The mucosal microbiome plays a key role in determining risk for HIV acquisition. Penile anaerobic bacterial abundance correlates with penile cytokine concentrations, and cytokines are associated with HIV target cell density in the foreskin. Furthermore, anaerobe abundance and penile cytokine concentrations are associated with increased incidence of HIV infection. Thus, it is plausible that alterations in the penile microbiome with resultant inflammatory changes may increase the risk of HIV. Similarly, vaginal microbial communities with high diversity or those dominated by anaerobic or facultative bacteria render women at higher risk of HIV acquisition and are associated with high genital inflammation, which is thought to attract or activate HIV target cells in the mucosa or alter mucosal integrity. In addition to bacteria, the mucosal microbiome also contains viruses, and shifts in one community may modulate shifts in the other. The gut bacteriome diversity is mirrored in the virome, the collection of pro- and eukaryote-infecting viruses, and that these patterns of diversity are driven by bacteriophages, not by eukaryotic viruses. Expansion of bacteriophage populations, viruses that infect bacteria, has been linked to immune cell expansion and increased inflammation in the gut. Viral communities can influence host immunity by direct activation, or indirectly by modifying the bacterial community. However, the impact of the penile virome on bacterial communities, immunity and HIV susceptibility are unknown. The CHAPS study, which is randomizing young men aged 13-24 years to placebo versus various oral doses of antiretrovirals prior to circumcision, affords us the unique opportunity to address some of these knowledge gaps. Enrolment is complete, and 144 foreskins and corresponding penile swabs have been stored, with valuable data including ex vivo HIV susceptibility and local tissue gene expression available. We will extend the study to test our hypothesis that there is an interlinkage between penile viral and bacterial microbiota, and that penile anaerobic bacteria relative abundance modulates epithelial inflammation and CD4 target cell availability, and therefore HIV susceptibility with the following Specific Aims: Aim 1: To assess inter-kingdom interactions at the penile mucosa. Hypothesis: The viral and bacterial microbiota of the penis are interrelated. Aim 2: To evaluate the interaction between the bacterial microbiome, epithelial inflammation, target cell availability and HIV susceptibility. Hypothesis Penile anaerobic bacterial relative abundance modulates epithelial inflammation, CD4 target cell availability, and hence HIV susceptibility. We propose a highly innovative, unique study to answer important questions regarding the penile microbiome and HIV susceptibility, that could lead to improved prevention interventions, such as probiotics or anti- inflammatories, for uncircumcised males.