Microglia Require CD4 T Cells to Complete the Fetal-to-Adult Transition.

The brain is a site of relative immune privilege. Although CD4 T cells have been reported in the central nervous system, their presence in the healthy brain remains controversial, and their function remains largely unknown. We used a combination of imaging, single cell, and surgical approaches to identify a CD69+ CD4 T cell population in both the mouse and human brain, distinct from circulating CD4 T cells. The brain-resident population was derived through in situ differentiation from activated circulatory cells and was shaped by self-antigen and the peripheral microbiome. Single-cell sequencing revealed that in the absence of murine CD4 T cells, resident microglia remained suspended between the fetal and adult states. This maturation defect resulted in excess immature neuronal synapses and behavioral abnormalities. These results illuminate a role for CD4 T cells in brain development and a potential interconnected dynamic between the evolution of the immunological and neurological systems. VIDEO ABSTRACT.

The virota and its transkingdom interactions in the healthy infant gut.

SignificanceMicrobes colonizing the infant gut during the first year(s) of life play an important role in immune system development. We show that after birth the (nearly) sterile gut is rapidly colonized by bacteria and their viruses (phages), which often show a strong cooccurrence. Most viruses infecting the infant do not cause clinical signs and their numbers strongly increase after day-care entrance. The infant diet is clearly reflected by identification of plant-infecting viruses, whereas fungi and parasites are not part of a stable gut microbiota. These temporal high-resolution baseline data about the gut colonization process will be valuable for further investigations of pathogenic viruses, dynamics between phages and their bacterial host, as well as studies investigating infants with a disturbed microbiota.

Quantitative microbiome profiling links gut community variation to microbial load.

Current sequencing-based analyses of faecal microbiota quantify microbial taxa and metabolic pathways as fractions of the sample sequence library generated by each analysis. Although these relative approaches permit detection of disease-associated microbiome variation, they are limited in their ability to reveal the interplay between microbiota and host health. Comparative analyses of relative microbiome data cannot provide information about the extent or directionality of changes in taxa abundance or metabolic potential. If microbial load varies substantially between samples, relative profiling will hamper attempts to link microbiome features to quantitative data such as physiological parameters or metabolite concentrations. Saliently, relative approaches ignore the possibility that altered overall microbiota abundance itself could be a key identifier of a disease-associated ecosystem configuration. To enable genuine characterization of host-microbiota interactions, microbiome research must exchange ratios for counts. Here we build a workflow for the quantitative microbiome profiling of faecal material, through parallelization of amplicon sequencing and flow cytometric enumeration of microbial cells. We observe up to tenfold differences in the microbial loads of healthy individuals and relate this variation to enterotype differentiation. We show how microbial abundances underpin both microbiota variation between individuals and covariation with host phenotype. Quantitative profiling bypasses compositionality effects in the reconstruction of gut microbiota interaction networks and reveals that the taxonomic trade-off between Bacteroides and Prevotella is an artefact of relative microbiome analyses. Finally, we identify microbial load as a key driver of observed microbiota alterations in a cohort of patients with Crohn's disease, here associated with a low-cell-count Bacteroides enterotype (as defined through relative profiling).

Associations of HIV and iron status with gut microbiota composition, gut inflammation and gut integrity in South African school-age children: a two-way factorial case-control study.

BACKGROUND: Human immunodeficiency virus (HIV) and iron deficiency (ID) affect many African children. Both HIV and iron status interact with gut microbiota composition and related biomarkers. The study's aim was to determine the associations of HIV and iron status with gut microbiota composition, gut inflammation and gut integrity in South African school-age children. METHODS: In this two-way factorial case-control study, 8- to 13-year-old children were enrolled into four groups based on their HIV and iron status: (1) With HIV (HIV+) and ID (n = 43), (2) HIV+ and iron-sufficient nonanaemic (n = 41), (3) without HIV (HIV-) and ID (n = 44) and (4) HIV- and iron-sufficient nonanaemic (n = 38). HIV+ children were virally suppressed (<50 HIV RNA copies/ml) on antiretroviral therapy (ART). Microbial composition of faecal samples (16S rRNA sequencing) and markers of gut inflammation (faecal calprotectin) and gut integrity (plasma intestinal fatty acid-binding protein [I-FABP]) were assessed. RESULTS: Faecal calprotectin was higher in ID versus iron-sufficient nonanaemic children (p = 0.007). I-FABP did not significantly differ by HIV or iron status. ART-treated HIV (redundancy analysis [RDA] R2 = 0.009, p = 0.029) and age (RDA R2 = 0.013 p = 0.004) explained the variance in the gut microbiota across the four groups. Probabilistic models showed that the relative abundance of the butyrate-producing genera Anaerostipes and Anaerotruncus was lower in ID versus iron-sufficient children. Fusicatenibacter was lower in HIV+ and in ID children versus their respective counterparts. The prevalence of the inflammation-associated genus Megamonas was 42% higher in children with both HIV and ID versus HIV- and iron-sufficient nonanaemic counterparts. CONCLUSIONS: In our sample of 8- to 13-year-old virally suppressed HIV+ and HIV- children with or without ID, ID was associated with increased gut inflammation and changes in the relative abundance of specific microbiota. Moreover, in HIV+ children, ID had a cumulative effect that further shifted the gut microbiota to an unfavourable composition.

The effect of oral iron supplementation on the gut microbiota, gut inflammation, and iron status in iron-depleted South African school-age children with virally suppressed HIV and without HIV.

PURPOSE: Both HIV and oral iron interventions may alter gut microbiota composition and increase gut inflammation. We determined the effect of oral iron supplementation on gut microbiota composition, gut inflammation, and iron status in iron-depleted South Africa school-aged children living with HIV (HIV+) but virally suppressed on antiretroviral therapy and children without HIV (HIV-ve). METHODS: In this before-after intervention study with case-control comparisons, we provided 55 mg elemental iron from ferrous sulphate, once daily for 3 months, to 33 virally suppressed (< 50 HIV RNA copies/mL) HIV+ and 31 HIV-ve children. At baseline and endpoint, we assessed microbial composition of faecal samples (16S rRNA sequencing), and markers of gut inflammation (faecal calprotectin), anaemia (haemoglobin) and iron status (plasma ferritin, soluble transferrin receptor). This study was nested within a larger trial registered at clinicaltrials.gov as NCT03572010. RESULTS: HIV+ (11.3y SD ± 1.8, 46% male) and HIV-ve (11.1y SD ± 1.7, 52% male) groups did not significantly differ in age or sex ratio. Following iron supplementation, improvements were observed in haemoglobin (HIV+ : 118 to 124 g/L, P = 0.003; HIV-ve: 120 to 124 g/L, P = 0.003), plasma ferritin (HIV+ : 15 to 34 µg/L, P < 0.001; HIV-ve: 18 to 37 µg/L, P < 0.001), and soluble transferrin receptor (HIV+ : 7.1 to 5.9 mg/L, P < 0.001; HIV-ve: 6.6 to 5.7 mg/L, P < 0.001), with no significant change in the relative abundance of any genera, alpha diversity of the gut microbiota (HIV+ : P = 0.37; HIV-ve: P = 0.77), or faecal calprotectin (HIV+ : P = 0.42; HIV-ve: P = 0.80). CONCLUSION: Our findings suggest that oral iron supplementation can significantly improve haemoglobin and iron status without increasing pathogenic gut microbial taxa or gut inflammation in iron-depleted virally suppressed HIV+ and HIV-ve school-age children.

Duodenal Dysbiosis and Relation to the Efficacy of Proton Pump Inhibitors in Functional Dyspepsia.

Proton pump inhibitors (PPI) may improve symptoms in functional dyspepsia (FD) through duodenal eosinophil-reducing effects. However, the contribution of the microbiome to FD symptoms and its interaction with PPI remains elusive. Aseptic duodenal brushings and biopsies were performed before and after PPI intake (4 weeks Pantoprazole 40 mg daily, FD-starters and controls) or withdrawal (2 months, FD-stoppers) for 16S-rRNA sequencing. Between- and within-group changes in genera or diversity and associations with symptoms or duodenal factors were analyzed. In total, 30 controls, 28 FD-starters and 19 FD-stoppers were followed. Mucus-associated Porphyromonas was lower in FD-starters vs. controls and correlated with symptoms in FD and duodenal eosinophils in both groups, while Streptococcus correlated with eosinophils in controls. Although clinical and eosinophil-reducing effects of PPI therapy were unrelated to microbiota changes in FD-starters, increased Streptococcus was associated with duodenal PPI effects in controls and remained higher despite withdrawal of long-term PPI therapy in FD-stoppers. Thus, duodenal microbiome analysis demonstrated differential mucus-associated genera, with a potential role of Porphyromonas in FD pathophysiology. While beneficial effects of short-term PPI therapy were not associated with microbial changes in FD-starters, increased Streptococcus and its association with PPIeffects in controls suggest a role for duodenal dysbiosis after long-term PPI therapy.

Population-level analysis of Blastocystis subtype prevalence and variation in the human gut microbiota.

OBJECTIVE: Human gut microbiome studies are mainly bacteria- and archaea-oriented, overlooking the presence of single-cell eukaryotes such as Blastocystis, an enteric stramenopiles with worldwide distribution. Here, we surveyed the prevalence and subtype variation of Blastocystis in faecal samples collected as part of the Flemish Gut Flora Project (FGFP), a Western population cohort. We assessed potential links between Blastocystis subtypes and identified microbiota-host covariates and quantified microbiota differentiation relative to subtype abundances. DESIGN: We profiled stool samples from 616 healthy individuals from the FGFP cohort as well as 107 patients with IBD using amplicon sequencing targeting the V4 variable region of the 16S rRNA and 18S rRNA genes. We evaluated associations of Blastocystis, and their subtypes, with host parameters, diversity and composition of bacterial and archaeal communities. RESULTS: Blastocystis prevalence in the non-clinical population cohort was 30% compared with 4% among Flemish patients with IBD. Within the FGFP cohort, out of 69 previously identified gut microbiota covariates, only age was associated with Blastocystis subtype carrier status. In contrast, a strong association between microbiota community composition and Blastocystis subtypes was observed, with effect sizes larger than that of host covariates. Microbial richness and diversity were linked to both Blastocystis prevalence and subtype variation. All Blastocystis subtypes detected in this cohort were found to be less prevalent in Bacteroides enterotyped samples. Interestingly, Blastocystis subtypes 3 and 4 were inversely correlated with Akkermansia, suggesting differential associations of subtypes with host health. CONCLUSIONS: These results emphasise the role of Blastocystis as a common constituent of the healthy gut microbiota. We show its prevalence is reduced in patients with active IBD and demonstrate that subtype characterisation is essential for assessing the relationship between Blastocystis, microbiota profile and host health. These findings have direct clinical applications, especially in donor selection for faecal transplantation.

Commensal microbiota influence systemic autoimmune responses.

Antinuclear antibodies are a hallmark feature of generalized autoimmune diseases, including systemic lupus erythematosus and systemic sclerosis. However, the processes underlying the loss of tolerance against nuclear self-constituents remain largely unresolved. Using mice deficient in lymphotoxin and Hox11, we report that approximately 25% of mice lacking secondary lymphoid organs spontaneously develop specific antinuclear antibodies. Interestingly, we find this phenotype is not caused by a defect in central tolerance. Rather, cell-specific deletion and in vivo lymphotoxin blockade link these systemic autoimmune responses to the formation of gut-associated lymphoid tissue in the neonatal period of life. We further demonstrate antinuclear antibody production is influenced by the presence of commensal gut flora, in particular increased colonization with segmented filamentous bacteria, and IL-17 receptor signaling. Together, these data indicate that neonatal colonization of gut microbiota influences generalized autoimmunity in adult life.

Citroniella saccharovorans gen. nov. sp. nov., a member of the family Peptoniphilaceae isolated from a human fecal sample from a coastal traditional community member.

A novel Gram-stain-positive, non-motile, non-spore-forming coccus-shaped obligately anaerobic bacterium was recovered from a fecal sample obtained from an individual from a traditional community located on the southern coast of Peru. The results of analysis based on 16S rRNA gene sequencing indicated the novel bacterium to be phylogenetically distinct from other genera of members of the Peptoniphilaceae family, sharing a loose affinity with the genera Ezakiella, Finegoldia, Gallicola and Parvimonas. The major cellular fatty acids of the novel isolate were determined to be C16:0, C17:1ω8c, and C18:1ω9c. The DNA G+C content was 29.9 mol%. End products of metabolism from peptone yeast glucose broth (PYG) were determined to be acetate and methyl succinate. The diagnostic diamino acid present in the cell wall was lysine. On the basis of the phenotypic, chemotaxonomic and phylogenetic results the organism is a member of a novel genus belonging to the family Peptoniphilaceae for which the name Citroniella saccharovorans gen nov. sp. nov., is proposed. The type strain is M6.X9T (DSM 29873T=CCUG 66799T).

Stool consistency is strongly associated with gut microbiota richness and composition, enterotypes and bacterial growth rates.

OBJECTIVE: The assessment of potentially confounding factors affecting colon microbiota composition is essential to the identification of robust microbiome based disease markers. Here, we investigate the link between gut microbiota variation and stool consistency using Bristol Stool Scale classification, which reflects faecal water content and activity, and is considered a proxy for intestinal colon transit time. DESIGN: Through 16S rDNA Illumina profiling of faecal samples of 53 healthy women, we evaluated associations between microbiome richness, Bacteroidetes:Firmicutes ratio, enterotypes, and genus abundance with self-reported, Bristol Stool Scale-based stool consistency. Each sample's microbiota growth potential was calculated to test whether transit time acts as a selective force on gut bacterial growth rates. RESULTS: Stool consistency strongly correlates with all known major microbiome markers. It is negatively correlated with species richness, positively associated to the Bacteroidetes:Firmicutes ratio, and linked to Akkermansia and Methanobrevibacter abundance. Enterotypes are distinctly distributed over the BSS-scores. Based on the correlations between microbiota growth potential and stool consistency scores within both enterotypes, we hypothesise that accelerated transit contributes to colon ecosystem differentiation. While shorter transit times can be linked to increased abundance of fast growing species in Ruminococcaceae-Bacteroides samples, hinting to a washout avoidance strategy of faster replication, this trend is absent in Prevotella-enterotyped individuals. Within this enterotype adherence to host tissue therefore appears to be a more likely bacterial strategy to cope with washout. CONCLUSIONS: The strength of the associations between stool consistency and species richness, enterotypes and community composition emphasises the crucial importance of stool consistency assessment in gut metagenome-wide association studies.

Peptoniphilus catoniae sp. nov., isolated from a human faecal sample from a traditional Peruvian coastal community.

A novel Gram-stain-positive, coccus-shaped, obligately anaerobic bacterium was isolated from a faecal sample obtained from an individual in a traditional community located off the southern coast of Peru. Comparative 16S rRNA gene sequence analysis showed the novel bacterium belonged to the genus Peptoniphilus but showed no particular relationship with any species, demonstrating less than 91 % 16S rRNA gene sequence similarity with all members of the genus. The major cellular fatty acids of the novel isolate were determined to be C10 : 0, C14 : 0, C16 : 0, C18 : 1ω9c and C18 : 2ω6,9c/anteiso-C18 : 0. The DNA G+C content was 34.4 mol%. End-products of metabolism from peptone-yeast-glucose broth (PYG) were determined to be acetate and butyrate. Based on the phenotypic, chemotaxonomic and phylogenetic results, the organism represents a novel species of the genus Peptoniphilus, for which the name Peptoniphilus catoniae sp. nov. is proposed. The type strain is M6.X2DT ( = DSM 29874T = CCUG 66798T).

Oral microbiome diversity among Cheyenne and Arapaho individuals from Oklahoma.

OBJECTIVES: There is a major ascertainment bias in microbiome research, with individuals of predominately European ancestry living within metropolitan areas dominating most studies. Here we present a study of the salivary microbiome within a North American Indian community. This research is the culmination of four years of collaboration and community engagement with Cheyenne & Arapaho (C&A) tribal members from western Oklahoma. MATERIALS AND METHODS: Using 16S rRNA gene amplification and next-generation sequencing, we generated microbial taxonomic inventories for 37 individuals representing five towns within the C&A tribes. For comparison, we performed the same laboratory techniques on saliva samples from 20 non-native individuals (NNI) from Norman, Oklahoma. RESULTS: The C&A participants differ from the NNI in having reduced within-individual species richness and higher between-individual variation. Unsupervised clustering analyses reveal that three ecological groupings best fit the data, and while C&A individuals include assignments to all three groups, the NNI individuals are assigned to only one group. One of the ecological groups found exclusively among C&A participants was characterized by high abundance of the oral bacterial genus Prevotella. DISCUSSION: The C&A and NNI participants from Oklahoma have notable differences in their microbiome diversity, with a wider range of variation observed among the C&A individuals, including a higher frequency of bacteria implicated in systemic disorders. Overall, this study highlights the importance of engagement with indigenous communities, and the need for an improved understanding of human microbiome diversity among underrepresented groups and those individuals living outside of metropolitan areas.

Origins of an Unmarked Georgia Cemetery Using Ancient DNA Analysis.

Determining the origins of those buried within undocumented cemeteries is of incredible importance to historical archaeologists and, in many cases, the nearby communities. In the case of Avondale Burial Place, a cemetery in Bibb County, Georgia, in use from 1820 to 1950, all written documentation of those interred within it has been lost. Osteological and archaeological evidence alone could not describe, with confidence, the ancestral origins of the 101 individuals buried there. In the present study, we used ancient DNA extraction methods in well-preserved skeletal fragments from 20 individuals buried in Avondale Burial Place to investigate the origins of the cemetery. Through examination of hypervariable region I (HVR1) in the mitochondrial genome (mtDNA), we determined haplotypes for all 20 of these individuals. Eighteen of these individuals belong to the L or U haplogroups, suggesting that Avondale Burial Place was most likely used primarily as a resting place for African Americans. After the surrounding Bibb County community expressed interest in investigating potential ancestral relationships to those within the cemetery, eight potential descendants provided saliva to obtain mtDNA HVR1 information. Three individuals from Avondale Burial Place matched three individuals with oral history ties to the cemetery. Using the online tool EMPOP, we calculated the likelihood of these exact matches occurring by chance alone (< 1%). The present findings exhibit the importance of genetic analysis of cemetery origins when archaeological and osteological data are inconclusive for estimating ancestry of anonymous historical individuals.

Clostridium amazonense sp. nov. an obliqately anaerobic bacterium isolated from a remote Amazonian community in Peru.

A strictly anaerobic Gram-stain positive, spore-forming, rod-shaped bacterium designated NE08V(T), was isolated from a fecal sample of an individual residing in a remote Amazonian community in Peru. Phylogenetic analysis based on the 16S rRNA gene sequence showed the organism belonged to the genus Clostridium and is most closely related to Clostridium vulturis (97.4% sequence similarity) and was further characterized using biochemical and chemotaxonomic methods. The major cellular fatty acids were anteiso C13:0 and C16:0 with a genomic DNA G + C content of 31.6 mol%. Fermentation products during growth with PYG were acetate and butyrate. Based on phylogenetic, phenotypic and chemotaxonomic information, strain NE08V was identified as representing a novel species of the genus Clostridium, for which the name Clostridium amazonense sp. nov. is proposed. The type strain is NE08V(T) (DSM 23598(T) = CCUG 59712(T)).

Ezakiella peruensis gen. nov., sp. nov. isolated from human fecal sample from a coastal traditional community in Peru.

A novel Gram-stain positive, non-motile, non-sporeforming coccus-shaped, obligately anaerobic bacterium was isolated from a fecal sample of an individual residing in a traditional Peruvian community. The organism was characterized using biochemical, chemotaxonomic and phylogenetic methods. Comparative 16S rRNA gene sequence analyses and phenotypic characteristics demonstrated that the organism was biochemically and phenotypically related, but distinct, from a group of organisms referred to as the Gram-stain positive anaerobic cocci (GPAC). The major cellular fatty acids of the novel isolate were determined to be C16:0 (18.3%), C18:1ω9c (39.8%), C18:2ω6,9c/C18:0 ANTE (13.2%). Fermentation end products from PYG are acetate and formate. Cell-wall peptidoglycan was found to be A4α (L-Lys-L-Ala-L-Glu) and the G + C content was determined to be 38.4 mol%. Based on the phenotypic, chemotaxonomic, and phylogenetic results, Ezakiella peruensis gen. nov., sp. nov., is now proposed. The type strain is M6.X2(T) (DSM 27367(T) = NBRC 109957 (T) = CCUG 64571(T)).

Patterns of genetic variation and the role of selection in HTR1A and HTR1B in macaques (Macaca).

BACKGROUND: Research has increasingly highlighted the role of serotonin in behavior. However, few researchers have examined serotonin in an evolutionary context, although such research could provide insight into the evolution of important behaviors. The genus Macaca represents a useful model to address this, as this genus shows a wide range of behavioral variation. In addition, many genetic features of the macaque serotonin system are similar to those of humans, and as common models in biomedical research, knowledge of the genetic variation and evolution of serotonin functioning in macaques are particularly relevant for studies of human evolution. Here, we examine the role of selection in the macaque serotonin system by comparing patterns of genetic variation for two genes that code for two types of serotonin receptors - HTR1A and HTR1B - across five species of macaques. RESULTS: The pattern of variation is significantly different for HTR1A compared to HTR1B. Specifically, there is an increase in between-species variation compared to within-species variation for HTR1A. Phylogenetic analyses indicate that portions of HTR1A show an elevated level of nonsynonymous substitutions. Together these analyses are indicative of positive selection acting on HTR1A, but not HTR1B. Furthermore, the haplotype network for HTR1A is inconsistent with the species tree, potentially due to both deep coalescence and selection. CONCLUSIONS: The results of this study indicate distinct evolutionary histories for HTR1A and HTR1B, with HTR1A showing evidence of selection and a high level of divergence among species, a factor which may have an impact on biomedical research that uses these species as models. The wide genetic variation of HTR1A may also explain some of the species differences in behavior, although further studies on the phenotypic effect of the sequenced polymorphisms are needed to confirm this.

Population genetic structure of traditional populations in the Peruvian Central Andes and implications for South American population history.

Molecular-based characterizations of Andean peoples are traditionally conducted in the service of elucidating continent-level evolutionary processes in South America. Consequently, genetic variation among "western" Andean populations is often represented in relation to variation among "eastern" Amazon and Orinoco River Basin populations. This west-east contrast in patterns of population genetic variation is typically attributed to large-scale phenomena, such as dual founder colonization events or differing long-term microevolutionary histories. However, alternative explanations that consider the nature and causes of population genetic diversity within the Andean region remain underexplored. Here we examine population genetic diversity in the Peruvian Central Andes using data from the mtDNA first hypervariable region and Y-chromosome short tandem repeats among 17 newly sampled populations and 15 published samples. Using this geographically comprehensive data set, we first reassessed the currently accepted pattern of western versus eastern population genetic structure, which our results ultimately reject: mtDNA population diversities were lower, rather than higher, within Andean versus eastern populations, and only highland Y-chromosomes exhibited significantly higher within-population diversities compared with eastern groups. Multiple populations, including several highland samples, exhibited low genetic diversities for both genetic systems. Second, we explored whether the implementation of Inca state and Spanish colonial policies starting at about ad 1400 could have substantially restructured population genetic variation and consequently constitute a primary explanation for the extant pattern of population diversity in the Peruvian Central Andes. Our results suggest that Peruvian Central Andean population structure cannot be parsimoniously explained as the sole outcome of combined Inca and Spanish policies on the region's population demography: highland populations differed from coastal and lowland populations in mtDNA genetic structure only; highland groups also showed strong evidence of female-biased gene flow and/or effective sizes relative to other Peruvian ecozones. Taken together, these findings indicate that population genetic structure in the Peruvian Central Andes is considerably more complex than previously reported and that characterizations of and explanations for genetic variation may be best pursued within more localized regions and defined time periods.

The evolutionary history of SLC6A4 and the role of plasticity in Macaca.

Serotonin has been repeatedly indicated as a biological marker of behavior. In particular, the serotonin transporter gene, SLC6A4, has been the focus of a large body of research. Interestingly, both rhesus macaques (Macaca mulatta) and humans have independently evolved a number of shared polymorphisms for this gene, which is indicative of parallel evolution between the two species. However, little is known about the evolution of this gene, particularly within macaques. Although there are several hypotheses as to the adaptive values of various polymorphisms, few authors have gone beyond theoretical discussion. Here, we examined the genetic variation in SLC6A4 within and between several species of macaques and investigate whether selection has played a significant role in its evolutionary history. In addition, we assayed the promoter region polymorphism, 5-HTTLPR, which is known to play a significant role in regulating both serotonin turnover and behavior. In examining the distribution of the 5-HTTLPR polymorphism, we identified significant differences between Indian and Chinese populations of Macaca mulatta; furthermore, we discovered its presence in Macaca cyclopis, which has not been described before. In regard to the evolutionary history of SLC6A4, we found little evidence for selection and conclude that SLC6A4 largely evolved through neutral processes, possibly due to its potential role in regulating behavioral plasticity. However, we also found very low levels of linkage between the coding regions and 5-HTTLPR. Because we limited evolutionary analyses to the coding regions, it is possible that the promoter region shows a distinct evolutionary history from SLC6A4.

Microbiome confounders and quantitative profiling challenge predicted microbial targets in colorectal cancer development.

Despite substantial progress in cancer microbiome research, recognized confounders and advances in absolute microbiome quantification remain underused; this raises concerns regarding potential spurious associations. Here we study the fecal microbiota of 589 patients at different colorectal cancer (CRC) stages and compare observations with up to 15 published studies (4,439 patients and controls total). Using quantitative microbiome profiling based on 16S ribosomal RNA amplicon sequencing, combined with rigorous confounder control, we identified transit time, fecal calprotectin (intestinal inflammation) and body mass index as primary microbial covariates, superseding variance explained by CRC diagnostic groups. Well-established microbiome CRC targets, such as Fusobacterium nucleatum, did not significantly associate with CRC diagnostic groups (healthy, adenoma and carcinoma) when controlling for these covariates. In contrast, the associations of Anaerococcus vaginalis, Dialister pneumosintes, Parvimonas micra, Peptostreptococcus anaerobius, Porphyromonas asaccharolytica and Prevotella intermedia remained robust, highlighting their future target potential. Finally, control individuals (age 22-80 years, mean 57.7 years, standard deviation 11.3) meeting criteria for colonoscopy (for example, through a positive fecal immunochemical test) but without colonic lesions are enriched for the dysbiotic Bacteroides2 enterotype, emphasizing uncertainties in defining healthy controls in cancer microbiome research. Together, these results indicate the importance of quantitative microbiome profiling and covariate control for biomarker identification in CRC microbiome studies.