# Microbiome dynamics in the congregate environment of U.S. Army Infantry training

## TL;DR

This study shows that the microbiomes of military trainees can become more similar over time due to shared environments and routines.

## Contribution

The study provides preliminary evidence of microbiome convergence in a military trainee cohort using shotgun metagenomic sequencing.

## Key findings

- Microbiome similarity increased over time in one platoon, with changes in species abundance.
- No strain transfer was observed, suggesting environmental and lifestyle factors drive convergence.
- Shifts in fungal and bacterial species were noted, including decreases in Malassezia restricta and Prevotella.

## Abstract

Within military training and operational environments, individuals from diverse backgrounds share common spaces, follow structured routines and diets, and engage in physically demanding tasks. While there has been interest in leveraging microbiome features to predict and improve military health and performance, the longitudinal convergence of microbiomes in such constrained environments has not been established. To assess the degree of microbiome convergence, we performed shotgun metagenomic sequencing on swab samples from a military trainee cohort. Samples were taken across four different body sites, three timepoints, and two spatially distinct platoons. We observed evidence of convergence in one platoon, whereby similarity in microbiome composition increased over time, with numerous differentially abundant species. We found no indication of strain transfer between individuals, suggesting that convergence was influenced by external environmental factors, diet, and lifestyle. Microbial shifts observed in the convergence process included a decrease in fungal species, such as Malassezia restricta in nasal cavities, and a decrease in Prevotella species at inguinal regions across time. Shifts in multiple Corynebacterium species were also observed with varying magnitudes depending on the body site. Overall, we provide preliminary evidence of convergence of host microbial communities in military-associated environments that were distinguishable using shotgun metagenomic sequencing approaches. The data presented here on microbiome convergence, dynamics, and stability may inform risk-based mitigation in congregate military settings facilitating development of targeted microbial, dietary, or other interventions to optimize health and performance of military populations.

Microbiome convergence in deployed environments could impact the health and readiness of the warfighter, with potential implications for susceptibility to biothreats. This study describes a shotgun metagenomic approach used to study the microbiomes of swab samples collected at different body sites in a military trainee cohort. The results presented here provide a foundation for developing future microbiome-based interventions and protocols to enhance operational readiness.