Biology subjects

Martijn, J.

Publications and source records attributed to Martijn, J..

3 recordsLinked to original sources

bioRxiv2021

The evolutionary origin of host association in an ancient bacterial clade

The evolution of obligate host-association of bacterial symbionts and pathogens remains poorly understood. The Rickettsiales represent an order of obligate alphaproteobacterial endosymbionts and parasites that infect a wide variety of eukaryotic hosts, including humans, livestock, insects and protists. Induced by their host-associated lifestyle, Rickettsiales genomes have undergone reductive evolution, leading to small, AT-rich genomes with limited metabolic capacities. We describe several genomes of deep-branching, environmental alphaproteobacteria that branch basal to previously sampled Rickettsiales, and whose genome content are reminiscent of free-living and biofilm-associated lifestyles. Ancestral genome content reconstruction across the Rickettsiales tree revealed that the free-living to host-association transition of this group occurred more recently than previously anticipated, and likely involved the repurposing of a type IV secretion system. One-Sentence SummaryDeep-branching Rickettsiales provide insights into the evolution of obligate host-associated lifestyle

microbiology↗

bioRxiv2019

Marine sediments illuminate Chlamydiae diversity and evolution

The bacterial phylum Chlamydiae, which is so far comprised of obligate symbionts of eukaryotic hosts, are well-known as human and animal pathogens1-3. However, the Chlamydiae also include so-called environmental lineages4-6 that primarily infect microbial eukaryotes7. Studying environmental chlamydiae, whose genomes display extended metabolic capabilities compared to their pathogenic relatives8-10 has provided first insights into the evolution of the pathogenic and obligate intracellular lifestyle that is characteristic for this phylum. Here, we report an unprecedented relative abundance and diversity of novel lineages of the Chlamydiae phylum, representing previously undetected, yet potentially important, community members in deep marine sediments. We discovered that chlamydial lineages dominate the microbial communities in the Arctic Mid-Ocean Ridge11, which revealed the dominance of chlamydial lineages at anoxic depths, reaching relative abundances of up to 43% of the bacterial community, and a maximum diversity of 163 different species-level taxonomic unit. Using genome-resolved metagenomics, we reconstructed 24 draft chlamydial genomes, thereby dramatically expanding known interspecies genomic diversity in this phylum. Phylogenomic and comparative analyses revealed several deep-branching Chlamydiae clades, including a sister clade of the pathogenic Chlamydiaceae. Altogether, our study provides new insights into the diversity, evolution and environmental distribution of the Chlamydiae.

microbiology↗

bioRxiv2017

Amplicon sequencing of the 16S-ITS-23S rRNA operon with long-read technology for improved phylogenetic classification of uncultured prokaryotes

Amplicon sequencing of the 16S rRNA gene is the predominant method to quantify microbial compositions of environmental samples and to discover previously unknown lineages. Its unique structure of interspersed conserved and variable regions is an excellent target for PCR and allows for classification of reads at all taxonomic levels. However, the relatively few phylogenetically informative sites prevent confident phylogenetic placements of novel lineages that are deep branching relative to reference taxa. This problem is exacerbated when only short 16S rRNA gene fragments are sequenced. To resolve their placement, it is common practice to gather more informative sites by combining multiple conserved genes into concatenated datasets. This however requires genomic data which may be obtained through relatively expensive metagenome sequencing and computationally demanding analyses. Here we develop a protocol that amplifies a large part of 16S and 23S rRNA genes within the rRNA operon, including the ITS region, and sequences the amplicons with PacBio long-read technology. We tested our method with a synthetic mock community and developed a read curation pipeline that reduces the overall error rate to 0.18%. Applying our method on four diverse environmental samples, we were able to capture near full-length rRNA operon amplicons from a large diversity of prokaryotes. Phylogenetic trees constructed with these sequences showed an increase in statistical support compared to trees inferred with shorter, Illumina-like sequences using only the 16S rRNA gene (250 bp). Our method is a cost-effective solution to generate high quality, near full-length 16S and 23S rRNA gene sequences from environmental prokaryotes.

microbiology↗