Biology subjects

Andersen, K. S.

Publications and source records attributed to Andersen, K. S..

6 recordsLinked to original sources

bioRxiv2026

Sensitive long-read amplicon sequence variant recovery with savont

Long-read amplicon sequencing can profile longer sequences compared to short reads, but recovering amplicon sequence variants (ASVs) is a challenge for long, noisy reads. We present savont, an algorithm for recovering ASVs from modern long-read amplicons with mean accuracy [≥] 98%, including Oxford Nanopore Technologies (ONT) R10.4 and PacBio HiFi reads. Savont requires 5 to 16 times lower sequencing depth for full-length 16S rRNA ONT reads than previous methods and generates up to 95 times more ASVs for complex environments. Savont makes ASV-based analysis from shallow and noisy long-read amplicon sequencing feasible.

bioinformatics↗

bioRxiv2026

Nanopore sequencing reaches amplicon sequence variant (ASV) resolution

Sequencing of ribosomal marker genes remains a cornerstone for profiling complex microbial communities. In recent years, there has been a shift from Illumina to long-read technologies, including PacBio and Oxford Nanopore Technologies (ONT). ONT is attractive due to its low startup cost and portability; however, historically high error rates have prevented direct amplicon sequencing variant (ASV) generation from raw nanopore reads. This has forced most workflows to rely on mapping raw reads against reference databases constraining analyses to taxa covered by these. With recent improvements in ONT sequencing accuracy, we sought to challenge this view by sequencing samples of increasing complexity using primer sets targeting amplicons of different lengths, and by sequencing the exact same PCR libraries on both PacBio and ONT. We demonstrate that error-free ASVs can now be generated directly from raw nanopore reads using standard denoising algorithms originally developed for Illumina data. Current ONT read quality enables reliable reconstruction of amplicons spanning [~]250 bp to [~]4,200 bp and allows resolution of intragenomic rRNA gene variants. These results extend beyond simple mock communities to complex fecal, anaerobic digester, activated sludge, and soil samples. When sequencing depth is sufficient, ONT accurately recovers all or nearly all intra-genomic 16S rRNA gene copy variants, showing perfect sequence identity to curated reference sequences in mock communities and to ASVs inferred from PacBio data in complex communities. Across the primer sets, ONT required higher sequencing depth than PacBio to fully resolve the communities, with this requirement increasing with amplicon length. For complex samples, ONT required approximately 2-3x more reads for V4 ([~]250 bp) and V1-V3 ([~]500 bp), 4.1-5.6x more reads for V1-V8 ([~]1400 bp), and 25-42x more reads for rRNA operon (OPR) amplicons ([~]4200 bp). Consequently, sequencing complex communities with OPR primers on ONT is currently not feasible due to the unrealistically high read depth required. This study provides evidence that ONT amplicon sequencing has matured to the point where true ASV-resolved profiling is practically and economically feasible, moving ONT amplicon analysis beyond reliance on OTU clustering or reference alignment to enable application in environments lacking comprehensive reference databases. Key FindingsO_LIIt is now straightforward to generate ASVs on ONT platforms (250-4200 bp) C_LIO_LIONT can resolve intragenomic 16S rRNA gene variants C_LIO_LIASV recovery is successful in both simple and complex communities C_LI

bioinformatics↗

bioRxiv2023

MiDAS 5: Global diversity of bacteria and archaea in anaerobic digesters

Anaerobic digestion represents a key biotechnology for the transformation of organic waste into renewable energy (biogas) and relies on complex microbial communities that work in concert to degrade the complex substrates into methane and carbon dioxide. Here, we sequenced more than half a million high-quality, full-length 16S rRNA gene sequences from 285 full-scale anaerobic digesters (ADs) across the world to expand our knowledge about diversity and function of the bacteria and archaea in ADs. The sequences were processed into full-length 16S rRNA amplicon sequence variants (FL-ASVs), which were added to the MiDAS 4 database for bacteria and archaea in wastewater treatment systems to create MiDAS 5. The expansion of the MiDAS database significantly increased the coverage for bacteria and archaea in ADs worldwide, leading to an improved rate of genus and species-level classification. Using MiDAS 5, we carried out an amplicon-based, global-scale microbial community profiling of the sampled ADs using three common sets of primers targeting different regions of the 16S rRNA gene in bacteria and/or archaea. We revealed how environmental conditions and biogeography shape the AD microbiota. We also identify core and conditionally rare or abundant taxa, encompassing 692 genera and 1013 species. These represent 84-99% and 18-61% of the accumulated read abundance respectively, across samples depending on the amplicon primers used. Finally, we examined the global diversity of functional groups with known importance for the anaerobic digestion process. Our online global MiDAS Field Guide presents the data generated in this study and summarizes present knowledge about all taxa.

microbiology↗

bioRxiv2021

MiDAS 4: A global catalogue of full-length 16S rRNA gene sequences and taxonomy for studies of bacterial communities in wastewater treatment plants

Biological wastewater treatment and an increased focus on resource recovery is fundamental for environmental protection, human health, and sustainable development. Microbial communities are responsible for these processes, but our knowledge of their diversity and function is still poor, partly due to the lack of good reference databases and comprehensive global studies. Here, we sequenced more than 5 million high-quality, full-length 16S rRNA gene sequences from 740 wastewater treatment plants (WWTPs) across the world and used the sequences to construct MiDAS 4, a full-length amplicon sequence variant resolved 16S rRNA gene reference database with a comprehensive taxonomy from the domain to species-level for all references. Using a study-independent amplicon dataset from the Global Water Microbiome Consortium project (269 WWTPs), we showed that the MiDAS 4 database provides much better coverage for bacteria in WWTPs worldwide compared to commonly applied universal references databases, and greatly improved the rate of genus and species-level classification. Hence, MiDAS 4 provides a unifying taxonomy for the majority of prokaryotic diversity in WWTPs globally, which can be used for linking microbial identities with their functions across studies. Taking advantage of MiDAS 4, we carried out an amplicon-based, global-scale microbial community profiling of activated sludge plants using two common sets of primers targeting the V1-V3 and V4 region of the 16S rRNA gene. We found that the V1-V3 primers were generally best suited for this ecosystem, and revealed how environmental conditions and biogeography shape the activated sludge microbiota. We also identified process-critical taxa (core and conditionally rare or abundant taxa), encompassing 966 genera and 1530 species. These represented approximately 80% and 50% of the accumulated read abundance, respectively, and represent targets for further investigations. Finally, we showed that for well-studied functional guilds, such as nitrifiers or polyphosphate accumulating organisms, the same genera were prevalent worldwide, with only a few abundant species in each genus.

microbiology↗

bioRxiv2020

Characterizing the growing microorganisms at species level in 46 anaerobic digesters at Danish wastewater treatment plants: A six-year survey on microbiome structure and key drivers

Anaerobic digestion (AD) is a key technology at many wastewater treatment plants (WWTPs) for converting surplus activated sludge to methane-rich biogas. However, the limited number of surveys and the lack of comprehensive data sets have hindered a deeper understanding of the characteristics and associations between key variables and the microbiome composition. Here, we present a six-year survey of 46 anaerobic digesters, located at 22 WWTPs in Denmark, which is the largest known study of the microbial ecology of AD at WWTPs at a regional scale. For three types of AD (mesophilic, mesophilic with thermal hydrolysis pretreatment, and thermophilic), we present the typical value range of 12 key parameters including operational variables and performance parameters. The bacterial and archaeal microbiomes were analyzed at species-level resolution using amplicon sequencing in >1,000 samples and the new ecosystem-specific MiDAS 3 reference database. We detected 42 phyla, 1,600 genera and 3,584 species in the bacterial microbiome, where 70% of the genera and 93% of the species represented uncultivated taxa that were only classified based on MiDAS 3 denovo placeholder taxonomy. More than 40% of the 100 most abundant bacterial species did not grow in the digesters and were only present due to immigration with the feed sludge. Temperature, ammonium concentration, and pH were the main drivers shaping the microbiome clusters of the three types of ADs for both bacteria and for archaea. Within mesophilic digesters, feed sludge composition and other key parameters (organic loading rate, biogas yield, and ammonium concentration) correlated with the growing bacterial microbiome. Furthermore, correlation analysis revealed the main drivers for specific species among growing bacteria and archaea, and revealed the potential ecological function of many novel taxa. Our study highlights the influence of immigration on bacterial AD microbiome. Subsetting the growing microbes improves the understanding of the diversity and main drivers of microbiome assembly, and elucidates functionality of specific species-level microorganisms. This six-year survey provides a comprehensive insight into microbiome structure at species level, engineering and ecological performance, and a foundation for future studies of the ecological significance/characteristics and function of the novel taxa.

microbiology↗

bioRxiv2019

Species-level microbiome composition of activated sludge - introducing the MiDAS 3 ecosystem-specific reference database and taxonomy

The function of microbial communities in wastewater treatment systems and anaerobic digesters is dictated by the physiological activity of its members and complex interactions between them. Since functional traits are often conserved at low taxonomic ranks (genus, species, strain), the development of high taxonomic resolution and reliable classification is the first crucial step towards understanding the role of microbes in any ecosystem. Here we present MiDAS 3, a comprehensive 16S rRNA gene reference database based on high-quality full-length sequences derived from activated sludge and anaerobic digester systems. The MiDAS 3 taxonomy proposes unique provisional names for all microorganisms down to species level. MiDAS 3 was applied for the detailed analysis of microbial communities in 20 Danish wastewater treatment plants with nutrient removal, sampled over 12 years, demonstrating community stability and many abundant core taxa. The top 50 most abundant species belonged to genera, of which >50% have no known function in the system, emphasizing the need for more efforts towards elucidating the role of important members of wastewater treatment ecosystems. The MiDAS 3 taxonomic database guided an update of the MiDAS Field Guide - an online resource linking the identity of microorganisms in wastewater treatment systems to available data related to their functional importance. The new field guide contains a complete list of genera (>1,800) and species (>4,200) found in activated sludge and anaerobic digesters. The identity of the microbes is linked to functional information, where available. The website also provides the possibility to BLAST the sequences against MiDAS 3 taxonomy directly online. The MiDAS Field Guide is a collaborative platform acting as an online knowledge repository and facilitating understanding of wastewater treatment ecosystem function.

microbiology↗