Laura S. Weyrich

Sequencing ancient calcified dental plaque shows changes in oral microbiota with dietary shifts of the Neolithic and Industrial revolutions

The importance of commensal microbes for human health is increasingly recognized, yet the impacts of evolutionary changes in human diet and culture on commensal microbiota remain almost unknown. Two of the greatest dietary shifts in human evolution involved the adoption of carbohydrate-rich Neolithic (farming) diets (beginning ∼10,000 years before the present) and the more recent advent of industrially processed flour and sugar (in ∼1850). Here, we show that calcified dental plaque (dental calculus) on ancient teeth preserves a detailed genetic record throughout this period. Data from 34 early European skeletons indicate that the transition from hunter-gatherer to farming shifted the oral microbial community to a disease-associated configuration. The composition of oral microbiota remained unexpectedly constant between Neolithic and medieval times, after which (the now ubiquitous) cariogenic bacteria became dominant, apparently during the Industrial Revolution. Modern oral microbiotic ecosystems are markedly less diverse than historic populations, which might be contributing to chronic oral (and other) disease in postindustrial lifestyles.

Environmental metabarcodes for insects: in silico PCR reveals potential for taxonomic bias

Studies of insect assemblages are suited to the simultaneous DNA‐based identification of multiple taxa known as metabarcoding. To obtain accurate estimates of diversity, metabarcoding markers ideally possess appropriate taxonomic coverage to avoid PCR‐amplification bias, as well as sufficient sequence divergence to resolve species. We used in silico PCR to compare the taxonomic coverage and resolution of newly designed insect metabarcodes (targeting 16S) with that of existing markers [16S and cytochrome oxidase c subunit I (COI)] and then compared their efficiency in vitro. Existing metabarcoding primers amplified in silico <75% of insect species with complete mitochondrial genomes available, whereas new primers targeting 16S provided >90% coverage. Furthermore, metabarcodes targeting COI appeared to introduce taxonomic PCR‐amplification bias, typically amplifying a greater percentage of Lepidoptera and Diptera species, while failing to amplify certain orders in silico. To test whether bias predicted in silico was observed in vitro, we created an artificial DNA blend containing equal amounts of DNA from 14 species, representing 11 insect orders and one arachnid. We PCR‐amplified the blend using five primer sets, targeting either COI or 16S, with high‐throughput amplicon sequencing yielding more than 6 million reads. In vitro results typically corresponded to in silico PCR predictions, with newly designed 16S primers detecting 11 insect taxa present, thus providing equivalent or better taxonomic coverage than COI metabarcodes. Our results demonstrate that in silico PCR is a useful tool for predicting taxonomic bias in mixed template PCR and that researchers should be wary of potential bias when selecting metabarcoding markers.

Neanderthal behaviour, diet, and disease inferred from ancient DNA in dental calculus

Recent genomic data have revealed multiple interactions between Neanderthals and modern humans, but there is currently little genetic evidence regarding Neanderthal behaviour, diet, or disease. Here we describe the shotgun-sequencing of ancient DNA from five specimens of Neanderthal calcified dental plaque (calculus) and the characterization of regional differences in Neanderthal ecology. At Spy cave, Belgium, Neanderthal diet was heavily meat based and included woolly rhinoceros and wild sheep (mouflon), characteristic of a steppe environment. In contrast, no meat was detected in the diet of Neanderthals from El Sidrón cave, Spain, and dietary components of mushrooms, pine nuts, and moss reflected forest gathering. Differences in diet were also linked to an overall shift in the oral bacterial community (microbiota) and suggested that meat consumption contributed to substantial variation within Neanderthal microbiota. Evidence for self-medication was detected in an El Sidrón Neanderthal with a dental abscess and a chronic gastrointestinal pathogen (Enterocytozoon bieneusi). Metagenomic data from this individual also contained a nearly complete genome of the archaeal commensal Methanobrevibacter oralis (10.2× depth of coverage)—the oldest draft microbial genome generated to date, at around 48,000 years old. DNA preserved within dental calculus represents a notable source of information about the behaviour and health of ancient hominin specimens, as well as a unique system that is useful for the study of long-term microbial evolution.

Ancient DNA analysis of dental calculus.

Dental calculus (calcified tartar or plaque) is today widespread on modern human teeth around the world. A combination of soft starchy foods, changing acidity of the oral environment, genetic pre-disposition, and the absence of dental hygiene all lead to the build-up of microorganisms and food debris on the tooth crown, which eventually calcifies through a complex process of mineralisation. Millions of oral microbes are trapped and preserved within this mineralised matrix, including pathogens associated with the oral cavity and airways, masticated food debris, and other types of extraneous particles that enter the mouth. As a result, archaeologists and anthropologists are increasingly using ancient human dental calculus to explore broad aspects of past human diet and health. Most recently, high-throughput DNA sequencing of ancient dental calculus has provided valuable insights into the evolution of the oral microbiome and shed new light on the impacts of some of the major biocultural transitions on human health throughout history and prehistory. Here, we provide a brief historical overview of archaeological dental calculus research, and discuss the current approaches to ancient DNA sampling and sequencing. Novel applications of ancient DNA from dental calculus are discussed, highlighting the considerable scope of this new research field for evolutionary biology and modern medicine.

Limitations and recommendations for successful DNA extraction from forensic soil samples: a review.

Soil is commonly used in forensic casework to provide discriminatory power to link a suspect to a crime scene. Standard analyses examine the intrinsic properties of soils, including mineralogy, geophysics, texture and colour; however, soils can also support a vast amount of organisms, which can be examined using DNA fingerprinting techniques. Many previous genetic analyses have relied on patterns of fragment length variation produced by amplification of unidentified taxa in the soil extract. In contrast, the development of advanced DNA sequencing technologies now provides the ability to generate a detailed picture of soil microbial communities and the taxa present, allowing for improved discrimination between samples. However, DNA must be efficiently extracted from the complex soil matrix to achieve accurate and reproducible DNA sequencing results, and extraction efficacy is highly dependent on the soil type and method used. As a result, a consideration of soil properties is important when estimating the likelihood of successful DNA extraction. This would include a basic understanding of soil components, their interactions with DNA molecules and the factors that affect such interactions. This review highlights some important considerations required prior to DNA extraction and discusses the use of common chemical reagents in soil DNA extraction protocols to achieve maximum efficacy. Together, the information presented here is designed to facilitate informed decisions about the most appropriate sampling and extraction methodology, relevant both to the soil type and the details of a specific forensic case, to ensure sufficient DNA yield and enable successful analysis.

Forensic soil DNA analysis using high-throughput sequencing: a comparison of four molecular markers

Soil analysis, such as mineralogy, geophysics, texture and colour, are commonly used in forensic casework to link a suspect to a crime scene. However, DNA analysis can also be applied to characterise the vast diversity of organisms present in soils. DNA metabarcoding and high-throughput sequencing (HTS) now offer a means to improve discrimination between forensic soil samples by identifying individual taxa and exploring non-culturable microbial species. Here, we compare the small-scale reproducibility and resolution of four molecular markers targeting different taxa (bacterial 16S rRNA, eukaryotic18S rRNA, plant trnL intron and fungal internal transcribed spacer I (ITS1) rDNA) to distinguish two sample sites. We also assess the background DNA level associated with each marker and examine the effects of filtering Operational Taxonomic Units (OTUs) detected in extraction blank controls. From this study, we show that non-bacterial taxa in soil, particularly fungi, can provide the greatest resolution between the sites, whereas plant markers may be problematic for forensic discrimination. ITS and 18S markers exhibit reliable amplification, and both show high discriminatory power with low background DNA levels. The 16S rRNA marker showed comparable discriminatory power post filtering; however, presented the highest level of background DNA. The discriminatory power of all markers was increased by applying OTU filtering steps, with the greatest improvement observed by the removal of any sequences detected in extraction blanks. This study demonstrates the potential use of multiple DNA markers for forensic soil analysis using HTS, and identifies some of the standardisation and evaluation steps necessary before this technique can be applied in casework.

The skin microbiome: Associations between altered microbial communities and disease

A single square centimetre of the human skin can contain up to one billion microorganisms. These diverse communities of bacteria, fungi, mites and viruses can provide protection against disease, but can also exacerbate skin lesions, promote disease and delay wound healing. This review addresses the current knowledge surrounding the healthy skin microbiome and examines how different alterations to the skin microbial communities can contribute to disease. Current methodologies are considered, changes in microbial diversity and colonisation by specific microorganisms are discussed in the context of atopic dermatitis, psoriasis, acne vulgaris and chronic wounds. The recent impact of modern Westernised lifestyles on the human skin microbiome is also examined, as well as the potential benefits and pitfalls of novel therapeutic strategies. Further analysis of the human skin microbiome, and its interactions with the host immune system and other commensal microorganisms, will undoubtedly elucidate molecular mechanisms for disease and reveal gateways for novel therapeutic treatment strategies.

Embracing the gut microbiota: the new frontier for inflammatory and infectious diseases

The gut microbiota provides essential signals for the development and appropriate function of the immune system. Through this critical contribution to immune fitness, the gut microbiota has a key role in health and disease. Recent advances in the technological applications to study microbial communities and their functions have contributed to a rapid increase in host–microbiota research. Although it still remains difficult to define a so‐called ‘normal’ or ‘healthy’ microbial composition, alterations in the gut microbiota have been shown to influence the susceptibility of the host to different diseases. Current translational research combined with recent technological and computational advances have enabled in‐depth study of the link between microbial composition and immune function, addressing the interplay between the gut microbiota and immune responses. As such, beneficial modulation of the gut microbiota is a promising clinical target for many prevalent diseases including inflammatory bowel disease, metabolic abnormalities such as obesity, reduced insulin sensitivity and low‐grade inflammation, allergy and protective immunity against infections.

Using Amplicon Sequencing To Characterize and Monitor Bacterial Diversity in Drinking Water Distribution Systems.

ABSTRACT Drinking water assessments use a variety of microbial, physical, and chemical indicators to evaluate water treatment efficiency and product water quality. However, these indicators do not allow the complex biological communities, which can adversely impact the performance of drinking water distribution systems (DWDSs), to be characterized. Entire bacterial communities can be studied quickly and inexpensively using targeted metagenomic amplicon sequencing. Here, amplicon sequencing of the 16S rRNA gene region was performed alongside traditional water quality measures to assess the health, quality, and efficiency of two distinct, full-scale DWDSs: (i) a linear DWDS supplied with unfiltered water subjected to basic disinfection before distribution and (ii) a complex, branching DWDS treated by a four-stage water treatment plant (WTP) prior to disinfection and distribution. In both DWDSs bacterial communities differed significantly after disinfection, demonstrating the effectiveness of both treatment regimes. However, bacterial repopulation occurred further along in the DWDSs, and some end-user samples were more similar to the source water than to the postdisinfection water. Three sample locations appeared to be nitrified, displaying elevated nitrate levels and decreased ammonia levels, and nitrifying bacterial species, such as Nitrospira, were detected. Burkholderiales were abundant in samples containing large amounts of monochloramine, indicating resistance to disinfection. Genera known to contain pathogenic and fecal-associated species were also identified in several locations. From this study, we conclude that metagenomic amplicon sequencing is an informative method to support current compliance-based methods and can be used to reveal bacterial community interactions with the chemical and physical properties of DWDSs.

Resident Microbiota Affect Bordetella pertussis Infectious Dose and Host Specificity

Before contacting host tissues, invading pathogens directly or indirectly interact with host microbiota, but the effects of such interactions on the initial stages of infection are poorly understood. Bordetella pertussis is highly infectious among humans but requires large doses to colonize rodents, unlike a closely related zoonotic pathogen, Bordetella bronchiseptica, raising important questions about the contributions of bacterial competition to initial colonization and host selection. We observed that <100 colony-forming units (CFU) of B. bronchiseptica efficiently infected mice and displaced culturable host microbiota, whereas 10 000 CFU of B. pertussis were required to colonize murine nasal cavities and did not displace host microorganisms. Bacteria isolated from murine nasal cavities but not those from the human lower respiratory tract limited B. pertussis growth in vitro, indicating that interspecies competition may limit B. pertussis colonization of mice. Further, a broad-spectrum antibiotic treatment delivered before B. pertussis inoculation reduced the infectious dose to <100 CFU, and reintroduction of single Staphylococcus or Klebsiella species was sufficient to inhibit B. pertussis colonization of antibiotic-treated mice. Together, these results reveal that resident microorganisms can prevent B. pertussis colonization and influence host specificity, and they provide rationale for manipulating microbiomes to create more-accurate animal models of infectious diseases.