Video 1

Movie S1. Day-by-day progression of microbial content for three different subjects. These three cases exemplify the general trend in the progression from Bacilli to Gammaproteobacteria, to Clostridia, in an animation format used in prior studies of microbial populations over time (1, 2). Other general characteristics portrayed by these subjects are frequent abruptions in microbial content, and the slower rate of accumulation of Clostridia in the most premature subject, and the most rapid rate of accumulation of this bacterial class in the least premature subject. Arrows change at one second intervals, but their pace of appearance is not proportional to the days between samples. Numbers at bottom of each graph provide the days of life of each sample. Dots are color-coded, with unique shading for each subject. Examples A, B, and C represent subjects 53, 47, and 39, born after 25, 28, and 31 wk gestation, respectively.