Vaginal Microbiota Dynamics as a Key Determinant of Pathogenesis in Fungal Vulvovaginitis

The complex and dynamic vaginal microbial ecosystem is critical to both health and disease of the host. Studies focusing on how vaginal microbiota influences HIV-1 infection may face limitations in selecting proper animal models. Given that northern pig-tailed macaques (Macaca leonina) are susceptible to HIV-1 infection, they may be an optimal animal model for elucidating the mechanisms by which vaginal microbiota contributes to resistance and susceptibility to HIV-1 infection. However, little is known about the composition and temporal variability of vaginal microbiota of the northern pig-tailed macaque. Here, we present a comprehensive catalog of the composition and temporal dynamics of vaginal microbiota of two healthy northern pig-tailed macaques over 19 weeks using 454-pyrosequencing of 16S rRNA genes. We found remarkably high proportions of a diverse array of anaerobic bacteria associated with bacterial vaginosis. Atopobium and Sneathia were dominant genera, and interestingly, we demonstrated the presence of Lactobacillus-dominated vaginal microbiota. Moreover, longitudinal analysis demonstrated that the temporal dynamics of the vaginal microbiota were considerably individualized. Finally, network analysis revealed that vaginal pH may influence the temporal dynamics of the vaginal microbiota, suggesting that inter-subject variability of vaginal bacterial communities could be mirrored in inter-subject variation in correlation profiles of species with each other and with vaginal pH over time. Our results suggest that the northern pig-tailed macaque could be an ideal animal model for prospective investigation of the mechanisms by which vaginal microbiota influence susceptibility and resistance to HIV-1 infection in the context of highly polymicrobial and Lactobacillus-dominated states.

Bacterial vaginosis (BV) is a significant global public health issue due to its high recurrence rate and association with various adverse health effects. Understanding the composition and dynamics of the vaginal microbiota (VMB) is essential for better understanding of vaginal health and for developing effective strategies to improve BV management. The study aimed to determine the composition and diversity of the VMB in Thai women with BV before and after metronidazole (MTZ) treatment, and in healthy women. Vaginal samples were collected from 20 women with BV (each sampled at three time points: pre-MTZ treatment, post-MTZ treatment and follow-up) and from 20 healthy women (each sampled once). The VMB was analyzed using 16S rRNA gene sequencing via next-generation sequencing on the Ion Torrent PGM platform. The VMB in Thai women with BV was predominantly composed of Gardnerella, Prevotella and Fannyhessea (formerly Atopobium), while Lactobacillus dominated in healthy controls. Women with BV exhibited greater bacterial diversity and higher prevalence of anaerobic species compared to healthy women. There was higher diversity and abundance in the VMB from pre-MTZ samples, while post-MTZ and follow-up samples displayed lower diversity. In the follow-up stage, the VMB was divided into two subgroups: the larger cured subgroup, which shifted towards a Lactobacillus-dominated composition resembling healthy controls, and the small treatment-failure subgroup, which exhibited a Gardnerella-dominated profile similar to pre-MTZ. This study provides valuable insights into the structure and dynamics of the VMB in Thai women with BV before and after treatment, offering potential markers for predicting treatment outcomes.

<h3>Introduction</h3> Alterations in vaginal microbiota (VMB) have been shown to increase HIV acquisition and transmission in women. We carried out a longitudinal characterisation of the VMB, soluble cervicovaginal immune mediators and their determinants in women from Sub-Saharan Africa. <h3>Methods</h3> Cervicovaginal lavages from two cohorts of sexually active women from Kenya, South Africa and Rwanda were analysed for IL-1α, IL-1β, IL-6, IL-12(p70), MIP-1β, IP-10, IL-8, GM-CSF, G-CSF, Elafin, SLPI, IL-1RA and total protein. qPCR was used to quantify total <i>Lactobacillus</i>, <i>L. crispatus, <i>L. iners</i>, L. jensenii</i>, <i>L. gasseri,</i><i>L. vaginalis, A. vaginae, <i>G. vaginalis</i>,</i><i>P. bivia </i>and<i> E. coli</i> in vaginal swab samples. Cohort A had 40 women with a healthy VMB (Nugent score &lt; 4) at all five bi–weekly visits. Cohort B consisted of 40 women with incident bacterial vaginosis (BV) (Nugent score &gt; 7) in the course of their visits. <h3>Results</h3> Cohort A: Individual<i>Lactobacillus</i> species were consistently present or absent within each woman over five study visits. Sexual activity was associated with reduced counts of total <i>Lactobacillus</i>, <i>L. iners</i> and <i>Prevotella bivia</i> but increased concentrations of IL-6, IL-12(p70) and IP-10. pH was positively associated with IL-1RA and IL1RA/IL1(α+β) ratio but negatively associated with total protein and SLPI. The amount of total <i>Lactobacillus</i> was significantly lower and total soluble immune mediators, MIP-1β and IL-8 higher in 14 women on progesterone-only contraception compared to those with a cycle (20 not on any contraceptives and 6 on combined pill). Cohort B: Total <i>Lactobacillus</i>, <i>L. crispatus</i>, IP-10, GM-CSF, Elafin, SLPI and total protein were all reduced during the first visit with BV. Conversely, <i>G. vaginalis</i>, A. vaginae, E. coli and IL-1β were increased with incident BV. <h3>Conclusion</h3> Sexual activity, progesterone, clinical symptoms of pathology and BV alter vaginal mucosal immunity in Sub-Saharan African women potentially increasing their susceptibility to HIV infection. <h3>Disclosure of interest statement</h3> This work was supported by the European and Developing Countries Clinical Trials Partnership (EDCTP) as part of a grant titled ‘‘Characterisation of novel microbicide safety biomarkers in East and South Africa.’’ The views expressed in this manuscript are those of the authors and do not necessarily represent the views of EDCTP. The authors report no conflict of interest.

The etiology and pathogenic mechanisms underlying recurrent spontaneous abortion (RSA) are poorly understood. Specifically, patients with unexplained recurrent spontaneous abortion (URSA) frequently exhibit dysbiosis of the vaginal microbiota and elevated blood inflammatory markers. Therefore, this study aimed to investigate the association between vaginal microbiota, blood inflammatory markers, and fibrinogen in URSA, with a specific focus on exploring the potential moderating role of inflammatory markers in the relationship between vaginal microbiota and fibrinogen dynamics. Thirty-one pregnant women with URSA and fifty pregnant women with normal pregnancies completed clinical biochemical indicator testing and vaginal secretion testing in early pregnancy. The characteristics of vaginal microbiomes in patients with URSA and healthy women were evaluated via 16S rRNA gene sequencing of the V3-V4 region using Illumina MiSeq sequencing. Hayes' regression was used to analyze the association among vaginal microbiota, blood inflammatory markers, and vaginal microbiota*blood inflammatory markers with fibrinogen. Simple slope analysis was applied to visualize the interaction. The URSA group showed decreased alpha diversity. Principal coordinates analysis revealed significant differences in vaginal microbiota between the URSA and control groups (unweighted UniFrac distance, R2 = 0.03, P = 0.007). Erysipelotrichaceae was positively associated with fibrinogen (B = 6.34, P < 0.05), and NLR was positively associated with fibrinogen (B = 1.46, P < 0.05). However, the combined effect of Erysipelotrichaceae and NLR was negatively associated with fibrinogen (B = -1.5, P < 0.05). The association between Erysipelotrichaceae and fibrinogen was significant in the low NLR group (1 standard deviation (SD) below the mean, B = 3.64, standard error (SE) = 1.15, P < 0.01) but not significant in the high NLR group (1 SD above the mean, B = 0.93, SE = 0.644, P > 0.05). Additionally, the association between Erysipelotrichaceae and fibrinogen was significant in the low WBC group (1 SD below the mean, B = 2.84, SE = 0.94, P < 0.01) but not significant in the high WBC group (1 SD above the mean, B = -0.137, SE = 0.89, P > 0.05). Blood inflammatory markers moderate the link between vaginal microbiota and fibrinogen. Further studies are needed to explore the potential biological mechanisms linking vaginal microbiota and coagulation markers for URSA treatment and to validate our findings.

A century after Robert Koch linked individual cultured microbes to specific diseases (Koch's postulates), it has become increasingly apparent that the complex community of microorganisms associated with the human body plays a key role in health and disease. The National Institutes of Health recently announced the Human Microbiome Project as part of the NIH Roadmap for medical research, with a primary goal of advancing our understanding of the relationships among host-associated microbial communities, health, and disease. Many physicians and researchers, however, have only passing familiarity with the concepts involved in the study and therapeutic manipulation of complex microbial communities. This special issue was conceived to accomplish several goals. We wanted to provide readily accessible overviews of the concepts and methods used in the study of complex microbial communities, and demonstrate how changes in indigenous microbial communities can play a role in diseases such as antibiotic-associated diarrhea and bacterial vaginosis. We also set out to find examples of how probiotics can be used for the therapeutic manipulation of the indigenous microbiota. We were fortunate to receive a strong collection of review articles and primary research manuscripts to meet the goals of this special issue. In the first article “Conceptualizing the human microbiota: from multicelled organ to ecological community,” B. Foxman et al. present a novel conceptualization of the human microbiome that blends perspectives of epidemiologists, classical ecologists and infectious diseases physicians. The second article “Application of ecological network theory to the human microbiome,” by J. Foster et al., outlines how ecological network theory can be applied to studies of the human microbiome, while the third article “Interactions of the intestinal epithelium with the pathogen and the indigenous microbiota: a three way crosstalk,” by C. V. Srikanth and B. McCormick, review the interactions between epithelial pathogens and the indigenous microbiota in the mammalian gut. In the fourth article “Application of sequence-dependent electrophoresis fingerprinting in exploring biodiversity and population dynamics of human intestinal microbiota: what can be revealed?” G. Huys et al. review the use of sequence-dependent fingerprinting methods for studying the structure and dynamics of complex microbial systems using the human intestinal microbiota as an example. The fifth article “Ecological characterization of the colonic microbiota of normal and diarrheic dogs,” by J. Bell, employs such a fingerprinting method to study the canine colonic microbiota. The sixth article “Emerging insights into antibiotic-associated diarrhea and Clostridium difficile infection through the lens of microbial ecology,” by S. Walk and V. Young, discusses the role of the gut microbiota in antibiotic-associated diarrhea and Clostridium difficile infection while Y. Sanz et al., in the seventh article “Insights into the roles of gut microbes in obesity,” review the evidence for the role of gut microbes in obesity. In the eighth article “The human vaginal bacterial biota and bacterial vaginosis,” by S. Srinivasan and D. Fredericks review the human vaginal bacterial microbiota and the ninth article “Temporal shifts in microbial communities in non-pregnant african-american women with and without bacterial vaginosis,” by J. Wertz et al., examines this microbial community in the setting of bacterial vaginosis. The tenth article “Vaginal microbiota and the use of probiotics,” by S. Cribby et al. discusses the use of probiotics to alter the vaginal microbiota. Finally, the eleventh article “Probiotics and gastrointestinal infections,” by R. Britton and J. Versalovic, and the twelveth article “Probiotic bacteria influence the composition and function of the intestinal microbiota,” by P. O’Toole and J. Cooney, summarize the potential role of probiotics to influence gastrointestinal health.

The microorganisms of the vaginal tract are critical for vaginal and reproductive health. However, the regulation of these microorganisms is not well understood. Therefore, we investigated whether different factors regulate the vaginal microbiota of healthy college-aged women (n = 26) with high temporal resolution by collecting daily self-administered vaginal swabs and using 16S rRNA sequencing for bacterial identification. As expected, vaginal microbiota clustered into five predefined community state types. Vaginal microbial diversity, stability, and Lactobacillus abundances were associated with the menstrual cycle and hormonal contraceptive use. Vaginal microbial diversity, as measured using the Shannon index, increased during menses (P < 0.001), while Lactobacillus abundances decreased (P = 0.01). The covariance of these microbial measures with previously established estradiol levels suggests that estrogens can regulate vaginal microbiota. Moreover, the use of hormonal contraceptives may alter the temporal dynamics of the vaginal microbiota and decrease Lactobacillus abundances, depending on hormonal content and release method. Interestingly, intrasample diversity was greater in participants on a vegetarian diet (P = 0.004) and among participants who exercised more (P = 0.04). These findings indicate that ovarian hormones, diet, and exercise can regulate vaginal microbial composition and stability and may impact vaginal and reproductive health.IMPORTANCE The vaginal microbiome is a critical component of women's sexual and reproductive health, with variations in microbial composition, particularly the loss of Lactobacillus species, being implicated in gynecologic and obstetric diseases. Given that the vaginal microbiome is so crucial, why do vaginal microbial profiles vary strikingly from person to person and even change over time within the same person? In the present study, which tracked the daily vaginal microbiomes of young healthy women through different lifestyles, we found that use of a locally released progestin contraceptive, a vegetarian diet, and intense exercise appear to lead to vaginal microbiome alterations and loss of Lactobacillus species. The impact of these vaginal microbiome changes on immediate and long-term health remain to be investigated.

This article provides an introductory exploration into the vaginal microbiota and its significance in maintaining gynecological health. The vaginal microbiota plays a crucial role in sustaining a balanced and harmonious vaginal ecosystem, influencing various aspects of reproductive well-being. By examining the composition and dynamics of the vaginal microbiota, this article highlights its impact on preventing dysbiosis and associated infections. A deeper understanding of the intricate interactions within the vaginal microbiota can pave the way for targeted therapeutic interventions aimed at promoting and preserving gynecological health.

Recent studies suggest that birth mode (Cesarean section [C-section] or vaginal delivery) is an important event in the initial colonization of the human microbiome and may be associated with long-term health outcomes. We sought to determine the association between a woman’s birth mode and her vaginal microbiota in adulthood. We re-contacted 144 adult women from two U.S. studies and administered a brief survey. Vaginal microbiota was characterized on a single sample by amplicon sequencing of the V3-V4 hypervariable regions of the 16S rRNA gene and clustered into community state types (CSTs). We evaluated the association between birth mode and a CST with low relative abundance of Lactobacillus spp. (“molecular bacterial vaginosis” [Molecular-BV]) compared to Lactobacillus-dominated CSTs in logistic regression modeling which adjusted for body mass index, a confounder in this analysis. Twenty-seven women (19%) reported C-section. Overall, C-section showed a non-significant trend towards increased odds of Molecular-BV (aOR = 1.22, 95% CI: 0.45, 3.32), and Prevotella bivia was the strongest single taxa associated with C-section. However, because the two archived studies had different inclusion criteria (interaction p = 0.048), we stratified the analysis by study site. In the study with a larger sample size (n = 88), women born by C-section had 3-fold higher odds of Molecular-BV compared to vaginally-delivered women (aOR = 3.55, p = 0.06, 95% CI: 0.97–13.02). No association was found in the smaller study (n = 56, aOR = 0.19, p = 0.14, 95% CI: 0.02–1.71). This pilot cross-sectional study suggests a possible association between C-section and Molecular-BV in adulthood. However, the analysis is limited by small sample size and lack of comparability in participant age and other characteristics between the study sites. Future longitudinal studies could recruit larger samples of women, address the temporal dynamics of vaginal microbiota, and explore other confounders, including maternal factors, breastfeeding history, and socioeconomic status, which may affect the relationship between birth mode and vaginal microbiota.

Recent studies suggest that birth mode (Cesarean section [C-section] or vaginal delivery) is an important event in the initial colonization of the human microbiome and may be associated with long-term health outcomes. We sought to determine the association between a woman's birth mode and her vaginal microbiota in adulthood. We re-contacted 144 adult women from two U.S. studies and administered a brief survey. Vaginal microbiota was characterized on a single sample by amplicon sequencing of the V3-V4 hypervariable regions of the 16S rRNA gene and clustered into community state types (CSTs). We evaluated the association between birth mode and a CST with low relative abundance of Lactobacillus spp. ("molecular bacterial vaginosis" [Molecular-BV]) compared to Lactobacillus-dominated CSTs in logistic regression modeling which adjusted for body mass index, a confounder in this analysis. Twenty-seven women (19%) reported C-section. Overall, C-section showed a non-significant trend towards increased odds of Molecular-BV (aOR = 1.22, 95% CI: 0.45, 3.32), and Prevotella bivia was the strongest single taxa associated with C-section. However, because the two archived studies had different inclusion criteria (interaction p = 0.048), we stratified the analysis by study site. In the study with a larger sample size (n = 88), women born by C-section had 3-fold higher odds of Molecular-BV compared to vaginally-delivered women (aOR = 3.55, p = 0.06, 95% CI: 0.97-13.02). No association was found in the smaller study (n = 56, aOR = 0.19, p = 0.14, 95% CI: 0.02-1.71). This pilot cross-sectional study suggests a possible association between C-section and Molecular-BV in adulthood. However, the analysis is limited by small sample size and lack of comparability in participant age and other characteristics between the study sites. Future longitudinal studies could recruit larger samples of women, address the temporal dynamics of vaginal microbiota, and explore other confounders, including maternal factors, breastfeeding history, and socioeconomic status, which may affect the relationship between birth mode and vaginal microbiota.

Infertility is a global public health issue which leads many couples to seek fertility treatments, of which in vitro fertilization (IVF) is considered to be the most effective. Still, only about one-third of the women achieve live birth after the first IVF embryo transfer (IVF-ET). Factors affecting embryo implantation are poorly known, but the female reproductive tract microbiota may play a key role. Our study confirms the beneficial role of vaginal lactobacilli, especially Lactobacillus crispatus, in the probability of achieving clinical pregnancy and live birth following IVF-ET. Our findings regarding the intra-individual shift of vaginal microbiota between non-pregnancy and pregnancy states are novel and provide new information about the dynamics of microbiota in the early steps of human reproduction. These findings may help clinicians in their attempts to optimize the conditions for ET by microbiota screening or modulation and timing the ET when the microbiota is the most favorable.

Alterations in the vaginal microbiota contribute to the pathogenesis of cervical neoplasia. However, the distinctions in microbiota changes related to different human papillomavirus (HPV) subtypes, as well as the variation in gut microbiota, have not been fully explored. In this research, we endeavored to explore the shifts in the vaginal and intestinal microbiota in correlation with the advancement of cervical neoplasia and HPV infection. A total of 578 vaginal and intestinal cross-sectional specimens were collected from 348 subjects and subjected to 16S rRNA sequencing. Statistical analyses were performed using R language, and Student's t-test was employed to assess the significance of differences. Both within and between, sample diversity of the vaginal and intestinal microbiota exhibited substantial alterations across cervical intraepithelial neoplasia (CIN) stages and cervical carcinoma. The vaginal genera Lactobacillus, Enterococcus, Peptoniphilus, Atobium, Anerococcus, and Veillonella were associated with different CIN stages and cervical cancer type, whereas Allisonella, Lachnospiracae, Lactobacillus, Staphylococcus, and Sellimonas were associated with varying HPV types. A Random Forest-driven classifier highlighted the predictive potential of differential bacteria in cervical neoplasia and HPV infection, with intestinal bacteria showing higher predictive accuracy in certain instances. Specifically, the accuracy of differentiating CIN I from CIN III was superior for the intestinal bacterial model compared to the vaginal bacterial model (85.52% vs. 83.33%). The model also demonstrated high accuracy in predicting HPV infection, particularly in distinguishing HPV-16 from HPV-18 and HPV-58, with AUC values of 81.61% and 83.07%, respectively, compared to less than 70% for vaginal bacteria. Our findings reveal the intricate interplay among cervical neoplasia, HPV infection, and microbiota, with potential diagnostic and therapeutic implications.

BackgroundThe study aimed to assess the effects of vaginal disinfection and sterile draping on the composition and dynamics of the vaginal microbiota during vaginal surgery.MethodsA prospective cohort study was conducted involving post-menopausal patients undergoing vaginal urogynecological surgery. The vaginal microbiota was assessed by partial 16 S rRNA gene sequencing at three time points: before disinfection (V1); immediately after disinfection and sterile draping (V2); and one-hour post-disinfection (V3).FindingsIn a cohort of 54 postmenopausal women (median age: 69.2 ± 7.6 years), with a mean operative time of 92.89 ± 45.92 min, native tissue prolapse repair was the most common urogynecological vaginal procedure performed (n = 47, 87%). The vaginal microbiota diversity was significantly increased after disinfection associated with reduced abundance of Lactobacillus and Bifidobacterium and increased Pseudomonas (p < 0.0001). Community state type (CST) I prevalence decreased notably from 20% at V1 to 6% at V3, primarily due to the disappearance of CST I-A, while CST IV prevalence rose from 31 to 44%, which was mainly secondary to an increase in CST IV-C (from 20 to 33%).ConclusionsThese findings highlight the impact of povidone-iodine on vaginal microbiota composition during vaginal urogynecological surgery. Disinfection significantly increased vaginal bacterial diversity and reducing Lactobacillus abundance. This observation requires further exploration in the context of development of optimized disinfection protocols aimed at preserving vaginal health during and after surgery.Supplementary InformationThe online version contains supplementary material available at 10.1186/s13756-025-01622-6.

The vaginal microbiota plays a pivotal role in reproductive, sexual, and perinatal health and disease. Unlike the well-established connections between diet, metabolism, and the intestinal microbiota, parallel mechanisms influencing the vaginal microbiota and pathogen colonization remain overlooked. In this study, we combine a mouse model of Streptococcus agalactiae strain COH1 [group B Streptococcus (GBS)] vaginal colonization with a mouse model of pubertal-onset obesity to assess diet as a determinant of vaginal microbiota composition and its role in colonization resistance. We leveraged culture-dependent assessment of GBS clearance and culture-independent, sequencing-based reconstruction of the vaginal microbiota in relation to diet, obesity, glucose tolerance, and microbial dynamics across time scales. Our findings demonstrate that excessive body weight gain and glucose intolerance are not associated with vaginal GBS density or timing of clearance. Diets high in fat and low in soluble fiber are associated with vaginal GBS persistence, and changes in vaginal microbiota structure and composition due to diet contribute to GBS clearance patterns in nonpregnant mice. These findings underscore a critical need for studies on diet as a key determinant of vaginal microbiota composition and its relevance to reproductive and perinatal outcomes.IMPORTANCEThis work sheds light on diet as a key determinant influencing the composition of vaginal microbiota and its involvement in group B Streptococcus (GBS) colonization in a mouse model. This study shows that mice fed diets with different nutritional composition display differences in GBS density and timing of clearance in the female reproductive tract. These findings are particularly significant given clear links between GBS and adverse reproductive and neonatal outcomes, advancing our understanding by identifying critical connections between dietary components, factors originating from the intestinal tract, vaginal microbiota, and reproductive outcomes.

The vaginal microbiota plays a key role in animals' health. Understanding its diversity and composition and associated changes occurring through the reproductive cycle represents valuable knowledge to disclose the mechanisms leading to dysbiosis and eventually to infection. Even if the human vaginal microbiota has been thoroughly studied, scarce research has been conducted on the vaginal microbiota of livestock. In this study, 16S rRNA gene-based sequencing was performed on vaginal samples of ten nulliparous ewes at three different sampling points: before the estrus synchronization protocol (T0), at the time of estrus before mating (Testrus), and the day of the pregnancy diagnosis (Tpreg). Preputial samples from the three males collected pre and post-mating were also analyzed. Firmicutes, Proteobacteria, Bacteroidetes, and Actinobacteria were the most abundant phyla in vaginal samples. The most abundant genera were Porphyromonas, Anaerococcus, and Peptinophilius. Vaginal microbiota biodiversity decreased during pregnancy. Tenericutes (Ureaplasma spp.) increased significantly at Tpreg in both pregnant and non-pregnant ewes. Differences were observed between pregnant and non-pregnant ewes at Tpreg where pregnant ewes had a significantly higher abundance of Actinobacillus spp. and Ureaplasma spp. Ewes that were diagnosed with pregnancy at Tpreg showed a decreased abundance of gram-negative bacteria such as Bacteroidales, Campylobacterales, and Enterobacteriales. In addition, a significant decrease in the relative abundances of genera within Firmicutes, such as Alloicoccus (Lactobacillales), Atopostipes (Lactobacillales), and an uncultured bacteria W5053 from Family XI (Firmicutes, Clostridiales) was observed in non-pregnant ewes at Tpreg. The four most abundant phyla in the rams' prepuce were the same as in the ewes' vagina. The most abundant genus was Corynebacterium. No major differences were observed in the ram's preputial microbiota between pre and post-mating samples. Nevertheless, the differences in the taxonomic composition of ewes' vaginal microbiota between Testrus and Tpreg could be explained by the exposure to the preputial microbiota. This study offers new insights into the effects of several key steps of the ewe's reproductive cycle such as estrus-synchronization protocol, mating, and pregnancy on ovine vaginal microbiota. The knowledge of the microbiota dynamics during the reproductive cycle can help improve the reproductive outcomes of dams by identifying biomarkers and putative probiotics.

Molecular methods to describe the spectrum and dynamics of the vaginal microbiota