microbiology↗

bioRxiv2019

Lokiarchaeon exhibits homoacetogenesis

The proposed Asgard superphylum of Archaea comprises the closest archaeal relatives of eukaryotes, whose genomes hold clues pertaining to the nature host cell that acquired the mitochondrion at the origin of eukaryotes1-4. Genomes of the Asgard candidate Phylum Candidatus Lokiarchaeota [Lokiarchaeon] suggest an acetogenic H2 -dependent lifestyle5 and mixotrophic capabilities6. However, data on the activity of Lokiarchaeon are currently lacking, and the ecology of the host cell that acquired the mitochondrion is debated4,7. Here, we show that in anoxic marine sediments underlying highly productive waters on the Namibian continental shelf Lokiarchaeon gene expression increases with depth below the seafloor, and was significantly different across a redox gradient spanning hypoxic to sulfidic conditions. Notably, Lokiarchaeon increased expression of genes involved in growth, carbohydrate metabolism, and the H2-dependent Wood-Ljungdahl (WLP) carbon fixation pathway under the most reducing (sulfidic) conditions. Quantitative stable isotope probing experiments revealed multiple populations of Lokiarchaeota utilizing both CO2 and diatomaceous extracellular polymeric substances (dEPS) as carbon sources over a 10-day incubation under anoxic conditions. This apparent anaerobic mixotrophic metabolism was consistent with the expression of Lokiarchaeon genes involved in transport and fermentation of sugars and amino acids. Remarkably, several Asgard populations were more enriched with 13C-dEPS compared to the community average, indicating a preference for dEPS as a growth substrate. The qSIP and gene expression data indicate a metabolism of \"Candidatus Lokiarchaeota\" similar to that of sugar fermenting homoacetogenic bacteria8, namely that Lokiarchaeon can couple fermentative H2 production from organic substrates with electron bifurcation and the autotrophic and H2-dependent WLP. Homoacetogenesis allows to access a wide range of substrates and relatively high ATP gain during acetogenic sugar fermentation8 thereby providing an ecological advantage for Lokiarchaeon in anoxic, energy limited settings.

microbiology↗

bioRxiv2017

A 16S rRNA gene sequencing and analysis protocol for the Illumina MiniSeq platform

High-throughput sequencing of the 16S rRNA gene is widely used in microbial ecology, with Illumina platforms being widely used in recent studies. The MiniSeq, Illuminas latest benchtop sequencer, enables more cost-efficient DNA sequencing relative to larger sequencing platforms (e.g. MiSeq). Here we used a modified custom primer sequencing approach to test the fidelity of the MiniSeq for high-throughput sequencing of the V4 hypervariable region of 16S rRNA genes from complex communities in environmental samples. To this end, we designed an additional sequencing primer that enabled application of a dual-index barcoding method on the MiniSeq. A mock community was sequenced alongside the environmental samples as a quality control benchmark. After careful filtering procedures, we were able to recapture a realistic richness of the mock community, and identify meaningful differences in alpha and beta diversity in the environmental samples. These results show that the MiniSeq can produce similar quantities of high quality V4 reads compared to the MiSeq, yet is a cost-effective option for any laboratory interested in performing high-throughput 16S rRNA gene sequencing.\n\nIMPORTANCEWe modified a custom sequencing approach and used a mock community to test the fidelity of high-throughput sequencing on the Illumina MiniSeq platform. Our results show that the MiniSeq can produce similar quantities of high quality V4 reads compared to the MiSeq. In addition, our protocol increases feasibility for small laboratories to perform their own high-throughput sequencing of the 16S rRNA marker gene.

microbiology↗