Despite the importance of the gut microbiome to health, the role of human genetic variation in shaping its composition remains poorly understood. Here we report genome-wide association analyses of harmonized metagenomic data from 16,017 adults in four Swedish population-based studies, with replication in 12,652 people from the Norwegian HUNT study. We identified variants in the OR51E1–OR51E2 locus, encoding sensors for microbiome-derived fatty acids, associated with microbial richness. We further identified 15 study-wide significant genetic associations ( P < 5.4 × 10 ⁻¹¹ ) involving eight loci and 14 common bacterial species, of which 11 associations at six loci were replicated. The results confirm previously reported associations at LCT , ABO and FUT2 , and provide evidence for new loci MUC12 , CORO7–HMOX2 , SLC5A11 , FOXP1 and FUT3–FUT6 , with supporting data from metabolomics and gene expression analyses. Our findings link gut microbial variation genetically to gastrointestinal functions, including enteroendocrine fatty acid sensing, bile composition and mucosal layer composition.

DNA analysis of traces from commonly found objects like knives, smartphones, tapes and garbage bags related to crime in aquatic environments is challenging for forensic DNA laboratories. The amount of recovered DNA may be affected by the water environment, time in the water, method for recovery, transport and storage routines of the objects before the objects arrive in the laboratory. The present study evaluated the effect of four storage conditions on the DNA retrieved from bloodstains, touch DNA, fingerprints and hairs, initially deposited on knives, smartphones, packing tapes, duct tapes and garbage bags, and submerged in lake water for three time periods. After retrieval, the objects were stored either through air-drying at room temperature, freezing at −30 °C, in nitrogen gas or in lake water. The results showed that the submersion time strongly influenced the amount and degradation of DNA, especially after the longest submersion time (21 days). A significant variation was observed in success for STR profiling, while mtDNA profiling was less affected by the submersion time interval and storage conditions. This study illustrates that retrieval from water as soon as possible and immediate storage through air-drying or freezing before DNA analysis is beneficial for the outcome of DNA profiling in crime scene investigations.

Background: It is essential to recover as much DNA as possible from evidence samples to ensure optimal DNA analysis in forensic casework. However, both DNA collection and purification procedures cause a substantial loss of genetic material. Thus, a large loss of DNA through the pre-PCR procedures, including swabbing and extraction, may significantly affect downstream analysis results. In this study, different cotton swabs and extraction kits used for forensic samples were compared separately. Methods: The recovery of cell-free DNA (control DNA) and cell-bound DNA (blood and saliva) was evaluated using five different extraction kits: Chelex^® 100 Resin, Wizard^® Genomic DNA Purification Kit, QIAamp^® DNA Micro Kit, QIAamp^® DNA Investigator Kit and DNeasy^® Blood & Tissue Kit. The DNA recovery efficiency of the different extraction kits was assessed using real-time quantitative PCR targeting nuclear and mitochondrial DNA targets. In addition, nine cotton swabs from four manufacturers (Selefa^®, Puritan^®, Texwipe^®, and Heinz Herenz) with different production lots were evaluated for DNA quantity and quality using real-time PCR and short tandem repeat (STR) analysis. Results: Overall, large differences in DNA recovery were observed between the different extraction kits. The QIAInvestigator kit demonstrated the highest recovery at low DNA amounts, which is particularly beneficial for minute forensic samples. The swab comparison revealed variations not only in DNA recovery between swab manufacturers but also between lots of the same swab brand, and the DNA quantity was not clearly correlated with downstream DNA profile quality. Conclusions: Our findings emphasise the importance of considering the choice of extraction kit, swab brand and batch-to-batch variation in forensic laboratory procedures, as they may influence DNA recoveries and affect the success rate in forensic casework.